Issue Templates

- Updating Issue Templates

.github/ISSUE_TEMPLATE/bug.yml

@@ -1,87 +1,78 @@
-name: Iris Bug Report
-description: File a bug report for Iris
-labels: [ bug ]
+name: Bug report
+description: Something in Iris isn't working.
+labels: [bug]
+type: Bug
+assignees: [SwiftSwamp]
 body:
   - type: markdown
     attributes:
       value: |
-        Thank you for taking the time to fill this out!
-        If this does not work for you, feel free to use the [blank](https://github.com/VolmitSoftware/Iris/issues/new) format.
+        Make sure you're on the [latest release](https://github.com/VolmitSoftware/Iris/releases/latest) and that it hasn't [already been reported](https://github.com/VolmitSoftware/Iris/issues?q=is%3Aissue).
+
+        The Iris plugin supports Minecraft 26.1.2 through 26.3 on Paper, Purpur, Leaf, Canvas, Folia, and Spigot. The Fabric, Forge, and NeoForge builds support 26.3. Both need Java 25.
   - type: textarea
-    id: how
+    id: issue
     attributes:
-      label: Problem
-      description: Please give a text description of how you reached the problem
-      value: |
-        1. Install Iris...
-        2. Do this...
-        3. Do that...
-        4. Observe the error...
+      label: What issue are you having?
+      description: Include any error message you saw.
     validations:
       required: true
   - type: textarea
-    id: what
+    id: steps
     attributes:
-      label: Solution
-      description: Explain where you think the problem comes from (optional)
-      placeholder: The code to place a is missing b and c...
+      label: Steps to reproduce
+      placeholder: |
+        1. Start a server with Iris installed
+        2. Change ... in the config
+        3. Run /iris ...
+        4. ... happens instead of ...
     validations:
-      required: false
+      required: true
+  - type: input
+    id: diagnostics
+    attributes:
+      label: Debug dump or latest log file
+      description: Run `/iris debug dump upload=true` and paste the link. If Iris won't start, upload `logs/latest.log` to [mclo.gs](https://mclo.gs) and paste that link instead.
+      placeholder: https://mclo.gs/...
+    validations:
+      required: true
+  - type: input
+    id: plugin-version
+    attributes:
+      label: "Iris version"
+      description: Run `/iris debug version` (`/iris version` on Fabric, Forge, and NeoForge).
+    validations:
+      required: true
   - type: dropdown
     id: platform
     attributes:
-      label: Platform
-      description: Which server platform is Iris running on? Pick the loader or server software, not the launcher.
+      label: Server software
       options:
-        - Paper
-        - Purpur
-        - Leaf
-        - Canvas
-        - Folia
-        - Spigot / CraftBukkit
-        - Fabric
-        - Forge
-        - NeoForge
-        - Other (describe under Problem)
-    validations:
-      required: true
-  - type: dropdown
-    id: mcversion
-    attributes:
-      label: Minecraft Version
-      description: What version of Minecraft is the server on? Iris 4.x supports 26.1.2 to 26.3 on Bukkit-family servers and 26.3 on Fabric, Forge and NeoForge; older versions are not supported.
-      options:
-        - '26.3'
-        - '26.2'
-        - '26.1.2'
+        - "Paper"
+        - "Purpur"
+        - "Leaf"
+        - "Canvas"
+        - "Folia"
+        - "Spigot"
+        - "Fabric"
+        - "Forge"
+        - "NeoForge"
         - Other (unsupported)
     validations:
       required: true
-  - type: input
-    id: loaderversion
+  - type: dropdown
+    id: minecraft
     attributes:
-      label: Platform / Loader Version
-      description: Exact server or loader build (see console). For example "Paper 26.3-133", "Fabric Loader 0.19.5", "NeoForge 26.3.0.33-beta".
-      placeholder: DO NOT SAY "LATEST"
+      label: Minecraft version
+      options:
+        - "26.3"
+        - "26.2"
+        - "26.1.2"
+        - Other (unsupported)
     validations:
       required: true
-  - type: input
-    id: irisversion
+  - type: textarea
+    id: extra
     attributes:
-      label: Iris Version
-      description: What version of Iris are you running? (see console)
-      placeholder: DO NOT SAY "LATEST"
-    validations:
-      required: true
-  - type: input
-    id: logs
-    attributes:
-      label: Log
-      description: Paste a full log. Always use [mclogs](https://mclo.gs) Or [Pastebin](https://pastebin.com/). Must not be a crash report. Must be a full log. Must not be a screenshot of a log.
-      placeholder: https://mslog.gs/...
-    validations:
-      required: true
-  - type: markdown
-    id: thanks
-    attributes:
-      value: "Thank you for filling out the form! We will be with you soon. Please do not ask support to review your report."
+      label: Anything else?
+      description: Other plugins involved, screenshots, or videos.

.github/ISSUE_TEMPLATE/config.yml

@@ -0,0 +1,8 @@
+blank_issues_enabled: false
+contact_links:
+  - name: Help and questions
+    url: https://volmitsoftware.com/discord
+    about: Ask setup and configuration questions on the Volmit Discord.
+  - name: "Iris documentation"
+    url: https://docs.volmitsoftware.com/iris
+    about: Installation, commands, permissions, and configuration.

.github/ISSUE_TEMPLATE/feature.yml

@@ -1,46 +1,28 @@
-name: Iris Feature Request
-description: File a feature request for Iris. If you want to report a bug this is not the place.
-labels: [ feature ]
+name: Suggestion
+description: Suggest a new feature or a change to Iris.
+labels: [enhancement]
+type: Feature
+assignees: [SwiftSwamp]
 body:
   - type: markdown
     attributes:
       value: |
-        Thank you for taking the time to fill this out!
-        If this does not work for you, feel free to use the [blank](https://github.com/VolmitSoftware/Iris/issues/new) format.
-  - type: dropdown
-    id: arc
+        Check the [existing suggestions](https://github.com/VolmitSoftware/Iris/issues?q=is%3Aissue+label%3Aenhancement) first and add relevant information to the existing issue.
+  - type: textarea
+    id: problem
     attributes:
-      label: Adding, Removing, or Changing
-      description: What are you doing
-      options:
-        - Adding
-        - Removing
-        - Changing
-    validations:
-      required: true
-  - type: input
-    id: atype
-    attributes:
-      label: Type of Modification
-      description: What is it for?
-      value: I want to ...
+      label: What are your suggestions for new features or changes?
     validations:
       required: true
   - type: textarea
-    id: desc
+    id: proposal
     attributes:
-      label: What are you trying to modify
-      description: Give as detailed of a description as you can for the modification that you want done (include pictures if applicable)
-      value: The way I would implement this is ...
+      label: How should it work?
+      description: Provide as much detail as possible on what you would like changed or added.
     validations:
       required: true
   - type: textarea
-    id: alternative
+    id: extra
     attributes:
-      label: Alternatives
-      description: What alternatives have you considered?
-      value: If this could not be implemented I would ...
-  - type: markdown
-    id: thanks
-    attributes:
-      value: "Thank you for filling out the form! We will be with you soon. Please do not ask support to review your report."
+      label: Anything else?
+      description: Any additional information such as screenshots, examples, etc.

.github/ISSUE_TEMPLATE/translation.yml

@@ -0,0 +1,55 @@
+name: Translation
+description: A message in Iris is wrong, missing, or unclear.
+labels: [bug]
+type: Bug
+assignees: [SwiftSwamp]
+body:
+  - type: markdown
+    attributes:
+      value: |
+        The language files are in [`core/src/main/resources/languages/`](https://github.com/VolmitSoftware/Iris/tree/HEAD/core/src/main/resources/languages).
+
+        You can create a pull request to modify the files directly.
+  - type: dropdown
+    id: language
+    attributes:
+      label: Language
+      options:
+        - English (en_US)
+        - German (de_DE)
+        - Spanish (es_ES)
+        - Finnish (fi_FI)
+        - French (fr_FR)
+        - Hebrew (he_IL)
+        - Italian (it_IT)
+        - Japanese (ja-JP)
+        - Korean (ko_KR)
+        - Lithuanian (lt_LT)
+        - Dutch (nl_NL)
+        - Polish (pl_PL)
+        - Portuguese (pt_PT)
+        - Russian (ru_RU)
+        - Turkish (tr_TR)
+        - Vietnamese (vi_VI)
+        - Chinese, Simplified (zh_CN)
+        - Chinese, Traditional (zh_TW)
+        - Another language (name it below)
+    validations:
+      required: true
+  - type: textarea
+    id: current
+    attributes:
+      label: Current text
+    validations:
+      required: true
+  - type: textarea
+    id: suggested
+    attributes:
+      label: Suggested text
+    validations:
+      required: true
+  - type: input
+    id: where
+    attributes:
+      label: Where does it appear?
+      description: The command used or message key where it is appearing.

LICENSE.md

@@ -1,160 +1,215 @@
                     GNU GENERAL PUBLIC LICENSE
                        Version 3, 29 June 2007
 
-Copyright (C) 2007 Free Software Foundation, Inc. <https://fsf.org/>
-Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.
+ Copyright (C) 2007 Free Software Foundation, Inc. <https://fsf.org/>
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
 
                             Preamble
 
-The GNU General Public License is a free, copyleft license for software and other kinds of works.
+  The GNU General Public License is a free, copyleft license for
+software and other kinds of works.
 
-The licenses for most software and other practical works are designed to take away your freedom to share and change the
-works. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change all
-versions of a program--to make sure it remains free software for all its users. We, the Free Software Foundation, use
-the GNU General Public License for most of our software; it applies also to any other work released this way by its
-authors. You can apply it to your programs, too.
+  The licenses for most software and other practical works are designed
+to take away your freedom to share and change the works.  By contrast,
+the GNU General Public License is intended to guarantee your freedom to
+share and change all versions of a program--to make sure it remains free
+software for all its users.  We, the Free Software Foundation, use the
+GNU General Public License for most of our software; it applies also to
+any other work released this way by its authors.  You can apply it to
+your programs, too.
 
-When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make
-sure that you have the freedom to distribute copies of free software (and charge for them if you wish), that you receive
-source code or can get it if you want it, that you can change the software or use pieces of it in new free programs, and
-that you know you can do these things.
+  When we speak of free software, we are referring to freedom, not
+price.  Our General Public Licenses are designed to make sure that you
+have the freedom to distribute copies of free software (and charge for
+them if you wish), that you receive source code or can get it if you
+want it, that you can change the software or use pieces of it in new
+free programs, and that you know you can do these things.
 
-To protect your rights, we need to prevent others from denying you these rights or asking you to surrender the rights.
-Therefore, you have certain responsibilities if you distribute copies of the software, or if you modify it:
-responsibilities to respect the freedom of others.
+  To protect your rights, we need to prevent others from denying you
+these rights or asking you to surrender the rights.  Therefore, you have
+certain responsibilities if you distribute copies of the software, or if
+you modify it: responsibilities to respect the freedom of others.
 
-For example, if you distribute copies of such a program, whether gratis or for a fee, you must pass on to the recipients
-the same freedoms that you received. You must make sure that they, too, receive or can get the source code. And you must
-show them these terms so they know their rights.
+  For example, if you distribute copies of such a program, whether
+gratis or for a fee, you must pass on to the recipients the same
+freedoms that you received.  You must make sure that they, too, receive
+or can get the source code.  And you must show them these terms so they
+know their rights.
 
-Developers that use the GNU GPL protect your rights with two steps:
-(1) assert copyright on the software, and (2) offer you this License giving you legal permission to copy, distribute
-and/or modify it.
+  Developers that use the GNU GPL protect your rights with two steps:
+(1) assert copyright on the software, and (2) offer you this License
+giving you legal permission to copy, distribute and/or modify it.
 
-For the developers' and authors' protection, the GPL clearly explains that there is no warranty for this free software.
-For both users' and authors' sake, the GPL requires that modified versions be marked as changed, so that their problems
-will not be attributed erroneously to authors of previous versions.
+  For the developers' and authors' protection, the GPL clearly explains
+that there is no warranty for this free software.  For both users' and
+authors' sake, the GPL requires that modified versions be marked as
+changed, so that their problems will not be attributed erroneously to
+authors of previous versions.
 
-Some devices are designed to deny users access to install or run modified versions of the software inside them, although
-the manufacturer can do so. This is fundamentally incompatible with the aim of protecting users' freedom to change the
-software. The systematic pattern of such abuse occurs in the area of products for individuals to use, which is precisely
-where it is most unacceptable. Therefore, we have designed this version of the GPL to prohibit the practice for those
-products. If such problems arise substantially in other domains, we stand ready to extend this provision to those
-domains in future versions of the GPL, as needed to protect the freedom of users.
+  Some devices are designed to deny users access to install or run
+modified versions of the software inside them, although the manufacturer
+can do so.  This is fundamentally incompatible with the aim of
+protecting users' freedom to change the software.  The systematic
+pattern of such abuse occurs in the area of products for individuals to
+use, which is precisely where it is most unacceptable.  Therefore, we
+have designed this version of the GPL to prohibit the practice for those
+products.  If such problems arise substantially in other domains, we
+stand ready to extend this provision to those domains in future versions
+of the GPL, as needed to protect the freedom of users.
 
-Finally, every program is threatened constantly by software patents. States should not allow patents to restrict
-development and use of software on general-purpose computers, but in those that do, we wish to avoid the special danger
-that patents applied to a free program could make it effectively proprietary. To prevent this, the GPL assures that
+  Finally, every program is threatened constantly by software patents.
+States should not allow patents to restrict development and use of
+software on general-purpose computers, but in those that do, we wish to
+avoid the special danger that patents applied to a free program could
+make it effectively proprietary.  To prevent this, the GPL assures that
 patents cannot be used to render the program non-free.
 
-The precise terms and conditions for copying, distribution and modification follow.
+  The precise terms and conditions for copying, distribution and
+modification follow.
 
                        TERMS AND CONDITIONS
 
-0. Definitions.
+  0. Definitions.
 
-"This License" refers to version 3 of the GNU General Public License.
+  "This License" refers to version 3 of the GNU General Public License.
 
-"Copyright" also means copyright-like laws that apply to other kinds of works, such as semiconductor masks.
+  "Copyright" also means copyright-like laws that apply to other kinds of
+works, such as semiconductor masks.
 
-"The Program" refers to any copyrightable work licensed under this License. Each licensee is addressed as "you".  "
-Licensees" and
+  "The Program" refers to any copyrightable work licensed under this
+License.  Each licensee is addressed as "you".  "Licensees" and
 "recipients" may be individuals or organizations.
 
-To "modify" a work means to copy from or adapt all or part of the work in a fashion requiring copyright permission,
-other than the making of an exact copy. The resulting work is called a "modified version" of the earlier work or a
-work "based on" the earlier work.
+  To "modify" a work means to copy from or adapt all or part of the work
+in a fashion requiring copyright permission, other than the making of an
+exact copy.  The resulting work is called a "modified version" of the
+earlier work or a work "based on" the earlier work.
 
-A "covered work" means either the unmodified Program or a work based on the Program.
+  A "covered work" means either the unmodified Program or a work based
+on the Program.
 
-To "propagate" a work means to do anything with it that, without permission, would make you directly or secondarily
-liable for infringement under applicable copyright law, except executing it on a computer or modifying a private copy.
-Propagation includes copying, distribution (with or without modification), making available to the public, and in some
-countries other activities as well.
+  To "propagate" a work means to do anything with it that, without
+permission, would make you directly or secondarily liable for
+infringement under applicable copyright law, except executing it on a
+computer or modifying a private copy.  Propagation includes copying,
+distribution (with or without modification), making available to the
+public, and in some countries other activities as well.
 
-To "convey" a work means any kind of propagation that enables other parties to make or receive copies. Mere interaction
-with a user through a computer network, with no transfer of a copy, is not conveying.
+  To "convey" a work means any kind of propagation that enables other
+parties to make or receive copies.  Mere interaction with a user through
+a computer network, with no transfer of a copy, is not conveying.
 
-An interactive user interface displays "Appropriate Legal Notices"
-to the extent that it includes a convenient and prominently visible feature that (1) displays an appropriate copyright
-notice, and (2)
-tells the user that there is no warranty for the work (except to the extent that warranties are provided), that
-licensees may convey the work under this License, and how to view a copy of this License. If the interface presents a
-list of user commands or options, such as a menu, a prominent item in the list meets this criterion.
+  An interactive user interface displays "Appropriate Legal Notices"
+to the extent that it includes a convenient and prominently visible
+feature that (1) displays an appropriate copyright notice, and (2)
+tells the user that there is no warranty for the work (except to the
+extent that warranties are provided), that licensees may convey the
+work under this License, and how to view a copy of this License.  If
+the interface presents a list of user commands or options, such as a
+menu, a prominent item in the list meets this criterion.
 
-1. Source Code.
+  1. Source Code.
 
-The "source code" for a work means the preferred form of the work for making modifications to it.  "Object code" means
-any non-source form of a work.
+  The "source code" for a work means the preferred form of the work
+for making modifications to it.  "Object code" means any non-source
+form of a work.
 
-A "Standard Interface" means an interface that either is an official standard defined by a recognized standards body,
-or, in the case of interfaces specified for a particular programming language, one that is widely used among developers
-working in that language.
+  A "Standard Interface" means an interface that either is an official
+standard defined by a recognized standards body, or, in the case of
+interfaces specified for a particular programming language, one that
+is widely used among developers working in that language.
 
-The "System Libraries" of an executable work include anything, other than the work as a whole, that (a) is included in
-the normal form of packaging a Major Component, but which is not part of that Major Component, and (b) serves only to
-enable use of the work with that Major Component, or to implement a Standard Interface for which an implementation is
-available to the public in source code form. A
+  The "System Libraries" of an executable work include anything, other
+than the work as a whole, that (a) is included in the normal form of
+packaging a Major Component, but which is not part of that Major
+Component, and (b) serves only to enable use of the work with that
+Major Component, or to implement a Standard Interface for which an
+implementation is available to the public in source code form.  A
 "Major Component", in this context, means a major essential component
 (kernel, window system, and so on) of the specific operating system
-(if any) on which the executable work runs, or a compiler used to produce the work, or an object code interpreter used
-to run it.
+(if any) on which the executable work runs, or a compiler used to
+produce the work, or an object code interpreter used to run it.
 
-The "Corresponding Source" for a work in object code form means all the source code needed to generate, install, and (
-for an executable work) run the object code and to modify the work, including scripts to control those activities.
-However, it does not include the work's System Libraries, or general-purpose tools or generally available free programs
-which are used unmodified in performing those activities but which are not part of the work. For example, Corresponding
-Source includes interface definition files associated with source files for the work, and the source code for shared
-libraries and dynamically linked subprograms that the work is specifically designed to require, such as by intimate data
-communication or control flow between those subprograms and other parts of the work.
+  The "Corresponding Source" for a work in object code form means all
+the source code needed to generate, install, and (for an executable
+work) run the object code and to modify the work, including scripts to
+control those activities.  However, it does not include the work's
+System Libraries, or general-purpose tools or generally available free
+programs which are used unmodified in performing those activities but
+which are not part of the work.  For example, Corresponding Source
+includes interface definition files associated with source files for
+the work, and the source code for shared libraries and dynamically
+linked subprograms that the work is specifically designed to require,
+such as by intimate data communication or control flow between those
+subprograms and other parts of the work.
 
-The Corresponding Source need not include anything that users can regenerate automatically from other parts of the
-Corresponding Source.
+  The Corresponding Source need not include anything that users
+can regenerate automatically from other parts of the Corresponding
+Source.
 
-The Corresponding Source for a work in source code form is that same work.
+  The Corresponding Source for a work in source code form is that
+same work.
 
-2. Basic Permissions.
+  2. Basic Permissions.
 
-All rights granted under this License are granted for the term of copyright on the Program, and are irrevocable provided
-the stated conditions are met. This License explicitly affirms your unlimited permission to run the unmodified Program.
-The output from running a covered work is covered by this License only if the output, given its content, constitutes a
-covered work. This License acknowledges your rights of fair use or other equivalent, as provided by copyright law.
+  All rights granted under this License are granted for the term of
+copyright on the Program, and are irrevocable provided the stated
+conditions are met.  This License explicitly affirms your unlimited
+permission to run the unmodified Program.  The output from running a
+covered work is covered by this License only if the output, given its
+content, constitutes a covered work.  This License acknowledges your
+rights of fair use or other equivalent, as provided by copyright law.
 
-You may make, run and propagate covered works that you do not convey, without conditions so long as your license
-otherwise remains in force. You may convey covered works to others for the sole purpose of having them make
-modifications exclusively for you, or provide you with facilities for running those works, provided that you comply with
-the terms of this License in conveying all material for which you do not control copyright. Those thus making or running
-the covered works for you must do so exclusively on your behalf, under your direction and control, on terms that
-prohibit them from making any copies of your copyrighted material outside their relationship with you.
+  You may make, run and propagate covered works that you do not
+convey, without conditions so long as your license otherwise remains
+in force.  You may convey covered works to others for the sole purpose
+of having them make modifications exclusively for you, or provide you
+with facilities for running those works, provided that you comply with
+the terms of this License in conveying all material for which you do
+not control copyright.  Those thus making or running the covered works
+for you must do so exclusively on your behalf, under your direction
+and control, on terms that prohibit them from making any copies of
+your copyrighted material outside their relationship with you.
 
-Conveying under any other circumstances is permitted solely under the conditions stated below. Sublicensing is not
-allowed; section 10 makes it unnecessary.
+  Conveying under any other circumstances is permitted solely under
+the conditions stated below.  Sublicensing is not allowed; section 10
+makes it unnecessary.
 
-3. Protecting Users' Legal Rights From Anti-Circumvention Law.
+  3. Protecting Users' Legal Rights From Anti-Circumvention Law.
 
-No covered work shall be deemed part of an effective technological measure under any applicable law fulfilling
-obligations under article 11 of the WIPO copyright treaty adopted on 20 December 1996, or similar laws prohibiting or
-restricting circumvention of such measures.
+  No covered work shall be deemed part of an effective technological
+measure under any applicable law fulfilling obligations under article
+11 of the WIPO copyright treaty adopted on 20 December 1996, or
+similar laws prohibiting or restricting circumvention of such
+measures.
 
-When you convey a covered work, you waive any legal power to forbid circumvention of technological measures to the
-extent such circumvention is effected by exercising rights under this License with respect to the covered work, and you
-disclaim any intention to limit operation or modification of the work as a means of enforcing, against the work's users,
-your or third parties' legal rights to forbid circumvention of technological measures.
+  When you convey a covered work, you waive any legal power to forbid
+circumvention of technological measures to the extent such circumvention
+is effected by exercising rights under this License with respect to
+the covered work, and you disclaim any intention to limit operation or
+modification of the work as a means of enforcing, against the work's
+users, your or third parties' legal rights to forbid circumvention of
+technological measures.
 
-4. Conveying Verbatim Copies.
+  4. Conveying Verbatim Copies.
 
-You may convey verbatim copies of the Program's source code as you receive it, in any medium, provided that you
-conspicuously and appropriately publish on each copy an appropriate copyright notice; keep intact all notices stating
-that this License and any non-permissive terms added in accord with section 7 apply to the code; keep intact all notices
-of the absence of any warranty; and give all recipients a copy of this License along with the Program.
+  You may convey verbatim copies of the Program's source code as you
+receive it, in any medium, provided that you conspicuously and
+appropriately publish on each copy an appropriate copyright notice;
+keep intact all notices stating that this License and any
+non-permissive terms added in accord with section 7 apply to the code;
+keep intact all notices of the absence of any warranty; and give all
+recipients a copy of this License along with the Program.
 
-You may charge any price or no price for each copy that you convey, and you may offer support or warranty protection for
-a fee.
+  You may charge any price or no price for each copy that you convey,
+and you may offer support or warranty protection for a fee.
 
-5. Conveying Modified Source Versions.
+  5. Conveying Modified Source Versions.
 
-You may convey a work based on the Program, or the modifications to produce it from the Program, in the form of source
-code under the terms of section 4, provided that you also meet all of these conditions:
+  You may convey a work based on the Program, or the modifications to
+produce it from the Program, in the form of source code under the
+terms of section 4, provided that you also meet all of these conditions:
 
     a) The work must carry prominent notices stating that you modified
     it, and giving a relevant date.
@@ -177,17 +232,22 @@ code under the terms of section 4, provided that you also meet all of these cond
     interfaces that do not display Appropriate Legal Notices, your
     work need not make them do so.
 
-A compilation of a covered work with other separate and independent works, which are not by their nature extensions of
-the covered work, and which are not combined with it such as to form a larger program, in or on a volume of a storage or
-distribution medium, is called an
-"aggregate" if the compilation and its resulting copyright are not used to limit the access or legal rights of the
-compilation's users beyond what the individual works permit. Inclusion of a covered work in an aggregate does not cause
-this License to apply to the other parts of the aggregate.
+  A compilation of a covered work with other separate and independent
+works, which are not by their nature extensions of the covered work,
+and which are not combined with it such as to form a larger program,
+in or on a volume of a storage or distribution medium, is called an
+"aggregate" if the compilation and its resulting copyright are not
+used to limit the access or legal rights of the compilation's users
+beyond what the individual works permit.  Inclusion of a covered work
+in an aggregate does not cause this License to apply to the other
+parts of the aggregate.
 
-6. Conveying Non-Source Forms.
+  6. Conveying Non-Source Forms.
 
-You may convey a covered work in object code form under the terms of sections 4 and 5, provided that you also convey the
-machine-readable Corresponding Source under the terms of this License, in one of these ways:
+  You may convey a covered work in object code form under the terms
+of sections 4 and 5, provided that you also convey the
+machine-readable Corresponding Source under the terms of this License,
+in one of these ways:
 
     a) Convey the object code in, or embodied in, a physical product
     (including a physical distribution medium), accompanied by the
@@ -230,55 +290,77 @@ machine-readable Corresponding Source under the terms of this License, in one of
     Source of the work are being offered to the general public at no
     charge under subsection 6d.
 
-A separable portion of the object code, whose source code is excluded from the Corresponding Source as a System Library,
-need not be included in conveying the object code work.
+  A separable portion of the object code, whose source code is excluded
+from the Corresponding Source as a System Library, need not be
+included in conveying the object code work.
 
-A "User Product" is either (1) a "consumer product", which means any tangible personal property which is normally used
-for personal, family, or household purposes, or (2) anything designed or sold for incorporation into a dwelling. In
-determining whether a product is a consumer product, doubtful cases shall be resolved in favor of coverage. For a
-particular product received by a particular user, "normally used" refers to a typical or common use of that class of
-product, regardless of the status of the particular user or of the way in which the particular user actually uses, or
-expects or is expected to use, the product. A product is a consumer product regardless of whether the product has
-substantial commercial, industrial or non-consumer uses, unless such uses represent the only significant mode of use of
-the product.
+  A "User Product" is either (1) a "consumer product", which means any
+tangible personal property which is normally used for personal, family,
+or household purposes, or (2) anything designed or sold for incorporation
+into a dwelling.  In determining whether a product is a consumer product,
+doubtful cases shall be resolved in favor of coverage.  For a particular
+product received by a particular user, "normally used" refers to a
+typical or common use of that class of product, regardless of the status
+of the particular user or of the way in which the particular user
+actually uses, or expects or is expected to use, the product.  A product
+is a consumer product regardless of whether the product has substantial
+commercial, industrial or non-consumer uses, unless such uses represent
+the only significant mode of use of the product.
 
-"Installation Information" for a User Product means any methods, procedures, authorization keys, or other information
-required to install and execute modified versions of a covered work in that User Product from a modified version of its
-Corresponding Source. The information must suffice to ensure that the continued functioning of the modified object code
-is in no case prevented or interfered with solely because modification has been made.
+  "Installation Information" for a User Product means any methods,
+procedures, authorization keys, or other information required to install
+and execute modified versions of a covered work in that User Product from
+a modified version of its Corresponding Source.  The information must
+suffice to ensure that the continued functioning of the modified object
+code is in no case prevented or interfered with solely because
+modification has been made.
 
-If you convey an object code work under this section in, or with, or specifically for use in, a User Product, and the
-conveying occurs as part of a transaction in which the right of possession and use of the User Product is transferred to
-the recipient in perpetuity or for a fixed term (regardless of how the transaction is characterized), the Corresponding
-Source conveyed under this section must be accompanied by the Installation Information. But this requirement does not
-apply if neither you nor any third party retains the ability to install modified object code on the User Product (for
-example, the work has been installed in ROM).
+  If you convey an object code work under this section in, or with, or
+specifically for use in, a User Product, and the conveying occurs as
+part of a transaction in which the right of possession and use of the
+User Product is transferred to the recipient in perpetuity or for a
+fixed term (regardless of how the transaction is characterized), the
+Corresponding Source conveyed under this section must be accompanied
+by the Installation Information.  But this requirement does not apply
+if neither you nor any third party retains the ability to install
+modified object code on the User Product (for example, the work has
+been installed in ROM).
 
-The requirement to provide Installation Information does not include a requirement to continue to provide support
-service, warranty, or updates for a work that has been modified or installed by the recipient, or for the User Product
-in which it has been modified or installed. Access to a network may be denied when the modification itself materially
-and adversely affects the operation of the network or violates the rules and protocols for communication across the
-network.
+  The requirement to provide Installation Information does not include a
+requirement to continue to provide support service, warranty, or updates
+for a work that has been modified or installed by the recipient, or for
+the User Product in which it has been modified or installed.  Access to a
+network may be denied when the modification itself materially and
+adversely affects the operation of the network or violates the rules and
+protocols for communication across the network.
 
-Corresponding Source conveyed, and Installation Information provided, in accord with this section must be in a format
-that is publicly documented (and with an implementation available to the public in source code form), and must require
-no special password or key for unpacking, reading or copying.
+  Corresponding Source conveyed, and Installation Information provided,
+in accord with this section must be in a format that is publicly
+documented (and with an implementation available to the public in
+source code form), and must require no special password or key for
+unpacking, reading or copying.
 
-7. Additional Terms.
+  7. Additional Terms.
 
-"Additional permissions" are terms that supplement the terms of this License by making exceptions from one or more of
-its conditions. Additional permissions that are applicable to the entire Program shall be treated as though they were
-included in this License, to the extent that they are valid under applicable law. If additional permissions apply only
-to part of the Program, that part may be used separately under those permissions, but the entire Program remains
-governed by this License without regard to the additional permissions.
+  "Additional permissions" are terms that supplement the terms of this
+License by making exceptions from one or more of its conditions.
+Additional permissions that are applicable to the entire Program shall
+be treated as though they were included in this License, to the extent
+that they are valid under applicable law.  If additional permissions
+apply only to part of the Program, that part may be used separately
+under those permissions, but the entire Program remains governed by
+this License without regard to the additional permissions.
 
-When you convey a copy of a covered work, you may at your option remove any additional permissions from that copy, or
-from any part of it.  (Additional permissions may be written to require their own removal in certain cases when you
-modify the work.)  You may place additional permissions on material, added by you to a covered work, for which you have
-or can give appropriate copyright permission.
+  When you convey a copy of a covered work, you may at your option
+remove any additional permissions from that copy, or from any part of
+it.  (Additional permissions may be written to require their own
+removal in certain cases when you modify the work.)  You may place
+additional permissions on material, added by you to a covered work,
+for which you have or can give appropriate copyright permission.
 
-Notwithstanding any other provision of this License, for material you add to a covered work, you may (if authorized by
-the copyright holders of that material) supplement the terms of this License with terms:
+  Notwithstanding any other provision of this License, for material you
+add to a covered work, you may (if authorized by the copyright holders of
+that material) supplement the terms of this License with terms:
 
     a) Disclaiming warranty or limiting liability differently from the
     terms of sections 15 and 16 of this License; or
@@ -303,182 +385,251 @@ the copyright holders of that material) supplement the terms of this License wit
     any liability that these contractual assumptions directly impose on
     those licensors and authors.
 
-All other non-permissive additional terms are considered "further restrictions" within the meaning of section 10. If the
-Program as you received it, or any part of it, contains a notice stating that it is governed by this License along with
-a term that is a further restriction, you may remove that term. If a license document contains a further restriction but
-permits relicensing or conveying under this License, you may add to a covered work material governed by the terms of
-that license document, provided that the further restriction does not survive such relicensing or conveying.
+  All other non-permissive additional terms are considered "further
+restrictions" within the meaning of section 10.  If the Program as you
+received it, or any part of it, contains a notice stating that it is
+governed by this License along with a term that is a further
+restriction, you may remove that term.  If a license document contains
+a further restriction but permits relicensing or conveying under this
+License, you may add to a covered work material governed by the terms
+of that license document, provided that the further restriction does
+not survive such relicensing or conveying.
 
-If you add terms to a covered work in accord with this section, you must place, in the relevant source files, a
-statement of the additional terms that apply to those files, or a notice indicating where to find the applicable terms.
+  If you add terms to a covered work in accord with this section, you
+must place, in the relevant source files, a statement of the
+additional terms that apply to those files, or a notice indicating
+where to find the applicable terms.
 
-Additional terms, permissive or non-permissive, may be stated in the form of a separately written license, or stated as
-exceptions; the above requirements apply either way.
+  Additional terms, permissive or non-permissive, may be stated in the
+form of a separately written license, or stated as exceptions;
+the above requirements apply either way.
 
-8. Termination.
+  8. Termination.
 
-You may not propagate or modify a covered work except as expressly provided under this License. Any attempt otherwise to
-propagate or modify it is void, and will automatically terminate your rights under this License (including any patent
-licenses granted under the third paragraph of section 11).
+  You may not propagate or modify a covered work except as expressly
+provided under this License.  Any attempt otherwise to propagate or
+modify it is void, and will automatically terminate your rights under
+this License (including any patent licenses granted under the third
+paragraph of section 11).
 
-However, if you cease all violation of this License, then your license from a particular copyright holder is
-reinstated (a)
-provisionally, unless and until the copyright holder explicitly and finally terminates your license, and (b)
-permanently, if the copyright holder fails to notify you of the violation by some reasonable means prior to 60 days
-after the cessation.
+  However, if you cease all violation of this License, then your
+license from a particular copyright holder is reinstated (a)
+provisionally, unless and until the copyright holder explicitly and
+finally terminates your license, and (b) permanently, if the copyright
+holder fails to notify you of the violation by some reasonable means
+prior to 60 days after the cessation.
 
-Moreover, your license from a particular copyright holder is reinstated permanently if the copyright holder notifies you
-of the violation by some reasonable means, this is the first time you have received notice of violation of this
-License (for any work) from that copyright holder, and you cure the violation prior to 30 days after your receipt of the
-notice.
+  Moreover, your license from a particular copyright holder is
+reinstated permanently if the copyright holder notifies you of the
+violation by some reasonable means, this is the first time you have
+received notice of violation of this License (for any work) from that
+copyright holder, and you cure the violation prior to 30 days after
+your receipt of the notice.
 
-Termination of your rights under this section does not terminate the licenses of parties who have received copies or
-rights from you under this License. If your rights have been terminated and not permanently reinstated, you do not
-qualify to receive new licenses for the same material under section 10.
+  Termination of your rights under this section does not terminate the
+licenses of parties who have received copies or rights from you under
+this License.  If your rights have been terminated and not permanently
+reinstated, you do not qualify to receive new licenses for the same
+material under section 10.
 
-9. Acceptance Not Required for Having Copies.
+  9. Acceptance Not Required for Having Copies.
 
-You are not required to accept this License in order to receive or run a copy of the Program. Ancillary propagation of a
-covered work occurring solely as a consequence of using peer-to-peer transmission to receive a copy likewise does not
-require acceptance. However, nothing other than this License grants you permission to propagate or modify any covered
-work. These actions infringe copyright if you do not accept this License. Therefore, by modifying or propagating a
+  You are not required to accept this License in order to receive or
+run a copy of the Program.  Ancillary propagation of a covered work
+occurring solely as a consequence of using peer-to-peer transmission
+to receive a copy likewise does not require acceptance.  However,
+nothing other than this License grants you permission to propagate or
+modify any covered work.  These actions infringe copyright if you do
+not accept this License.  Therefore, by modifying or propagating a
 covered work, you indicate your acceptance of this License to do so.
 
-10. Automatic Licensing of Downstream Recipients.
+  10. Automatic Licensing of Downstream Recipients.
 
-Each time you convey a covered work, the recipient automatically receives a license from the original licensors, to run,
-modify and propagate that work, subject to this License. You are not responsible for enforcing compliance by third
-parties with this License.
+  Each time you convey a covered work, the recipient automatically
+receives a license from the original licensors, to run, modify and
+propagate that work, subject to this License.  You are not responsible
+for enforcing compliance by third parties with this License.
 
-An "entity transaction" is a transaction transferring control of an organization, or substantially all assets of one, or
-subdividing an organization, or merging organizations. If propagation of a covered work results from an entity
-transaction, each party to that transaction who receives a copy of the work also receives whatever licenses to the work
-the party's predecessor in interest had or could give under the previous paragraph, plus a right to possession of the
-Corresponding Source of the work from the predecessor in interest, if the predecessor has it or can get it with
-reasonable efforts.
+  An "entity transaction" is a transaction transferring control of an
+organization, or substantially all assets of one, or subdividing an
+organization, or merging organizations.  If propagation of a covered
+work results from an entity transaction, each party to that
+transaction who receives a copy of the work also receives whatever
+licenses to the work the party's predecessor in interest had or could
+give under the previous paragraph, plus a right to possession of the
+Corresponding Source of the work from the predecessor in interest, if
+the predecessor has it or can get it with reasonable efforts.
 
-You may not impose any further restrictions on the exercise of the rights granted or affirmed under this License. For
-example, you may not impose a license fee, royalty, or other charge for exercise of rights granted under this License,
-and you may not initiate litigation
-(including a cross-claim or counterclaim in a lawsuit) alleging that any patent claim is infringed by making, using,
-selling, offering for sale, or importing the Program or any portion of it.
+  You may not impose any further restrictions on the exercise of the
+rights granted or affirmed under this License.  For example, you may
+not impose a license fee, royalty, or other charge for exercise of
+rights granted under this License, and you may not initiate litigation
+(including a cross-claim or counterclaim in a lawsuit) alleging that
+any patent claim is infringed by making, using, selling, offering for
+sale, or importing the Program or any portion of it.
 
-11. Patents.
+  11. Patents.
 
-A "contributor" is a copyright holder who authorizes use under this License of the Program or a work on which the
-Program is based. The work thus licensed is called the contributor's "contributor version".
+  A "contributor" is a copyright holder who authorizes use under this
+License of the Program or a work on which the Program is based.  The
+work thus licensed is called the contributor's "contributor version".
 
-A contributor's "essential patent claims" are all patent claims owned or controlled by the contributor, whether already
-acquired or hereafter acquired, that would be infringed by some manner, permitted by this License, of making, using, or
-selling its contributor version, but do not include claims that would be infringed only as a consequence of further
-modification of the contributor version. For purposes of this definition, "control" includes the right to grant patent
-sublicenses in a manner consistent with the requirements of this License.
+  A contributor's "essential patent claims" are all patent claims
+owned or controlled by the contributor, whether already acquired or
+hereafter acquired, that would be infringed by some manner, permitted
+by this License, of making, using, or selling its contributor version,
+but do not include claims that would be infringed only as a
+consequence of further modification of the contributor version.  For
+purposes of this definition, "control" includes the right to grant
+patent sublicenses in a manner consistent with the requirements of
+this License.
 
-Each contributor grants you a non-exclusive, worldwide, royalty-free patent license under the contributor's essential
-patent claims, to make, use, sell, offer for sale, import and otherwise run, modify and propagate the contents of its
-contributor version.
+  Each contributor grants you a non-exclusive, worldwide, royalty-free
+patent license under the contributor's essential patent claims, to
+make, use, sell, offer for sale, import and otherwise run, modify and
+propagate the contents of its contributor version.
 
-In the following three paragraphs, a "patent license" is any express agreement or commitment, however denominated, not
-to enforce a patent
-(such as an express permission to practice a patent or covenant not to sue for patent infringement). To "grant" such a
-patent license to a party means to make such an agreement or commitment not to enforce a patent against the party.
+  In the following three paragraphs, a "patent license" is any express
+agreement or commitment, however denominated, not to enforce a patent
+(such as an express permission to practice a patent or covenant not to
+sue for patent infringement).  To "grant" such a patent license to a
+party means to make such an agreement or commitment not to enforce a
+patent against the party.
 
-If you convey a covered work, knowingly relying on a patent license, and the Corresponding Source of the work is not
-available for anyone to copy, free of charge and under the terms of this License, through a publicly available network
-server or other readily accessible means, then you must either (1) cause the Corresponding Source to be so available,
-or (2) arrange to deprive yourself of the benefit of the patent license for this particular work, or (3) arrange, in a
-manner consistent with the requirements of this License, to extend the patent license to downstream recipients.  "
-Knowingly relying" means you have actual knowledge that, but for the patent license, your conveying the covered work in
-a country, or your recipient's use of the covered work in a country, would infringe one or more identifiable patents in
-that country that you have reason to believe are valid.
+  If you convey a covered work, knowingly relying on a patent license,
+and the Corresponding Source of the work is not available for anyone
+to copy, free of charge and under the terms of this License, through a
+publicly available network server or other readily accessible means,
+then you must either (1) cause the Corresponding Source to be so
+available, or (2) arrange to deprive yourself of the benefit of the
+patent license for this particular work, or (3) arrange, in a manner
+consistent with the requirements of this License, to extend the patent
+license to downstream recipients.  "Knowingly relying" means you have
+actual knowledge that, but for the patent license, your conveying the
+covered work in a country, or your recipient's use of the covered work
+in a country, would infringe one or more identifiable patents in that
+country that you have reason to believe are valid.
 
-If, pursuant to or in connection with a single transaction or arrangement, you convey, or propagate by procuring
-conveyance of, a covered work, and grant a patent license to some of the parties receiving the covered work authorizing
-them to use, propagate, modify or convey a specific copy of the covered work, then the patent license you grant is
-automatically extended to all recipients of the covered work and works based on it.
+  If, pursuant to or in connection with a single transaction or
+arrangement, you convey, or propagate by procuring conveyance of, a
+covered work, and grant a patent license to some of the parties
+receiving the covered work authorizing them to use, propagate, modify
+or convey a specific copy of the covered work, then the patent license
+you grant is automatically extended to all recipients of the covered
+work and works based on it.
 
-A patent license is "discriminatory" if it does not include within the scope of its coverage, prohibits the exercise of,
-or is conditioned on the non-exercise of one or more of the rights that are specifically granted under this License. You
-may not convey a covered work if you are a party to an arrangement with a third party that is in the business of
-distributing software, under which you make payment to the third party based on the extent of your activity of conveying
-the work, and under which the third party grants, to any of the parties who would receive the covered work from you, a
-discriminatory patent license (a) in connection with copies of the covered work conveyed by you (or copies made from
-those copies), or (b) primarily for and in connection with specific products or compilations that contain the covered
-work, unless you entered into that arrangement, or that patent license was granted, prior to 28 March 2007.
+  A patent license is "discriminatory" if it does not include within
+the scope of its coverage, prohibits the exercise of, or is
+conditioned on the non-exercise of one or more of the rights that are
+specifically granted under this License.  You may not convey a covered
+work if you are a party to an arrangement with a third party that is
+in the business of distributing software, under which you make payment
+to the third party based on the extent of your activity of conveying
+the work, and under which the third party grants, to any of the
+parties who would receive the covered work from you, a discriminatory
+patent license (a) in connection with copies of the covered work
+conveyed by you (or copies made from those copies), or (b) primarily
+for and in connection with specific products or compilations that
+contain the covered work, unless you entered into that arrangement,
+or that patent license was granted, prior to 28 March 2007.
 
-Nothing in this License shall be construed as excluding or limiting any implied license or other defenses to
-infringement that may otherwise be available to you under applicable patent law.
+  Nothing in this License shall be construed as excluding or limiting
+any implied license or other defenses to infringement that may
+otherwise be available to you under applicable patent law.
 
-12. No Surrender of Others' Freedom.
+  12. No Surrender of Others' Freedom.
 
-If conditions are imposed on you (whether by court order, agreement or otherwise) that contradict the conditions of this
-License, they do not excuse you from the conditions of this License. If you cannot convey a covered work so as to
-satisfy simultaneously your obligations under this License and any other pertinent obligations, then as a consequence
-you may not convey it at all. For example, if you agree to terms that obligate you to collect a royalty for further
-conveying from those to whom you convey the Program, the only way you could satisfy both those terms and this License
-would be to refrain entirely from conveying the Program.
+  If conditions are imposed on you (whether by court order, agreement or
+otherwise) that contradict the conditions of this License, they do not
+excuse you from the conditions of this License.  If you cannot convey a
+covered work so as to satisfy simultaneously your obligations under this
+License and any other pertinent obligations, then as a consequence you may
+not convey it at all.  For example, if you agree to terms that obligate you
+to collect a royalty for further conveying from those to whom you convey
+the Program, the only way you could satisfy both those terms and this
+License would be to refrain entirely from conveying the Program.
 
-13. Use with the GNU Affero General Public License.
+  13. Use with the GNU Affero General Public License.
 
-Notwithstanding any other provision of this License, you have permission to link or combine any covered work with a work
-licensed under version 3 of the GNU Affero General Public License into a single combined work, and to convey the
-resulting work. The terms of this License will continue to apply to the part which is the covered work, but the special
-requirements of the GNU Affero General Public License, section 13, concerning interaction through a network will apply
-to the combination as such.
+  Notwithstanding any other provision of this License, you have
+permission to link or combine any covered work with a work licensed
+under version 3 of the GNU Affero General Public License into a single
+combined work, and to convey the resulting work.  The terms of this
+License will continue to apply to the part which is the covered work,
+but the special requirements of the GNU Affero General Public License,
+section 13, concerning interaction through a network will apply to the
+combination as such.
 
-14. Revised Versions of this License.
+  14. Revised Versions of this License.
 
-The Free Software Foundation may publish revised and/or new versions of the GNU General Public License from time to
-time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new
-problems or concerns.
+  The Free Software Foundation may publish revised and/or new versions of
+the GNU General Public License from time to time.  Such new versions will
+be similar in spirit to the present version, but may differ in detail to
+address new problems or concerns.
 
-Each version is given a distinguishing version number. If the Program specifies that a certain numbered version of the
-GNU General Public License "or any later version" applies to it, you have the option of following the terms and
-conditions either of that numbered version or of any later version published by the Free Software Foundation. If the
-Program does not specify a version number of the GNU General Public License, you may choose any version ever published
+  Each version is given a distinguishing version number.  If the
+Program specifies that a certain numbered version of the GNU General
+Public License "or any later version" applies to it, you have the
+option of following the terms and conditions either of that numbered
+version or of any later version published by the Free Software
+Foundation.  If the Program does not specify a version number of the
+GNU General Public License, you may choose any version ever published
 by the Free Software Foundation.
 
-If the Program specifies that a proxy can decide which future versions of the GNU General Public License can be used,
-that proxy's public statement of acceptance of a version permanently authorizes you to choose that version for the
-Program.
+  If the Program specifies that a proxy can decide which future
+versions of the GNU General Public License can be used, that proxy's
+public statement of acceptance of a version permanently authorizes you
+to choose that version for the Program.
 
-Later license versions may give you additional or different permissions. However, no additional obligations are imposed
-on any author or copyright holder as a result of your choosing to follow a later version.
+  Later license versions may give you additional or different
+permissions.  However, no additional obligations are imposed on any
+author or copyright holder as a result of your choosing to follow a
+later version.
 
-15. Disclaimer of Warranty.
+  15. Disclaimer of Warranty.
 
-THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING
-THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR
-IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
-THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU
-ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
+  THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY
+APPLICABLE LAW.  EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT
+HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY
+OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO,
+THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+PURPOSE.  THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM
+IS WITH YOU.  SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF
+ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
 
-16. Limitation of Liability.
+  16. Limitation of Liability.
 
-IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO
-MODIFIES AND/OR CONVEYS THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL,
-INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO
-LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM
-TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
-DAMAGES.
+  IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
+THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
+GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
+USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
+DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
+PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
+EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGES.
 
-17. Interpretation of Sections 15 and 16.
+  17. Interpretation of Sections 15 and 16.
 
-If the disclaimer of warranty and limitation of liability provided above cannot be given local legal effect according to
-their terms, reviewing courts shall apply local law that most closely approximates an absolute waiver of all civil
-liability in connection with the Program, unless a warranty or assumption of liability accompanies a copy of the Program
-in return for a fee.
+  If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
 
                      END OF TERMS AND CONDITIONS
 
             How to Apply These Terms to Your New Programs
 
-If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve
-this is to make it free software which everyone can redistribute and change under these terms.
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
 
-To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to
-most effectively state the exclusion of warranty; and each file should have at least the "copyright" line and a pointer
-to where the full notice is found.
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
 
     <one line to give the program's name and a brief idea of what it does.>
     Copyright (C) <year>  <name of author>
@@ -498,21 +649,26 @@ to where the full notice is found.
 
 Also add information on how to contact you by electronic and paper mail.
 
-If the program does terminal interaction, make it output a short notice like this when it starts in an interactive mode:
+  If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
 
     <program>  Copyright (C) <year>  <name of author>
     This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
     This is free software, and you are welcome to redistribute it
     under certain conditions; type `show c' for details.
 
-The hypothetical commands `show w' and `show c' should show the appropriate parts of the General Public License. Of
-course, your program's commands might be different; for a GUI interface, you would use an "about box".
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, your program's commands
+might be different; for a GUI interface, you would use an "about box".
 
-You should also get your employer (if you work as a programmer) or school, if any, to sign a "copyright disclaimer" for
-the program, if necessary. For more information on this, and how to apply and follow the GNU GPL, see
+  You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
 <https://www.gnu.org/licenses/>.
 
-The GNU General Public License does not permit incorporating your program into proprietary programs. If your program is
-a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If
-this is what you want to do, use the GNU Lesser General Public License instead of this License. But first, please read
+  The GNU General Public License does not permit incorporating your program
+into proprietary programs.  If your program is a subroutine library, you
+may consider it more useful to permit linking proprietary applications with
+the library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.  But first, please read
 <https://www.gnu.org/licenses/why-not-lgpl.html>.

README.md

@@ -25,7 +25,7 @@ Canonical English is defined in the typed Java catalogs under `core/src/main/jav
 | Spigot / CraftBukkit | plugin jar | 26.1.2 - 26.3 | Managed `iris:*` creation and generation; exact vanilla-slot `/iris replace` is unavailable |
 | Fabric | mod jar | 26.3 | Server worldgen + client HUD; requires Fabric Loader 0.19.5+ |
 | Forge | mod jar | 26.3 | Server worldgen + client HUD; current target is Forge 26.3-66.0.8 |
-| NeoForge | mod jar | 26.3 | Server worldgen + client HUD; current target is NeoForge 26.3.0.33-beta |
+| NeoForge | mod jar | 26.3 | Server worldgen + client HUD; requires NeoForge 26.3.0.65-beta+; current target is NeoForge 26.3.0.83 |
 
 Java 25 is required on every platform.
 
@@ -252,7 +252,9 @@ Requirements: JDK 25 (set `JAVA_HOME` to it). The Gradle wrapper handles everyth
 ./gradlew buildAllToOut
 ```
 
-builds every platform artifact into the workspace-level `../PluginOuts/` directory:
+builds every platform artifact into the workspace-level `../PluginOuts/` directory: the Bukkit jar
+and a Fabric, Forge and NeoForge jar for every Minecraft version in `gradle/mod-targets.json`
+(1.21.1, 26.1.2, 26.2 and 26.3):
 
 ```
 Iris v<version> [CraftBukkit] <mc>.jar
@@ -261,14 +263,18 @@ Iris v<version> [Forge] <mc>+<loader>.jar
 Iris v<version> [NeoForge] <mc>+<loader>.jar
 ```
 
-Per-platform tasks: `./gradlew buildBukkit`, `buildFabric`, `buildForge`, `buildNeoforge`. The
+Per-platform tasks: `./gradlew buildBukkit`, and `build<Loader><mc>` for one mod jar, for example
+`buildFabric26_2` or `buildNeoForge1_21_1`. `buildFabric`, `buildForge` and `buildNeoforge` export the
+26.3 jars. `./gradlew checkAll` runs every check, then builds and verifies all twelve mod jars and runs their
+unit tests; Forge 1.21.1 only compiles its tests because Forge 52 cannot bootstrap Minecraft outside
+FML. The
 SPI jar (the pure-JVM adapter/platform contract, not the stable plugin API) is built to `spi/build/libs/` by
 `./gradlew :spi:jar`.
 
 `./gradlew buildAll` also runs `buildAllToOut` and copies the jars into a consumer dropin tree
 for a local test server. The consumer directory defaults to `../../[Minecraft Server]/consumers/`
 when it exists, otherwise `build/consumers/` inside the repo. `-Plocation=/path/to/consumers`
-changes only the consumer directory. Both tasks copy all four verified platform jars into
+changes only the consumer directory. Both tasks copy every verified platform jar into
 `../PluginOuts/`.
 
 VolmLib is built from source when a `VolmLib` checkout sits beside the repo or in a parent directory

adapters/bukkit/plugin/src/main/java/art/arcane/iris/Iris.java

@@ -223,7 +223,6 @@ public class Iris extends VolmitPlugin implements Listener, ReloadAware {
     private IrisUpdateNotifier updateNotifier;
     private BukkitDebugDump debugDump;
     private volatile SettingsHotloadWatch settingsHotloadWatch;
-    private volatile Thread serverLifecycleThread;
     private volatile ServerShutdownBoundary serverShutdownBoundary;
 
     public static VolmitSender getSender() {
@@ -832,7 +831,6 @@ public class Iris extends VolmitPlugin implements Listener, ReloadAware {
 
     public void addShutdownHook() {
         removeShutdownHook();
-        serverLifecycleThread = Thread.currentThread();
         serverShutdownBoundary = INMS.isBound() ? INMS.get().createServerShutdownBoundary() : null;
         shutdownHook = new Thread(this::runShutdownHook, "Iris-ShutdownHook");
         try {
@@ -1164,7 +1162,7 @@ public class Iris extends VolmitPlugin implements Listener, ReloadAware {
             if (generator == null) {
                 continue;
             }
-            IrisToolbelt.beginWorldMaintenance(world, reason, true);
+            IrisToolbelt.beginWorldMaintenance(world, reason);
             if (!deferredShutdownGenerators.contains(generator)) {
                 deferredShutdownGenerators.add(generator);
             }
@@ -1176,52 +1174,32 @@ public class Iris extends VolmitPlugin implements Listener, ReloadAware {
         if (!postStopFinisherStarted.compareAndSet(false, true)) {
             return;
         }
-        Thread activeServerThread = serverLifecycleThread;
-        if (activeServerThread == null) {
-            Iris.warn("Iris could not start its post-stop runtime finisher because the server lifecycle thread is unavailable.");
-            return;
-        }
-
-        Thread finisher = new Thread(() -> {
-            if (!awaitServerThreadTermination(activeServerThread)) {
-                return;
-            }
-            finishDeferredRuntimeTeardown("post-server-stop", 30L);
-        }, "Iris-PostStop-Finisher");
+        Thread finisher = new Thread(() -> finishRuntimeAfterServerShutdown("post-server-stop"),
+                "Iris-PostStop-Finisher");
         finisher.setDaemon(false);
         finisher.start();
     }
 
-    static boolean awaitServerThreadTermination(Thread serverThread) {
-        if (serverThread == null || serverThread == Thread.currentThread()) {
-            return false;
-        }
-        try {
-            serverThread.join();
-            return true;
-        } catch (InterruptedException e) {
-            Thread.currentThread().interrupt();
-            Iris.reportError("Iris post-stop runtime finisher was interrupted.", e);
-            return false;
-        }
-    }
-
     private void runShutdownHook() {
         if (startupBoundaryRestart.get()) {
             finishDeferredRuntimeTeardown("startup-boundary-restart-hook", 30L);
             return;
         }
+        finishRuntimeAfterServerShutdown("shutdown-hook");
+    }
+
+    private void finishRuntimeAfterServerShutdown(String reason) {
         if (!awaitServerShutdownBoundary()) {
-            SHUTDOWN_ERRORS.println("[Iris] Paper did not reach its post-world-close boundary; retaining the runtime and plugin class loader until JVM exit.");
+            SHUTDOWN_ERRORS.println("[Iris] The server did not reach its post-world-close boundary; retaining the runtime and plugin class loader until JVM exit.");
             return;
         }
-        finishDeferredRuntimeTeardown("shutdown-hook", 30L);
+        finishDeferredRuntimeTeardown(reason, 30L);
     }
 
     private boolean awaitServerShutdownBoundary() {
         ServerShutdownBoundary boundary = serverShutdownBoundary;
         if (boundary == null) {
-            return true;
+            return false;
         }
         try {
             return boundary.await(
@@ -1508,12 +1486,15 @@ public class Iris extends VolmitPlugin implements Listener, ReloadAware {
     public int getIrisVersion() {
         String input = getDescription().getVersion();
         int hyphenIndex = input.indexOf('-');
-        if (hyphenIndex != -1) {
-            String result = input.substring(0, hyphenIndex);
-            result = result.replaceAll("\\.", "");
-            return Integer.parseInt(result);
+        String release = hyphenIndex < 0 ? input : input.substring(0, hyphenIndex);
+        if (!release.matches("[0-9]+(?:\\.[0-9]+)*")) {
+            return -1;
+        }
+        try {
+            return Integer.parseInt(release.replace(".", ""));
+        } catch (NumberFormatException invalid) {
+            return -1;
         }
-        return -1;
     }
 
     public int getMCVersion() {

adapters/bukkit/plugin/src/main/java/art/arcane/iris/command/CommandStudio.java

@@ -81,7 +81,6 @@ import org.bukkit.FluidCollisionMode;
 import org.bukkit.Location;
 import org.bukkit.World;
 import org.bukkit.entity.Player;
-import org.bukkit.event.inventory.InventoryType;
 import org.bukkit.inventory.Inventory;
 import org.bukkit.util.Vector;
 
@@ -309,23 +308,33 @@ public class CommandStudio implements DirectorExecutor {
         O<Integer> ta = new O<>();
         ta.set(-1);
 
-        var sender = sender();
-        var player = player();
-        var engine = engine();
+        VolmitSender sender = sender();
+        Player player = player();
+        Engine engine = engine();
 
-        ta.set(J.sr(() ->
-        {
-            if (!player.getOpenInventory().getType().equals(InventoryType.CHEST)) {
+        ta.set(J.sr(() -> {
+            if (!J.runEntity(player, () -> {
+                if (player.getOpenInventory().getTopInventory() != inv) {
+                    J.csr(ta.get());
+                    sender.sendMessage(IrisLanguage.text(BukkitCommandMessages.COMMAND_STUDIO_OPENED_INVENTORY));
+                    return;
+                }
+                if (!add) {
+                    inv.clear();
+                }
+                Location location = player.getLocation();
+                try {
+                    EngineBukkitOps.addItems(engine, true, inv, tables, InventorySlotType.STORAGE,
+                            location.getWorld(), location.getBlockX(), location.getBlockY(), location.getBlockZ());
+                } catch (RuntimeException | Error failure) {
+                    J.csr(ta.get());
+                    Iris.reportError(failure);
+                    sender.sendMessage(IrisLanguage.text(BukkitCommandMessagesExtended.COMMAND_STUDIO_CANNOT_ADD_ITEMS_VIRTUAL_INVENTORY_BECAUSE,
+                            MessageArgument.untrusted("value", String.valueOf(failure.getMessage()))));
+                }
+            }, 0, () -> J.csr(ta.get()))) {
                 J.csr(ta.get());
-                sender.sendMessage(IrisLanguage.text(BukkitCommandMessages.COMMAND_STUDIO_OPENED_INVENTORY));
-                return;
             }
-
-            if (!add) {
-                inv.clear();
-            }
-
-            EngineBukkitOps.addItems(engine, true, inv, tables, InventorySlotType.STORAGE, player.getWorld(), player.getLocation().getBlockX(), player.getLocation().getBlockY(), player.getLocation().getBlockZ());
         }, fast ? 5 : 35));
 
         sender().sendMessage(IrisLanguage.text(BukkitCommandMessagesExtended.COMMAND_STUDIO_OPENING_INVENTORY_NOW));

adapters/bukkit/plugin/src/main/java/art/arcane/iris/world/IrisWorldGeneratorResolver.java

@@ -896,14 +896,10 @@ public final class IrisWorldGeneratorResolver {
     }
 
     private static String dimensionTypeKey(IrisData data, IrisDimension dimension) {
-        return IrisPlatforms.get()
-                .registries()
-                .generationRegistry()
-                .dimensionTypeResourceKey(
-                        data.getDataFolder().getName(),
-                        dimension.getLoadKey(),
-                        dimension.getDimensionTypeKey()
-                );
+        return dimension.dimensionTypeResourceKey(
+                IrisPlatforms.get().registries().generationRegistry(),
+                data.getDataFolder().getName()
+        );
     }
 
     private record LoadedHistory(GenerationHistory history, File activePack) {

adapters/bukkit/plugin/src/test/gameplay/native-lifecycle-fixture/resources/plugin.yml

@@ -2,6 +2,7 @@ name: IrisNativeLifecycleFixture
 version: 1.0.0
 main: art.arcane.iris.fixture.NativeLifecycleFixture
 api-version: '26.1.2'
+folia-supported: true
 depend: [Iris]
 commands:
   irislifecycle:

adapters/bukkit/plugin/src/test/gameplay/native-lifecycle-fixture/src/art/arcane/iris/fixture/NativeLifecycleFixture.java

@@ -1,8 +1,12 @@
 package art.arcane.iris.fixture;
 
+import art.arcane.iris.Iris;
 import art.arcane.volmlib.nativelib.NativeAdapters;
 import art.arcane.iris.world.runtime.RuntimeInjection;
+import art.arcane.iris.generation.runtime.Engine;
+import art.arcane.iris.structure.placement.IrisStructureLocator;
 import art.arcane.iris.world.IrisCreator;
+import art.arcane.iris.world.task.J;
 import art.arcane.iris.world.IrisToolbelt;
 import art.arcane.iris.world.IrisWorldStorage;
 import art.arcane.iris.world.WorldCreatorCompat;
@@ -13,6 +17,15 @@ import org.bukkit.entity.Player;
 import org.bukkit.configuration.file.YamlConfiguration;
 import org.bukkit.Material;
 import org.bukkit.block.Biome;
+import org.bukkit.block.Container;
+import org.bukkit.loot.Lootable;
+import org.bukkit.loot.LootTable;
+import org.bukkit.inventory.Inventory;
+import org.bukkit.inventory.ItemStack;
+import org.bukkit.inventory.meta.MapMeta;
+import org.bukkit.map.MapView;
+import org.bukkit.generator.structure.Structure;
+import org.bukkit.util.StructureSearchResult;
 import art.arcane.volmlib.nativelib.terrain.NativeTerrainAccess;
 import art.arcane.volmlib.nativelib.terrain.NativeStructureReader;
 import art.arcane.volmlib.nativelib.terrain.NativeWorldRuntime;
@@ -38,12 +51,15 @@ public final class NativeLifecycleFixture extends JavaPlugin implements WorldRun
     private static final NamespacedKey WORLD_KEY = NamespacedKey.minecraft("native_lifecycle_probe");
     private static final NamespacedKey TERRAIN_KEY = new NamespacedKey("iris", "native_terrain_probe");
     private static final NamespacedKey COMMAND_KEY = new NamespacedKey("iris", "lifecycle_probe");
+    private static final NamespacedKey TREASURE_KEY = new NamespacedKey("iris", "treasure_map_probe");
     private static final long WORLD_SEED = 78264193L;
     private NativeWorldRuntime runtime;
+    private TreasureLootChecks treasureLootChecks;
 
     @Override
     public void onEnable() {
         runtime = NativeAdapters.require(NativeWorldRuntime.class);
+        treasureLootChecks = new TreasureLootChecks(this);
         NativeTerrainAccess terrain = NativeAdapters.require(NativeTerrainAccess.class);
         getLogger().info("Native lifecycle ready: " + runtime.description()
                 + "; terrain provider=" + terrain.getClass().getName());
@@ -56,12 +72,32 @@ public final class NativeLifecycleFixture extends JavaPlugin implements WorldRun
 
     @Override
     public boolean onCommand(CommandSender sender, Command command, String label, String[] arguments) {
-        if (arguments.length != 1) {
+        if (arguments.length == 0) {
             sender.sendMessage("Use /irislifecycle create|unload|status|structures|terrain-create|terrain-check|terrain-unload|lifecycle-status|lifecycle-entry");
             return true;
         }
         try {
             switch (arguments[0]) {
+                case "treasure-map-create" -> createTreasureMapWorld(sender);
+                case "treasure-map-limit" -> runTreasureRegion(sender, () -> checkTreasureMapLimit(sender));
+                case "treasure-map-chest" -> {
+                    if (arguments.length != 3) {
+                        throw new IllegalArgumentException("Use treasure-map-chest <destination> <CHEST|COPPER_CHEST>");
+                    }
+                    runTreasureRegion(sender, () -> prepareTreasureMapChest(sender, arguments[1], arguments[2]));
+                }
+                case "treasure-map-inspect" -> {
+                    if (arguments.length != 2) {
+                        throw new IllegalArgumentException("Use treasure-map-inspect <destination>");
+                    }
+                    runTreasureRegion(sender, () -> inspectTreasureMapChest(sender, arguments[1]));
+                }
+                case "treasure-map-check" -> runTreasureRegion(sender, () -> verifyTreasureMapLoot(sender));
+                case "treasure-extra-check" -> runTreasureRegion(sender, () -> treasureLootChecks.verify(sender));
+                case "treasure-region-check" -> runTreasureRegion(sender, () -> treasureLootChecks.verifyRegion(sender));
+                case "treasure-reload-before" -> runTreasureRegion(sender, () -> treasureLootChecks.verifyReload(sender, false));
+                case "treasure-reload-after" -> runTreasureRegion(sender, () -> treasureLootChecks.verifyReload(sender, true));
+                case "treasure-resources" -> treasureLootChecks.reportResourceReloads(sender);
                 case "create" -> create(sender);
                 case "unload" -> unload(sender);
                 case "structures" -> structures(sender);
@@ -80,6 +116,177 @@ public final class NativeLifecycleFixture extends JavaPlugin implements WorldRun
         return true;
     }
 
+    private void createTreasureMapWorld(CommandSender sender) {
+        if (!(sender instanceof Player player)) {
+            throw new IllegalStateException("Treasure map fixture requires a player");
+        }
+        runTreasureRegion(sender, () -> prepareTreasureMapWorld(player));
+    }
+
+    private void runTreasureRegion(CommandSender sender, Runnable task) {
+        ensureTreasureMapWorld()
+                .thenCompose(ignored -> J.runRegionFuture(Bukkit.getWorld(TREASURE_KEY), 0, 0, task))
+                .whenComplete((ignored, failure) -> {
+                    if (failure != null) {
+                        fail(sender, failure);
+                    }
+                });
+    }
+
+    private CompletableFuture<?> ensureTreasureMapWorld() {
+        if (Bukkit.getWorld(TREASURE_KEY) != null) {
+            return CompletableFuture.completedFuture(null);
+        }
+        if (WorldCreatorCompat.persistentLevelRoot(TREASURE_KEY).exists()) {
+            return Iris.instance.worldReconciler().loadWorld(ServerProperties.BUKKIT_YML, TREASURE_KEY.toString());
+        }
+        return runAsync(() -> {
+            try {
+                new IrisCreator().name(TREASURE_KEY.toString()).dimension("treasure-map-fixture")
+                        .seed(WORLD_SEED).create();
+            } catch (Exception failure) {
+                throw new IllegalStateException("Treasure map fixture creation failed", failure);
+            }
+        });
+    }
+
+    private void prepareTreasureMapWorld(Player player) {
+        World world = Bukkit.getWorld(TREASURE_KEY);
+        if (world == null || !IrisToolbelt.isIrisWorld(world) || world.getSeed() != WORLD_SEED
+                || !"treasure-map-fixture".equals(IrisToolbelt.access(world).getEngine().getDimension().getLoadKey())) {
+            throw new IllegalStateException("Treasure map fixture world identity is invalid");
+        }
+        for (int x = 0; x <= 8; x++) {
+            for (int z = 0; z <= 8; z++) {
+                world.getBlockAt(x, 160, z).setType(Material.STONE, false);
+                for (int y = 161; y <= 164; y++) {
+                    world.getBlockAt(x, y, z).setType(Material.AIR, false);
+                }
+            }
+        }
+        if (!J.runEntity(player, () -> player.teleportAsync(new Location(world, 0.5, 161, 0.5)).whenComplete((teleported, failure) -> {
+            if (failure != null) {
+                fail(player, failure);
+            } else if (!Boolean.TRUE.equals(teleported)) {
+                fail(player, new IllegalStateException("Treasure map fixture teleport failed"));
+            } else {
+                player.sendMessage("TREASURE_MAP_READY world=" + TREASURE_KEY
+                        + " version=" + Bukkit.getMinecraftVersion() + " folia=" + J.isFolia());
+            }
+        }))) {
+            throw new IllegalStateException("Could not schedule treasure map fixture teleport");
+        }
+    }
+
+    private void checkTreasureMapLimit(CommandSender sender) {
+        World world = Bukkit.getWorld(TREASURE_KEY);
+        if (world == null) {
+            throw new IllegalStateException("Treasure map fixture world is absent");
+        }
+        Engine engine = IrisToolbelt.access(world).getEngine();
+        IrisStructureLocator.LocateResult located = IrisStructureLocator.locateInPlacementRings(
+                engine, "minecraft:buried_treasure", 2, 2, 50, (x, z) -> true);
+        if (located.status() != IrisStructureLocator.LocateStatus.SEARCH_LIMIT_REACHED) {
+            throw new IllegalStateException("Blocked treasure placement returned " + located.status());
+        }
+        sender.sendMessage("TREASURE_MAP_LIMIT status=" + located.status());
+    }
+
+    private void prepareTreasureMapChest(CommandSender sender, String destination, String material) {
+        World world = Bukkit.getWorld(TREASURE_KEY);
+        treasureMapChest(world, destination, material);
+        sender.sendMessage("TREASURE_MAP_CHEST destination=" + destination + " material=" + material);
+    }
+
+    private Container treasureMapChest(World world, String destination, String material) {
+        requireTreasureDestination(destination);
+        if (!List.of("CHEST", "COPPER_CHEST").contains(material)) {
+            throw new IllegalArgumentException("Unknown treasure map container: " + material);
+        }
+        LootTable loot = Bukkit.getLootTable(new NamespacedKey("iris_qa", destination));
+        if (loot == null) {
+            throw new IllegalStateException("Treasure map loot table is absent: " + destination);
+        }
+        world.getBlockAt(2, 161, 2).setType(Material.AIR, false);
+        world.getBlockAt(2, 161, 2).setType(Material.valueOf(material), false);
+        Container chest = (Container) world.getBlockAt(2, 161, 2).getState();
+        ((Lootable) chest).setLootTable(loot);
+        ((Lootable) chest).setSeed(WORLD_SEED);
+        if (!chest.update(true, false)) {
+            throw new IllegalStateException("Treasure map loot chest was not installed");
+        }
+        return (Container) world.getBlockAt(2, 161, 2).getState();
+    }
+
+    private void verifyTreasureMapLoot(CommandSender sender) {
+        checkTreasureMapLimit(sender);
+        World world = Bukkit.getWorld(TREASURE_KEY);
+        for (String destination : List.of("blocked", "disabled", "found", "mixed")) {
+            Inventory inventory = treasureMapChest(world, destination, "CHEST").getInventory();
+            inspectTreasureMapChest(sender, destination);
+            inventory.remove(Material.DIAMOND);
+            Inventory reopened = ((Container) world.getBlockAt(2, 161, 2).getState()).getInventory();
+            if (reopened.contains(Material.DIAMOND)
+                    || !(reopened.contains(Material.FILLED_MAP) || reopened.contains(Material.MAP))) {
+                throw new IllegalStateException("Reopening changed " + destination + " chest loot");
+            }
+        }
+        sender.sendMessage("TREASURE_MAP_CHECK destinations=4 retained=true");
+    }
+
+    private void inspectTreasureMapChest(CommandSender sender, String destination) {
+        requireTreasureDestination(destination);
+        World world = Bukkit.getWorld(TREASURE_KEY);
+        Inventory inventory = ((Container) world.getBlockAt(2, 161, 2).getState()).getInventory();
+        ItemStack map = null;
+        int diamonds = 0;
+        for (ItemStack item : inventory.getContents()) {
+            if (item == null) {
+                continue;
+            }
+            if ((item.getType() == Material.MAP || item.getType() == Material.FILLED_MAP)
+                    && item.getAmount() == 1 && map == null) {
+                map = item;
+            } else if (item.getType() == Material.DIAMOND) {
+                diamonds += item.getAmount();
+            } else {
+                throw new IllegalStateException("Unexpected chest loot: " + item);
+            }
+        }
+        if (map == null || diamonds != 1) {
+            throw new IllegalStateException("Invalid " + destination + " chest: map=" + map + " diamonds=" + diamonds);
+        }
+        boolean expectedLocated = destination.equals("found") || destination.equals("mixed");
+        MapView view = map.getItemMeta() instanceof MapMeta meta && meta.hasMapView() ? meta.getMapView() : null;
+        if ((view != null) != expectedLocated) {
+            throw new IllegalStateException("Unexpected map data for " + destination + ": " + map);
+        }
+        String result = "TREASURE_MAP_INSPECT destination=" + destination + " diamonds=1 located=" + expectedLocated;
+        if (view != null) {
+            StructureSearchResult target = world.locateNearestStructure(
+                    new Location(world, 2, 161, 2), Structure.DESERT_PYRAMID, 50, false);
+            if (target == null || target.getStructure() != Structure.DESERT_PYRAMID) {
+                throw new IllegalStateException("Map has no verified pyramid target");
+            }
+            int targetX = target.getLocation().getBlockX();
+            int targetZ = target.getLocation().getBlockZ();
+            if (view.getWorld() != world || view.getScale() != MapView.Scale.CLOSEST
+                    || view.getCenterX() != Math.floorDiv(targetX + 64, 128) * 128
+                    || view.getCenterZ() != Math.floorDiv(targetZ + 64, 128) * 128) {
+                throw new IllegalStateException("Map data does not cover the verified pyramid at " + target.getLocation());
+            }
+            result += " mapId=" + view.getId() + " targetX=" + targetX + " targetZ=" + targetZ
+                    + " centerX=" + view.getCenterX() + " centerZ=" + view.getCenterZ();
+        }
+        sender.sendMessage(result);
+    }
+
+    private void requireTreasureDestination(String destination) {
+        if (!List.of("blocked", "disabled", "found", "mixed").contains(destination)) {
+            throw new IllegalArgumentException("Unknown treasure map destination: " + destination);
+        }
+    }
+
     private void lifecycleStatus(CommandSender sender) throws Exception {
         World world = Bukkit.getWorld(COMMAND_KEY);
         Path storage = WorldCreatorCompat.persistentLevelRoot(COMMAND_KEY).toPath();
@@ -282,11 +489,11 @@ public final class NativeLifecycleFixture extends JavaPlugin implements WorldRun
     }
 
     public boolean regionized() {
-        return false;
+        return J.isFolia();
     }
 
     public boolean primaryThread() {
-        return Bukkit.isPrimaryThread();
+        return J.isFolia() ? Bukkit.isGlobalTickThread() : Bukkit.isPrimaryThread();
     }
 
     public CompletableFuture<Void> runGlobal(Runnable task) {
@@ -299,10 +506,10 @@ public final class NativeLifecycleFixture extends JavaPlugin implements WorldRun
                 result.completeExceptionally(failure);
             }
         };
-        if (Bukkit.isPrimaryThread()) {
+        if (primaryThread()) {
             wrapped.run();
-        } else {
-            Bukkit.getScheduler().runTask(this, wrapped);
+        } else if (!J.runGlobal(wrapped)) {
+            result.completeExceptionally(new IllegalStateException("Could not schedule fixture task"));
         }
         return result;
     }

adapters/bukkit/plugin/src/test/gameplay/native-lifecycle-fixture/src/art/arcane/iris/fixture/TreasureLootChecks.java

@@ -0,0 +1,259 @@
+package art.arcane.iris.fixture;
+
+import art.arcane.iris.generation.runtime.Engine;
+import art.arcane.iris.platform.bukkit.BukkitBlockResolution;
+import art.arcane.iris.platform.generation.EngineBukkitOps;
+import art.arcane.iris.world.IrisToolbelt;
+import art.arcane.iris.world.loot.InventorySlotType;
+import art.arcane.iris.world.loot.IrisVanillaLootTable;
+import art.arcane.iris.world.loot.IrisLootTable;
+import art.arcane.volmlib.util.collection.KList;
+import art.arcane.volmlib.util.mantle.runtime.MantleChunk;
+import art.arcane.iris.world.task.J;
+import art.arcane.volmlib.util.matter.Matter;
+import io.papermc.paper.event.world.StructuresLocateEvent;
+import io.papermc.paper.event.server.ServerResourcesReloadedEvent;
+import io.papermc.paper.math.Position;
+import org.bukkit.Bukkit;
+import org.bukkit.Location;
+import org.bukkit.Material;
+import org.bukkit.NamespacedKey;
+import org.bukkit.World;
+import org.bukkit.block.Block;
+import org.bukkit.block.Container;
+import org.bukkit.block.Chest;
+import org.bukkit.command.CommandSender;
+import org.bukkit.event.EventHandler;
+import org.bukkit.event.Listener;
+import org.bukkit.event.world.LootGenerateEvent;
+import org.bukkit.generator.structure.Structure;
+import org.bukkit.inventory.ItemStack;
+import org.bukkit.inventory.Inventory;
+import org.bukkit.plugin.java.JavaPlugin;
+import org.bukkit.util.StructureSearchResult;
+
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Proxy;
+import java.util.Collection;
+import java.util.List;
+import java.util.concurrent.atomic.AtomicInteger;
+
+public final class TreasureLootChecks implements Listener {
+    private static final NamespacedKey WORLD_KEY = new NamespacedKey("iris", "treasure_map_probe");
+    private static final List<String> CHESTS = List.of(
+            "CHEST", "COPPER_CHEST", "EXPOSED_COPPER_CHEST", "WEATHERED_COPPER_CHEST",
+            "OXIDIZED_COPPER_CHEST", "WAXED_COPPER_CHEST", "WAXED_EXPOSED_COPPER_CHEST",
+            "WAXED_WEATHERED_COPPER_CHEST", "WAXED_OXIDIZED_COPPER_CHEST");
+    private final IrisVanillaLootTable reloadTable = new IrisVanillaLootTable("iris_qa:reload");
+    private final AtomicInteger resourceReloads = new AtomicInteger();
+    private LocateAction locateAction = LocateAction.PASS;
+    private int locateEvents;
+    private int lootEvents;
+    private boolean lootEventsOwned = true;
+
+    public TreasureLootChecks(JavaPlugin plugin) {
+        Bukkit.getPluginManager().registerEvents(this, plugin);
+    }
+
+    public void verify(CommandSender sender) {
+        World world = requireWorld();
+        verifyCopperLoot(world);
+        sender.sendMessage("TREASURE_COPPER_LOOT variants=8 normal=true diamonds=1");
+        verifyInventoryRollback(world);
+        sender.sendMessage("TREASURE_LOOT_ROLLBACK contents=true nativeTable=true seed=true retry=true");
+        verifyLocateEvents(world);
+        sender.sendMessage("TREASURE_LOCATE_EVENTS cancelled=true replaced=true calls=2");
+        sender.sendMessage("TREASURE_EXTRA_CHECK variants=9 rollback=true locateEvents=true");
+    }
+
+    public void verifyRegion(CommandSender sender) {
+        World world = requireWorld();
+        if (!J.isOwnedByCurrentRegion(world, 0, 0)) {
+            throw new IllegalStateException("Fixture does not own its loot region");
+        }
+        lootEvents = 0;
+        lootEventsOwned = true;
+        verifyCopperLoot(world);
+        if (lootEvents != CHESTS.size() || !lootEventsOwned) {
+            throw new IllegalStateException("Loot event ownership failed: count=" + lootEvents
+                    + " owned=" + lootEventsOwned);
+        }
+        sender.sendMessage("TREASURE_REGION_LOOT copper=8 normal=1 events=" + lootEvents
+                + " owned=true folia=" + J.isFolia());
+    }
+
+    @EventHandler
+    public void onLoot(LootGenerateEvent event) {
+        if (event.getWorld().getKey().equals(WORLD_KEY) && event.isPlugin()) {
+            Location origin = event.getLootContext().getLocation();
+            lootEvents++;
+            lootEventsOwned &= J.isOwnedByCurrentRegion(event.getWorld(),
+                    origin.getBlockX() >> 4, origin.getBlockZ() >> 4);
+        }
+    }
+
+    public void verifyReload(CommandSender sender, boolean reloaded) {
+        World world = requireWorld();
+        Material expected = reloaded ? Material.EMERALD : Material.DIAMOND;
+        Collection<ItemStack> items = reloadTable.getLoot(
+                false, 783L, InventorySlotType.STORAGE, world, 2, 161, 2);
+        if (items.size() != 1 || items.iterator().next().getType() != expected) {
+            throw new IllegalStateException("Reloaded loot did not contain " + expected + ": " + items);
+        }
+        sender.sendMessage("TREASURE_RELOAD material=" + expected);
+    }
+
+    public void reportResourceReloads(CommandSender sender) {
+        sender.sendMessage("TREASURE_RESOURCES revision=" + resourceReloads.get());
+    }
+
+    @EventHandler
+    public void onResourcesReloaded(ServerResourcesReloadedEvent event) {
+        resourceReloads.incrementAndGet();
+    }
+
+    @EventHandler
+    public void onLocate(StructuresLocateEvent event) {
+        if (!event.getWorld().getKey().equals(WORLD_KEY) || locateAction == LocateAction.PASS) {
+            return;
+        }
+        locateEvents++;
+        if (locateAction == LocateAction.CANCEL) {
+            event.setCancelled(true);
+        } else {
+            event.setResult(new StructuresLocateEvent.Result(Position.block(123, 100, 456), Structure.DESERT_PYRAMID));
+        }
+    }
+
+    private void verifyCopperLoot(World world) {
+        Engine engine = IrisToolbelt.access(world).getEngine();
+        Block block = world.getBlockAt(4, 161, 4);
+        MantleChunk<Matter> mantle = engine.getMantle().getMantle().useChunk(block.getChunk());
+        try {
+            for (String name : CHESTS) {
+                block.setType(Material.AIR, false);
+                block.setType(Material.valueOf(name), false);
+                if (!BukkitBlockResolution.isStorageChest(block.getBlockData())) {
+                    throw new IllegalStateException("Chest is excluded from Iris loot: " + name);
+                }
+                EngineBukkitOps.update(engine, 4, 161, 4, block.getChunk(), mantle);
+                Container chest = (Container) block.getState();
+                int diamonds = 0;
+                for (ItemStack item : chest.getInventory().getContents()) {
+                    if (item == null) {
+                        continue;
+                    }
+                    if (item.getType() != Material.DIAMOND) {
+                        throw new IllegalStateException("Unexpected " + name + " loot: " + item);
+                    }
+                    diamonds += item.getAmount();
+                }
+                if (diamonds != 1) {
+                    throw new IllegalStateException(name + " contains " + diamonds + " diamonds");
+                }
+            }
+        } finally {
+            mantle.release();
+        }
+    }
+
+    private void verifyInventoryRollback(World world) {
+        Engine engine = IrisToolbelt.access(world).getEngine();
+        Block block = world.getBlockAt(6, 161, 4);
+        block.setType(Material.AIR, false);
+        block.setType(Material.CHEST, false);
+        Chest chest = (Chest) block.getState();
+        chest.getBlockInventory().setItem(0, new ItemStack(Material.EMERALD, 3));
+        chest = (Chest) block.getState();
+        NamespacedKey key = new NamespacedKey("iris_qa", "reload");
+        chest.setLootTable(Bukkit.getLootTable(key));
+        chest.setSeed(913L);
+        if (!chest.update(true, false)) {
+            throw new IllegalStateException("Could not set native loot for rollback check");
+        }
+        Inventory inventory = chest.getBlockInventory();
+        IllegalStateException injected = new IllegalStateException("Fixture insertion interruption");
+        Inventory interrupted = (Inventory) Proxy.newProxyInstance(Inventory.class.getClassLoader(),
+                new Class<?>[]{Inventory.class}, (proxy, method, arguments) -> {
+                    Object result;
+                    try {
+                        result = method.invoke(inventory, arguments);
+                    } catch (InvocationTargetException failure) {
+                        throw failure.getCause();
+                    }
+                    if (method.getName().equals("addItem")) {
+                        throw injected;
+                    }
+                    return result;
+                });
+        KList<IrisLootTable> tables = new KList<>();
+        tables.add(new IrisVanillaLootTable("iris_qa:reload"));
+        try {
+            EngineBukkitOps.addItems(engine, false, interrupted, tables, InventorySlotType.STORAGE,
+                    world, 6, 161, 4);
+            throw new IllegalStateException("Interrupted insertion did not fail");
+        } catch (IllegalStateException failure) {
+            if (failure != injected) {
+                throw failure;
+            }
+        }
+        Chest restored = (Chest) block.getState();
+        if (restored.getLootTable() == null || !restored.getLootTable().getKey().equals(key)
+                || restored.getSeed() != 913L) {
+            throw new IllegalStateException("Rollback lost the native loot table or seed");
+        }
+        ItemStack existing = restored.getSnapshotInventory().getItem(0);
+        if (existing == null || existing.getType() != Material.EMERALD || existing.getAmount() != 3) {
+            throw new IllegalStateException("Rollback lost the original contents: " + existing);
+        }
+        EngineBukkitOps.addItems(engine, false, restored.getBlockInventory(), tables, InventorySlotType.STORAGE,
+                world, 6, 161, 4);
+        int diamonds = 0;
+        int emeralds = 0;
+        for (ItemStack item : restored.getBlockInventory().getContents()) {
+            if (item == null) {
+                continue;
+            }
+            if (item.getType() == Material.DIAMOND) {
+                diamonds += item.getAmount();
+            } else if (item.getType() == Material.EMERALD) {
+                emeralds += item.getAmount();
+            }
+        }
+        if (diamonds != 2 || emeralds != 3 || ((Chest) block.getState()).getLootTable() != null) {
+            throw new IllegalStateException("Loot retry failed: diamonds=" + diamonds + " emeralds=" + emeralds);
+        }
+    }
+
+    private void verifyLocateEvents(World world) {
+        Location origin = new Location(world, 2, 161, 2);
+        locateEvents = 0;
+        try {
+            locateAction = LocateAction.CANCEL;
+            if (world.locateNearestStructure(origin, Structure.DESERT_PYRAMID, 50, false) != null) {
+                throw new IllegalStateException("Cancelled structure search returned a target");
+            }
+            locateAction = LocateAction.REPLACE;
+            StructureSearchResult result = world.locateNearestStructure(origin, Structure.DESERT_PYRAMID, 50, false);
+            if (result == null || result.getStructure() != Structure.DESERT_PYRAMID
+                    || result.getLocation().getBlockX() != 123 || result.getLocation().getBlockY() != 100
+                    || result.getLocation().getBlockZ() != 456 || locateEvents != 2) {
+                throw new IllegalStateException("Structure search ignored event result: " + result);
+            }
+        } finally {
+            locateAction = LocateAction.PASS;
+        }
+    }
+
+    private World requireWorld() {
+        World world = Bukkit.getWorld(WORLD_KEY);
+        if (world == null || !IrisToolbelt.isIrisWorld(world)) {
+            throw new IllegalStateException("Treasure map fixture world is absent");
+        }
+        return world;
+    }
+
+    private enum LocateAction {
+        PASS, CANCEL, REPLACE
+    }
+}

adapters/bukkit/plugin/src/test/gameplay/treasure-map-datapack-26.2/data/iris_qa/loot_table/blocked.json

@@ -0,0 +1,33 @@
+{
+  "type": "minecraft:chest",
+  "pools": [
+    {
+      "rolls": 1,
+      "entries": [
+        {
+          "type": "minecraft:item",
+          "name": "minecraft:map",
+          "functions": [
+            {
+              "destination": "iris_qa:blocked",
+              "decoration": "minecraft:red_x",
+              "zoom": 0,
+              "search_radius": 50,
+              "skip_existing_chunks": false,
+              "function": "minecraft:exploration_map"
+            }
+          ]
+        }
+      ]
+    },
+    {
+      "rolls": 1,
+      "entries": [
+        {
+          "type": "minecraft:item",
+          "name": "minecraft:diamond"
+        }
+      ]
+    }
+  ]
+}

adapters/bukkit/plugin/src/test/gameplay/treasure-map-datapack-26.2/data/iris_qa/loot_table/disabled.json

@@ -0,0 +1,33 @@
+{
+  "type": "minecraft:chest",
+  "pools": [
+    {
+      "rolls": 1,
+      "entries": [
+        {
+          "type": "minecraft:item",
+          "name": "minecraft:map",
+          "functions": [
+            {
+              "destination": "iris_qa:disabled",
+              "decoration": "minecraft:red_x",
+              "zoom": 0,
+              "search_radius": 50,
+              "skip_existing_chunks": false,
+              "function": "minecraft:exploration_map"
+            }
+          ]
+        }
+      ]
+    },
+    {
+      "rolls": 1,
+      "entries": [
+        {
+          "type": "minecraft:item",
+          "name": "minecraft:diamond"
+        }
+      ]
+    }
+  ]
+}

adapters/bukkit/plugin/src/test/gameplay/treasure-map-datapack-26.2/data/iris_qa/loot_table/found.json

@@ -0,0 +1,33 @@
+{
+  "type": "minecraft:chest",
+  "pools": [
+    {
+      "rolls": 1,
+      "entries": [
+        {
+          "type": "minecraft:item",
+          "name": "minecraft:map",
+          "functions": [
+            {
+              "destination": "iris_qa:found",
+              "decoration": "minecraft:red_x",
+              "zoom": 0,
+              "search_radius": 50,
+              "skip_existing_chunks": false,
+              "function": "minecraft:exploration_map"
+            }
+          ]
+        }
+      ]
+    },
+    {
+      "rolls": 1,
+      "entries": [
+        {
+          "type": "minecraft:item",
+          "name": "minecraft:diamond"
+        }
+      ]
+    }
+  ]
+}

adapters/bukkit/plugin/src/test/gameplay/treasure-map-datapack-26.2/data/iris_qa/loot_table/mixed.json

@@ -0,0 +1,33 @@
+{
+  "type": "minecraft:chest",
+  "pools": [
+    {
+      "rolls": 1,
+      "entries": [
+        {
+          "type": "minecraft:item",
+          "name": "minecraft:map",
+          "functions": [
+            {
+              "destination": "iris_qa:mixed",
+              "decoration": "minecraft:red_x",
+              "zoom": 0,
+              "search_radius": 50,
+              "skip_existing_chunks": false,
+              "function": "minecraft:exploration_map"
+            }
+          ]
+        }
+      ]
+    },
+    {
+      "rolls": 1,
+      "entries": [
+        {
+          "type": "minecraft:item",
+          "name": "minecraft:diamond"
+        }
+      ]
+    }
+  ]
+}

adapters/bukkit/plugin/src/test/gameplay/treasure-map-datapack-26.2/data/iris_qa/loot_table/reload.json

@@ -0,0 +1,14 @@
+{
+  "type": "minecraft:chest",
+  "pools": [
+    {
+      "rolls": 1,
+      "entries": [
+        {
+          "type": "minecraft:item",
+          "name": "minecraft:diamond"
+        }
+      ]
+    }
+  ]
+}

adapters/bukkit/plugin/src/test/gameplay/treasure-map-datapack-26.2/data/iris_qa/tags/worldgen/structure/blocked.json

@@ -0,0 +1,5 @@
+{
+  "values": [
+    "minecraft:buried_treasure"
+  ]
+}

adapters/bukkit/plugin/src/test/gameplay/treasure-map-datapack-26.2/data/iris_qa/tags/worldgen/structure/disabled.json

@@ -0,0 +1,5 @@
+{
+  "values": [
+    "minecraft:mansion"
+  ]
+}

adapters/bukkit/plugin/src/test/gameplay/treasure-map-datapack-26.2/data/iris_qa/tags/worldgen/structure/found.json

@@ -0,0 +1,5 @@
+{
+  "values": [
+    "minecraft:desert_pyramid"
+  ]
+}

adapters/bukkit/plugin/src/test/gameplay/treasure-map-datapack-26.2/data/iris_qa/tags/worldgen/structure/mixed.json

@@ -0,0 +1,6 @@
+{
+  "values": [
+    "minecraft:buried_treasure",
+    "minecraft:desert_pyramid"
+  ]
+}

adapters/bukkit/plugin/src/test/gameplay/treasure-map-datapack-26.2/pack.mcmeta

@@ -0,0 +1,13 @@
+{
+  "pack": {
+    "description": "Treasure map gameplay fixtures",
+    "min_format": [
+      107,
+      1
+    ],
+    "max_format": [
+      107,
+      1
+    ]
+  }
+}

adapters/bukkit/plugin/src/test/gameplay/treasure-map-datapack/data/iris_qa/loot_table/blocked.json

@@ -0,0 +1,31 @@
+{
+  "type": "minecraft:chest",
+  "pools": [
+    {
+      "rolls": 1,
+      "entries": [
+        {
+          "type": "minecraft:item",
+          "name": "minecraft:filled_map",
+          "modifier": {
+            "destination": "#iris_qa:blocked",
+            "decoration": "minecraft:red_x",
+            "zoom": 0,
+            "search_radius": 50,
+            "skip_existing_chunks": false,
+            "type": "minecraft:exploration_map"
+          }
+        }
+      ]
+    },
+    {
+      "rolls": 1,
+      "entries": [
+        {
+          "type": "minecraft:item",
+          "name": "minecraft:diamond"
+        }
+      ]
+    }
+  ]
+}

adapters/bukkit/plugin/src/test/gameplay/treasure-map-datapack/data/iris_qa/loot_table/disabled.json

@@ -0,0 +1,31 @@
+{
+  "type": "minecraft:chest",
+  "pools": [
+    {
+      "rolls": 1,
+      "entries": [
+        {
+          "type": "minecraft:item",
+          "name": "minecraft:filled_map",
+          "modifier": {
+            "destination": "#iris_qa:disabled",
+            "decoration": "minecraft:red_x",
+            "zoom": 0,
+            "search_radius": 50,
+            "skip_existing_chunks": false,
+            "type": "minecraft:exploration_map"
+          }
+        }
+      ]
+    },
+    {
+      "rolls": 1,
+      "entries": [
+        {
+          "type": "minecraft:item",
+          "name": "minecraft:diamond"
+        }
+      ]
+    }
+  ]
+}

adapters/bukkit/plugin/src/test/gameplay/treasure-map-datapack/data/iris_qa/loot_table/found.json

@@ -0,0 +1,31 @@
+{
+  "type": "minecraft:chest",
+  "pools": [
+    {
+      "rolls": 1,
+      "entries": [
+        {
+          "type": "minecraft:item",
+          "name": "minecraft:filled_map",
+          "modifier": {
+            "destination": "#iris_qa:found",
+            "decoration": "minecraft:red_x",
+            "zoom": 0,
+            "search_radius": 50,
+            "skip_existing_chunks": false,
+            "type": "minecraft:exploration_map"
+          }
+        }
+      ]
+    },
+    {
+      "rolls": 1,
+      "entries": [
+        {
+          "type": "minecraft:item",
+          "name": "minecraft:diamond"
+        }
+      ]
+    }
+  ]
+}

adapters/bukkit/plugin/src/test/gameplay/treasure-map-datapack/data/iris_qa/loot_table/mixed.json

@@ -0,0 +1,31 @@
+{
+  "type": "minecraft:chest",
+  "pools": [
+    {
+      "rolls": 1,
+      "entries": [
+        {
+          "type": "minecraft:item",
+          "name": "minecraft:filled_map",
+          "modifier": {
+            "destination": "#iris_qa:mixed",
+            "decoration": "minecraft:red_x",
+            "zoom": 0,
+            "search_radius": 50,
+            "skip_existing_chunks": false,
+            "type": "minecraft:exploration_map"
+          }
+        }
+      ]
+    },
+    {
+      "rolls": 1,
+      "entries": [
+        {
+          "type": "minecraft:item",
+          "name": "minecraft:diamond"
+        }
+      ]
+    }
+  ]
+}

adapters/bukkit/plugin/src/test/gameplay/treasure-map-datapack/data/iris_qa/loot_table/reload.json

@@ -0,0 +1,14 @@
+{
+  "type": "minecraft:chest",
+  "pools": [
+    {
+      "rolls": 1,
+      "entries": [
+        {
+          "type": "minecraft:item",
+          "name": "minecraft:diamond"
+        }
+      ]
+    }
+  ]
+}

adapters/bukkit/plugin/src/test/gameplay/treasure-map-datapack/data/iris_qa/tags/worldgen/structure/blocked.json

@@ -0,0 +1,5 @@
+{
+  "values": [
+    "minecraft:buried_treasure"
+  ]
+}

adapters/bukkit/plugin/src/test/gameplay/treasure-map-datapack/data/iris_qa/tags/worldgen/structure/disabled.json

@@ -0,0 +1,5 @@
+{
+  "values": [
+    "minecraft:mansion"
+  ]
+}

adapters/bukkit/plugin/src/test/gameplay/treasure-map-datapack/data/iris_qa/tags/worldgen/structure/found.json

@@ -0,0 +1,5 @@
+{
+  "values": [
+    "minecraft:desert_pyramid"
+  ]
+}

adapters/bukkit/plugin/src/test/gameplay/treasure-map-datapack/data/iris_qa/tags/worldgen/structure/mixed.json

@@ -0,0 +1,6 @@
+{
+  "values": [
+    "minecraft:buried_treasure",
+    "minecraft:desert_pyramid"
+  ]
+}

adapters/bukkit/plugin/src/test/gameplay/treasure-map-datapack/pack.mcmeta

@@ -0,0 +1,13 @@
+{
+  "pack": {
+    "description": "Treasure map gameplay fixtures",
+    "min_format": [
+      121,
+      0
+    ],
+    "max_format": [
+      121,
+      0
+    ]
+  }
+}

adapters/bukkit/plugin/src/test/gameplay/treasure-map-pack/biomes/flat.json

@@ -0,0 +1,32 @@
+{
+  "name": "Flat",
+  "derivative": "minecraft:plains",
+  "vanillaDerivative": "minecraft:plains",
+  "layers": [
+    {
+      "minHeight": 1,
+      "maxHeight": 1,
+      "palette": [
+        {
+          "block": "minecraft:lime_wool"
+        }
+      ]
+    },
+    {
+      "minHeight": 384,
+      "maxHeight": 384,
+      "palette": [
+        {
+          "block": "minecraft:green_concrete"
+        }
+      ]
+    }
+  ],
+  "generators": [
+    {
+      "generator": "flat",
+      "min": 96,
+      "max": 96
+    }
+  ]
+}

adapters/bukkit/plugin/src/test/gameplay/treasure-map-pack/dimensions/treasure-map-fixture.json

@@ -0,0 +1,64 @@
+{
+  "name": "Treasure Map Fixture",
+  "version": 1,
+  "mode": {
+    "type": "OVERWORLD"
+  },
+  "regions": [
+    "flat"
+  ],
+  "focusRegion": "flat",
+  "focus": "flat",
+  "landChance": 1,
+  "environment": "NORMAL",
+  "dimensionHeight": {
+    "min": -64,
+    "max": 320
+  },
+  "logicalHeight": 384,
+  "fluidHeight": 0,
+  "bedrock": false,
+  "rockPalette": {
+    "palette": [
+      {
+        "block": "minecraft:red_concrete"
+      }
+    ]
+  },
+  "importedStructures": {
+    "disabled": [
+      "minecraft:"
+    ]
+  },
+  "structures": [
+    {
+      "placementId": "blocked-treasure",
+      "nativeStructures": [
+        {
+          "structure": "minecraft:buried_treasure"
+        }
+      ],
+      "distribution": "RANDOM_SPREAD",
+      "spacing": 1,
+      "separation": 0,
+      "minHeight": 0,
+      "maxHeight": 0
+    },
+    {
+      "placementId": "reachable-pyramid",
+      "nativeStructures": [
+        {
+          "structure": "minecraft:desert_pyramid"
+        }
+      ],
+      "distribution": "RANDOM_SPREAD",
+      "spacing": 16,
+      "separation": 4
+    }
+  ],
+  "loot": {
+    "tables": [
+      "fixture-diamond"
+    ]
+  }
+}

adapters/bukkit/plugin/src/test/gameplay/treasure-map-pack/generators/flat.json

@@ -0,0 +1,15 @@
+{
+  "interpolator": {
+    "function": "NONE",
+    "horizontalScale": 1
+  },
+  "seed": 310,
+  "composite": [
+    {
+      "seed": 310,
+      "style": {
+        "style": "FLAT"
+      }
+    }
+  ]
+}

adapters/bukkit/plugin/src/test/gameplay/treasure-map-pack/loot/fixture-diamond.json

@@ -0,0 +1,15 @@
+{
+  "name": "Fixture Diamond",
+  "rarity": 1,
+  "minPicked": 1,
+  "maxPicked": 1,
+  "maxTries": 1,
+  "loot": [
+    {
+      "type": "diamond",
+      "rarity": 1,
+      "minAmount": 1,
+      "maxAmount": 1
+    }
+  ]
+}

adapters/bukkit/plugin/src/test/gameplay/treasure-map-pack/regions/flat.json

@@ -0,0 +1,12 @@
+{
+  "name": "Flat",
+  "landBiomes": [
+    "flat"
+  ],
+  "seaBiomes": [
+    "flat"
+  ],
+  "shoreBiomes": [
+    "flat"
+  ]
+}

adapters/bukkit/plugin/src/test/gameplay/treasure-maps.mjs

@@ -0,0 +1,211 @@
+import { readFile, writeFile } from 'node:fs/promises'
+import path from 'node:path'
+
+const simplifyNbt = value => {
+  if (Array.isArray(value)) return value.map(simplifyNbt)
+  if (value === null || typeof value !== 'object') return value
+  if ('type' in value && 'value' in value) return simplifyNbt(value.value)
+  return Object.fromEntries(Object.entries(value).map(([key, entry]) => [key, simplifyNbt(entry)]))
+}
+
+const completeClientTicks = context => {
+  const client = context.bot._client
+  context.expect(context.bot.supportFeature('sendsClientTickEndPacket'), 'Fixture client supports tick delimiters')
+  let tickTimer
+  const finishTick = () => {
+    clearTimeout(tickTimer)
+    client.write('tick_end', {})
+    tickTimer = setTimeout(finishTick, 50)
+  }
+  context.bot.on('move', finishTick)
+  finishTick()
+  context.signal.addEventListener('abort', () => {
+    clearTimeout(tickTimer)
+    context.bot.removeListener('move', finishTick)
+  }, { once: true })
+}
+
+export default {
+  name: 'iris-treasure-maps',
+  description: 'Verify exploration-map targets, bounded misses, retained loot, and normal/copper storage on Iris.',
+  async run(context) {
+    completeClientTicks(context)
+    context.bot.physicsEnabled = false
+    context.bot.clearControlStates()
+    context.bot.entity.velocity.set(0, 0, 0)
+    const source = await readFile(path.join(context.server.directory, '.server-source'), 'utf8')
+    context.expect(/^isolated=true\s*$/m.test(source), 'Treasure map fixtures require an isolated instance')
+    const command = async (operation, expected, timeoutMs = 30000) => {
+      const token = expected.split(' ')[0]
+      const response = await context.command(`/irislifecycle ${operation}`,
+        new RegExp(`${token}|NATIVE_FAILED|TREASURE_.*_FAILED`), timeoutMs)
+      context.expect(response.includes(expected), response)
+      return response
+    }
+    const bounded = (label, action) => context.waitUntil(async () => {
+      await action()
+      return true
+    }, { label, timeoutMs: 10000 })
+    let lastActivation = 0
+    const openChest = async material => {
+      const position = context.bot.entity.position.clone().set(2, 161, 2)
+      await context.waitUntil(() => context.bot.blockAt(position)?.name === material, {
+        label: `${material} reached the client`, timeoutMs: 10000
+      })
+      const delay = 150 - (performance.now() - lastActivation)
+      if (delay > 0) await context.sleep(delay)
+      const opened = context.waitForEvent('windowOpen', undefined, 30000)
+      await bounded(`Activate ${material}`, () => context.bot.activateBlock(context.bot.blockAt(position)))
+      lastActivation = performance.now()
+      const [window] = await opened
+      return window
+    }
+    const chestItems = window => window.slots.slice(0, window.inventoryStart).filter(Boolean)
+    const mapId = item => item.componentMap?.get('map_id')?.data
+    let missItem
+    await context.step('create and enter the Iris treasure map world', async () => {
+      const response = await command('treasure-map-create', 'TREASURE_MAP_READY world=iris:treasure_map_probe', 180000)
+      const version = response.match(/version=(\S+)/)?.[1]
+      context.expect(/^26\.[23](?:[.-]|$)/.test(version ?? ''), 'Fixture requires its matching 26.2 or 26.3 data pack', { version })
+      missItem = version.startsWith('26.2') ? 'map' : 'filled_map'
+      context.report.treasurePlatform = { version, folia: response.includes('folia=true'), missItem }
+      await context.waitUntil(() => context.bot.entity.position.distanceTo(
+        context.bot.entity.position.clone().set(0.5, 161, 0.5)
+      ) < 2, { label: 'Fixture teleport reached the client', timeoutMs: 30000 })
+    })
+    await context.step('confirm the missing target exhausts the placement search budget', async () => {
+      await command('treasure-map-limit', 'TREASURE_MAP_LIMIT status=SEARCH_LIMIT_REACHED', 120000)
+    })
+    for (const material of ['chest', 'copper_chest']) {
+      for (const destination of ['blocked', 'disabled', 'found', 'mixed']) {
+        await context.step(`open ${material} with ${destination} map target and retain all loot`, async () => {
+          const evidence = { destination, material, phase: 'prepare' }
+          context.report.treasureMaps ??= []
+          context.report.treasureMaps.push(evidence)
+          const located = destination === 'found' || destination === 'mixed'
+          const mapName = located ? 'filled_map' : missItem
+          await command(`treasure-map-chest ${destination} ${material.toUpperCase()}`,
+            `TREASURE_MAP_CHEST destination=${destination} material=${material.toUpperCase()}`)
+          evidence.phase = 'open'
+          const window = await openChest(material)
+          evidence.windowType = window.type
+          evidence.inventoryStart = window.inventoryStart
+          let targetId
+          let diamondType
+          let diamondsBefore
+          let marker
+          let verified
+          try {
+            await context.waitUntil(() => {
+              const items = chestItems(window)
+              return items.some(item => item.name === mapName) && items.some(item => item.name === 'diamond')
+            }, { label: `${destination} chest contains map and diamond`, timeoutMs: 30000 })
+            const items = chestItems(window)
+            const map = items.find(item => item.name === mapName)
+            const diamond = items.find(item => item.name === 'diamond')
+            targetId = mapId(map)
+            context.expect(items.length === 2 && map.count === 1 && diamond.count === 1,
+              'Loot table must produce exactly one map and one diamond')
+            context.expect((targetId !== undefined) === located, 'Only reachable destinations receive map data', {
+              destination, components: map.components
+            })
+            const response = await command(`treasure-map-inspect ${destination}`,
+              `TREASURE_MAP_INSPECT destination=${destination} diamonds=1 located=${located}`, 120000)
+            verified = Object.fromEntries([...response.matchAll(/(mapId|targetX|targetZ|centerX|centerZ)=(-?\d+)/g)]
+              .map(([, key, value]) => [key, Number(value)]))
+            const decorations = simplifyNbt(map.componentMap?.get('map_decorations')?.data)
+            marker = decorations?.['+']
+            if (located) {
+              context.expect(targetId === verified.mapId, 'Client and saved map IDs agree', { targetId, verified })
+              context.expect(marker?.type === 'minecraft:red_x'
+                && marker.x === verified.targetX && marker.z === verified.targetZ,
+              'Map marker points to the verified pyramid', { marker, verified, components: map.components })
+            } else {
+              context.expect(marker === undefined, 'Missing destinations must not invent a map marker', { decorations })
+            }
+            diamondType = diamond.type
+            diamondsBefore = context.bot.inventory.count(diamondType)
+            evidence.phase = 'withdraw'
+            evidence.diamondSlot = diamond.slot
+            await bounded(`Withdraw diamond from ${material} ${destination}`,
+              () => context.bot.clickWindow(diamond.slot, 0, 1))
+            evidence.phase = 'withdrawn'
+            await context.waitUntil(() => chestItems(window).every(item => item.name !== 'diamond'), {
+              label: 'Diamond transferred out of the chest', timeoutMs: 10000
+            })
+          } finally {
+            context.bot.closeWindow(window)
+          }
+          evidence.phase = 'reopen'
+          const reopened = await openChest(material)
+          try {
+            await context.waitUntil(() => chestItems(reopened).some(item => item.name === mapName), {
+              label: 'Saved map remains in the reopened chest', timeoutMs: 10000
+            })
+            const retained = chestItems(reopened)
+            context.expect(retained.length === 1 && retained[0].name === mapName && retained[0].count === 1,
+              'Reopening must not regenerate chest loot')
+            context.expect(mapId(retained[0]) === targetId, 'Reopening must retain the same map data')
+            context.expect(JSON.stringify(simplifyNbt(retained[0].componentMap?.get('map_decorations')?.data)?.['+'])
+              === JSON.stringify(marker), 'Reopening must retain the same destination marker')
+            await context.waitUntil(() => context.bot.inventory.count(diamondType) === diamondsBefore + 1, {
+              label: 'Chest awards exactly one diamond', timeoutMs: 10000
+            })
+            Object.assign(evidence, { phase: 'complete', mapItem: mapName,
+              mapId: targetId ?? null, marker: marker ?? null, verified, reopened: true })
+          } finally {
+            context.bot.closeWindow(reopened)
+          }
+        })
+      }
+    }
+    await context.step('verify storage variants, insertion rollback, and locate event results', async () => {
+      await command('treasure-extra-check', 'TREASURE_EXTRA_CHECK variants=9 rollback=true locateEvents=true', 120000)
+    })
+    await context.step('verify plugin loot runs on its owning region', async () => {
+      await command('treasure-region-check', 'TREASURE_REGION_LOOT copper=8 normal=1 events=9 owned=true', 120000)
+    })
+    await context.step('verify native loot table reload support', async () => {
+      await command('treasure-reload-before', 'TREASURE_RELOAD material=DIAMOND')
+      if (context.report.treasurePlatform.folia) {
+        const response = await context.command('/minecraft:reload', /Unknown or incomplete command|Reloading/i, 10000)
+        context.expect(response.includes('Unknown or incomplete command'),
+          'Folia fixture expects its unavailable data pack reload command', { response })
+        context.report.treasureReload = { status: 'unavailable', before: 'diamond', evidence: response }
+        return
+      }
+      const properties = await readFile(path.join(context.server.directory, 'server.properties'), 'utf8')
+      const levelName = properties.match(/^level-name=(.+)$/m)?.[1].trim() ?? 'world'
+      const tablePath = path.join(context.server.directory, levelName, 'datapacks', 'iris_treasure',
+        'data', 'iris_qa', 'loot_table', 'reload.json')
+      const original = await readFile(tablePath, 'utf8')
+      const replacement = JSON.parse(original)
+      context.expect(replacement.pools[0].entries[0].name === 'minecraft:diamond',
+        'Reload fixture must start with its diamond table')
+      const revision = async () => {
+        const response = await command('treasure-resources', 'TREASURE_RESOURCES revision=')
+        return Number(response.match(/revision=(\d+)/)?.[1])
+      }
+      const reload = async () => {
+        const before = await revision()
+        await context.command('/minecraft:reload', /Reloading/i, 30000)
+        await context.waitUntil(async () => await revision() > before, {
+          label: 'Server resource reload completed', timeoutMs: 120000, intervalMs: 500
+        })
+      }
+      replacement.pools[0].entries[0].name = 'minecraft:emerald'
+      try {
+        await writeFile(tablePath, `${JSON.stringify(replacement, null, 2)}\n`)
+        await reload()
+        await command('treasure-reload-after', 'TREASURE_RELOAD material=EMERALD')
+        context.report.treasureReload = { status: 'passed', before: 'diamond', after: 'emerald' }
+      } finally {
+        await writeFile(tablePath, original)
+        if (!context.signal.aborted) {
+          await reload()
+          await command('treasure-reload-before', 'TREASURE_RELOAD material=DIAMOND')
+        }
+      }
+    })
+  }
+}

adapters/bukkit/plugin/src/test/java/art/arcane/iris/IrisShutdownMaintenanceTest.java

@@ -0,0 +1,230 @@
+package art.arcane.iris;
+
+import art.arcane.iris.configuration.IrisSettings;
+import art.arcane.iris.generation.runtime.Engine;
+import art.arcane.iris.generation.runtime.GenerationSessionLease;
+import art.arcane.iris.generation.runtime.GenerationSessionManager;
+import art.arcane.iris.platform.bukkit.BukkitWorldBinding;
+import art.arcane.iris.platform.bukkit.nms.INMS;
+import art.arcane.iris.platform.bukkit.nms.INMSBinding;
+import art.arcane.iris.spi.IrisServices;
+import art.arcane.iris.platform.generation.PlatformChunkGenerator;
+import art.arcane.iris.studio.view.PregeneratorJob;
+import art.arcane.iris.testsupport.PlatformBinding;
+import art.arcane.iris.world.IrisToolbelt;
+import art.arcane.iris.world.IrisWorld;
+import art.arcane.iris.world.WorldMaintenance;
+import art.arcane.iris.world.runtime.BukkitEnginePlatformHooks;
+import art.arcane.iris.world.task.J;
+import art.arcane.volmlib.nativelib.terrain.ServerShutdownBoundary;
+import org.bukkit.Bukkit;
+import org.bukkit.NamespacedKey;
+import org.bukkit.World;
+import org.junit.ClassRule;
+import org.junit.Test;
+import org.mockito.MockedStatic;
+
+import java.lang.reflect.Field;
+import java.lang.reflect.Method;
+import java.util.List;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CopyOnWriteArrayList;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicReference;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+import static org.mockito.ArgumentMatchers.anyLong;
+import static org.mockito.ArgumentMatchers.eq;
+import static org.mockito.Mockito.CALLS_REAL_METHODS;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.mockStatic;
+import static org.mockito.Mockito.never;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+public class IrisShutdownMaintenanceTest {
+    @ClassRule
+    public static final PlatformBinding PLATFORM = PlatformBinding.mockPlatform();
+
+    @Test
+    public void finisherRetainsResourcesWhileTheAuthoritativeBoundaryIsPending() throws Exception {
+        try (Fixture fixture = new Fixture()) {
+            ServerShutdownBoundary boundary = mock(ServerShutdownBoundary.class);
+            CountDownLatch waiting = new CountDownLatch(1);
+            CountDownLatch release = new CountDownLatch(1);
+            AtomicReference<Thread> finisher = new AtomicReference<>();
+            when(boundary.await(anyLong(), eq(TimeUnit.SECONDS))).thenAnswer(invocation -> {
+                finisher.set(Thread.currentThread());
+                waiting.countDown();
+                assertTrue(release.await(5, TimeUnit.SECONDS));
+                return false;
+            });
+            setField(fixture.plugin, "serverShutdownBoundary", boundary);
+            fixture.quiesce();
+            fixture.startFinisher();
+            try {
+                assertTrue(waiting.await(5, TimeUnit.SECONDS));
+                fixture.startFinisher();
+                verify(fixture.generator, never()).closeAsync();
+                verify(fixture.binding, never()).releasePluginClassLoaderClose();
+            } finally {
+                release.countDown();
+                Thread running = finisher.get();
+                if (running != null) {
+                    running.join(5_000L);
+                    assertFalse(running.isAlive());
+                }
+            }
+            verify(boundary, times(1)).await(anyLong(), eq(TimeUnit.SECONDS));
+            verify(fixture.generator, never()).closeAsync();
+        }
+    }
+
+    @Test
+    public void missingShutdownBoundaryDoesNotAuthorizeResourceRelease() throws Exception {
+        try (Fixture fixture = new Fixture()) {
+            Method method = Iris.class.getDeclaredMethod("awaitServerShutdownBoundary");
+            method.setAccessible(true);
+            assertEquals(false, method.invoke(fixture.plugin));
+        }
+    }
+
+    @Test
+    public void serverStopKeepsFoliaGenerationAdmittedUntilTheServerDrains() throws Exception {
+        try (Fixture fixture = new Fixture()) {
+            GenerationSessionManager sessions = new GenerationSessionManager();
+            try (GenerationSessionLease active = sessions.acquireForEngine(fixture.engine, "active_chunk")) {
+                fixture.quiesce();
+
+                assertTrue(WorldMaintenance.isWorldMaintenanceActive(fixture.identity));
+                assertFalse(fixture.hooks.shouldRefuseGeneration(fixture.engine));
+                try (GenerationSessionLease queued = sessions.acquireForEngine(fixture.engine, "queued_chunk")) {
+                    assertEquals(active.sessionId(), queued.sessionId());
+                    assertEquals(2, sessions.activeLeases());
+                }
+                verify(fixture.generator).quiesceForServerShutdown();
+                verify(fixture.generator, never()).closeAsync();
+                fixture.nms.verify(INMS::get);
+                verify(fixture.binding).deferPluginClassLoaderClose();
+                verify(fixture.binding, never()).releasePluginClassLoaderClose();
+            }
+            assertEquals(0, sessions.activeLeases());
+            fixture.drain();
+            verify(fixture.generator).closeAsync();
+        }
+    }
+
+    @Test
+    public void serverStopDoesNotOverrideExistingBlockingMaintenance() throws Exception {
+        try (Fixture fixture = new Fixture()) {
+            WorldMaintenance.beginWorldMaintenance(fixture.identity, "world_unload", true);
+            try {
+                fixture.quiesce();
+                assertTrue(fixture.hooks.shouldRefuseGeneration(fixture.engine));
+            } finally {
+                WorldMaintenance.endWorldMaintenance(fixture.identity, "world_unload", true);
+            }
+            assertFalse(fixture.hooks.shouldRefuseGeneration(fixture.engine));
+        }
+    }
+
+    @Test
+    public void manualDisableStillBlocksGenerationBeforeClosingTheGenerator() throws Exception {
+        try (Fixture fixture = new Fixture()) {
+            when(fixture.generator.closeAsync()).thenAnswer(invocation -> {
+                assertTrue(fixture.hooks.shouldRefuseGeneration(fixture.engine));
+                return CompletableFuture.completedFuture(null);
+            });
+            try {
+                fixture.drain();
+                assertTrue(fixture.hooks.shouldRefuseGeneration(fixture.engine));
+                verify(fixture.generator).closeAsync();
+                verify(fixture.generator, never()).quiesceForServerShutdown();
+            } finally {
+                WorldMaintenance.endWorldMaintenance(fixture.identity, "manual_disable", true);
+            }
+        }
+    }
+
+    private static void setField(Iris plugin, String name, Object value) throws ReflectiveOperationException {
+        Field field = Iris.class.getDeclaredField(name);
+        field.setAccessible(true);
+        field.set(plugin, value);
+    }
+
+    private static final class Fixture implements AutoCloseable {
+        private final Iris plugin = mock(Iris.class);
+        private final World world = mock(World.class);
+        private final IrisWorld irisWorld = mock(IrisWorld.class);
+        private final Engine engine = mock(Engine.class);
+        private final PlatformChunkGenerator generator = mock(PlatformChunkGenerator.class);
+        private final BukkitEnginePlatformHooks hooks = new BukkitEnginePlatformHooks();
+        private final INMSBinding binding = mock(INMSBinding.class);
+        private final String identity = "iris:shutdown_test";
+        private final IrisSettings previousSettings = IrisSettings.settings;
+        private final MockedStatic<Bukkit> bukkit = mockStatic(Bukkit.class);
+        private final MockedStatic<IrisToolbelt> toolbelt = mockStatic(IrisToolbelt.class, CALLS_REAL_METHODS);
+        private final MockedStatic<BukkitWorldBinding> worlds = mockStatic(BukkitWorldBinding.class);
+        private final MockedStatic<IrisServices> services = mockStatic(IrisServices.class);
+        private final MockedStatic<INMS> nms = mockStatic(INMS.class);
+        private final MockedStatic<J> tasks = mockStatic(J.class, CALLS_REAL_METHODS);
+        private final MockedStatic<PregeneratorJob> pregenerator = mockStatic(PregeneratorJob.class);
+        private int quiesces;
+
+        private Fixture() throws ReflectiveOperationException {
+            IrisSettings.settings = new IrisSettings();
+            setField(plugin, "serverStopTeardownDeferred", new AtomicBoolean());
+            setField(plugin, "postStopFinisherStarted", new AtomicBoolean());
+            setField(plugin, "deferredShutdownGenerators", new CopyOnWriteArrayList<PlatformChunkGenerator>());
+            when(world.getKey()).thenReturn(NamespacedKey.fromString(identity));
+            when(engine.getWorld()).thenReturn(irisWorld);
+            when(irisWorld.hasPlatformWorld()).thenReturn(true);
+            when(irisWorld.identity()).thenReturn(identity);
+            when(generator.closeAsync()).thenReturn(CompletableFuture.completedFuture(null));
+            bukkit.when(Bukkit::getWorlds).thenReturn(List.of(world));
+            toolbelt.when(() -> IrisToolbelt.access(world)).thenReturn(generator);
+            worlds.when(() -> BukkitWorldBinding.world(irisWorld)).thenReturn(world);
+            nms.when(INMS::get).thenReturn(binding);
+            tasks.when(J::isFolia).thenReturn(true);
+        }
+
+        private void quiesce() throws ReflectiveOperationException {
+            Method method = Iris.class.getDeclaredMethod("quiesceRuntimeForServerShutdown", String.class);
+            method.setAccessible(true);
+            method.invoke(plugin, "server_stop");
+            quiesces++;
+        }
+
+        private void drain() throws ReflectiveOperationException {
+            Method method = Iris.class.getDeclaredMethod("drainWorldGenerators", String.class, long.class);
+            method.setAccessible(true);
+            method.invoke(plugin, "manual_disable", 5L);
+        }
+
+        private void startFinisher() throws ReflectiveOperationException {
+            Method method = Iris.class.getDeclaredMethod("startPostStopFinisher");
+            method.setAccessible(true);
+            method.invoke(plugin);
+        }
+
+        @Override
+        public void close() {
+            for (int index = 0; index < quiesces; index++) {
+                WorldMaintenance.endWorldMaintenance(identity, "server_stop");
+            }
+            pregenerator.close();
+            tasks.close();
+            nms.close();
+            services.close();
+            worlds.close();
+            toolbelt.close();
+            bukkit.close();
+            IrisSettings.settings = previousSettings;
+        }
+    }
+}

adapters/bukkit/plugin/src/test/java/art/arcane/iris/IrisVersionNumberTest.java

@@ -0,0 +1,67 @@
+package art.arcane.iris;
+
+import org.bukkit.Bukkit;
+import org.bukkit.plugin.PluginDescriptionFile;
+import org.junit.Test;
+import org.mockito.MockedStatic;
+
+import java.io.InputStream;
+import java.util.List;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotEquals;
+import static org.junit.Assert.assertNotNull;
+import static org.mockito.Answers.CALLS_REAL_METHODS;
+import static org.mockito.Mockito.doReturn;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.mockStatic;
+
+public class IrisVersionNumberTest {
+    @Test
+    public void releaseAndQualifiedBuildsUseTheSameVersionNumber() {
+        for (String version : List.of("4.3.3", "4.3.3-SNAPSHOT", "4.3.3-test")) {
+            assertEquals(version, 433, plugin(version).getIrisVersion());
+        }
+    }
+
+    @Test
+    public void processedPluginMetadataProvidesAValidEngineVersion() throws Exception {
+        try (InputStream stream = getClass().getResourceAsStream("/plugin.yml")) {
+            assertNotNull(stream);
+            PluginDescriptionFile description = new PluginDescriptionFile(stream);
+            Iris plugin = mock(Iris.class, CALLS_REAL_METHODS);
+            doReturn(description).when(plugin).getDescription();
+
+            assertNotEquals(-1, plugin.getIrisVersion());
+        }
+    }
+
+    @Test
+    public void malformedAndOverflowingReleaseNumbersStayInvalid() {
+        for (String version : List.of("development", "4..3", ".4.3.3", "4.3.3.", "4.3a.3-test",
+                "2147483648", "999999999999999999999-SNAPSHOT", "-SNAPSHOT")) {
+            assertEquals(version, -1, plugin(version).getIrisVersion());
+        }
+    }
+
+    @Test
+    public void supportedMinecraftVersionsRetainTheirEngineNumbers() {
+        Iris plugin = mock(Iris.class, CALLS_REAL_METHODS);
+        try (MockedStatic<Bukkit> bukkit = mockStatic(Bukkit.class)) {
+            bukkit.when(Bukkit::getVersion).thenReturn("26.1.2-74-ver/26.1.2@e4e17fc (MC: 26.1.2)");
+            assertEquals(2612, plugin.getMCVersion());
+            bukkit.when(Bukkit::getVersion).thenReturn("26.1.2-8-ver/26.1.x@62dc0f2 (MC: 26.1.2)");
+            assertEquals(2612, plugin.getMCVersion());
+            bukkit.when(Bukkit::getVersion).thenReturn("26.2-133 (MC: 26.2)");
+            assertEquals(262, plugin.getMCVersion());
+            bukkit.when(Bukkit::getVersion).thenReturn("26.3-169 (MC: 26.3)");
+            assertEquals(263, plugin.getMCVersion());
+        }
+    }
+
+    private static Iris plugin(String version) {
+        Iris plugin = mock(Iris.class, CALLS_REAL_METHODS);
+        doReturn(new PluginDescriptionFile("Iris", version, Iris.class.getName())).when(plugin).getDescription();
+        return plugin;
+    }
+}

adapters/fabric/build.gradle

@@ -22,6 +22,7 @@ import org.gradle.api.file.FileCopyDetails
 import org.gradle.api.file.FileSystemOperations
 import org.gradle.api.file.FileTree
 import org.gradle.api.tasks.compile.JavaCompile
+import org.gradle.api.attributes.Bundling
 import org.gradle.jvm.toolchain.JavaLanguageVersion
 
 import javax.inject.Inject
@@ -38,10 +39,14 @@ buildscript {
 
 plugins {
     id 'java'
-    id 'net.fabricmc.fabric-loom' version '1.17.14'
+    id 'net.fabricmc.fabric-loom' version '1.17.21' apply false
+    id 'net.fabricmc.fabric-loom-remap' version '1.17.21' apply false
     alias(libs.plugins.shadow)
 }
 
+apply from: file('../../gradle/mod-target.gradle')
+
+apply plugin: irisModTarget.fabricRemap ? 'net.fabricmc.fabric-loom-remap' : 'net.fabricmc.fabric-loom'
 apply plugin: 'art.arcane.volmit-packaging'
 
 interface IrisFileOperations {
@@ -56,9 +61,9 @@ apply from: file('../../gradle/volmlib-stamp.gradle')
 
 Properties rootProperties = new Properties()
 file('../../gradle.properties').withInputStream { InputStream stream -> rootProperties.load(stream) }
-String irisVersion = providers.gradleProperty('irisVersion').getOrElse(rootProperties.getProperty('irisVersion', '4.3.3-26.2'))
+String irisVersion = providers.gradleProperty('irisVersion').getOrElse(rootProperties.getProperty('irisVersion', '4.3.3'))
 String minecraftVersion = providers.gradleProperty('minecraftVersion').getOrElse(rootProperties.getProperty('minecraftVersion', '26.3'))
-String fabricLoaderVersion = providers.gradleProperty('fabricLoaderVersion').getOrElse(rootProperties.getProperty('fabricLoaderVersion', '0.19.5'))
+String fabricLoaderVersion = providers.gradleProperty('fabricLoaderVersion').getOrElse(irisModTarget.fabricLoader.toString())
 Closure<String> irisArtifactName = { String platform, String targetVersion ->
     return "Iris v${project.version} [${platform}] ${targetVersion}.jar"
 }
@@ -141,7 +146,11 @@ configurations.create('jij') {
 
 dependencies {
     minecraft("com.mojang:minecraft:${minecraftVersion}")
-    implementation("net.fabricmc:fabric-loader:${fabricLoaderVersion}")
+    if (irisModTarget.fabricRemap) {
+        mappings(loom.officialMojangMappings())
+    }
+    String modConfiguration = irisModTarget.fabricRemap ? 'modImplementation' : 'implementation'
+    add(modConfiguration, "net.fabricmc:fabric-loader:${fabricLoaderVersion}")
     testImplementation('junit:junit:4.13.2')
     testImplementation('org.mockito:mockito-core:5.23.0')
     testImplementation(testFixtures('art.arcane:core'))
@@ -168,11 +177,19 @@ dependencies {
         libs.fabricApi.keyMapping,
         libs.fabricApi.permission
     ]
+    if (irisModTarget.fabricModules != null) {
+        fabricApi = ((Map<String, String>) irisModTarget.fabricModules).collect { String module, String moduleVersion ->
+            "net.fabricmc.fabric-api:${module}:${moduleVersion}".toString()
+        }
+    }
+    if (irisModTarget.fabricPermissions != null) {
+        fabricApi.add("me.lucko:fabric-permissions-api:${irisModTarget.fabricPermissions}".toString())
+    }
     fabricApi.each { Object notation ->
         add('jij', notation)
-        add('implementation', notation)
+        add(modConfiguration, notation)
     }
-    compileOnly('org.slf4j:slf4j-api:2.0.17')
+    compileOnly("org.slf4j:slf4j-api:${irisModTarget.slf4j}")
     compileOnly(libs.spigot) {
         transitive = false
     }
@@ -201,21 +218,28 @@ dependencies {
         libs.jaxen
     ]
     shared.each { Object notation ->
-        add('bundle', notation)
-        add('devBundle', notation)
+        ['bundle', 'devBundle'].each { String configuration ->
+            add(configuration, notation) {
+                if (group == 'art.arcane' && name == 'core') {
+                    attributes {
+                        attribute(Bundling.BUNDLING_ATTRIBUTE, objects.named(Bundling, Bundling.EXTERNAL))
+                    }
+                }
+            }
+        }
     }
 }
 
 tasks.named('compileJava', JavaCompile).configure {
     options.encoding = 'UTF-8'
-    options.release.set(25)
+    options.release.set((int) irisModTarget.java)
 }
 
 tasks.named('test').configure {
 }
 
 loom {
-    accessWidenerPath = art.arcane.volmit.packaging.NativeAccessRules.prepare(nativeSourceImplementation, "fabric", layout.buildDirectory.dir("native-access").get().asFile)
+    accessWidenerPath = art.arcane.volmit.packaging.NativeAccessRules.prepare(irisModTarget.nativeAccess.toString(), "fabric", layout.buildDirectory.dir("native-access").get().asFile)
     runs {
         client {
             runDir(providers.gradleProperty('irisClientRunDir').getOrElse('run'))
@@ -270,6 +294,15 @@ Map<String, String> nestedFabricApiJars = [
     'fabric-permission-api-v1'   : 'fabric-permission-api-v1.jar'
 ]
 
+if (irisModTarget.fabricModules != null) {
+    nestedFabricApiJars = ((Map<String, String>) irisModTarget.fabricModules).collectEntries { String module, String ignored ->
+        [(module): "${module}.jar".toString()]
+    }
+}
+if (irisModTarget.fabricPermissions != null) {
+    nestedFabricApiJars.put('fabric-permissions-api', 'fabric-permissions-api.jar')
+}
+
 FileTree staleLoaderJars = fileTree(layout.buildDirectory.dir('libs')) {
     include('Iris v* [Fabric] *.jar')
     include('iris-fabric-*.jar')
@@ -288,6 +321,10 @@ tasks.named('shadowJar', ShadowJar).configure {
     archiveFileName.set(irisArtifactName('Fabric', "${minecraftVersion}+${fabricLoaderVersion}"))
     configurations = [project.configurations.named('bundle').get()]
     mergeServiceFiles()
+    if ((int) irisModTarget.java == 21) {
+        exclude('art/arcane/volmlib/util/noise/NativeBillowLoader*.class')
+        exclude('art/arcane/volmlib/util/noise/BillowBatch*.class')
+    }
     exclude('META-INF/maven/**')
     exclude('META-INF/proguard/**')
     exclude('META-INF/*.SF')
@@ -346,28 +383,39 @@ tasks.named('shadowJar', ShadowJar).configure {
     }
 }
 
-// The thin `jar`/`remapJar` outputs carry valid fabric.mod.json metadata but bundle zero
-// dependencies. Installing one is an instant NoClassDefFoundError, and they sit in build/libs right
-// next to the real artifact. shadowJar is the only shippable Fabric jar.
+// The thin jar omits bundled dependencies. Obfuscated targets remap the complete shadow jar.
 tasks.named('jar').configure {
     enabled = false
 }
 
 tasks.matching { it.name == 'remapJar' }.configureEach {
-    enabled = false
+    enabled = (boolean) irisModTarget.fabricRemap
+    if (irisModTarget.fabricRemap) {
+        dependsOn(tasks.named('shadowJar'))
+        inputFile.set(tasks.named('shadowJar', ShadowJar).flatMap { it.archiveFile })
+        archiveFileName.set(irisArtifactName('Fabric', "${minecraftVersion}+${fabricLoaderVersion}"))
+        addNestedDependencies.set(false)
+    }
+}
+if (irisModTarget.fabricRemap) {
+    tasks.named('shadowJar', ShadowJar).configure {
+        destinationDirectory.set(layout.buildDirectory.dir('devlibs'))
+    }
 }
 
 tasks.named('assemble').configure {
-    dependsOn(tasks.named('shadowJar'))
+    dependsOn(tasks.named(irisModTarget.fabricRemap ? 'remapJar' : 'shadowJar'))
 }
 
 pluginPackaging {
     artifacts {
         create('distribution') {
-            taskName = 'shadowJar'
+            taskName = irisModTarget.fabricRemap ? 'remapJar' : 'shadowJar'
             policyName = 'Iris Fabric'
             prunePrefixes = ['art/arcane/volmlib/']
             keepPrefixes = ['art/arcane/volmlib/util/matter/slices/']
         }
     }
 }
+
+apply from: file('../../gradle/modded-version-sources.gradle')

adapters/fabric/src/versions/1.21.1/resources/fabric.mod.json

@@ -0,0 +1,78 @@
+{
+  "schemaVersion": 1,
+  "id": "irisworldgen",
+  "version": "${version}",
+  "name": "Iris",
+  "description": "Iris World Generation Engine (Fabric adapter - native chunk generator, explicit Iris world datapack workflow, engine lifecycle)",
+  "authors": [
+    "Arcane Arts (Volmit Software)"
+  ],
+  "contributors": [
+    "cyberpwn",
+    "NextdoorPsycho",
+    "Vatuu"
+  ],
+  "contact": {
+    "homepage": "https://docs.volmit.com/iris/",
+    "issues": "https://github.com/VolmitSoftware/Iris/issues",
+    "sources": "https://github.com/VolmitSoftware/Iris"
+  },
+  "license": "GPL-3.0",
+  "icon": "assets/irisworldgen/icon.png",
+  "environment": "*",
+  "accessWidener": "volmlib.accesswidener",
+  "mixins": [
+    "volmlib.fabric.mixins.json",
+    "volmlib.entity.mixins.json",
+    {
+      "config": "volmlib.client.mixins.json",
+      "environment": "client"
+    }
+  ],
+  "entrypoints": {
+    "main": [
+      "art.arcane.iris.fabric.IrisFabricBootstrap"
+    ],
+    "client": [
+      "art.arcane.iris.fabric.IrisFabricClient"
+    ]
+  },
+  "jars": [
+    {
+      "file": "META-INF/jars/fabric-api-base.jar"
+    },
+    {
+      "file": "META-INF/jars/fabric-registry-sync-v0.jar"
+    },
+    {
+      "file": "META-INF/jars/fabric-resource-loader-v0.jar"
+    },
+    {
+      "file": "META-INF/jars/fabric-lifecycle-events-v1.jar"
+    },
+    {
+      "file": "META-INF/jars/fabric-command-api-v2.jar"
+    },
+    {
+      "file": "META-INF/jars/fabric-events-interaction-v0.jar"
+    },
+    {
+      "file": "META-INF/jars/fabric-networking-api-v1.jar"
+    },
+    {
+      "file": "META-INF/jars/fabric-rendering-v1.jar"
+    },
+    {
+      "file": "META-INF/jars/fabric-key-binding-api-v1.jar"
+    },
+    {
+      "file": "META-INF/jars/fabric-permissions-api.jar"
+    }
+  ],
+  "depends": {
+    "fabricloader": ">=0.19.5",
+    "minecraft": "${minecraftVersion}",
+    "java": ">=21",
+    "fabric-permissions-api-v0": "*"
+  }
+}

adapters/fabric/src/versions/1.21.1/test/java/art/arcane/volmlib/nativelib/minecraft26_2/fabric/NativeFabricBiomeDefinitionTest.java

@@ -0,0 +1,102 @@
+package art.arcane.volmlib.nativelib.minecraft26_2.fabric;
+
+import art.arcane.volmlib.nativelib.minecraft26_2.terrain.NativeRegistryDefinitions;
+import art.arcane.volmlib.nativelib.modded.NativeLoaderOptions;
+import com.google.gson.JsonParser;
+import com.mojang.serialization.JsonOps;
+import com.mojang.serialization.Lifecycle;
+import net.minecraft.SharedConstants;
+import net.minecraft.core.Holder;
+import net.minecraft.core.HolderSet;
+import net.minecraft.core.MappedRegistry;
+import net.minecraft.core.RegistrationInfo;
+import net.minecraft.core.RegistryAccess;
+import net.minecraft.core.registries.Registries;
+import net.minecraft.resources.ResourceLocation;
+import net.minecraft.resources.RegistryOps;
+import net.minecraft.resources.ResourceKey;
+import net.minecraft.server.Bootstrap;
+import net.minecraft.world.level.biome.Biome;
+import net.minecraft.world.level.biome.BiomeGenerationSettings;
+import net.minecraft.world.level.levelgen.GenerationStep;
+import net.minecraft.world.level.levelgen.carver.ConfiguredWorldCarver;
+import net.minecraft.world.level.levelgen.feature.ConfiguredFeature;
+import net.minecraft.world.level.levelgen.placement.PlacedFeature;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import java.lang.reflect.Constructor;
+import java.lang.reflect.Field;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.function.BooleanSupplier;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+import static org.mockito.Mockito.mock;
+
+public class NativeFabricBiomeDefinitionTest {
+    private static final String BIOME_REGISTRY = "minecraft:worldgen/biome";
+    private static final String BIOME_KEY = "iris:biomes/fabric_modified";
+    private static final String SOURCE_JSON = "{\"has_precipitation\":true,\"temperature\":0.8,\"downfall\":0.4,"
+            + "\"effects\":{\"fog_color\":12638463,\"water_color\":4159204,\"water_fog_color\":329011,\"sky_color\":7907327},"
+            + "\"carvers\":{},\"features\":[],\"spawners\":{},\"spawn_costs\":{}}";
+
+    @BeforeClass
+    public static void bootstrap() {
+        SharedConstants.tryDetectVersion();
+        Bootstrap.bootStrap();
+    }
+
+    @Test
+    public void generatedBiomeDefinitionExcludesFabricBiomeModifications() throws Exception {
+        MappedRegistry<PlacedFeature> features = new MappedRegistry<>(Registries.PLACED_FEATURE, Lifecycle.stable());
+        Holder.Reference<PlacedFeature> ore = features.register(
+                ResourceKey.create(Registries.PLACED_FEATURE, ResourceLocation.parse("iris:modded_ore")),
+                new PlacedFeature(Holder.direct(mock(ConfiguredFeature.class)), List.of()),
+                RegistrationInfo.BUILT_IN);
+        features.freeze();
+        MappedRegistry<ConfiguredWorldCarver<?>> carvers = new MappedRegistry<>(Registries.CONFIGURED_CARVER, Lifecycle.stable());
+        carvers.freeze();
+        MappedRegistry<Biome> biomes = new MappedRegistry<>(Registries.BIOME, Lifecycle.stable());
+        RegistryAccess access = new RegistryAccess.ImmutableRegistryAccess(List.of(biomes, features, carvers));
+        Biome source = Biome.DIRECT_CODEC.parse(RegistryOps.create(JsonOps.INSTANCE, access),
+                JsonParser.parseString(SOURCE_JSON)).getOrThrow();
+        NativeFabricLoader loader = new NativeFabricLoader(new NativeLoaderOptions("irisworldgen", "treefeller",
+                BooleanSupplier::getAsBoolean));
+        loader.recordOriginalBiome(source);
+        Holder.Reference<Biome> biome = biomes.register(
+                ResourceKey.create(Registries.BIOME, ResourceLocation.parse(BIOME_KEY)), source, RegistrationInfo.BUILT_IN);
+        biomes.freeze();
+        addFeatureInPlace(biome.value().getGenerationSettings(), ore);
+        warmInPlace(biome.value());
+        NativeRegistryDefinitions definitions = new NativeRegistryDefinitions(() -> access, loader::unmodifiedBiome);
+
+        assertEquals(0.1F, biome.value().getBaseTemperature(), 0.0F);
+        assertTrue(biome.value().getGenerationSettings().features()
+                .get(GenerationStep.Decoration.UNDERGROUND_ORES.ordinal()).contains(ore));
+        assertEquals(JsonParser.parseString(definitions.canonicalDefinition(BIOME_REGISTRY, BIOME_KEY, SOURCE_JSON).value()),
+                JsonParser.parseString(definitions.generatedDefinition(BIOME_REGISTRY, BIOME_KEY).value()));
+    }
+
+    private static void addFeatureInPlace(BiomeGenerationSettings settings, Holder<PlacedFeature> feature)
+            throws ReflectiveOperationException {
+        List<HolderSet<PlacedFeature>> steps = new ArrayList<>(settings.features());
+        while (steps.size() <= GenerationStep.Decoration.UNDERGROUND_ORES.ordinal()) {
+            steps.add(HolderSet.direct());
+        }
+        steps.set(GenerationStep.Decoration.UNDERGROUND_ORES.ordinal(), HolderSet.direct(feature));
+        Field features = BiomeGenerationSettings.class.getDeclaredField("features");
+        features.setAccessible(true);
+        features.set(settings, List.copyOf(steps));
+    }
+
+    private static void warmInPlace(Biome biome) throws ReflectiveOperationException {
+        Constructor<Biome.ClimateSettings> climate = Biome.ClimateSettings.class.getDeclaredConstructor(
+                boolean.class, float.class, Biome.TemperatureModifier.class, float.class);
+        climate.setAccessible(true);
+        Field climateSettings = Biome.class.getDeclaredField("climateSettings");
+        climateSettings.setAccessible(true);
+        climateSettings.set(biome, climate.newInstance(true, 0.1F, Biome.TemperatureModifier.NONE, 0.4F));
+    }
+}

adapters/forge/build.gradle

@@ -22,6 +22,7 @@ import org.gradle.api.file.FileCopyDetails
 import org.gradle.api.file.FileSystemOperations
 import org.gradle.api.file.FileTree
 import org.gradle.api.tasks.compile.JavaCompile
+import org.gradle.api.attributes.Bundling
 import org.gradle.jvm.toolchain.JavaLanguageVersion
 
 import javax.inject.Inject
@@ -42,6 +43,8 @@ plugins {
     alias(libs.plugins.shadow)
 }
 
+apply from: file('../../gradle/mod-target.gradle')
+
 apply plugin: 'art.arcane.volmit-packaging'
 
 interface IrisFileOperations {
@@ -56,9 +59,9 @@ apply from: file('../../gradle/volmlib-stamp.gradle')
 
 Properties rootProperties = new Properties()
 file('../../gradle.properties').withInputStream { InputStream stream -> rootProperties.load(stream) }
-String irisVersion = providers.gradleProperty('irisVersion').getOrElse(rootProperties.getProperty('irisVersion', '4.3.3-26.2'))
+String irisVersion = providers.gradleProperty('irisVersion').getOrElse(rootProperties.getProperty('irisVersion', '4.3.3'))
 String minecraftVersion = providers.gradleProperty('minecraftVersion').getOrElse(rootProperties.getProperty('minecraftVersion', '26.3'))
-String forgeVersion = providers.gradleProperty('forgeVersion').getOrElse(rootProperties.getProperty('forgeVersion', '26.3-66.0.8'))
+String forgeVersion = providers.gradleProperty('forgeVersion').getOrElse(irisModTarget.forge.toString())
 Closure<String> loaderDisplayVersion = { String loaderVersion ->
     String coordinatePrefix = "${minecraftVersion}-"
     if (loaderVersion.startsWith(coordinatePrefix)) {
@@ -165,7 +168,7 @@ dependencies {
     testImplementation(libs.spigot) {
         transitive = false
     }
-    compileOnly('org.slf4j:slf4j-api:2.0.17')
+    compileOnly("org.slf4j:slf4j-api:${irisModTarget.slf4j}")
     compileOnly(libs.spigot) {
         transitive = false
     }
@@ -200,14 +203,23 @@ dependencies {
         libs.jaxen
     ]
     shared.each { Object notation ->
-        add('bundle', notation)
-        add('devBundle', notation)
-        add('runBundle', notation)
+        ['bundle', 'devBundle', 'runBundle'].each { String configuration ->
+            add(configuration, notation) {
+                if (group == 'art.arcane' && name == 'core') {
+                    attributes {
+                        attribute(Bundling.BUNDLING_ATTRIBUTE, objects.named(Bundling, Bundling.EXTERNAL))
+                    }
+                }
+            }
+        }
     }
 }
 
 minecraft {
-    accessTransformer.from(art.arcane.volmit.packaging.NativeAccessRules.prepare(nativeSourceImplementation, "forge", layout.buildDirectory.dir("native-access").get().asFile))
+    if (irisModTarget.fabricRemap) {
+        mappings channel: 'official', version: minecraftVersion
+    }
+    accessTransformer.from(art.arcane.volmit.packaging.NativeAccessRules.prepare(irisModTarget.nativeAccess.toString(), "forge", layout.buildDirectory.dir("native-access").get().asFile))
     runs {
         register('client') {
             workingDir = layout.projectDirectory.dir('run')
@@ -241,7 +253,8 @@ minecraft {
 
 tasks.named('compileJava', JavaCompile).configure {
     options.encoding = 'UTF-8'
-    options.release.set(25)
+    options.compilerArgs.addAll(['-Xmaxerrs', '2000'])
+    options.release.set((int) irisModTarget.java)
 }
 
 tasks.named('test').configure {
@@ -250,8 +263,9 @@ tasks.named('test').configure {
 processResources {
     inputs.property('version', irisVersion)
     inputs.property('minecraftVersion', minecraftVersion)
+    inputs.property('loaderRange', irisModTarget.forgeRange.toString())
     filesMatching('META-INF/mods.toml') {
-        expand('version': irisVersion, 'minecraftVersion': minecraftVersion)
+        expand('version': irisVersion, 'minecraftVersion': minecraftVersion, 'loaderRange': irisModTarget.forgeRange.toString())
     }
 }
 
@@ -280,6 +294,10 @@ tasks.named('shadowJar', ShadowJar).configure {
     configurations = [project.configurations.named('bundle').get()]
     from(sourceSets.main.output)
     mergeServiceFiles()
+    if ((int) irisModTarget.java == 21) {
+        exclude('art/arcane/volmlib/util/noise/NativeBillowLoader*.class')
+        exclude('art/arcane/volmlib/util/noise/BillowBatch*.class')
+    }
     exclude('META-INF/maven/**')
     exclude('META-INF/proguard/**')
     exclude('META-INF/*.SF')
@@ -345,3 +363,5 @@ pluginPackaging {
         }
     }
 }
+
+apply from: file('../../gradle/modded-version-sources.gradle')

adapters/forge/src/main/resources/META-INF/mods.toml

@@ -1,5 +1,5 @@
 modLoader = "javafml"
-loaderVersion = "[66,67)"
+loaderVersion = "${loaderRange}"
 license = "GPL-3.0"
 issueTrackerURL = "https://github.com/VolmitSoftware/Iris/issues"
 
@@ -16,7 +16,7 @@ logoFile = "assets/irisworldgen/icon.png"
 [[dependencies.irisworldgen]]
 modId = "forge"
 mandatory = true
-versionRange = "[66,67)"
+versionRange = "${loaderRange}"
 ordering = "NONE"
 side = "BOTH"
 

adapters/forge/src/versions/1.21.1/java/art/arcane/iris/forge/IrisForgeBootstrap.java

@@ -0,0 +1,29 @@
+package art.arcane.iris.forge;
+
+import art.arcane.iris.modded.IrisModdedChunkGenerator;
+import art.arcane.iris.modded.ModdedEngineBootstrap;
+import art.arcane.iris.modded.ModdedLifecycleCallbacks;
+import art.arcane.iris.modded.service.ModdedTreeFellerService;
+import art.arcane.volmlib.nativelib.modded.NativeLoaderOptions;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeChunkGeneratorDefinition;
+import art.arcane.volmlib.nativelib.minecraft26_2.forge.NativeForgeLoader;
+import art.arcane.volmlib.nativelib.minecraft26_2.forge.NativeForgeBootstrap;
+import net.minecraftforge.fml.common.Mod;
+import net.minecraftforge.fml.javafmlmod.FMLJavaModLoadingContext;
+import net.minecraftforge.fml.loading.FMLLoader;
+
+@Mod("irisworldgen")
+public final class IrisForgeBootstrap {
+    public IrisForgeBootstrap(FMLJavaModLoadingContext context) {
+        NativeForgeLoader loader = new NativeForgeLoader(new NativeLoaderOptions(
+                "irisworldgen", "treefeller", ModdedTreeFellerService::runBreakProbe));
+        NativeChunkGeneratorDefinition generator = IrisModdedChunkGenerator.DEFINITION;
+        ModdedEngineBootstrap.bootCommon(loader, "Forge " + FMLLoader.versionInfo().forgeVersion(),
+                () -> NativeForgeBootstrap.registerGenerators(context, generator, "block_drops"));
+        ForgeProtocolNetworking.register();
+        if (loader.clientEnvironment()) {
+            IrisForgeClient.init(context);
+        }
+        NativeForgeBootstrap.install(context, loader, ModdedLifecycleCallbacks.create());
+    }
+}

adapters/forge/src/versions/1.21.1/java/art/arcane/iris/forge/IrisForgeClient.java

@@ -0,0 +1,25 @@
+package art.arcane.iris.forge;
+
+import art.arcane.iris.client.IrisClient;
+import net.minecraftforge.fml.javafmlmod.FMLJavaModLoadingContext;
+import art.arcane.volmlib.nativelib.minecraft26_2.forge.NativeForgeClientHooks;
+import art.arcane.iris.client.IrisClientHud;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeProtocolChannel;
+
+public final class IrisForgeClient {
+    private IrisForgeClient() {
+    }
+
+    public static void init(FMLJavaModLoadingContext context) {
+        IrisClient.bindSender(IrisForgeClient::sendToServer);
+        NativeForgeClientHooks.install(context, IrisClientHud.binding(), IrisClient::onWorldJoin, IrisClient::onDisconnect);
+    }
+
+    private static void sendToServer(byte[] frame) {
+        NativeProtocolChannel channel = ForgeProtocolNetworking.channel();
+        if (channel == null) {
+            return;
+        }
+        channel.sendToServer(frame);
+    }
+}

adapters/forge/src/versions/1.21.1/test/java/art/arcane/volmlib/nativelib/minecraft26_2/forge/NativeForgeBiomeDefinitionTest.java

@@ -0,0 +1,100 @@
+package art.arcane.volmlib.nativelib.minecraft26_2.forge;
+
+import art.arcane.volmlib.nativelib.minecraft26_2.terrain.NativeRegistryDefinitions;
+import art.arcane.volmlib.nativelib.modded.NativeLoaderOptions;
+import com.google.gson.JsonParser;
+import com.mojang.serialization.JsonOps;
+import com.mojang.serialization.Lifecycle;
+import com.mojang.serialization.MapCodec;
+import net.minecraft.SharedConstants;
+import net.minecraft.core.Holder;
+import net.minecraft.core.MappedRegistry;
+import net.minecraft.core.RegistrationInfo;
+import net.minecraft.core.RegistryAccess;
+import net.minecraft.core.registries.Registries;
+import net.minecraft.resources.ResourceLocation;
+import net.minecraft.resources.RegistryOps;
+import net.minecraft.resources.ResourceKey;
+import net.minecraft.server.Bootstrap;
+import net.minecraft.world.entity.EntityType;
+import net.minecraft.world.entity.MobCategory;
+import net.minecraft.world.level.biome.Biome;
+import net.minecraft.world.level.biome.MobSpawnSettings;
+import net.minecraft.world.level.levelgen.GenerationStep;
+import net.minecraft.world.level.levelgen.carver.ConfiguredWorldCarver;
+import net.minecraft.world.level.levelgen.feature.ConfiguredFeature;
+import net.minecraft.world.level.levelgen.placement.PlacedFeature;
+import net.minecraftforge.common.world.BiomeModifier;
+import net.minecraftforge.common.world.ModifiableBiomeInfo;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import java.util.List;
+import java.util.function.BooleanSupplier;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+import static org.mockito.Mockito.mock;
+
+public class NativeForgeBiomeDefinitionTest {
+    private static final String BIOME_REGISTRY = "minecraft:worldgen/biome";
+    private static final String BIOME_KEY = "iris:biomes/forge_modified";
+    private static final String SOURCE_JSON = "{\"has_precipitation\":true,\"temperature\":0.8,\"downfall\":0.4,"
+            + "\"effects\":{\"fog_color\":12638463,\"water_color\":4159204,\"water_fog_color\":329011,\"sky_color\":7907327},"
+            + "\"carvers\":{},\"features\":[],\"spawners\":{},\"spawn_costs\":{}}";
+
+    @BeforeClass
+    public static void bootstrap() {
+        SharedConstants.tryDetectVersion();
+        Bootstrap.bootStrap();
+    }
+
+    @Test
+    public void generatedBiomeDefinitionExcludesForgeBiomeModifierOutput() {
+        MappedRegistry<PlacedFeature> features = new MappedRegistry<>(Registries.PLACED_FEATURE, Lifecycle.stable());
+        Holder.Reference<PlacedFeature> ore = features.register(
+                ResourceKey.create(Registries.PLACED_FEATURE, ResourceLocation.parse("iris:modded_ore")),
+                new PlacedFeature(Holder.direct(mock(ConfiguredFeature.class)), List.of()),
+                RegistrationInfo.BUILT_IN);
+        features.freeze();
+        MappedRegistry<ConfiguredWorldCarver<?>> carvers = new MappedRegistry<>(Registries.CONFIGURED_CARVER, Lifecycle.stable());
+        carvers.freeze();
+        MappedRegistry<Biome> biomes = new MappedRegistry<>(Registries.BIOME, Lifecycle.stable());
+        RegistryAccess access = new RegistryAccess.ImmutableRegistryAccess(List.of(biomes, features, carvers));
+        Biome source = Biome.DIRECT_CODEC.parse(RegistryOps.create(JsonOps.INSTANCE, access),
+                JsonParser.parseString(SOURCE_JSON)).getOrThrow();
+        Holder.Reference<Biome> biome = biomes.register(
+                ResourceKey.create(Registries.BIOME, ResourceLocation.parse(BIOME_KEY)), source, RegistrationInfo.BUILT_IN);
+        biomes.freeze();
+        biome.value().modifiableBiomeInfo().applyBiomeModifiers(biome, List.of(new ModdedContent(ore)));
+        NativeRegistryDefinitions definitions = new NativeRegistryDefinitions(() -> access,
+                new NativeForgeLoader(new NativeLoaderOptions("irisworldgen", "treefeller",
+                        BooleanSupplier::getAsBoolean))::unmodifiedBiome);
+
+        assertEquals(0.1F, biome.value().getBaseTemperature(), 0.0F);
+        assertEquals(0x102030, biome.value().getWaterColor() & 0xFFFFFF);
+        assertTrue(biome.value().getGenerationSettings().hasFeature(ore.value()));
+        assertTrue(biome.value().getMobSettings().getMobs(MobCategory.MONSTER).unwrap().stream()
+                .anyMatch(spawn -> spawn.type == EntityType.ZOMBIE));
+        assertEquals(JsonParser.parseString(definitions.canonicalDefinition(BIOME_REGISTRY, BIOME_KEY, SOURCE_JSON).value()),
+                JsonParser.parseString(definitions.generatedDefinition(BIOME_REGISTRY, BIOME_KEY).value()));
+    }
+
+    private record ModdedContent(Holder<PlacedFeature> ore) implements BiomeModifier {
+        @Override
+        public void modify(Holder<Biome> biome, Phase phase, ModifiableBiomeInfo.BiomeInfo.Builder builder) {
+            if (phase != Phase.ADD) {
+                return;
+            }
+            builder.getClimateSettings().setTemperature(0.1F);
+            builder.getSpecialEffects().waterColor(0x102030);
+            builder.getMobSpawnSettings().addSpawn(MobCategory.MONSTER, new MobSpawnSettings.SpawnerData(EntityType.ZOMBIE, 5, 1, 2));
+            builder.getGenerationSettings().addFeature(GenerationStep.Decoration.UNDERGROUND_ORES, ore);
+        }
+
+        @Override
+        public MapCodec<? extends BiomeModifier> codec() {
+            throw new UnsupportedOperationException();
+        }
+    }
+}

adapters/forge/src/versions/1.21.1/test/java/art/arcane/volmlib/nativelib/minecraft26_2/forge/NativeForgeSpawnPositionTest.java

@@ -0,0 +1,54 @@
+package art.arcane.volmlib.nativelib.minecraft26_2.forge;
+
+import art.arcane.volmlib.nativelib.modded.NativeLoaderOptions;
+import net.minecraft.SharedConstants;
+import net.minecraft.server.Bootstrap;
+import net.minecraft.world.entity.MobSpawnType;
+import net.minecraft.world.entity.Mob;
+import net.minecraft.world.level.ServerLevelAccessor;
+import net.minecraftforge.common.MinecraftForge;
+import net.minecraftforge.event.entity.living.MobSpawnEvent;
+import net.minecraftforge.eventbus.api.Event;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import java.util.concurrent.atomic.AtomicReference;
+import java.util.function.BooleanSupplier;
+import java.util.function.Consumer;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+public class NativeForgeSpawnPositionTest {
+    @BeforeClass
+    public static void bootstrap() {
+        SharedConstants.tryDetectVersion();
+        Bootstrap.bootStrap();
+    }
+
+    @Test
+    public void chunkGenerationSpawnsFireThePositionCheckEventAndHonorItsDenial() {
+        NativeForgeLoader loader = new NativeForgeLoader(
+                new NativeLoaderOptions("irisworldgen", "treefeller", BooleanSupplier::getAsBoolean));
+        ServerLevelAccessor level = mock(ServerLevelAccessor.class);
+        Mob mob = mock(Mob.class);
+        when(mob.checkSpawnRules(level, MobSpawnType.CHUNK_GENERATION)).thenReturn(true);
+        when(mob.checkSpawnObstruction(level)).thenReturn(true);
+        AtomicReference<MobSpawnType> observed = new AtomicReference<>();
+        Consumer<MobSpawnEvent.PositionCheck> listener = event -> {
+            observed.set(event.getSpawnType());
+            event.setResult(Event.Result.DENY);
+        };
+        MinecraftForge.EVENT_BUS.addListener(listener);
+        try {
+            assertFalse(loader.checkSpawnPosition(mob, level, MobSpawnType.CHUNK_GENERATION));
+        } finally {
+            MinecraftForge.EVENT_BUS.unregister(listener);
+        }
+        assertEquals(MobSpawnType.CHUNK_GENERATION, observed.get());
+        assertTrue(loader.checkSpawnPosition(mob, level, MobSpawnType.CHUNK_GENERATION));
+    }
+}

adapters/forge/src/versions/26.2/test/java/art/arcane/volmlib/nativelib/minecraft26_2/forge/NativeForgeBiomeDefinitionTest.java

@@ -0,0 +1,101 @@
+package art.arcane.volmlib.nativelib.minecraft26_2.forge;
+
+import art.arcane.volmlib.nativelib.minecraft26_2.terrain.NativeRegistryDefinitions;
+import art.arcane.volmlib.nativelib.modded.NativeLoaderOptions;
+import com.google.gson.JsonParser;
+import com.mojang.serialization.JsonOps;
+import com.mojang.serialization.Lifecycle;
+import com.mojang.serialization.MapCodec;
+import net.minecraft.SharedConstants;
+import net.minecraft.core.Holder;
+import net.minecraft.core.MappedRegistry;
+import net.minecraft.core.RegistrationInfo;
+import net.minecraft.core.RegistryAccess;
+import net.minecraft.core.registries.Registries;
+import net.minecraft.resources.Identifier;
+import net.minecraft.resources.RegistryOps;
+import net.minecraft.resources.ResourceKey;
+import net.minecraft.server.Bootstrap;
+import net.minecraft.world.entity.EntityTypes;
+import net.minecraft.world.entity.MobCategory;
+import net.minecraft.world.level.biome.Biome;
+import net.minecraft.world.level.biome.MobSpawnSettings;
+import net.minecraft.world.level.levelgen.GenerationStep;
+import net.minecraft.world.level.levelgen.carver.ConfiguredWorldCarver;
+import net.minecraft.world.level.levelgen.feature.ConfiguredFeature;
+import net.minecraft.world.level.levelgen.placement.PlacedFeature;
+import net.minecraftforge.common.world.BiomeModifier;
+import net.minecraftforge.common.world.ModifiableBiomeInfo;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import java.util.List;
+import java.util.function.BooleanSupplier;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+import static org.mockito.Mockito.mock;
+
+public class NativeForgeBiomeDefinitionTest {
+    private static final String BIOME_REGISTRY = "minecraft:worldgen/biome";
+    private static final String BIOME_KEY = "iris:biomes/forge_modified";
+    private static final String SOURCE_JSON = "{\"has_precipitation\":true,\"temperature\":0.8,\"downfall\":0.4,"
+            + "\"effects\":{\"water_color\":\"#3f76e4\"},\"carvers\":[],\"features\":[],"
+            + "\"spawners\":{},\"spawn_costs\":{}}";
+
+    @BeforeClass
+    public static void bootstrap() {
+        SharedConstants.tryDetectVersion();
+        Bootstrap.bootStrap();
+    }
+
+    @Test
+    public void generatedBiomeDefinitionExcludesForgeBiomeModifierOutput() {
+        MappedRegistry<PlacedFeature> features = new MappedRegistry<>(Registries.PLACED_FEATURE, Lifecycle.stable());
+        Holder.Reference<PlacedFeature> ore = features.register(
+                ResourceKey.create(Registries.PLACED_FEATURE, Identifier.parse("iris:modded_ore")),
+                new PlacedFeature(Holder.direct(mock(ConfiguredFeature.class)), List.of()),
+                RegistrationInfo.BUILT_IN);
+        features.freeze();
+        MappedRegistry<ConfiguredWorldCarver<?>> carvers = new MappedRegistry<>(Registries.CONFIGURED_CARVER, Lifecycle.stable());
+        carvers.freeze();
+        MappedRegistry<Biome> biomes = new MappedRegistry<>(Registries.BIOME, Lifecycle.stable());
+        RegistryAccess access = new RegistryAccess.ImmutableRegistryAccess(List.of(biomes, features, carvers));
+        Biome source = Biome.DIRECT_CODEC.parse(RegistryOps.create(JsonOps.INSTANCE, access),
+                JsonParser.parseString(SOURCE_JSON)).getOrThrow();
+        Holder.Reference<Biome> biome = biomes.register(
+                ResourceKey.create(Registries.BIOME, Identifier.parse(BIOME_KEY)), source, RegistrationInfo.BUILT_IN);
+        biomes.freeze();
+        biome.value().modifiableBiomeInfo().applyBiomeModifiers(biome, List.of(new ModdedContent(ore)));
+        NativeRegistryDefinitions definitions = new NativeRegistryDefinitions(() -> access,
+                new NativeForgeLoader(new NativeLoaderOptions("irisworldgen", "treefeller",
+                        BooleanSupplier::getAsBoolean))::unmodifiedBiome);
+
+        assertEquals(0.1F, biome.value().modifiableBiomeInfo().get().climateSettings().temperature(), 0.0F);
+        assertEquals(0x102030, biome.value().modifiableBiomeInfo().get().effects().waterColor() & 0xFFFFFF);
+        assertTrue(biome.value().getGenerationSettings().hasFeature(ore.value()));
+        assertTrue(biome.value().getMobSettings().getMobs(MobCategory.MONSTER).unwrap().stream()
+                .anyMatch(spawn -> spawn.value().type() == EntityTypes.ZOMBIE));
+        assertEquals(JsonParser.parseString(definitions.canonicalDefinition(BIOME_REGISTRY, BIOME_KEY, SOURCE_JSON).value()),
+                JsonParser.parseString(definitions.generatedDefinition(BIOME_REGISTRY, BIOME_KEY).value()));
+    }
+
+    private record ModdedContent(Holder<PlacedFeature> ore) implements BiomeModifier {
+        @Override
+        public void modify(Holder<Biome> biome, Phase phase, ModifiableBiomeInfo.BiomeInfo.Builder builder) {
+            if (phase != Phase.ADD) {
+                return;
+            }
+            builder.getClimateSettings().setTemperature(0.1F);
+            builder.getSpecialEffects().waterColor(0x102030);
+            builder.getMobSpawnSettings().addSpawn(MobCategory.MONSTER, 5,
+                    new MobSpawnSettings.SpawnerData(EntityTypes.ZOMBIE, 1, 2));
+            builder.getGenerationSettings().addFeature(GenerationStep.Decoration.UNDERGROUND_ORES, ore);
+        }
+
+        @Override
+        public MapCodec<? extends BiomeModifier> codec() {
+            throw new UnsupportedOperationException();
+        }
+    }
+}

adapters/modded-common/src/main/java/art/arcane/iris/modded/IrisModdedChunkGenerator.java

@@ -100,6 +100,7 @@ import java.util.Collection;
 import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Objects;
+import java.util.OptionalLong;
 import java.util.Set;
 import java.util.TreeSet;
 import java.util.concurrent.TimeUnit;
@@ -477,6 +478,7 @@ public final class IrisModdedChunkGenerator implements NativeGeneratorOwner, Nat
                 return existing;
             }
             try {
+                applyReplacementSeed(level);
                 Engine created = ModdedWorldEngines.get(
                         level,
                         activePack,
@@ -511,6 +513,16 @@ public final class IrisModdedChunkGenerator implements NativeGeneratorOwner, Nat
         }
     }
 
+    private void applyReplacementSeed(NativeWorld level) {
+        if (seedOverride != Long.MIN_VALUE) {
+            return;
+        }
+        OptionalLong replacementSeed = ModdedDimensionReplacements.loadedSeed(level.name());
+        if (replacementSeed.isPresent()) {
+            seedOverride = replacementSeed.getAsLong();
+        }
+    }
+
     private void recordBindFailure(NativeWorld level, Throwable error) {
         // A runtime that is stopping says nothing about the world: fail this call, let the next bind try again.
         if (GenerationFailures.isShutdownFailure(error)) {
@@ -743,14 +755,8 @@ public final class IrisModdedChunkGenerator implements NativeGeneratorOwner, Nat
                 PackValidationRegistry.requireLoadable(packRoot);
                 packDirectory = packRoot.toFile();
             }
-            IrisData data = IrisData.get(packDirectory);
-            IrisDimension dimension = data.getDimensionLoader().load(activeDimensionKey);
-            if (dimension == null) {
-                throw new IllegalStateException("Iris dimension '" + activeDimensionKey
-                        + "' missing from pack " + packDirectory.getAbsolutePath());
-            }
-            ModdedDimensionMetadata.ConfiguredPack resolved = new ModdedDimensionMetadata.ConfiguredPack(
-                    data, dimension, ModdedDimensionMetadata.dimensionMetadata(dimension));
+            ModdedDimensionMetadata.ConfiguredPack resolved =
+                    ModdedDimensionMetadata.ConfiguredPack.load(packDirectory, activeDimensionKey);
             configuredPack = resolved;
             heightMetadata = resolved.metadata();
             return resolved;

adapters/modded-common/src/main/java/art/arcane/iris/modded/MainWorldService.java

@@ -239,50 +239,21 @@ public final class MainWorldService {
 
     private static Path quarantineVanillaDimensions(Path worldRoot) throws IOException {
         Path recovery = markerFile().getParent().resolve("mainworld-recovery-" + UUID.randomUUID());
-        List<Path> moved = new ArrayList<>();
+        List<Path> sources = new ArrayList<>();
         for (String file : NativeServerWorldLayout.metadataFiles()) {
-            moveToRecovery(worldRoot, worldRoot.resolve(file), recovery, moved);
+            sources.add(worldRoot.resolve(file));
         }
         for (String folder : NativeServerWorldLayout.primaryFolders()) {
-            moveToRecovery(worldRoot, worldRoot.resolve(folder), recovery, moved);
+            sources.add(worldRoot.resolve(folder));
         }
-        moveToRecovery(worldRoot, worldRoot.resolve(IrisEngineMantle.STORAGE_FOLDER_NAME), recovery, moved);
+        sources.add(worldRoot.resolve(IrisEngineMantle.STORAGE_FOLDER_NAME));
         for (String folder : NativeServerWorldLayout.dimensionFolders()) {
-            moveToRecovery(worldRoot, worldRoot.resolve(folder), recovery, moved);
-        }
-        if (moved.isEmpty()) {
-            Files.deleteIfExists(recovery);
+            sources.add(worldRoot.resolve(folder));
         }
+        ModdedWorldQuarantine.move(worldRoot, sources, recovery);
         return recovery;
     }
 
-    private static void moveToRecovery(Path worldRoot, Path source, Path recovery,
-                                       List<Path> moved) throws IOException {
-        if (!Files.exists(source)) {
-            return;
-        }
-        Path relative = worldRoot.relativize(source);
-        Path target = recovery.resolve(relative);
-        Files.createDirectories(target.getParent());
-        try {
-            Files.move(source, target);
-            moved.add(relative);
-        } catch (IOException failure) {
-            for (int index = moved.size() - 1; index >= 0; index--) {
-                Path rollbackRelative = moved.get(index);
-                Path rollbackSource = recovery.resolve(rollbackRelative);
-                Path rollbackTarget = worldRoot.resolve(rollbackRelative);
-                try {
-                    Files.createDirectories(rollbackTarget.getParent());
-                    Files.move(rollbackSource, rollbackTarget);
-                } catch (IOException rollbackFailure) {
-                    failure.addSuppressed(rollbackFailure);
-                }
-            }
-            throw failure;
-        }
-    }
-
     private static String escape(String value) {
         return value.replace(":", "\\:");
     }

adapters/modded-common/src/main/java/art/arcane/iris/modded/MissingPackDimensionException.java

@@ -0,0 +1,38 @@
+/*
+ * Iris is a World Generator for Minecraft Servers
+ * Copyright (c) 2026 Arcane Arts (Volmit Software)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package art.arcane.iris.modded;
+
+public final class MissingPackDimensionException extends IllegalStateException {
+    private final String pack;
+    private final String dimensionKey;
+
+    public MissingPackDimensionException(String pack, String dimensionKey) {
+        super("Pack '" + pack + "' does not contain dimensions/" + dimensionKey + ".json");
+        this.pack = pack;
+        this.dimensionKey = dimensionKey;
+    }
+
+    public String pack() {
+        return pack;
+    }
+
+    public String dimensionKey() {
+        return dimensionKey;
+    }
+}

adapters/modded-common/src/main/java/art/arcane/iris/modded/ModdedBiomePolicy.java

@@ -42,6 +42,7 @@ import art.arcane.iris.generation.biome.IrisBiome;
 import art.arcane.iris.generation.biome.IrisBiomeCustom;
 import art.arcane.iris.generation.terrain.IrisDimension;
 import art.arcane.iris.generation.context.IrisContext;
+import art.arcane.iris.generation.locator.BiomeSearchFilter;
 import art.arcane.volmlib.util.math.RNG;
 
 import java.io.IOException;
@@ -300,10 +301,6 @@ final class ModdedBiomePolicy<H, S> implements NativeModdedBiomePolicy<H, S> {
             if (!isReady(engine)) {
                 throw new IllegalStateException("Iris visible biome search has no active engine runtime");
             }
-            DimensionStackContext stackContext = engine.getDimensionStackContext();
-            if (stackContext == null) {
-                return query.defaultFallback().get();
-            }
             Set<H> candidates = new HashSet<>();
             for (H biome : collectVisibleBiomeHolders()) {
                 if (query.allowed().test(biome)) {
@@ -313,16 +310,86 @@ final class ModdedBiomePolicy<H, S> implements NativeModdedBiomePolicy<H, S> {
             if (candidates.isEmpty()) {
                 return null;
             }
+            DimensionStackContext stackContext = engine.getDimensionStackContext();
+            if (stackContext != null) {
+                return query.search().search(candidates, (blockX, blockZ) -> {
+                    int quartX = blockX >> 2;
+                    int quartZ = blockZ >> 2;
+                    DimensionStackLayout stackLayout = stackContext.sample(quartX << 2, quartZ << 2);
+                    return blockY -> resolveVisibleBiome(engine, quartX, blockY >> 2, quartZ,
+                            query.sampler(), stackLayout);
+                });
+            }
+            BiomeSearchFilter filter = BiomeSearchFilter.of(engine, searchBiomeKeys(engine, candidates));
+            int minHeight = engine.getMinHeight();
             return query.search().search(candidates, (blockX, blockZ) -> {
                 int quartX = blockX >> 2;
                 int quartZ = blockZ >> 2;
-                DimensionStackLayout stackLayout = stackContext.sample(quartX << 2, quartZ << 2);
-                return blockY -> resolveVisibleBiome(engine, quartX, blockY >> 2, quartZ,
-                        query.sampler(), stackLayout);
+                BiomeSearchFilter.Column column = filter.column(quartX << 2, quartZ << 2);
+                return blockY -> column.admits(((blockY >> 2) << 2) - minHeight)
+                        ? locateVisibleBiome(engine, quartX, blockY >> 2, quartZ, query.sampler())
+                        : null;
             });
         }
     }
 
+    private H locateVisibleBiome(Engine engine, int quartX, int quartY, int quartZ, S sampler) {
+        try (GenerationHistoryRuntimeRouter.CoordinateScope ignored = openHistoryCoordinateScope(
+                engine, quartX << 2, quartZ << 2, "modded_locate_visible_biome")) {
+            return resolveVisibleBiome(engine, quartX, quartY, quartZ, sampler, null);
+        }
+    }
+
+    private Set<String> searchBiomeKeys(Engine engine, Set<H> candidates) {
+        NativeBiomeSourceAccess.RegistryView<H> registry = biomeRegistry();
+        if (registry == null) {
+            throw new IllegalStateException("Iris visible biome search has no biome registry");
+        }
+        H plains = resolveHolder(registry, "minecraft:plains");
+        boolean fallbackCandidate = plains != null && candidates.contains(plains);
+        Set<String> keys = new HashSet<>();
+        for (OwnedBiome ownedBiome : getOwnedBiomes(engine)) {
+            if (emitsCandidate(engine, ownedBiome, registry, candidates, fallbackCandidate)) {
+                keys.add(ownedBiome.biome().getLoadKey());
+            }
+        }
+        return keys;
+    }
+
+    private boolean emitsCandidate(Engine engine, OwnedBiome ownedBiome, NativeBiomeSourceAccess.RegistryView<H> registry,
+                                   Set<H> candidates, boolean fallbackCandidate) {
+        IrisBiome irisBiome = ownedBiome.biome();
+        if (irisBiome.isCustom()) {
+            for (IrisBiomeCustom customBiome : irisBiome.getCustomDerivitives()) {
+                if (customBiome == null) {
+                    if (fallbackCandidate) {
+                        return true;
+                    }
+                    continue;
+                }
+                String key = ownedBiome.dimension() == engine.getDimension() && ownedBiome.data() == engine.getData()
+                        ? ModdedWorldgenIds.biomeRef(engine, customBiome.getId())
+                        : ownedBiome.data().customBiomeResourceKey(ownedBiome.dimension(), customBiome);
+                if (emits(registry, key, candidates, fallbackCandidate)) {
+                    return true;
+                }
+            }
+            return false;
+        }
+        for (String key : irisBiome.getVisibleBiomeKeys(engine)) {
+            if (emits(registry, key, candidates, fallbackCandidate)) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    private static <H> boolean emits(NativeBiomeSourceAccess.RegistryView<H> registry, String key,
+                                     Set<H> candidates, boolean fallbackCandidate) {
+        H holder = key == null ? null : resolveHolder(registry, key);
+        return holder == null ? fallbackCandidate : candidates.contains(holder);
+    }
+
     private H getNoiseBiome(Engine engine, int quartX, int quartY, int quartZ,
                                         S sampler) {
         if (isGuaranteedSurfaceBiome(engine, quartY)) {

adapters/modded-common/src/main/java/art/arcane/iris/modded/ModdedDatapackTagMerge.java

@@ -0,0 +1,92 @@
+/*
+ * Iris is a World Generator for Minecraft Servers
+ * Copyright (c) 2026 Arcane Arts (Volmit Software)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package art.arcane.iris.modded;
+
+import art.arcane.volmlib.util.json.JSONArray;
+import art.arcane.volmlib.util.json.JSONObject;
+
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.LinkedHashMap;
+import java.util.Map;
+
+final class ModdedDatapackTagMerge {
+    private static final String REPLACE = "replace";
+    private static final String VALUES = "values";
+    private static final String REMOVE = "remove";
+
+    private ModdedDatapackTagMerge() {
+    }
+
+    static boolean isTag(Path relative) {
+        return relative.getNameCount() >= 4
+                && "data".equals(relative.getName(0).toString())
+                && "tags".equals(relative.getName(2).toString())
+                && relative.getFileName().toString().endsWith(".json");
+    }
+
+    static void merge(Path source, Path destination) throws IOException {
+        JSONObject incoming = read(source);
+        JSONObject existing = read(destination);
+        JSONObject tag = new JSONObject();
+        tag.put(REPLACE, existing.optBoolean(REPLACE, false) || incoming.optBoolean(REPLACE, false));
+        tag.put(VALUES, union(existing, incoming, VALUES, source, destination));
+        if (existing.has(REMOVE) || incoming.has(REMOVE)) {
+            tag.put(REMOVE, union(existing, incoming, REMOVE, source, destination));
+        }
+        Files.writeString(destination, tag.toString(4), StandardCharsets.UTF_8);
+    }
+
+    private static JSONArray union(JSONObject existing, JSONObject incoming, String field, Path source, Path destination)
+            throws IOException {
+        Map<String, Object> entries = new LinkedHashMap<>();
+        collect(existing, field, entries, destination);
+        collect(incoming, field, entries, source);
+        JSONArray merged = new JSONArray();
+        for (Object entry : entries.values()) {
+            merged.put(entry);
+        }
+        return merged;
+    }
+
+    private static JSONObject read(Path tag) throws IOException {
+        try {
+            return new JSONObject(Files.readString(tag, StandardCharsets.UTF_8));
+        } catch (RuntimeException invalid) {
+            throw new IOException("Iris cannot merge the invalid datapack tag " + tag + ".", invalid);
+        }
+    }
+
+    private static void collect(JSONObject tag, String field, Map<String, Object> entries, Path origin) throws IOException {
+        JSONArray values = tag.optJSONArray(field);
+        if (values == null) {
+            return;
+        }
+        for (int index = 0; index < values.length(); index++) {
+            Object entry = values.get(index);
+            String key = entry instanceof JSONObject object ? object.optString("id", "") : entry.toString();
+            if (key.isBlank()) {
+                throw new IOException("Iris cannot merge datapack tag " + origin + ": " + field + " entry " + index + " has no id.");
+            }
+            entries.putIfAbsent(key, entry);
+        }
+    }
+}

adapters/modded-common/src/main/java/art/arcane/iris/modded/ModdedDimensionCreations.java

@@ -0,0 +1,148 @@
+/*
+ * Iris is a World Generator for Minecraft Servers
+ * Copyright (c) 2026 Arcane Arts (Volmit Software)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package art.arcane.iris.modded;
+
+import art.arcane.iris.generation.runtime.Engine;
+import art.arcane.iris.modded.command.ModdedPackCommands;
+import art.arcane.iris.pack.loading.IrisData;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeModdedServer;
+
+import java.io.File;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ConcurrentHashMap;
+
+public final class ModdedDimensionCreations {
+    private static final Map<String, ModdedDimensionInjection.Async<?, ?, ?>> ACTIVE = new ConcurrentHashMap<>();
+
+    private ModdedDimensionCreations() {
+    }
+
+    public static CompletableFuture<Void> create(
+            NativeModdedServer server,
+            String dimensionId,
+            String pack,
+            String packDimensionKey,
+            long seed
+    ) {
+        if (ModdedDimensionRegistryStore.get(server, dimensionId) != null) {
+            return CompletableFuture.failedFuture(new IllegalStateException(
+                    ModdedDimensionManager.alreadyExists(dimensionId)));
+        }
+        ModdedDimensionRegistryStore.PersistentDimension dimension =
+                new ModdedDimensionRegistryStore.PersistentDimension(dimensionId, pack, packDimensionKey, seed);
+        ModdedDimensionInjection.Async<ModdedWorldEngines.PreparedPack, ModdedDimensionManager.PendingInjection, Engine> creation =
+                ModdedDimensionInjection.async(dimension, new CreationSteps(server), server::execute);
+        if (ACTIVE.putIfAbsent(dimensionId, creation) != null) {
+            return CompletableFuture.failedFuture(new IllegalStateException(beingCreated(dimensionId)));
+        }
+        CompletableFuture<Void> created = creation.result().handle(
+                (ModdedDimensionInjection.Result result, Throwable failure) -> settle(creation, dimension, result));
+        creation.start();
+        return created;
+    }
+
+    public static boolean isCreating(String dimensionId) {
+        return ACTIVE.containsKey(dimensionId);
+    }
+
+    public static void requireNotCreating(String dimensionId) {
+        if (isCreating(dimensionId)) {
+            throw new IllegalStateException(beingCreated(dimensionId));
+        }
+    }
+
+    public static void cancelAll() {
+        List<ModdedDimensionInjection.Async<?, ?, ?>> active = new ArrayList<>(ACTIVE.values());
+        for (ModdedDimensionInjection.Async<?, ?, ?> creation : active) {
+            creation.cancel();
+        }
+    }
+
+    private static Void settle(
+            ModdedDimensionInjection.Async<?, ?, ?> creation,
+            ModdedDimensionRegistryStore.PersistentDimension dimension,
+            ModdedDimensionInjection.Result result
+    ) {
+        ACTIVE.remove(dimension.id(), creation);
+        Throwable cause = result == null
+                ? new IllegalStateException("Iris dimension creation for '" + dimension.id() + "' ended without a result")
+                : result.failure();
+        if (cause instanceof Error fatal) {
+            throw fatal;
+        }
+        if (cause != null) {
+            throw cause instanceof RuntimeException runtimeException ? runtimeException : new IllegalStateException(cause);
+        }
+        ModdedIrisLog.info("Iris created runtime dimension '{}' (pack={} dim={}): prepared {}ms, engine {}ms",
+                dimension.id(), dimension.pack(), dimension.dimension(), result.preparedMillis(), result.builtMillis());
+        return null;
+    }
+
+    private static String beingCreated(String dimensionId) {
+        return "Iris dimension '" + dimensionId + "' is still being created. Try again when it is live.";
+    }
+
+    private record CreationSteps(NativeModdedServer server)
+            implements ModdedDimensionInjection.Steps<ModdedWorldEngines.PreparedPack, ModdedDimensionManager.PendingInjection, Engine> {
+        @Override
+        public ModdedWorldEngines.PreparedPack prepare(ModdedDimensionRegistryStore.PersistentDimension dimension) {
+            ModdedStartup.requirePackForWorldCreation(dimension.pack());
+            IrisData data = IrisData.get(new File(ModdedPackCommands.packsRoot(), dimension.pack()));
+            if (data.getDimensionLoader().load(dimension.dimension()) == null) {
+                throw new MissingPackDimensionException(dimension.pack(), dimension.dimension());
+            }
+            return ModdedWorldEngines.prepareCreated(server, dimension);
+        }
+
+        @Override
+        public ModdedDimensionManager.PendingInjection begin(
+                ModdedDimensionRegistryStore.PersistentDimension dimension,
+                ModdedWorldEngines.PreparedPack prepared
+        ) {
+            return ModdedDimensionManager.beginCreation(server, dimension, prepared.active());
+        }
+
+        @Override
+        public Engine build(ModdedDimensionManager.PendingInjection level, ModdedWorldEngines.PreparedPack prepared) {
+            if (level.present()) {
+                prepared.close();
+                return null;
+            }
+            return ModdedWorldEngines.createPrepared(level.handle().level(), level.handle().seed(), prepared);
+        }
+
+        @Override
+        public void complete(ModdedDimensionManager.PendingInjection level, Engine engine) {
+            ModdedDimensionManager.completeCreation(server, level, engine);
+        }
+
+        @Override
+        public void abandon(ModdedDimensionManager.PendingInjection level, Engine engine, Throwable failure) {
+            ModdedDimensionManager.abandonCreation(server, level, engine, failure);
+        }
+
+        @Override
+        public void discard(ModdedWorldEngines.PreparedPack prepared) {
+            prepared.close();
+        }
+    }
+}

adapters/modded-common/src/main/java/art/arcane/iris/modded/ModdedDimensionInjection.java

@@ -0,0 +1,434 @@
+/*
+ * Iris is a World Generator for Minecraft Servers
+ * Copyright (c) 2026 Arcane Arts (Volmit Software)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package art.arcane.iris.modded;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Objects;
+import java.util.concurrent.CancellationException;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CompletionException;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.Executor;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
+import java.util.concurrent.atomic.AtomicBoolean;
+
+final class ModdedDimensionInjection<P, L, E> implements AutoCloseable {
+    private static final int MINIMUM_WORKERS = 2;
+    private static final long CANCEL_BUILD_WAIT_SECONDS = 120L;
+
+    private final List<Preparation<P>> preparations;
+    private final Steps<P, L, E> steps;
+    private final ExecutorService workers;
+    private final AtomicBoolean finished = new AtomicBoolean();
+
+    private ModdedDimensionInjection(List<Preparation<P>> preparations, Steps<P, L, E> steps, ExecutorService workers) {
+        this.preparations = preparations;
+        this.steps = steps;
+        this.workers = workers;
+    }
+
+    static <P, L, E> ModdedDimensionInjection<P, L, E> start(
+            List<ModdedDimensionRegistryStore.PersistentDimension> dimensions,
+            Steps<P, L, E> steps
+    ) {
+        Steps<P, L, E> requiredSteps = Objects.requireNonNull(steps, "steps");
+        ExecutorService workers = Executors.newFixedThreadPool(workerCount(dimensions.size()),
+                Thread.ofPlatform().name("Iris Dimension Restore ", 1L).daemon(true).factory());
+        List<Preparation<P>> preparations = new ArrayList<>(dimensions.size());
+        for (ModdedDimensionRegistryStore.PersistentDimension dimension : dimensions) {
+            preparations.add(new Preparation<>(dimension, CompletableFuture.supplyAsync(
+                    () -> timed(() -> requiredSteps.prepare(dimension)), workers)));
+        }
+        return new ModdedDimensionInjection<>(List.copyOf(preparations), requiredSteps, workers);
+    }
+
+    static <P, L, E> Async<P, L, E> async(
+            ModdedDimensionRegistryStore.PersistentDimension dimension,
+            Steps<P, L, E> steps,
+            Executor serverThread
+    ) {
+        return new Async<>(dimension, steps, serverThread);
+    }
+
+    void awaitPreparations() {
+        List<CompletableFuture<Timed<P>>> futures = new ArrayList<>(preparations.size());
+        for (Preparation<P> preparation : preparations) {
+            futures.add(preparation.future());
+        }
+        CompletableFuture.allOf(futures.toArray(CompletableFuture[]::new))
+                .handle((Void ignored, Throwable failure) -> null)
+                .join();
+    }
+
+    List<Result> finish() {
+        if (!finished.compareAndSet(false, true)) {
+            throw new IllegalStateException("Iris dimension injection already finished");
+        }
+        try {
+            List<Building<L, E>> building = new ArrayList<>(preparations.size());
+            Result[] results = new Result[preparations.size()];
+            for (int index = 0; index < preparations.size(); index++) {
+                Preparation<P> preparation = preparations.get(index);
+                Timed<P> prepared;
+                try {
+                    prepared = join(preparation.future());
+                } catch (Throwable failure) {
+                    results[index] = new Result(preparation.dimension(), failure, 0L, 0L);
+                    continue;
+                }
+                L level;
+                try {
+                    level = steps.begin(preparation.dimension(), prepared.value());
+                } catch (Throwable failure) {
+                    discard(steps, prepared.value(), failure);
+                    results[index] = new Result(preparation.dimension(), failure, prepared.millis(), 0L);
+                    continue;
+                }
+                CompletableFuture<Timed<E>> engine = CompletableFuture.supplyAsync(
+                        () -> timed(() -> steps.build(level, prepared.value())), workers);
+                building.add(new Building<>(index, preparation.dimension(), prepared.millis(), level, engine));
+            }
+            for (Building<L, E> pending : building) {
+                results[pending.index()] = complete(pending);
+            }
+            return List.of(results);
+        } finally {
+            workers.shutdown();
+        }
+    }
+
+    @Override
+    public void close() {
+        if (finished.compareAndSet(false, true)) {
+            for (Preparation<P> preparation : preparations) {
+                preparation.future().whenComplete((Timed<P> prepared, Throwable failure) -> {
+                    if (prepared != null) {
+                        discard(steps, prepared.value(), null);
+                    }
+                });
+            }
+        }
+        workers.shutdown();
+    }
+
+    private Result complete(Building<L, E> pending) {
+        Timed<E> engine;
+        try {
+            engine = join(pending.engine());
+        } catch (Throwable failure) {
+            abandon(steps, pending.level(), null, failure);
+            return new Result(pending.dimension(), failure, pending.preparedMillis(), 0L);
+        }
+        try {
+            steps.complete(pending.level(), engine.value());
+            return new Result(pending.dimension(), null, pending.preparedMillis(), engine.millis());
+        } catch (Throwable failure) {
+            return new Result(pending.dimension(), failure, pending.preparedMillis(), engine.millis());
+        }
+    }
+
+    private static <P, L, E> void abandon(Steps<P, L, E> steps, L level, E engine, Throwable failure) {
+        try {
+            steps.abandon(level, engine, failure);
+        } catch (Throwable cleanupFailure) {
+            failure.addSuppressed(cleanupFailure);
+        }
+    }
+
+    private static <P, L, E> void discard(Steps<P, L, E> steps, P prepared, Throwable failure) {
+        try {
+            steps.discard(prepared);
+        } catch (Throwable cleanupFailure) {
+            if (failure != null) {
+                failure.addSuppressed(cleanupFailure);
+                return;
+            }
+            ModdedIrisLog.error("Iris could not release an unused dimension preparation", cleanupFailure);
+        }
+    }
+
+    private static int workerCount(int dimensions) {
+        int processors = Runtime.getRuntime().availableProcessors();
+        return Math.max(1, Math.min(dimensions, Math.max(MINIMUM_WORKERS, processors / 2)));
+    }
+
+    private static <T> Timed<T> timed(Step<T> step) {
+        long startedAt = System.nanoTime();
+        try {
+            T value = step.run();
+            return new Timed<>(value, (System.nanoTime() - startedAt) / 1_000_000L);
+        } catch (RuntimeException | Error failure) {
+            throw failure;
+        } catch (Exception failure) {
+            throw new CompletionException(failure);
+        }
+    }
+
+    private static Throwable unwrap(Throwable failure) {
+        Throwable current = failure;
+        while (current instanceof CompletionException && current.getCause() != null) {
+            current = current.getCause();
+        }
+        return current;
+    }
+
+    private static <T> T join(CompletableFuture<T> future) throws Throwable {
+        try {
+            return future.get();
+        } catch (ExecutionException failure) {
+            Throwable cause = failure.getCause();
+            if (cause instanceof CompletionException wrapped && wrapped.getCause() != null) {
+                throw wrapped.getCause();
+            }
+            throw cause == null ? failure : cause;
+        } catch (InterruptedException interrupted) {
+            Thread.currentThread().interrupt();
+            throw new IllegalStateException("Interrupted while injecting Iris dimensions", interrupted);
+        }
+    }
+
+    interface Steps<P, L, E> {
+        P prepare(ModdedDimensionRegistryStore.PersistentDimension dimension) throws Exception;
+
+        L begin(ModdedDimensionRegistryStore.PersistentDimension dimension, P prepared) throws Exception;
+
+        E build(L level, P prepared) throws Exception;
+
+        void complete(L level, E engine) throws Exception;
+
+        void abandon(L level, E engine, Throwable failure);
+
+        void discard(P prepared);
+    }
+
+    record Result(
+            ModdedDimensionRegistryStore.PersistentDimension dimension,
+            Throwable failure,
+            long preparedMillis,
+            long builtMillis
+    ) {
+    }
+
+    static final class Async<P, L, E> {
+        private final ModdedDimensionRegistryStore.PersistentDimension dimension;
+        private final Steps<P, L, E> steps;
+        private final Executor serverThread;
+        private final ExecutorService worker;
+        private final CompletableFuture<Result> result = new CompletableFuture<>();
+        private State state = State.UNSTARTED;
+        private Timed<P> prepared;
+        private L level;
+        private CompletableFuture<Timed<E>> engine;
+
+        private Async(
+                ModdedDimensionRegistryStore.PersistentDimension dimension,
+                Steps<P, L, E> steps,
+                Executor serverThread
+        ) {
+            this.dimension = Objects.requireNonNull(dimension, "dimension");
+            this.steps = Objects.requireNonNull(steps, "steps");
+            this.serverThread = Objects.requireNonNull(serverThread, "serverThread");
+            this.worker = Executors.newSingleThreadExecutor(
+                    Thread.ofPlatform().name("Iris Dimension Create " + dimension.id()).daemon(true).factory());
+        }
+
+        CompletableFuture<Result> result() {
+            return result;
+        }
+
+        synchronized void start() {
+            if (state != State.UNSTARTED) {
+                throw new IllegalStateException("Iris dimension injection for '" + dimension.id() + "' already started");
+            }
+            state = State.PREPARING;
+            CompletableFuture.supplyAsync(() -> timed(() -> steps.prepare(dimension)), worker)
+                    .whenComplete(this::prepared);
+        }
+
+        void cancel() {
+            Timed<P> unused = null;
+            CompletableFuture<Timed<E>> building = null;
+            L created = null;
+            synchronized (this) {
+                if (state == State.DONE || state == State.CANCELLED) {
+                    return;
+                }
+                if (state == State.PREPARED) {
+                    unused = prepared;
+                } else if (state == State.BUILDING) {
+                    building = engine;
+                    created = level;
+                }
+                state = State.CANCELLED;
+            }
+            CancellationException cancellation = new CancellationException("Iris dimension injection for '"
+                    + dimension.id() + "' was cancelled because the server is stopping");
+            long preparedMillis = 0L;
+            if (unused != null) {
+                discard(steps, unused.value(), cancellation);
+                preparedMillis = unused.millis();
+            }
+            if (building != null) {
+                abandon(steps, created, awaitCancelledEngine(building, cancellation), cancellation);
+            }
+            done(new Result(dimension, cancellation, preparedMillis, 0L));
+        }
+
+        private void prepared(Timed<P> value, Throwable failure) {
+            synchronized (this) {
+                if (state == State.CANCELLED) {
+                    if (value != null) {
+                        discard(steps, value.value(), null);
+                    }
+                    worker.shutdown();
+                    return;
+                }
+                if (failure != null) {
+                    state = State.DONE;
+                } else {
+                    prepared = value;
+                    state = State.PREPARED;
+                }
+            }
+            if (failure != null) {
+                done(new Result(dimension, unwrap(failure), 0L, 0L));
+                return;
+            }
+            serverThread.execute(this::begin);
+        }
+
+        private void begin() {
+            Timed<P> ready;
+            synchronized (this) {
+                if (state != State.PREPARED) {
+                    return;
+                }
+                ready = prepared;
+                state = State.BEGINNING;
+            }
+            L created;
+            try {
+                created = steps.begin(dimension, ready.value());
+            } catch (Throwable failure) {
+                discard(steps, ready.value(), failure);
+                synchronized (this) {
+                    state = State.DONE;
+                }
+                done(new Result(dimension, failure, ready.millis(), 0L));
+                return;
+            }
+            CompletableFuture<Timed<E>> building;
+            synchronized (this) {
+                level = created;
+                state = State.BUILDING;
+                building = CompletableFuture.supplyAsync(() -> timed(() -> steps.build(created, ready.value())), worker);
+                engine = building;
+            }
+            building.whenComplete((Timed<E> built, Throwable failure) -> serverThread.execute(this::complete));
+        }
+
+        private void complete() {
+            CompletableFuture<Timed<E>> building;
+            L created;
+            long preparedMillis;
+            synchronized (this) {
+                if (state != State.BUILDING) {
+                    return;
+                }
+                state = State.DONE;
+                building = engine;
+                created = level;
+                preparedMillis = prepared.millis();
+            }
+            Timed<E> built;
+            try {
+                built = join(building);
+            } catch (Throwable failure) {
+                abandon(steps, created, null, failure);
+                done(new Result(dimension, failure, preparedMillis, 0L));
+                return;
+            }
+            try {
+                steps.complete(created, built.value());
+                done(new Result(dimension, null, preparedMillis, built.millis()));
+            } catch (Throwable failure) {
+                done(new Result(dimension, failure, preparedMillis, built.millis()));
+            }
+        }
+
+        private E awaitCancelledEngine(CompletableFuture<Timed<E>> building, CancellationException cancellation) {
+            try {
+                return building.get(CANCEL_BUILD_WAIT_SECONDS, TimeUnit.SECONDS).value();
+            } catch (ExecutionException failure) {
+                return null;
+            } catch (TimeoutException failure) {
+                ModdedIrisLog.error("Iris dimension engine for '{}' did not finish within {}s of shutdown; abandoning its level",
+                        dimension.id(), CANCEL_BUILD_WAIT_SECONDS);
+                cancellation.addSuppressed(failure);
+                return null;
+            } catch (InterruptedException interrupted) {
+                Thread.currentThread().interrupt();
+                cancellation.addSuppressed(interrupted);
+                return null;
+            }
+        }
+
+        private void done(Result outcome) {
+            worker.shutdown();
+            result.complete(outcome);
+        }
+
+        private enum State {
+            UNSTARTED,
+            PREPARING,
+            PREPARED,
+            BEGINNING,
+            BUILDING,
+            DONE,
+            CANCELLED
+        }
+    }
+
+    @FunctionalInterface
+    private interface Step<T> {
+        T run() throws Exception;
+    }
+
+    private record Timed<T>(T value, long millis) {
+    }
+
+    private record Preparation<P>(
+            ModdedDimensionRegistryStore.PersistentDimension dimension,
+            CompletableFuture<Timed<P>> future
+    ) {
+    }
+
+    private record Building<L, E>(
+            int index,
+            ModdedDimensionRegistryStore.PersistentDimension dimension,
+            long preparedMillis,
+            L level,
+            CompletableFuture<Timed<E>> engine
+    ) {
+    }
+}

adapters/modded-common/src/main/java/art/arcane/iris/modded/ModdedDimensionManager.java

@@ -107,150 +107,172 @@ public final class ModdedDimensionManager {
     ) {
         return create(
                 server,
-                dimensionId,
-                pack,
-                packDimensionKey,
-                seed,
-                ModdedGenerationMode.TRANSIENT_STUDIO
+                new DimensionRequest(dimensionId, pack, packDimensionKey, seed),
+                () -> transientStudioPack(pack, packDimensionKey)
         );
     }
 
-    static Handle restorePersistent(
+    static PendingInjection beginInjection(
             NativeModdedServer server,
-            String dimensionId,
-            String pack,
-            String packDimensionKey,
-            long seed
-    ) {
-        return create(
-                server,
-                dimensionId,
-                pack,
-                packDimensionKey,
-                seed,
-                ModdedGenerationMode.PERSISTENT_RESTORE
-        );
-    }
-
-    private static Handle create(
-            NativeModdedServer server,
-            String dimensionId,
-            String pack,
-            String packDimensionKey,
-            long seed,
+            ModdedDimensionRegistryStore.PersistentDimension dimension,
+            ModdedGenerationHistoryStorage.ActivePack active,
             ModdedGenerationMode generationMode
     ) {
         NativeDimensionRuntime serverAccess = requireAccess();
+        DimensionRequest requested = new DimensionRequest(dimension.id(), dimension.pack(), dimension.dimension(), dimension.seed());
         synchronized (LOCK) {
-            String key = dimensionId;
-            RuntimePack runtimePack = switch (generationMode) {
-                case TRANSIENT_STUDIO -> transientStudioPack(pack, packDimensionKey);
-                case PERSISTENT_CREATE -> persistentRuntimePack(
-                        ModdedGenerationHistoryStorage.createOrStage(
-                                server,
-                                key,
-                                pack,
-                                packDimensionKey,
-                                seed
-                        ),
-                        generationMode
-                );
-                case PERSISTENT_RESTORE -> persistentRuntimePack(
-                        ModdedGenerationHistoryStorage.restoreOrAdopt(
-                                server,
-                                key,
-                                pack,
-                                packDimensionKey,
-                                seed
-                        ),
-                        generationMode
-                );
-            };
-            Handle existing = HANDLES.get(dimensionId);
-            if (existing != null && serverAccess.hasLevel(server, key)) {
-                Handle refreshed = new Handle(dimensionId, pack, packDimensionKey, seed, existing.level(), existing.generator());
-                HANDLES.put(dimensionId, refreshed);
-                return refreshed;
+            Handle present = presentHandle(server, serverAccess, requested);
+            if (present != null) {
+                return new PendingInjection(present, true);
             }
-            if (serverAccess.hasLevel(server, key)) {
-                NativeWorld present = level(server, dimensionId);
-                IrisModdedChunkGenerator generator = NativeWorldGenerators.find(present, IrisModdedChunkGenerator.class);
-                if (generator == null) {
-                    throw new IllegalStateException("Iris cannot inject dimension '" + dimensionId + "': a non-Iris level with that id is already loaded");
-                }
-                ModdedIrisLog.warn("Iris dimension '{}' is already present in the running server; reusing it", dimensionId);
-                Handle handle = new Handle(dimensionId, pack, packDimensionKey, seed, present, generator);
-                HANDLES.put(dimensionId, handle);
-                return handle;
-            }
-
             try {
-                Handle handle = inject(
-                        server,
-                        serverAccess,
-                        dimensionId,
-                        key,
-                        pack,
-                        packDimensionKey,
-                        seed,
-                        runtimePack
-                );
-                HANDLES.put(dimensionId, handle);
-                ModdedIrisLog.info("Iris injected runtime dimension '{}' (pack={} dim={} seed={})", dimensionId, pack, packDimensionKey, seed);
-                return handle;
+                RuntimePack runtimePack = persistentRuntimePack(active, generationMode);
+                return new PendingInjection(createLevel(server, serverAccess, requested, runtimePack), false);
             } catch (Throwable e) {
-                ModdedIrisLog.error("Iris failed to inject runtime dimension '{}' (pack={} dim={} seed={})", dimensionId, pack, packDimensionKey, seed, e);
-                throw new IllegalStateException("Iris runtime dimension injection failed for " + dimensionId, e);
+                throw injectionFailure(requested, e);
             }
         }
     }
 
-    public static Handle createPersistent(NativeModdedServer server, String dimensionId, String pack, String packDimensionKey, long seed) {
+    static Handle completeInjection(NativeModdedServer server, PendingInjection pending, Engine engine) {
+        if (pending.present()) {
+            return pending.handle();
+        }
+        NativeDimensionRuntime serverAccess = requireAccess();
         synchronized (LOCK) {
-            ModdedDimensionRegistryStore.PersistentDimension previous =
-                    ModdedDimensionRegistryStore.get(server, dimensionId);
-            if (previous != null) {
-                throw new IllegalStateException("Iris dimension '" + dimensionId
-                        + "' already exists. Use the Iris world update command to stage a pack update.");
-            }
-            ModdedDimensionRegistryStore.put(server, new ModdedDimensionRegistryStore.PersistentDimension(
-                    dimensionId,
-                    pack,
-                    packDimensionKey,
-                    seed
-            ));
             try {
-                return create(
-                        server,
-                        dimensionId,
-                        pack,
-                        packDimensionKey,
-                        seed,
-                        ModdedGenerationMode.PERSISTENT_CREATE
-                );
+                return register(publishLevel(server, serverAccess, pending.handle(), engine));
             } catch (Throwable e) {
-                try {
-                    ModdedDimensionRegistryStore.remove(server, dimensionId);
-                } catch (Throwable rollbackFailure) {
-                    e.addSuppressed(rollbackFailure);
-                }
-                if (e instanceof RuntimeException runtimeException) {
-                    throw runtimeException;
-                }
-                if (e instanceof Error fatalError) {
-                    throw fatalError;
-                }
-                throw new IllegalStateException("Iris runtime dimension injection failed for " + dimensionId, e);
+                throw injectionFailure(DimensionRequest.of(pending.handle()), e);
             }
         }
     }
 
+    static void abandonInjection(NativeModdedServer server, PendingInjection pending, Engine engine, Throwable failure) {
+        if (engine != null) {
+            try {
+                ModdedWorldEngines.closeUnregistered(engine);
+            } catch (Throwable cleanupFailure) {
+                failure.addSuppressed(cleanupFailure);
+                ModdedIrisLog.error("Iris failed to close the abandoned engine for '{}'",
+                        pending.handle().dimensionId(), cleanupFailure);
+            }
+        }
+        if (pending.present()) {
+            return;
+        }
+        NativeDimensionRuntime serverAccess = requireAccess();
+        Handle handle = pending.handle();
+        synchronized (LOCK) {
+            rollbackInjection(server, serverAccess, handle.dimensionId(), handle.level(), handle.generator(), false, failure);
+        }
+    }
+
+    static PendingInjection beginCreation(
+            NativeModdedServer server,
+            ModdedDimensionRegistryStore.PersistentDimension dimension,
+            ModdedGenerationHistoryStorage.ActivePack active
+    ) {
+        synchronized (LOCK) {
+            if (ModdedDimensionRegistryStore.get(server, dimension.id()) != null) {
+                throw new IllegalStateException(alreadyExists(dimension.id()));
+            }
+            ModdedDimensionRegistryStore.put(server, dimension);
+            try {
+                return beginInjection(server, dimension, active, ModdedGenerationMode.PERSISTENT_CREATE);
+            } catch (RuntimeException | Error failure) {
+                forgetCreation(server, dimension.id(), failure);
+                throw failure;
+            }
+        }
+    }
+
+    static Handle completeCreation(NativeModdedServer server, PendingInjection pending, Engine engine) {
+        try {
+            return completeInjection(server, pending, engine);
+        } catch (RuntimeException | Error failure) {
+            forgetCreation(server, pending.handle().dimensionId(), failure);
+            throw failure;
+        }
+    }
+
+    static void abandonCreation(NativeModdedServer server, PendingInjection pending, Engine engine, Throwable failure) {
+        abandonInjection(server, pending, engine, failure);
+        forgetCreation(server, pending.handle().dimensionId(), failure);
+    }
+
+    static String alreadyExists(String dimensionId) {
+        return "Iris dimension '" + dimensionId
+                + "' already exists. Use the Iris world update command to stage a pack update.";
+    }
+
+    private static void forgetCreation(NativeModdedServer server, String dimensionId, Throwable failure) {
+        try {
+            ModdedDimensionRegistryStore.remove(server, dimensionId);
+        } catch (Throwable rollbackFailure) {
+            failure.addSuppressed(rollbackFailure);
+        }
+    }
+
+    private static Handle create(NativeModdedServer server, DimensionRequest requested, RuntimePackSource source) {
+        NativeDimensionRuntime serverAccess = requireAccess();
+        synchronized (LOCK) {
+            RuntimePack runtimePack = source.open();
+            Handle present = presentHandle(server, serverAccess, requested);
+            if (present != null) {
+                return present;
+            }
+            try {
+                return register(publishLevel(server, serverAccess,
+                        createLevel(server, serverAccess, requested, runtimePack), null));
+            } catch (Throwable e) {
+                throw injectionFailure(requested, e);
+            }
+        }
+    }
+
+    private static Handle presentHandle(NativeModdedServer server, NativeDimensionRuntime serverAccess, DimensionRequest requested) {
+        String dimensionId = requested.dimensionId();
+        Handle existing = HANDLES.get(dimensionId);
+        if (existing != null && serverAccess.hasLevel(server, dimensionId)) {
+            Handle refreshed = requested.bind(existing.level(), existing.generator());
+            HANDLES.put(dimensionId, refreshed);
+            return refreshed;
+        }
+        if (!serverAccess.hasLevel(server, dimensionId)) {
+            return null;
+        }
+        NativeWorld present = level(server, dimensionId);
+        IrisModdedChunkGenerator generator = NativeWorldGenerators.find(present, IrisModdedChunkGenerator.class);
+        if (generator == null) {
+            throw new IllegalStateException("Iris cannot inject dimension '" + dimensionId + "': a non-Iris level with that id is already loaded");
+        }
+        ModdedIrisLog.warn("Iris dimension '{}' is already present in the running server; reusing it", dimensionId);
+        Handle handle = requested.bind(present, generator);
+        HANDLES.put(dimensionId, handle);
+        return handle;
+    }
+
+    private static Handle register(Handle handle) {
+        HANDLES.put(handle.dimensionId(), handle);
+        ModdedIrisLog.info("Iris injected runtime dimension '{}' (pack={} dim={} seed={})",
+                handle.dimensionId(), handle.pack(), handle.packDimensionKey(), handle.seed());
+        return handle;
+    }
+
+    private static IllegalStateException injectionFailure(DimensionRequest requested, Throwable failure) {
+        ModdedIrisLog.error("Iris failed to inject runtime dimension '{}' (pack={} dim={} seed={})",
+                requested.dimensionId(), requested.pack(), requested.packDimensionKey(), requested.seed(), failure);
+        return new IllegalStateException("Iris runtime dimension injection failed for " + requested.dimensionId(), failure);
+    }
+
     public static UpdateResult stagePersistentUpdate(
             NativeModdedServer server,
             String dimensionId,
             String pack,
             String packDimensionKey
     ) {
+        ModdedDimensionCreations.requireNotCreating(dimensionId);
         synchronized (LOCK) {
             ModdedDimensionRegistryStore.PersistentDimension previous =
                     ModdedDimensionRegistryStore.get(server, dimensionId);
@@ -313,6 +335,7 @@ public final class ModdedDimensionManager {
     }
 
     public static boolean removePersistent(NativeModdedServer server, String dimensionId, boolean wipeStorage) {
+        ModdedDimensionCreations.requireNotCreating(dimensionId);
         ModdedDimensionRegistryStore.PersistentDimension previous =
                 ModdedDimensionRegistryStore.get(server, dimensionId);
         ModdedDimensionRegistryStore.remove(server, dimensionId);
@@ -392,16 +415,16 @@ public final class ModdedDimensionManager {
         }
     }
 
-    private static Handle inject(
+    private static Handle createLevel(
             NativeModdedServer server,
             NativeDimensionRuntime serverAccess,
-            String dimensionId,
-            String key,
-            String pack,
-            String packDimensionKey,
-            long seed,
+            DimensionRequest requested,
             RuntimePack runtimePack
     ) {
+        String dimensionId = requested.dimensionId();
+        String pack = requested.pack();
+        String packDimensionKey = requested.packDimensionKey();
+        long seed = requested.seed();
         String typeRef = runtimePack.dimensionTypeKey();
         ModdedForcedDatapack.requireRegisteredDimensionType(typeRef,
                 serverAccess.hasDimensionType(server, typeRef) ? Optional.of(Boolean.TRUE) : Optional.empty(),
@@ -414,35 +437,54 @@ public final class ModdedDimensionManager {
                             runtimePack.generationMode());
                     return generator;
                 }));
-        NativeWorld level = created.world();
-        IrisModdedChunkGenerator generator = created.generator();
+        try {
+            serverAccess.initialize(server, created.world());
+            return requested.bind(created.world(), created.generator());
+        } catch (Throwable error) {
+            rollbackInjection(server, serverAccess, dimensionId, created.world(), created.generator(), false, error);
+            throw rethrow(dimensionId, error);
+        }
+    }
 
+    private static Handle publishLevel(
+            NativeModdedServer server,
+            NativeDimensionRuntime serverAccess,
+            Handle created,
+            Engine prepared
+    ) {
+        NativeWorld level = created.level();
+        IrisModdedChunkGenerator generator = created.generator();
         boolean loadEventStarted = false;
         try {
-            serverAccess.initialize(server, level);
+            if (prepared != null) {
+                ModdedWorldEngines.installPrepared(level, prepared);
+            }
             generator.bindLevel(level);
-            Handle handle = new Handle(dimensionId, pack, packDimensionKey, seed, level, generator);
             NativeWorld previous = serverAccess.publish(server, level);
             if (previous != null) {
-                throw new IllegalStateException("Iris cannot inject dimension '" + dimensionId
+                throw new IllegalStateException("Iris cannot inject dimension '" + created.dimensionId()
                         + "': the level was registered concurrently");
             }
             serverAccess.addWorldBorderListener(server, level);
             loadEventStarted = true;
             ModdedEngineBootstrap.loader().fireDynamicLevelLoad(level);
-            return handle;
+            return created;
         } catch (Throwable error) {
-            rollbackInjection(server, serverAccess, key, level, generator, loadEventStarted, error);
-            if (error instanceof RuntimeException runtimeException) {
-                throw runtimeException;
-            }
-            if (error instanceof Error fatalError) {
-                throw fatalError;
-            }
-            throw new IllegalStateException("Iris runtime dimension injection failed for " + dimensionId, error);
+            rollbackInjection(server, serverAccess, created.dimensionId(), level, generator, loadEventStarted, error);
+            throw rethrow(created.dimensionId(), error);
         }
     }
 
+    private static RuntimeException rethrow(String dimensionId, Throwable error) {
+        if (error instanceof RuntimeException runtimeException) {
+            return runtimeException;
+        }
+        if (error instanceof Error fatalError) {
+            throw fatalError;
+        }
+        return new IllegalStateException("Iris runtime dimension injection failed for " + dimensionId, error);
+    }
+
     private static void rollbackInjection(NativeModdedServer server, NativeDimensionRuntime serverAccess,
                                           String key, NativeWorld level,
                                           IrisModdedChunkGenerator generator, boolean loadEventStarted,
@@ -511,19 +553,21 @@ public final class ModdedDimensionManager {
                 .normalize();
         PackValidationRegistry.requireLoadable(packRoot);
         IrisData data = IrisData.openDatapackCompiler(packRoot.toFile());
+        String dimensionTypeRef;
         try {
             IrisDimension dimension = data.getDimensionLoader().load(dimensionKey, false);
             if (dimension == null) {
                 throw new IllegalStateException("Transient Iris Studio pack does not contain dimension '"
                         + dimensionKey + "'.");
             }
+            dimensionTypeRef = ModdedWorldgenIds.dimensionTypeRef(pack, dimension);
         } finally {
             data.close();
         }
         return new RuntimePack(
                 packRoot,
                 dimensionKey,
-                ModdedWorldgenIds.dimensionTypeRef(pack, dimensionKey),
+                dimensionTypeRef,
                 ModdedGenerationMode.TRANSIENT_STUDIO
         );
     }
@@ -542,9 +586,30 @@ public final class ModdedDimensionManager {
         }
     }
 
+    @FunctionalInterface
+    private interface RuntimePackSource {
+        RuntimePack open();
+    }
+
+    private record DimensionRequest(String dimensionId, String pack, String packDimensionKey, long seed) {
+        private static DimensionRequest of(Handle handle) {
+            return new DimensionRequest(handle.dimensionId(), handle.pack(), handle.packDimensionKey(), handle.seed());
+        }
+
+        private Handle bind(NativeWorld level, IrisModdedChunkGenerator generator) {
+            return new Handle(dimensionId, pack, packDimensionKey, seed, level, generator);
+        }
+    }
+
     public record Handle(String dimensionId, String pack, String packDimensionKey, long seed, NativeWorld level, IrisModdedChunkGenerator generator) {
     }
 
+    record PendingInjection(Handle handle, boolean present) {
+        PendingInjection {
+            handle = Objects.requireNonNull(handle, "handle");
+        }
+    }
+
     public record UpdateResult(
             boolean pending,
             boolean restartRequired,

adapters/modded-common/src/main/java/art/arcane/iris/modded/ModdedDimensionMetadata.java

@@ -28,6 +28,7 @@ import art.arcane.iris.generation.terrain.IrisDimension;
 import art.arcane.iris.generation.terrain.IrisRegion;
 import art.arcane.volmlib.nativelib.minecraft26_2.terrain.NativeResourceKeys;
 
+import java.io.File;
 import java.util.LinkedHashSet;
 import java.util.Locale;
 import java.util.Set;
@@ -126,6 +127,20 @@ final class ModdedDimensionMetadata {
         }
     }
 
+    static void warmConfiguredPack(File packDirectory, String dimensionKey) {
+        ConfiguredPack configured = ConfiguredPack.load(packDirectory, dimensionKey);
+        collectConfiguredBiomeKeys(configured.dimension(), configured.data());
+    }
+
     record ConfiguredPack(IrisData data, IrisDimension dimension, DimensionMetadata metadata) {
+        static ConfiguredPack load(File packDirectory, String dimensionKey) {
+            IrisData data = IrisData.get(packDirectory);
+            IrisDimension dimension = data.getDimensionLoader().load(dimensionKey);
+            if (dimension == null) {
+                throw new IllegalStateException("Iris dimension '" + dimensionKey
+                        + "' missing from pack " + packDirectory.getAbsolutePath());
+            }
+            return new ConfiguredPack(data, dimension, dimensionMetadata(dimension));
+        }
     }
 }

adapters/modded-common/src/main/java/art/arcane/iris/modded/ModdedDimensionRegistryStore.java

@@ -194,6 +194,11 @@ public final class ModdedDimensionRegistryStore {
         write(file, dimensions, List.of());
     }
 
+    static synchronized void writeWorldRoot(Path worldRoot, List<PersistentDimension> dimensions) {
+        Path file = storeFile(worldRoot);
+        write(file, dimensions, contents(file).unparsed());
+    }
+
     private static void write(Path file, List<PersistentDimension> dimensions, List<Object> unparsed) {
         JSONArray entries = new JSONArray();
         for (PersistentDimension dimension : dimensions) {

adapters/modded-common/src/main/java/art/arcane/iris/modded/ModdedDimensionReplacement.java

@@ -0,0 +1,144 @@
+/*
+ * Iris is a World Generator for Minecraft Servers
+ * Copyright (c) 2026 Arcane Arts (Volmit Software)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package art.arcane.iris.modded;
+
+import art.arcane.volmlib.util.json.JSONObject;
+
+import java.nio.file.Path;
+import java.util.Objects;
+import java.util.OptionalLong;
+import java.util.regex.Pattern;
+
+public record ModdedDimensionReplacement(String levelKey, String pack, String packDimension, OptionalLong seed) {
+    private static final Pattern NAMESPACE = Pattern.compile("[a-z0-9_.-]+");
+    private static final Pattern PATH = Pattern.compile("[a-z0-9_.-]+(?:/[a-z0-9_.-]+)*");
+    private static final Pattern PACK = Pattern.compile("[A-Za-z0-9_.-]+");
+    private static final Pattern PACK_DIMENSION = Pattern.compile("[A-Za-z0-9_.-]+(?:/[A-Za-z0-9_.-]+)*");
+    private static final String TYPE = "type";
+    private static final String SEED = "seed";
+
+    public ModdedDimensionReplacement {
+        Objects.requireNonNull(levelKey, "levelKey");
+        Objects.requireNonNull(pack, "pack");
+        Objects.requireNonNull(packDimension, "packDimension");
+        Objects.requireNonNull(seed, "seed");
+    }
+
+    public static ModdedDimensionReplacement parse(String levelKey, String type, OptionalLong seed) {
+        String level = requireLevelKey(levelKey);
+        String reference = type == null ? "" : type.trim();
+        int packColon = reference.indexOf(':');
+        String pack = packColon >= 0 ? reference.substring(0, packColon) : reference;
+        String packDimension = packColon >= 0 ? reference.substring(packColon + 1) : reference;
+        if (!PACK.matcher(pack).matches()
+                || !PACK_DIMENSION.matcher(packDimension).matches()
+                || pack.contains("..")
+                || packDimension.contains("..")) {
+            throw new IllegalArgumentException("Invalid replacement type '" + type
+                    + "' for " + level + ". Use pack or pack:dimensionKey.");
+        }
+        OptionalLong replacementSeed = Objects.requireNonNull(seed, "seed");
+        if (replacementSeed.isPresent()) {
+            requireUsableSeed(replacementSeed.getAsLong());
+        }
+        return new ModdedDimensionReplacement(level, pack, packDimension, replacementSeed);
+    }
+
+    public static long requireUsableSeed(long seed) {
+        if (seed == Long.MIN_VALUE) {
+            throw new IllegalArgumentException("Seed " + Long.MIN_VALUE
+                    + " is reserved on mod loaders; choose any other signed 64-bit integer");
+        }
+        return seed;
+    }
+
+    public static ModdedDimensionReplacement fromJson(String levelKey, Object value) {
+        if (!(value instanceof JSONObject entry)) {
+            throw new IllegalArgumentException("the replacement must be an object with a \"type\" and an optional \"seed\"");
+        }
+        Object type = entry.opt(TYPE);
+        if (!(type instanceof String typeRef)) {
+            throw new IllegalArgumentException("the replacement \"type\" must be a pack or pack:dimensionKey string");
+        }
+        if (!entry.has(SEED) || entry.isNull(SEED)) {
+            return parse(levelKey, typeRef, OptionalLong.empty());
+        }
+        Object seed = entry.opt(SEED);
+        if (!(seed instanceof Integer) && !(seed instanceof Long)) {
+            throw new IllegalArgumentException("the replacement \"seed\" must be a signed 64-bit integer");
+        }
+        return parse(levelKey, typeRef, OptionalLong.of(((Number) seed).longValue()));
+    }
+
+    public JSONObject toJson() {
+        JSONObject json = new JSONObject();
+        json.put(TYPE, packRef());
+        if (seed.isPresent()) {
+            json.put(SEED, seed.getAsLong());
+        }
+        return json;
+    }
+
+    public String packRef() {
+        return pack.equals(packDimension) ? pack : pack + ":" + packDimension;
+    }
+
+    public ModdedDimensionReplacement withSeed(long replacementSeed) {
+        return new ModdedDimensionReplacement(levelKey, pack, packDimension, OptionalLong.of(replacementSeed));
+    }
+
+    public ModdedDimensionReplacement withPack(String canonicalPack, String canonicalPackDimension) {
+        return new ModdedDimensionReplacement(levelKey, canonicalPack, canonicalPackDimension, seed);
+    }
+
+    public String namespace() {
+        return levelKey.substring(0, levelKey.indexOf(':'));
+    }
+
+    public String path() {
+        return levelKey.substring(levelKey.indexOf(':') + 1);
+    }
+
+    public Path storageFolder(Path worldRoot) {
+        return storageFolder(worldRoot, levelKey);
+    }
+
+    public static Path storageFolder(Path worldRoot, String levelKey) {
+        String level = requireLevelKey(levelKey);
+        int colon = level.indexOf(':');
+        Path folder = worldRoot.resolve("dimensions").resolve(level.substring(0, colon));
+        for (String segment : level.substring(colon + 1).split("/")) {
+            folder = folder.resolve(segment);
+        }
+        return folder;
+    }
+
+    public static String requireLevelKey(String levelKey) {
+        String level = levelKey == null ? "" : levelKey.trim();
+        int colon = level.indexOf(':');
+        if (colon <= 0
+                || !NAMESPACE.matcher(level.substring(0, colon)).matches()
+                || !PATH.matcher(level.substring(colon + 1)).matches()
+                || level.contains("..")) {
+            throw new IllegalArgumentException("Invalid dimension key '" + levelKey
+                    + "'. Use namespace:path, for example examplemod:skylands.");
+        }
+        return level;
+    }
+}

adapters/modded-common/src/main/java/art/arcane/iris/modded/ModdedDimensionReplacements.java

@@ -0,0 +1,315 @@
+/*
+ * Iris is a World Generator for Minecraft Servers
+ * Copyright (c) 2026 Arcane Arts (Volmit Software)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package art.arcane.iris.modded;
+
+import art.arcane.iris.modded.catalog.ModdedWorldgenCatalogs;
+import art.arcane.iris.pack.ingest.catalog.CatalogLevelStem;
+import art.arcane.iris.pack.ingest.catalog.WorldgenCatalog;
+import art.arcane.iris.pack.ingest.catalog.WorldgenCatalogStore;
+import art.arcane.iris.spi.IrisPlatforms;
+import art.arcane.volmlib.util.json.JSONObject;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.OptionalLong;
+import java.util.Set;
+import java.util.TreeMap;
+import java.util.TreeSet;
+
+public final class ModdedDimensionReplacements {
+    public static final String IRIS_GENERATOR = "irisworldgen:iris";
+    private static final Set<String> VANILLA_LEVELS = Set.of("minecraft:overworld", "minecraft:the_nether",
+            "minecraft:the_end");
+    private static volatile RecordedCatalog recordedCatalog;
+    private static final String PLACEHOLDER_BIOME_SOURCE = "minecraft:fixed";
+    private static final String PLACEHOLDER_BIOME = "minecraft:plains";
+    private static final String DIMENSIONS = "dimensions";
+    private static final String JSON = ".json";
+
+    private ModdedDimensionReplacements() {
+    }
+
+    public static String levelStemJson(String dimensionTypeKey, ModdedDimensionReplacement replacement) {
+        JSONObject biomeSource = new JSONObject();
+        biomeSource.put("type", PLACEHOLDER_BIOME_SOURCE);
+        biomeSource.put("biome", PLACEHOLDER_BIOME);
+        JSONObject generator = new JSONObject();
+        generator.put("type", IRIS_GENERATOR);
+        generator.put("biome_source", biomeSource);
+        generator.put("dimension", replacement.packRef());
+        JSONObject stem = new JSONObject();
+        stem.put("type", Objects.requireNonNull(dimensionTypeKey, "dimensionTypeKey"));
+        stem.put("generator", generator);
+        return stem.toString(2) + "\n";
+    }
+
+    public static Path writeLevelStem(Path datapackRoot, ModdedDimensionReplacement replacement, String dimensionTypeKey)
+            throws IOException {
+        Path output = datapackRoot.resolve("data").resolve(replacement.namespace()).resolve("dimension");
+        String[] segments = replacement.path().split("/");
+        for (int index = 0; index < segments.length - 1; index++) {
+            output = output.resolve(segments[index]);
+        }
+        output = output.resolve(segments[segments.length - 1] + ".json");
+        Files.createDirectories(output.getParent());
+        Files.writeString(output, levelStemJson(dimensionTypeKey, replacement), StandardCharsets.UTF_8);
+        return output;
+    }
+
+    public static void writeLevelStems(Path datapackRoot, Map<String, ModdedDimensionReplacement> configured,
+                                       StagedTypes staged, Path worldRoot, ReplaceableLevels levels) throws IOException {
+        for (ModdedDimensionReplacement replacement : new TreeMap<>(configured).values()) {
+            if (!levels.replaceable(replacement.levelKey())) {
+                ModdedIrisLog.error(unreplaceableReason(replacement.levelKey(), levels)
+                        + " Iris writes no dimension override for it.");
+                continue;
+            }
+            String typeRef = staged.typeRef(replacement, worldRoot);
+            if (typeRef == null) {
+                skipUnstaged(replacement, staged, worldRoot);
+                continue;
+            }
+            writeLevelStem(datapackRoot, replacement, typeRef);
+            ModdedIrisLog.info("Iris dimension replacement staged: {} generates from {} with dimension type {}",
+                    replacement.levelKey(), replacement.packRef(), typeRef);
+        }
+    }
+
+    public static Map<String, ModdedDimensionReplacement> configured() throws IOException {
+        return canonical(ModdedModConfig.get().dimensionReplacements(), IrisPlatforms.get().packsFolderNoCreate().toPath());
+    }
+
+    public static Map<String, ModdedDimensionReplacement> stageable(Map<String, ModdedDimensionReplacement> configured,
+                                                                   ReplaceableLevels levels) {
+        Map<String, ModdedDimensionReplacement> stageable = new TreeMap<>();
+        for (ModdedDimensionReplacement replacement : configured.values()) {
+            if (levels.replaceable(replacement.levelKey())) {
+                stageable.put(replacement.levelKey(), replacement);
+            }
+        }
+        return Map.copyOf(stageable);
+    }
+
+    public static ReplaceableLevels replaceableLevels(Path worldRoot, Map<String, ModdedDimensionReplacement> configured)
+            throws IOException {
+        if (configured.isEmpty()) {
+            return ReplaceableLevels.unknown();
+        }
+        return replaceableLevels(worldRoot);
+    }
+
+    public static ReplaceableLevels replaceableLevels(Path worldRoot) throws IOException {
+        Set<String> applied = worldRoot == null
+                ? Set.of()
+                : ModdedReplacementReconciler.readState(worldRoot).applied().keySet();
+        Optional<WorldgenCatalog> catalog = ModdedWorldgenCatalogs.latest();
+        if (catalog.isEmpty()) {
+            catalog = recordedCatalog();
+        }
+        return catalog.isEmpty()
+                ? ReplaceableLevels.unknown()
+                : ReplaceableLevels.of(catalog.get().levelStems(), applied);
+    }
+
+    public static String unreplaceableReason(String levelKey, ReplaceableLevels levels) {
+        if (!levels.known()) {
+            return "Iris refuses to replace " + levelKey + ": it has no record of which dimensions this server loads"
+                    + " from level stems yet. Start the server once so Iris can read the dimension registry.";
+        }
+        return "Iris refuses to replace " + levelKey + ": it is not a dimension the server loads from a level stem;"
+                + " a mod creates it while the server runs, so its data stays untouched.";
+    }
+
+    private static Optional<WorldgenCatalog> recordedCatalog() {
+        Path file = ModdedWorldgenCatalogs.catalogFile();
+        if (!Files.isRegularFile(file)) {
+            return Optional.empty();
+        }
+        try {
+            long modified = Files.getLastModifiedTime(file).toMillis();
+            RecordedCatalog cached = recordedCatalog;
+            if (cached != null && cached.file().equals(file) && cached.modified() == modified) {
+                return Optional.of(cached.catalog());
+            }
+            WorldgenCatalog catalog = WorldgenCatalogStore.read(file);
+            recordedCatalog = new RecordedCatalog(file, modified, catalog);
+            return Optional.of(catalog);
+        } catch (IOException | RuntimeException unreadable) {
+            ModdedIrisLog.error("Iris could not read the recorded worldgen catalog at {}; only the vanilla dimensions are replaceable until the next start records it",
+                    file, unreadable);
+            return Optional.empty();
+        }
+    }
+
+    public static OptionalLong loadedSeed(String levelKey) {
+        ModdedModConfig config = ModdedModConfig.loaded();
+        if (config == null) {
+            return OptionalLong.empty();
+        }
+        ModdedDimensionReplacement replacement = config.dimensionReplacements().get(levelKey);
+        return replacement == null ? OptionalLong.empty() : replacement.seed();
+    }
+
+    static Map<String, ModdedDimensionReplacement> canonical(Map<String, ModdedDimensionReplacement> configured,
+                                                            Path packsRoot) throws IOException {
+        Map<String, ModdedDimensionReplacement> canonical = new TreeMap<>();
+        for (ModdedDimensionReplacement replacement : configured.values()) {
+            canonical.put(replacement.levelKey(), canonical(replacement, packsRoot));
+        }
+        return Map.copyOf(canonical);
+    }
+
+    public static ModdedDimensionReplacement canonical(ModdedDimensionReplacement replacement, Path packsRoot)
+            throws IOException {
+        Path pack = packsRoot.resolve(replacement.pack());
+        if (!Files.isDirectory(pack)) {
+            return replacement;
+        }
+        String packName = sameIgnoringCase(pack.toRealPath().getFileName().toString(), replacement.pack());
+        Path dimensions = pack.resolve(DIMENSIONS);
+        Path dimensionFile = dimensions.resolve(replacement.packDimension() + JSON);
+        String dimension = replacement.packDimension();
+        if (Files.isRegularFile(dimensionFile)) {
+            String relative = dimensions.toRealPath().relativize(dimensionFile.toRealPath()).toString()
+                    .replace(File.separatorChar, '/');
+            dimension = sameIgnoringCase(relative.substring(0, relative.length() - JSON.length()), replacement.packDimension());
+        }
+        return replacement.withPack(packName, dimension);
+    }
+
+    public static boolean installed(ModdedDimensionReplacement replacement, Path packsRoot) {
+        return Files.isRegularFile(packsRoot.resolve(replacement.pack()).resolve(DIMENSIONS)
+                .resolve(replacement.packDimension() + JSON));
+    }
+
+    public static boolean matches(ModdedDimensionReplacement applied, ModdedDimensionReplacement configured) {
+        if (applied == null || configured == null) {
+            return applied == configured;
+        }
+        if (!applied.packRef().equals(configured.packRef())) {
+            return false;
+        }
+        return configured.seed().isEmpty() || configured.seed().equals(applied.seed());
+    }
+
+    public static Set<String> changedLevels(Map<String, ModdedDimensionReplacement> applied,
+                                            Map<String, ModdedDimensionReplacement> configured) {
+        Set<String> levels = new TreeSet<>(applied.keySet());
+        levels.addAll(configured.keySet());
+        Set<String> changed = new TreeSet<>();
+        for (String level : levels) {
+            if (!matches(applied.get(level), configured.get(level))) {
+                changed.add(level);
+            }
+        }
+        return changed;
+    }
+
+    private static void skipUnstaged(ModdedDimensionReplacement replacement, StagedTypes staged, Path worldRoot)
+            throws IOException {
+        String reason = "pack '" + replacement.pack() + "' dimension '" + replacement.packDimension()
+                + "' is not installed or failed validation" + caseHint(replacement, staged);
+        if (worldRoot != null && ModdedReplacementReconciler.hasReplacementRecord(worldRoot, replacement.levelKey())) {
+            throw new IOException("Iris refused to stage the replacement of " + replacement.levelKey() + ": " + reason
+                    + ", and the level already has an applied replacement or Iris generation history. Restore the pack, or remove the "
+                    + replacement.levelKey() + " entry from dimensionReplacements in modded.json to hand the level back to its own generator.");
+        }
+        ModdedIrisLog.error("Iris skipped the replacement of {}: {}, so the dimension keeps its own generator and the replacement stays unapplied",
+                replacement.levelKey(), reason);
+    }
+
+    private static String caseHint(ModdedDimensionReplacement replacement, StagedTypes staged) {
+        String wanted = replacement.pack() + ":" + replacement.packDimension();
+        for (String installed : staged.installed().keySet()) {
+            if (installed.equalsIgnoreCase(wanted)) {
+                return "; pack names and dimension keys are case-sensitive, the installed dimension is " + installed;
+            }
+        }
+        return "";
+    }
+
+    private static String sameIgnoringCase(String actual, String configured) {
+        return actual.equalsIgnoreCase(configured) ? actual : configured;
+    }
+
+    public static String fingerprint(Map<String, ModdedDimensionReplacement> configured) {
+        StringBuilder canonical = new StringBuilder();
+        for (Map.Entry<String, ModdedDimensionReplacement> entry : new TreeMap<>(configured).entrySet()) {
+            canonical.append(entry.getKey()).append('=').append(entry.getValue().packRef()).append('\n');
+        }
+        return canonical.toString();
+    }
+
+    private record RecordedCatalog(Path file, long modified, WorldgenCatalog catalog) {
+    }
+
+    public record ReplaceableLevels(boolean known, Map<String, String> stemGenerators, Set<String> applied) {
+        public ReplaceableLevels {
+            stemGenerators = Map.copyOf(stemGenerators);
+            applied = Set.copyOf(applied);
+        }
+
+        public static ReplaceableLevels unknown() {
+            return new ReplaceableLevels(false, Map.of(), Set.of());
+        }
+
+        public static ReplaceableLevels of(List<CatalogLevelStem> stems, Set<String> applied) {
+            Map<String, String> generators = new TreeMap<>();
+            for (CatalogLevelStem stem : stems) {
+                generators.put(stem.key(), stem.generatorType());
+            }
+            return new ReplaceableLevels(true, generators, applied);
+        }
+
+        public boolean replaceable(String levelKey) {
+            if (VANILLA_LEVELS.contains(levelKey)) {
+                return true;
+            }
+            String generator = stemGenerators.get(levelKey);
+            if (generator == null) {
+                return false;
+            }
+            return !IRIS_GENERATOR.equals(generator) || applied.contains(levelKey);
+        }
+    }
+
+    public record StagedTypes(Map<String, String> installed, Map<Path, String> retained) {
+        public static StagedTypes create() {
+            return new StagedTypes(new LinkedHashMap<>(), new LinkedHashMap<>());
+        }
+
+        String typeRef(ModdedDimensionReplacement replacement, Path worldRoot) {
+            if (worldRoot != null) {
+                String retainedType = retained.get(replacement.storageFolder(worldRoot).toAbsolutePath().normalize());
+                if (retainedType != null) {
+                    return retainedType;
+                }
+            }
+            return installed.get(replacement.pack() + ":" + replacement.packDimension());
+        }
+    }
+}

adapters/modded-common/src/main/java/art/arcane/iris/modded/ModdedDimensionStorage.java

@@ -43,6 +43,10 @@ public final class ModdedDimensionStorage {
     private ModdedDimensionStorage() {
     }
 
+    static List<String> chunkDataFolders() {
+        return CHUNK_DATA_FOLDERS;
+    }
+
     public static File storageFolder(NativeModdedServer server, String dimension) {
         return server.dimensionFolder(dimension).toFile();
     }

adapters/modded-common/src/main/java/art/arcane/iris/modded/ModdedEngineBootstrap.java

@@ -58,6 +58,7 @@ import art.arcane.iris.generation.block.BlockDataMergeSupport;
 import art.arcane.iris.structure.object.IrisObjectRotation;
 import art.arcane.iris.generation.block.TileData;
 import art.arcane.iris.modded.api.ModdedCustomContentRegistry;
+import art.arcane.iris.modded.catalog.ModdedWorldgenCatalogs;
 import art.arcane.iris.modded.command.IrisModdedCommands;
 import art.arcane.iris.modded.command.ModdedGuiHost;
 import art.arcane.iris.modded.command.ModdedObjectUndo;
@@ -144,6 +145,7 @@ public final class ModdedEngineBootstrap {
         }
         IrisModdedCommands.openDownloadAdmission();
         ModdedStartup.prepareForStartup();
+        ModdedStartup.prepareDimensionRestore(server);
         IrisModdedChunkGenerator.startGenPool();
         bindWorldGenerators(server);
         services().enableAll();
@@ -163,6 +165,13 @@ public final class ModdedEngineBootstrap {
         finishPreviousServer("server start");
         captureInitialSpawn(server);
         ModdedStartup.prepareForStartup();
+        ModdedStartup.prepareDimensionRestore(server);
+    }
+
+    public static void levelsReady(NativeModdedServer server) {
+        server.refreshWorlds();
+        bindWorldGenerators(server);
+        ModdedStartup.reinjectPersistentDimensions(server);
     }
 
     public static void serverStarted(NativeModdedServer server) {
@@ -171,8 +180,15 @@ public final class ModdedEngineBootstrap {
         server.refreshWorlds();
         bindWorldGenerators(server);
         ModdedStartup.runOnce(server);
-        reconcileSpawn(server);
+        boolean replacedOverworld = !loader().clientEnvironment() && ModdedReplacementEntry.prepare(server);
+        reconcileSpawn(server, replacedOverworld);
+        if (!loader().clientEnvironment()) {
+            ModdedReplacementReconciler.recordApplied(server);
+            ModdedReplacementReconciler.stopUnpublishedEngines(server);
+            ModdedReplacementEntry.retireIfComplete();
+        }
         ModdedWorldCheck.serverStarted(server);
+        ModdedWorldgenCatalogs.capture(server);
     }
 
     public static void levelLoaded(NativeWorld world) {
@@ -203,6 +219,7 @@ public final class ModdedEngineBootstrap {
         stoppedPending = true;
         Throwable failure = null;
         failure = runStopStage(failure, "pack downloads", IrisModdedCommands::shutdownDownloads);
+        failure = runStopStage(failure, "dimension creations", ModdedDimensionCreations::cancelAll);
         failure = runStopStage(failure, "world check", () -> ModdedWorldCheck.serverStopped(stoppingServer));
         failure = runStopStage(failure, "protocol", ModdedProtocolHandler::stop);
         failure = runStopStage(failure, "pregenerator", ModdedPregenJob::shutdown);
@@ -270,6 +287,7 @@ public final class ModdedEngineBootstrap {
         Throwable failure = null;
         failure = runStopStage(failure, "world engines", ModdedWorldEngines::shutdown);
         failure = runStopStage(failure, "primary world router", ModdedPrimaryWorldRouter::clear);
+        failure = runStopStage(failure, "replacement entry guard", ModdedReplacementEntry::clear);
         failure = runStopStage(failure, "dimension manager", ModdedDimensionManager::clear);
         ModdedScheduler scheduler = schedulerOrNull();
         if (scheduler != null) {
@@ -325,7 +343,7 @@ public final class ModdedEngineBootstrap {
         spawnCaptureServer = server;
     }
 
-    private static void reconcileSpawn(NativeModdedServer server) {
+    private static void reconcileSpawn(NativeModdedServer server, boolean replacedOverworld) {
         NativeServerSpawn spawn = new NativeServerSpawn(server);
         NativeServerSpawn.Respawn current = spawn.current();
         if (current == null || current.world() == null) {
@@ -337,7 +355,8 @@ public final class ModdedEngineBootstrap {
         }
         String dimensionId = level.name();
         boolean studio = dimensionId.startsWith("irisworldgen:studio_");
-        if (!shouldReconcileSpawn(initialSpawnWasDefault, studio, current.position().x(), current.position().z())) {
+        if (!shouldReconcileSpawn(initialSpawnWasDefault || replacedOverworld, studio,
+                current.position().x(), current.position().z())) {
             return;
         }
         int surfaceY = spawn.surfaceAtOrigin(level);
@@ -367,6 +386,9 @@ public final class ModdedEngineBootstrap {
         selfTest(moddedLoader.getClass().getClassLoader());
         bind();
         IrisLanguage.initialize();
+        if (!moddedLoader.clientEnvironment()) {
+            ModdedReplacementReconciler.reconcileEarly();
+        }
         ModdedStartup.prefetchStartupDatapack();
         if (!moddedLoader.clientEnvironment()) {
             MainWorldService.reconcileEarly();

adapters/modded-common/src/main/java/art/arcane/iris/modded/ModdedForcedDatapack.java

@@ -324,6 +324,10 @@ public final class ModdedForcedDatapack {
                 false
         );
         digest.update(inputFingerprint.getBytes(StandardCharsets.UTF_8));
+        Map<String, ModdedDimensionReplacement> replacements = ModdedDimensionReplacements.configured();
+        digest.update(ModdedDimensionReplacements.fingerprint(ModdedDimensionReplacements.stageable(replacements,
+                        ModdedDimensionReplacements.replaceableLevels(worldRootOrNull(), replacements)))
+                .getBytes(StandardCharsets.UTF_8));
         return HexFormat.of().formatHex(digest.digest());
     }
 
@@ -333,15 +337,21 @@ public final class ModdedForcedDatapack {
 
         int packCount = 0;
         KList<String> presetIds = new KList<>();
+        ModdedDimensionReplacements.StagedTypes stagedDimensionTypes = ModdedDimensionReplacements.StagedTypes.create();
         Path worldRoot = worldRootOrNull();
         Set<PackSelection> legacySelections = unadoptedSelections(worldRoot);
         List<File> packRoots = compilationPackRoots(worldRoot);
         for (File pack : packRoots) {
             PackStageContext context = packStageContext(pack.toPath(), legacySelections);
-            if (stagePack(context, fixer, stagingDirectory, seenBiomes, presetIds)) {
+            if (stagePack(context, fixer, stagingDirectory, seenBiomes, presetIds, stagedDimensionTypes)) {
                 packCount++;
             }
         }
+        if (!ModdedEngineBootstrap.loader().clientEnvironment()) {
+            Map<String, ModdedDimensionReplacement> replacements = ModdedDimensionReplacements.configured();
+            ModdedDimensionReplacements.writeLevelStems(stagingDirectory, replacements, stagedDimensionTypes, worldRoot,
+                    ModdedDimensionReplacements.replaceableLevels(worldRoot, replacements));
+        }
 
         IrisDatapackCompiler.installRetainedRegistrySources(packRoots, List.of(stagingDirectory.toFile()), fixer);
         writePackMeta(stagingDirectory);
@@ -362,7 +372,8 @@ public final class ModdedForcedDatapack {
 
     private static boolean stagePack(PackStageContext context, IDataFixer fixer, Path stagingDirectory,
                                      Map<String, KSet<String>> seenBiomes,
-                                     KList<String> presetIds) throws IOException {
+                                     KList<String> presetIds,
+                                     ModdedDimensionReplacements.StagedTypes stagedDimensionTypes) throws IOException {
         File sourcePack = context.packRoot().toFile();
         PackValidationResult validation;
         try {
@@ -392,11 +403,12 @@ public final class ModdedForcedDatapack {
                 stagingDirectory.getParent(), PACK_FOLDER + ".pack-" + sourcePack.getName() + "-");
         Map<String, KSet<String>> packBiomes = new LinkedHashMap<>();
         KList<String> packPresetIds = new KList<>();
+        ModdedDimensionReplacements.StagedTypes packDimensionTypes = ModdedDimensionReplacements.StagedTypes.create();
         KList<File> packFolders = new KList<>();
         packFolders.add(packStagingDirectory.toFile());
         boolean installed;
         try {
-            installed = installPack(context, fixer, packFolders, packBiomes, packPresetIds);
+            installed = installPack(context, fixer, packFolders, packBiomes, packPresetIds, packDimensionTypes);
         } catch (Throwable installationFailure) {
             if (context.required()) {
                 throw requiredPackFailure(context, "datapack serialization", installationFailure);
@@ -414,6 +426,8 @@ public final class ModdedForcedDatapack {
             mergeDirectory(packStagingDirectory, stagingDirectory);
             mergeBiomes(seenBiomes, packBiomes);
             presetIds.addAll(packPresetIds);
+            stagedDimensionTypes.installed().putAll(packDimensionTypes.installed());
+            stagedDimensionTypes.retained().putAll(packDimensionTypes.retained());
             return true;
         } finally {
             try {
@@ -454,6 +468,8 @@ public final class ModdedForcedDatapack {
                 Files.createDirectories(destination);
             } else if (!Files.exists(destination)) {
                 Files.copy(source, destination);
+            } else if (Files.isRegularFile(destination) && ModdedDatapackTagMerge.isTag(relative)) {
+                ModdedDatapackTagMerge.merge(source, destination);
             } else if (!Files.isRegularFile(destination) || Files.mismatch(source, destination) != -1L) {
                 throw new IOException("Conflicting Iris datapack output at " + destination + ".");
             }
@@ -470,7 +486,8 @@ public final class ModdedForcedDatapack {
 
     private static boolean installPack(PackStageContext context, IDataFixer fixer, KList<File> folders,
                                        Map<String, KSet<String>> seenBiomes,
-                                       KList<String> presetIds) throws IOException {
+                                       KList<String> presetIds,
+                                       ModdedDimensionReplacements.StagedTypes dimensionTypes) throws IOException {
         File packFolder = context.packRoot().toFile();
         String packName = context.packName();
         File dimensionsDirectory = new File(packFolder, "dimensions");
@@ -504,18 +521,30 @@ public final class ModdedForcedDatapack {
                         biomesForNamespace(seenBiomes, "iris"),
                         context
                 );
-                writeDimensionType(
-                        folders,
-                        fixer,
-                        dimension,
-                        context.dimensionTypeRef(dimensionKey),
-                        context.emitLegacyDimensionTypeAlias(),
-                        context
-                );
+                String typeRef = context.dimensionTypeRef(dimensionKey);
+                if (dimension.hasBorrowedDimensionType()) {
+                    typeRef = requireBorrowedType(context, dimension, typeRef);
+                } else {
+                    requireScopedType(context, typeRef);
+                    writeDimensionType(
+                            folders,
+                            fixer,
+                            dimension,
+                            typeRef,
+                            context.emitLegacyDimensionTypeAlias(),
+                            context
+                    );
+                }
+                if (context.retainedDimensionRoot() != null) {
+                    dimensionTypes.retained().put(context.retainedDimensionRoot(), typeRef);
+                }
                 if (context.emitPresets()) {
-                    String presetRef = ModdedWorldgenIds.presetRef(packName, dimensionKey);
-                    writeWorldPreset(folders, packName, dimensionKey, presetRef);
-                    presetIds.add(presetRef);
+                    dimensionTypes.installed().put(packName + ":" + dimensionKey, typeRef);
+                    if (!dimension.hasBorrowedDimensionType()) {
+                        String presetRef = ModdedWorldgenIds.presetRef(packName, dimensionKey);
+                        writeWorldPreset(folders, packName, dimensionKey, presetRef);
+                        presetIds.add(presetRef);
+                    }
                 }
                 installedDimensions++;
             }
@@ -542,6 +571,22 @@ public final class ModdedForcedDatapack {
                         + " (datapack source injection failed; see the Iris boot ERROR), so a restart alone will not register it.")));
     }
 
+    private static void requireScopedType(PackStageContext context, String stagedTypeRef) throws IOException {
+        if (context.required() && ModdedWorldgenIds.scopedDimensionType(stagedTypeRef).isEmpty()) {
+            throw new IOException("Retained Iris dimension type key is not scoped: " + stagedTypeRef);
+        }
+    }
+
+    private static String requireBorrowedType(PackStageContext context, IrisDimension dimension, String stagedTypeRef)
+            throws IOException {
+        String borrowed = dimension.getBorrowedDimensionType().trim();
+        if (context.required() && !borrowed.equals(stagedTypeRef)) {
+            throw new IOException("Retained Iris generation pack at " + context.packRoot() + " borrows dimension type "
+                    + borrowed + ", but its generation history records " + stagedTypeRef + ".");
+        }
+        return borrowed;
+    }
+
     private static void writeWorldPreset(KList<File> folders, String packName, String dimensionKey,
                                          String presetRef) throws IOException {
         String dimensionRef = dimensionKey.equals(packName) ? packName : packName + ":" + dimensionKey;
@@ -789,14 +834,16 @@ public final class ModdedForcedDatapack {
         Path normalizedRoot = packRoot.toAbsolutePath().normalize();
         RetainedPack retained = retainedPack(normalizedRoot);
         if (retained != null) {
-            ModdedWorldgenIds.ScopedDimension identity = ModdedWorldgenIds
-                    .scopedDimensionType(retained.epoch().dimensionContract().dimensionTypeKey())
-                    .orElseThrow(() -> new IOException("Retained Iris dimension type key is not scoped: "
-                            + retained.epoch().dimensionContract().dimensionTypeKey()));
-            if (!identity.dimension().equals(retained.epoch().dimensionContract().dimensionKey())) {
+            GenerationEpoch.DimensionContract contract = retained.epoch().dimensionContract();
+            Optional<ModdedWorldgenIds.ScopedDimension> scoped = ModdedWorldgenIds.scopedDimensionType(contract.dimensionTypeKey());
+            if (scoped.isEmpty()) {
+                return PackStageContext.retained(normalizedRoot, retainedPackName(retained.epoch(), normalizedRoot), retained);
+            }
+            ModdedWorldgenIds.ScopedDimension identity = scoped.get();
+            if (!identity.dimension().equals(contract.dimensionKey())) {
                 throw new IOException("Retained Iris dimension type identity does not match its epoch contract.");
             }
-            return PackStageContext.retained(normalizedRoot, identity.pack(), retained.epoch());
+            return PackStageContext.retained(normalizedRoot, identity.pack(), retained);
         }
 
         String packName = normalizedRoot.getFileName().toString();
@@ -809,6 +856,16 @@ public final class ModdedForcedDatapack {
         return PackStageContext.installed(normalizedRoot, packName, legacyDimensions);
     }
 
+    static String retainedPackName(GenerationEpoch epoch, Path packRoot) throws IOException {
+        String dimensionKey = epoch.dimensionContract().dimensionKey();
+        Set<String> packs = ModdedWorldgenIds.aliasPacks(epoch.registryContract(), dimensionKey);
+        if (packs.size() > 1) {
+            throw new IOException("Retained Iris generation pack at " + packRoot
+                    + " records scoped biome aliases from several packs " + packs + ".");
+        }
+        return packs.isEmpty() ? dimensionKey : packs.iterator().next();
+    }
+
     private static RetainedPack retainedPack(Path packRoot) throws IOException {
         Path epochRoot = packRoot.getParent();
         Path epochsRoot = epochRoot == null ? null : epochRoot.getParent();
@@ -868,7 +925,8 @@ public final class ModdedForcedDatapack {
             boolean emitLegacyDimensionTypeAlias,
             boolean required,
             Set<String> legacyDimensions,
-            GenerationRegistryContract retainedContract
+            GenerationRegistryContract retainedContract,
+            Path retainedDimensionRoot
     ) implements IrisCustomBiomeAliasResolver {
         private static PackStageContext installed(
                 Path packRoot,
@@ -884,6 +942,7 @@ public final class ModdedForcedDatapack {
                     true,
                     false,
                     Set.copyOf(legacyDimensions),
+                    null,
                     null
             );
         }
@@ -891,8 +950,9 @@ public final class ModdedForcedDatapack {
         private static PackStageContext retained(
                 Path packRoot,
                 String packName,
-                GenerationEpoch epoch
+                RetainedPack retained
         ) {
+            GenerationEpoch epoch = retained.epoch();
             return new PackStageContext(
                     packRoot,
                     packName,
@@ -902,7 +962,8 @@ public final class ModdedForcedDatapack {
                     true,
                     true,
                     Set.of(),
-                    epoch.registryContract()
+                    epoch.registryContract(),
+                    retained.history().paths().dimensionRoot().toAbsolutePath().normalize()
             );
         }
 

adapters/modded-common/src/main/java/art/arcane/iris/modded/ModdedGenerationHistoryStorage.java

@@ -9,6 +9,7 @@ import art.arcane.iris.pack.BrokenPackException;
 import art.arcane.iris.pack.PackFingerprints;
 import art.arcane.iris.pack.PackValidationRegistry;
 import art.arcane.iris.pack.PackValidationResult;
+import art.arcane.iris.world.history.GenerationAdmission;
 import art.arcane.iris.world.history.GenerationEpoch;
 import art.arcane.iris.world.history.GenerationEpochContractFactory;
 import art.arcane.iris.world.history.GenerationHistory;
@@ -28,6 +29,7 @@ import java.util.Collection;
 import java.util.List;
 import java.util.Objects;
 import java.util.Optional;
+import java.util.stream.Stream;
 
 final class ModdedGenerationHistoryStorage {
     private ModdedGenerationHistoryStorage() {
@@ -52,7 +54,7 @@ final class ModdedGenerationHistoryStorage {
                     ModdedGenerationHistoryStorage::requireRegistryDefinitions,
                     IrisSettings.get().getGenerator().getGenerationTransitionWidthBlocks()
             );
-            return resolveActive(history);
+            return resolveActive(history, source);
         } catch (IOException failure) {
             throw historyFailure(levelKey, failure);
         }
@@ -67,25 +69,85 @@ final class ModdedGenerationHistoryStorage {
     ) {
         Path dimensionRoot = dimensionRoot(server, levelKey);
         try {
-            GenerationHistory history = restoreOrAdopt(
-                    dimensionRoot,
-                    worldSeed,
-                    () -> {
-                        Path source = selectedPackSource(selectedPack, selectedDimensionKey);
-                        return new AdoptionSource(source, captureCandidate(
-                                source,
-                                selectedDimensionKey,
-                                GenerationRegistryContractFactory.CustomBiomeAliasPolicy.RETAIN_LEGACY_ALIASES
-                        ));
-                    },
-                    ModdedGenerationHistoryStorage::requireRegistryDefinitions
-            );
-            return resolveActive(history);
+            GenerationHistory history = openForRestore(dimensionRoot, selectedPack, selectedDimensionKey, worldSeed);
+            return resolveActive(history, installedPackSource(selectedPack));
         } catch (IOException failure) {
             throw historyFailure(levelKey, failure);
         }
     }
 
+    static PreparedHistory prepareRestore(
+            NativeModdedServer server,
+            String levelKey,
+            String selectedPack,
+            String selectedDimensionKey,
+            long worldSeed
+    ) {
+        Path dimensionRoot = dimensionRoot(server, levelKey);
+        try {
+            GenerationHistory history = openForRestore(dimensionRoot, selectedPack, selectedDimensionKey, worldSeed);
+            return prepare(history, installedPackSource(selectedPack));
+        } catch (IOException failure) {
+            throw historyFailure(levelKey, failure);
+        }
+    }
+
+    static PreparedHistory prepareCreate(
+            NativeModdedServer server,
+            String levelKey,
+            String selectedPack,
+            String selectedDimensionKey,
+            long worldSeed
+    ) {
+        Path dimensionRoot = dimensionRoot(server, levelKey);
+        try {
+            Path source = selectedPackSource(selectedPack, selectedDimensionKey);
+            GenerationHistory history = createOrStage(
+                    dimensionRoot,
+                    source,
+                    worldSeed,
+                    captureCandidate(source, selectedDimensionKey),
+                    ModdedGenerationHistoryStorage::requireRegistryDefinitions,
+                    IrisSettings.get().getGenerator().getGenerationTransitionWidthBlocks()
+            );
+            return prepare(history, source);
+        } catch (IOException failure) {
+            throw historyFailure(levelKey, failure);
+        }
+    }
+
+    private static PreparedHistory prepare(GenerationHistory history, Path validatedSource) throws IOException {
+        GenerationAdmission.RuntimeLease lease = history.retainRuntime();
+        try {
+            history.prepareCurrentGenerator(IrisSettings.get().getGenerator().getGenerationTransitionWidthBlocks());
+            return new PreparedHistory(resolveActive(history, validatedSource), lease);
+        } catch (IOException | RuntimeException | Error failure) {
+            lease.close();
+            throw failure;
+        }
+    }
+
+    private static GenerationHistory openForRestore(
+            Path dimensionRoot,
+            String selectedPack,
+            String selectedDimensionKey,
+            long worldSeed
+    ) throws IOException {
+        return restoreOrAdopt(
+                dimensionRoot,
+                worldSeed,
+                () -> {
+                    Path source = selectedPackSource(selectedPack, selectedDimensionKey);
+                    return new AdoptionSource(source, captureCandidate(
+                            source,
+                            selectedDimensionKey,
+                            adoptionAliasPolicy(dimensionRoot)
+                    ));
+                },
+                ModdedGenerationHistoryStorage::requireRegistryDefinitions
+        );
+    }
+
     static ActivePack openOrAdopt(
             NativeWorld level,
             String selectedPack,
@@ -170,10 +232,23 @@ final class ModdedGenerationHistoryStorage {
         );
     }
 
-    static ActivePack resolveActive(GenerationHistory history) throws IOException {
+    static GenerationRegistryContractFactory.CustomBiomeAliasPolicy adoptionAliasPolicy(Path dimensionRoot)
+            throws IOException {
+        Path regions = dimensionRoot.resolve("region");
+        if (!Files.isDirectory(regions)) {
+            return GenerationRegistryContractFactory.CustomBiomeAliasPolicy.CONTENT_ADDRESSED_ONLY;
+        }
+        try (Stream<Path> files = Files.list(regions)) {
+            return files.anyMatch((Path file) -> file.getFileName().toString().endsWith(".mca"))
+                    ? GenerationRegistryContractFactory.CustomBiomeAliasPolicy.RETAIN_LEGACY_ALIASES
+                    : GenerationRegistryContractFactory.CustomBiomeAliasPolicy.CONTENT_ADDRESSED_ONLY;
+        }
+    }
+
+    static ActivePack resolveActive(GenerationHistory history, Path validatedSource) throws IOException {
         GenerationEpoch epoch = history.activeEpoch();
         Path packRoot = normalize(history.activePackRoot());
-        validatePack(packRoot);
+        validatePack(packRoot, validatedSource);
         validateDimension(packRoot, epoch);
         return new ActivePack(
                 packRoot,
@@ -183,9 +258,12 @@ final class ModdedGenerationHistoryStorage {
         );
     }
 
-    static PackValidationResult validatePack(Path packRoot) {
-        PackValidationResult validation = PackValidationRegistry.getMatching(
-                packRoot, PackFingerprints.computePackTreeFingerprint(packRoot.toFile()));
+    static PackValidationResult validatePack(Path packRoot, Path validatedSource) {
+        String contentFingerprint = PackFingerprints.computePackTreeFingerprint(packRoot.toFile());
+        PackValidationResult validation = PackValidationRegistry.getMatching(packRoot, contentFingerprint);
+        if (validation == null && validatedSource != null) {
+            validation = PackValidationRegistry.publishMatchingCopy(validatedSource, packRoot, contentFingerprint);
+        }
         if (validation == null) {
             validation = ModdedStartup.validatePack(packRoot.toFile());
         }
@@ -246,10 +324,9 @@ final class ModdedGenerationHistoryStorage {
             PlatformGenerationRegistry generationRegistry = IrisPlatforms.get()
                     .registries()
                     .generationRegistry();
-            String dimensionTypeKey = generationRegistry.dimensionTypeResourceKey(
-                    source.getFileName().toString(),
-                    dimension.getLoadKey(),
-                    dimension.getDimensionTypeKey()
+            String dimensionTypeKey = dimension.dimensionTypeResourceKey(
+                    generationRegistry,
+                    source.getFileName().toString()
             );
             GenerationEpoch.DimensionContract dimensionContract = GenerationEpochContractFactory.create(
                     dimension,
@@ -273,6 +350,11 @@ final class ModdedGenerationHistoryStorage {
         return normalize(ModdedWorldEngines.resolvePack(pack, dimensionKey).toPath());
     }
 
+    private static Path installedPackSource(String pack) {
+        File folder = ModdedWorldEngines.packFolder(pack);
+        return folder.isDirectory() ? normalize(folder.toPath()) : null;
+    }
+
     private static GenerationRegistryContract requireRegistryDefinitions(
             Collection<GenerationRegistryContract> contracts
     )
@@ -333,6 +415,13 @@ final class ModdedGenerationHistoryStorage {
         }
     }
 
+    record PreparedHistory(ActivePack active, GenerationAdmission.RuntimeLease lease) {
+        PreparedHistory {
+            active = Objects.requireNonNull(active, "active");
+            lease = Objects.requireNonNull(lease, "lease");
+        }
+    }
+
     record Candidate(
             String packFingerprint,
             GenerationEpoch.DimensionContract dimensionContract,

adapters/modded-common/src/main/java/art/arcane/iris/modded/ModdedGenerationRegistry.java

@@ -46,6 +46,11 @@ final class ModdedGenerationRegistry implements PlatformGenerationRegistry {
         );
     }
 
+    @Override
+    public boolean supportsBorrowedDimensionTypes() {
+        return true;
+    }
+
     @Override
     public Definition definition(String registryKey, String resourceKey) {
         return nativeRegistry.definition(registryKey, resourceKey);

adapters/modded-common/src/main/java/art/arcane/iris/modded/ModdedLifecycleCallbacks.java

@@ -14,6 +14,7 @@ public final class ModdedLifecycleCallbacks {
         return new NativeModdedCallbacks(
                 ModdedEngineBootstrap::serverAboutToStart,
                 ModdedEngineBootstrap::start,
+                ModdedEngineBootstrap::levelsReady,
                 ModdedEngineBootstrap::serverStarted,
                 ModdedEngineBootstrap::stop,
                 ModdedEngineBootstrap::stopped,

adapters/modded-common/src/main/java/art/arcane/iris/modded/ModdedMixinAudit.java

@@ -45,6 +45,9 @@ public final class ModdedMixinAudit {
     private static final AtomicBoolean AUDITED = new AtomicBoolean(false);
 
     static final List<ExpectedMixin> EXPECTED = List.of(
+            new ExpectedMixin(ENTITY_CONFIG, "ServerLevelsReadyMixin",
+                    NativeMixinTarget.SERVER, "volmlib$levelsReady",
+                    false, NativeMixinFlags::levelsReadyRan),
             new ExpectedMixin(ENTITY_CONFIG, "RegistryClientNamesMixin",
                     NativeMixinTarget.REGISTRY_PACKET, "volmlib$clientRegistryNames",
                     false, NativeMixinFlags::registryClientNamesRan),
@@ -61,6 +64,10 @@ public final class ModdedMixinAudit {
                     NativeMixinTarget.STRUCTURE_PALETTE,
                     "iris$installConcurrentBlockCache",
                     false, NativeMixinFlags::structureTemplatePaletteRan),
+            new ExpectedMixin(ENTITY_CONFIG, "PackRepositorySelectionMixin",
+                    NativeMixinTarget.PACK_REPOSITORY,
+                    "volmlib$keepNativeDatapacksLast",
+                    false, NativeMixinFlags::packSelectionRan),
             new ExpectedMixin(CLIENT_CONFIG, "NativeWorldOpenFlowsMixin",
                     NativeMixinTarget.WORLD_OPEN_FLOWS,
                     "volmlib$openWorldCheckWorldStemCompatibility",
@@ -111,7 +118,7 @@ public final class ModdedMixinAudit {
             ModdedIrisLog.error("  missing: {}", entry);
         }
         ModdedIrisLog.error("The mixin config was not registered for this loader (fabric.mod.json mixins, neoforge.mods.toml [[mixins]], forge MixinConfigs manifest attribute).");
-        ModdedIrisLog.error("Entity persistence, custom mob loot, parallel structure safety, readable biome identifiers, or Iris world-type labels are disabled until this is fixed.");
+        ModdedIrisLog.error("Entity persistence, custom mob loot, parallel structure safety, Iris datapack priority, readable biome identifiers, or Iris world-type labels are disabled until this is fixed.");
         ModdedIrisLog.error("===============================================================");
     }
 

adapters/modded-common/src/main/java/art/arcane/iris/modded/ModdedModConfig.java

@@ -24,9 +24,15 @@ import java.io.IOException;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.nio.file.Path;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.TreeMap;
+import java.util.TreeSet;
 
 public final class ModdedModConfig {
     private static final Object LOCK = new Object();
+    private static final String DIMENSION_REPLACEMENTS = "dimensionReplacements";
     private static volatile ModdedModConfig instance;
 
     private final String defaultPack;
@@ -35,15 +41,20 @@ public final class ModdedModConfig {
     private final String mainWorldPack;
     private final long mainWorldSeed;
     private final boolean mainWorldAutoRestart;
+    private final Map<String, ModdedDimensionReplacement> dimensionReplacements;
+    private final List<String> replacementProblems;
 
     private ModdedModConfig(String defaultPack, String primaryWorld, boolean routePlayersToPrimaryWorld,
-                           String mainWorldPack, long mainWorldSeed, boolean mainWorldAutoRestart) {
+                           String mainWorldPack, long mainWorldSeed, boolean mainWorldAutoRestart,
+                           Replacements replacements) {
         this.defaultPack = defaultPack;
         this.primaryWorld = primaryWorld == null ? "" : primaryWorld.trim();
         this.routePlayersToPrimaryWorld = routePlayersToPrimaryWorld;
         this.mainWorldPack = mainWorldPack == null ? "" : mainWorldPack.trim();
         this.mainWorldSeed = mainWorldSeed;
         this.mainWorldAutoRestart = mainWorldAutoRestart;
+        this.dimensionReplacements = Map.copyOf(replacements.entries());
+        this.replacementProblems = List.copyOf(replacements.problems());
     }
 
     public static ModdedModConfig get() {
@@ -60,11 +71,15 @@ public final class ModdedModConfig {
         }
     }
 
+    public static ModdedModConfig loaded() {
+        return instance;
+    }
+
     public static void setPrimaryWorld(String dimensionId) {
         synchronized (LOCK) {
-            ModdedModConfig current = get();
+            ModdedModConfig current = writable();
             ModdedModConfig updated = new ModdedModConfig(current.defaultPack, dimensionId, current.routePlayersToPrimaryWorld,
-                    current.mainWorldPack, current.mainWorldSeed, current.mainWorldAutoRestart);
+                    current.mainWorldPack, current.mainWorldSeed, current.mainWorldAutoRestart, current.replacements());
             instance = updated;
             write(configFile(), updated);
         }
@@ -72,14 +87,22 @@ public final class ModdedModConfig {
 
     public static void setMainWorld(String packRef, long seed) {
         synchronized (LOCK) {
-            ModdedModConfig current = get();
+            ModdedModConfig current = writable();
             ModdedModConfig updated = new ModdedModConfig(current.defaultPack, current.primaryWorld, current.routePlayersToPrimaryWorld,
-                    packRef == null ? "" : packRef.trim(), seed, current.mainWorldAutoRestart);
+                    packRef == null ? "" : packRef.trim(), seed, current.mainWorldAutoRestart, current.replacements());
             instance = updated;
             write(configFile(), updated);
         }
     }
 
+    public static boolean setDimensionReplacement(ModdedDimensionReplacement replacement) {
+        return updateDimensionReplacement(replacement.levelKey(), replacement);
+    }
+
+    public static boolean clearDimensionReplacement(String levelKey) {
+        return updateDimensionReplacement(levelKey, null);
+    }
+
     public String defaultPack() {
         return defaultPack;
     }
@@ -104,30 +127,108 @@ public final class ModdedModConfig {
         return mainWorldAutoRestart;
     }
 
+    public Map<String, ModdedDimensionReplacement> dimensionReplacements() {
+        return dimensionReplacements;
+    }
+
+    public List<String> replacementProblems() {
+        return replacementProblems;
+    }
+
+    static ModdedModConfig read(Path file) {
+        ModdedModConfig defaults = defaults();
+        JSONObject json;
+        try {
+            json = new JSONObject(Files.readString(file, StandardCharsets.UTF_8));
+        } catch (RuntimeException | IOException unreadable) {
+            ModdedIrisLog.error("Iris modded config at {} is unreadable; using defaults", file, unreadable);
+            return new ModdedModConfig(defaults.defaultPack, defaults.primaryWorld, defaults.routePlayersToPrimaryWorld,
+                    defaults.mainWorldPack, defaults.mainWorldSeed, defaults.mainWorldAutoRestart,
+                    new Replacements(Map.of(), List.of("Iris could not read " + file + ": " + unreadable.getMessage())));
+        }
+        return new ModdedModConfig(
+                json.optString("defaultPack", defaults.defaultPack),
+                json.optString("primaryWorld", defaults.primaryWorld),
+                json.optBoolean("routePlayersToPrimaryWorld", defaults.routePlayersToPrimaryWorld),
+                json.optString("mainWorldPack", defaults.mainWorldPack),
+                json.optLong("mainWorldSeed", defaults.mainWorldSeed),
+                json.optBoolean("mainWorldAutoRestart", defaults.mainWorldAutoRestart),
+                readDimensionReplacements(json, file));
+    }
+
+    private Replacements replacements() {
+        return new Replacements(dimensionReplacements, replacementProblems);
+    }
+
+    private static ModdedModConfig writable() {
+        ModdedModConfig current = get();
+        if (!current.replacementProblems.isEmpty()) {
+            throw new IllegalStateException("Iris will not rewrite " + configFile()
+                    + " while its dimension replacements are unreadable: " + String.join("; ", current.replacementProblems)
+                    + ". Fix the file and restart first.");
+        }
+        return current;
+    }
+
+    private static ModdedModConfig defaults() {
+        return new ModdedModConfig("overworld", "", true, "", 0L, false, new Replacements(Map.of(), List.of()));
+    }
+
+    private static boolean updateDimensionReplacement(String levelKey, ModdedDimensionReplacement replacement) {
+        synchronized (LOCK) {
+            ModdedModConfig current = writable();
+            Map<String, ModdedDimensionReplacement> replacements = new TreeMap<>(current.dimensionReplacements);
+            ModdedDimensionReplacement previous = replacement == null
+                    ? replacements.remove(levelKey)
+                    : replacements.put(levelKey, replacement);
+            if (replacement == null ? previous == null : replacement.equals(previous)) {
+                return false;
+            }
+            ModdedModConfig updated = new ModdedModConfig(current.defaultPack, current.primaryWorld, current.routePlayersToPrimaryWorld,
+                    current.mainWorldPack, current.mainWorldSeed, current.mainWorldAutoRestart, new Replacements(replacements, List.of()));
+            instance = updated;
+            write(configFile(), updated);
+            return true;
+        }
+    }
+
     private static Path configFile() {
         return ModdedEngineBootstrap.loader().configDir().resolve("irisworldgen").resolve("modded.json");
     }
 
     private static ModdedModConfig load() {
         Path file = configFile();
-        ModdedModConfig defaults = new ModdedModConfig("overworld", "", true, "", 0L, false);
         if (!Files.isRegularFile(file)) {
+            ModdedModConfig defaults = defaults();
             write(file, defaults);
             return defaults;
         }
-        try {
-            JSONObject json = new JSONObject(Files.readString(file, StandardCharsets.UTF_8));
-            return new ModdedModConfig(
-                    json.optString("defaultPack", defaults.defaultPack),
-                    json.optString("primaryWorld", defaults.primaryWorld),
-                    json.optBoolean("routePlayersToPrimaryWorld", defaults.routePlayersToPrimaryWorld),
-                    json.optString("mainWorldPack", defaults.mainWorldPack),
-                    json.optLong("mainWorldSeed", defaults.mainWorldSeed),
-                    json.optBoolean("mainWorldAutoRestart", defaults.mainWorldAutoRestart));
-        } catch (RuntimeException | IOException e) {
-            ModdedIrisLog.error("Iris modded config at {} is invalid; using defaults", file, e);
-            return defaults;
+        return read(file);
+    }
+
+    private static Replacements readDimensionReplacements(JSONObject json, Path file) {
+        if (!json.has(DIMENSION_REPLACEMENTS) || json.isNull(DIMENSION_REPLACEMENTS)) {
+            return new Replacements(Map.of(), List.of());
         }
+        JSONObject section = json.optJSONObject(DIMENSION_REPLACEMENTS);
+        if (section == null) {
+            return new Replacements(Map.of(), List.of("Iris could not read " + DIMENSION_REPLACEMENTS + " in " + file
+                    + ": it must be an object mapping dimension keys to replacements"));
+        }
+        Map<String, ModdedDimensionReplacement> replacements = new TreeMap<>();
+        List<String> problems = new ArrayList<>();
+        for (String levelKey : new TreeSet<>(section.keySet())) {
+            try {
+                ModdedDimensionReplacement replacement = ModdedDimensionReplacement.fromJson(levelKey, section.opt(levelKey));
+                replacements.put(replacement.levelKey(), replacement);
+            } catch (IllegalArgumentException invalid) {
+                problems.add("Iris could not read dimension replacement '" + levelKey + "' in " + file + ": " + invalid.getMessage());
+            }
+        }
+        for (String problem : problems) {
+            ModdedIrisLog.error(problem);
+        }
+        return new Replacements(replacements, problems);
     }
 
     private static void write(Path file, ModdedModConfig config) {
@@ -138,6 +239,11 @@ public final class ModdedModConfig {
         json.put("mainWorldPack", config.mainWorldPack);
         json.put("mainWorldSeed", config.mainWorldSeed);
         json.put("mainWorldAutoRestart", config.mainWorldAutoRestart);
+        JSONObject replacements = new JSONObject();
+        for (Map.Entry<String, ModdedDimensionReplacement> entry : new TreeMap<>(config.dimensionReplacements).entrySet()) {
+            replacements.put(entry.getKey(), entry.getValue().toJson());
+        }
+        json.put(DIMENSION_REPLACEMENTS, replacements);
         try {
             Files.createDirectories(file.getParent());
             Files.writeString(file, json.toString(4), StandardCharsets.UTF_8);
@@ -145,4 +251,7 @@ public final class ModdedModConfig {
             ModdedIrisLog.error("Iris failed to write modded config at {}", file, e);
         }
     }
+
+    private record Replacements(Map<String, ModdedDimensionReplacement> entries, List<String> problems) {
+    }
 }

adapters/modded-common/src/main/java/art/arcane/iris/modded/ModdedPlatform.java

@@ -80,6 +80,11 @@ public final class ModdedPlatform implements IrisPlatform {
         return loader.platformName();
     }
 
+    @Override
+    public boolean supportsBorrowedDimensionTypes() {
+        return true;
+    }
+
     @Override
     public String minecraftVersion() {
         return loader.minecraftVersion();

adapters/modded-common/src/main/java/art/arcane/iris/modded/ModdedProtocolHandler.java

@@ -127,6 +127,7 @@ public final class ModdedProtocolHandler {
         if (player == null || ModdedPrimaryWorldRouter.refuseIfUnavailable(player)) {
             return;
         }
+        ModdedReplacementEntry.onPlayerJoin(ModdedEngineBootstrap.currentServer(), player);
         String sessionId = sessionId(player);
         ModdedStartup.warnStartupFailuresTo(player);
         ModdedPackUpdateService packUpdates = ModdedEngineBootstrap.services().service(ModdedPackUpdateService.class);

adapters/modded-common/src/main/java/art/arcane/iris/modded/ModdedReplacementEntry.java

@@ -0,0 +1,150 @@
+/*
+ * Iris is a World Generator for Minecraft Servers
+ * Copyright (c) 2026 Arcane Arts (Volmit Software)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package art.arcane.iris.modded;
+
+import art.arcane.iris.world.lifecycle.WorldReplacementEntryGuard;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeDimensionRuntime;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeModdedServer;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeProtocolPlayer;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeServerSpawn;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeWorldTeleport;
+import art.arcane.volmlib.nativelib.terrain.NativeWorld;
+
+import java.io.IOException;
+import java.nio.file.Path;
+import java.util.Optional;
+import java.util.Set;
+import java.util.UUID;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ConcurrentHashMap;
+
+public final class ModdedReplacementEntry {
+    private static final Set<UUID> PENDING = ConcurrentHashMap.newKeySet();
+    private static volatile Path guardedWorld;
+    private static volatile UUID transaction;
+
+    private ModdedReplacementEntry() {
+    }
+
+    public static boolean prepare(NativeModdedServer server) {
+        clear();
+        Path overworld = ModdedDimensionReplacement.storageFolder(server.root(), ModdedReplacementReconciler.OVERWORLD);
+        Optional<WorldReplacementEntryGuard.Entry> entry;
+        try {
+            entry = WorldReplacementEntryGuard.load(overworld);
+        } catch (IOException failure) {
+            ModdedIrisLog.error("Iris could not read the Overworld replacement entry marker under {}", overworld, failure);
+            return false;
+        }
+        if (entry.isEmpty()) {
+            return false;
+        }
+        PENDING.addAll(entry.get().pendingPlayers());
+        transaction = entry.get().transactionId();
+        guardedWorld = overworld;
+        ModdedIrisLog.info("Iris replaced the Overworld; {} returning player(s) are checked for a safe position on their next join",
+                PENDING.size());
+        return true;
+    }
+
+    public static void retireIfComplete() {
+        Path world = guardedWorld;
+        UUID current = transaction;
+        if (world == null || current == null || !PENDING.isEmpty()) {
+            return;
+        }
+        CompletableFuture.runAsync(() -> retire(world, current));
+    }
+
+    public static void onPlayerJoin(NativeModdedServer server, NativeProtocolPlayer player) {
+        if (guardedWorld == null || server == null || player == null || !PENDING.contains(player.id())) {
+            return;
+        }
+        NativeWorld overworld = server.overworld();
+        if (overworld == null || !player.isInWorld(overworld) || standingSafely(overworld, player)) {
+            complete(player.id());
+            return;
+        }
+        NativeServerSpawn.Respawn spawn = new NativeServerSpawn(server).current();
+        boolean overworldSpawn = spawn != null && NativeDimensionRuntime.sameWorld(spawn.world(), overworld);
+        double x = overworldSpawn ? spawn.position().x() + 0.5D : 0.5D;
+        double z = overworldSpawn ? spawn.position().z() + 0.5D : 0.5D;
+        UUID playerId = player.id();
+        NativeWorldTeleport.teleport(player, new NativeWorldTeleport.Destination(server, overworld, x, Double.MIN_VALUE, z,
+                        ModdedTeleportDeadline.fromNow()))
+                .whenComplete((Boolean moved, Throwable failure) -> {
+                    if (failure != null || !Boolean.TRUE.equals(moved)) {
+                        ModdedIrisLog.error("Iris could not move {} out of the replaced Overworld terrain to the spawn surface",
+                                playerId, failure);
+                        return;
+                    }
+                    ModdedIrisLog.info("Iris moved {} from an unsafe position in the replaced Overworld to the spawn surface",
+                            playerId);
+                    complete(playerId);
+                });
+    }
+
+    public static void clear() {
+        PENDING.clear();
+        guardedWorld = null;
+        transaction = null;
+    }
+
+    static boolean standingSafely(NativeWorld world, NativeProtocolPlayer player) {
+        int y = player.blockY();
+        if (y < world.minHeight() || y + 1 >= world.maxHeight()) {
+            return false;
+        }
+        return !world.getBlock(player.blockX(), y, player.blockZ()).isSolid()
+                && !world.getBlock(player.blockX(), y + 1, player.blockZ()).isSolid();
+    }
+
+    private static void complete(UUID playerId) {
+        Path world = guardedWorld;
+        UUID current = transaction;
+        if (world == null || current == null || !PENDING.remove(playerId)) {
+            return;
+        }
+        CompletableFuture.runAsync(() -> persistCompletion(world, current, playerId));
+    }
+
+    private static synchronized void persistCompletion(Path world, UUID current, UUID playerId) {
+        try {
+            Optional<WorldReplacementEntryGuard.Entry> updated = WorldReplacementEntryGuard.completePlayer(world, current, playerId);
+            if (updated.isPresent() && updated.get().pendingPlayers().isEmpty()) {
+                retire(world, current);
+            }
+        } catch (IOException | RuntimeException failure) {
+            ModdedIrisLog.error("Iris could not record the safe Overworld replacement entry of {}", playerId, failure);
+        }
+    }
+
+    private static synchronized void retire(Path world, UUID current) {
+        try {
+            if (WorldReplacementEntryGuard.retireIfEmpty(world, current)) {
+                ModdedIrisLog.info("Iris retired the Overworld replacement entry marker: every known player entered safely");
+                if (world.equals(guardedWorld)) {
+                    clear();
+                }
+            }
+        } catch (IOException | RuntimeException failure) {
+            ModdedIrisLog.error("Iris could not retire the Overworld replacement entry marker under {}", world, failure);
+        }
+    }
+}

adapters/modded-common/src/main/java/art/arcane/iris/modded/ModdedReplacementReconciler.java

@@ -0,0 +1,449 @@
+/*
+ * Iris is a World Generator for Minecraft Servers
+ * Copyright (c) 2026 Arcane Arts (Volmit Software)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package art.arcane.iris.modded;
+
+import art.arcane.iris.spi.IrisPlatforms;
+import art.arcane.iris.world.history.GenerationEpoch;
+import art.arcane.iris.world.history.GenerationHistory;
+import art.arcane.iris.world.history.GenerationHistoryPaths;
+import art.arcane.iris.world.lifecycle.WorldReplacementEntryGuard;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeModdedServer;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeWorldGenerators;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeWorldPaths;
+import art.arcane.volmlib.nativelib.terrain.NativeWorld;
+import art.arcane.volmlib.util.json.JSONObject;
+
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.LinkOption;
+import java.nio.file.Path;
+import java.nio.file.StandardCopyOption;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.OptionalLong;
+import java.util.Set;
+import java.util.TreeMap;
+import java.util.TreeSet;
+import java.util.UUID;
+import java.util.function.Predicate;
+
+public final class ModdedReplacementReconciler {
+    public static final String OVERWORLD = "minecraft:overworld";
+    private static final String STATE_FILE = "data/irisworldgen/dimension-replacements.json";
+    private static final String APPLIED = "replacements";
+    private static final String PENDING = "pending";
+    private static final String IRIS_WORLD_NAMESPACE = "irisworldgen:";
+
+    private ModdedReplacementReconciler() {
+    }
+
+    public static void reconcileEarly() {
+        try {
+            ModdedModConfig config = ModdedModConfig.get();
+            Map<String, ModdedDimensionReplacement> configured = ModdedDimensionReplacements.configured();
+            Path worldRoot = MainWorldService.configuredWorldRootIfPresent();
+            if (worldRoot == null) {
+                if (!configured.isEmpty()) {
+                    ModdedIrisLog.info("Iris dimension replacements {} apply to a new world; nothing to move aside",
+                            configured.keySet());
+                }
+                return;
+            }
+            Path recoveryParent = ModdedEngineBootstrap.loader().configDir().resolve("irisworldgen");
+            Path packsRoot = IrisPlatforms.get().packsFolderNoCreate().toPath();
+            Result result = reconcile(new Request(worldRoot, configured, config.replacementProblems(),
+                    (ModdedDimensionReplacement replacement) -> ModdedDimensionReplacements.installed(replacement, packsRoot),
+                    recoveryParent, ModdedDimensionReplacements.replaceableLevels(worldRoot, configured)));
+            if (!result.adoptedLevels().isEmpty()) {
+                ModdedIrisLog.info("Iris kept the existing terrain of {}: its Iris generation history already uses the configured pack and seed; the replacement is recorded once the level generates from it",
+                        result.adoptedLevels());
+            }
+            if (!result.replacedWorlds().isEmpty()) {
+                ModdedIrisLog.warn("Iris replaced the Iris worlds {} from their staged packs", result.replacedWorlds());
+            }
+            if (result.quarantinedLevels().isEmpty() && result.replacedWorlds().isEmpty()) {
+                return;
+            }
+            ModdedIrisLog.warn("Iris dimension replacement changed for {}: {}", movedLevels(result),
+                    result.recovery() == null
+                            ? "no existing chunk data to move aside"
+                            : "moved their chunk, entity, POI, and Iris Mantle data to " + result.recovery()
+                            + " so they regenerate (player data kept)");
+        } catch (Throwable failure) {
+            ModdedIrisLog.error("Iris dimension replacement reconciliation failed", failure);
+            throw new IllegalStateException("Iris refused startup after dimension replacement reconciliation failed", failure);
+        }
+    }
+
+    public static void recordApplied(NativeModdedServer server) {
+        Optional<Path> worldRoot = NativeWorldPaths.root(server);
+        if (worldRoot.isEmpty()) {
+            return;
+        }
+        try {
+            recordApplied(worldRoot.get(), ModdedDimensionReplacements.configured(),
+                    (String levelKey) -> liveLevel(server, levelKey));
+        } catch (IOException | RuntimeException failure) {
+            ModdedIrisLog.error("Iris is stopping the server because it could not record the applied dimension replacements under {}; an unrecorded replacement would be moved aside again on the next start",
+                    worldRoot.get(), failure);
+            server.halt(false);
+        }
+    }
+
+    public static void stopUnpublishedEngines(NativeModdedServer server) {
+        for (String levelKey : ModdedWorldEngines.evictUnpublished(server,
+                ModdedModConfig.get().dimensionReplacements().keySet())) {
+            ModdedIrisLog.error("Iris stopped the engine it started for {}: a mod replaced that level with its own chunk generator while the server started",
+                    levelKey);
+        }
+    }
+
+    static synchronized Map<String, ModdedDimensionReplacement> recordApplied(Path worldRoot,
+                                                                Map<String, ModdedDimensionReplacement> configured,
+                                                                LiveLevels levels) throws IOException {
+        State state = readState(worldRoot);
+        Map<String, ModdedDimensionReplacement> recorded = new TreeMap<>(state.applied());
+        for (ModdedDimensionReplacement replacement : new TreeMap<>(configured).values()) {
+            Optional<LiveLevel> live = levels.level(replacement.levelKey());
+            if (live.isPresent() && live.get().generates(replacement)) {
+                recorded.put(replacement.levelKey(), replacement.withSeed(live.get().seed()));
+                continue;
+            }
+            if (live.isPresent() && !live.get().iris()) {
+                recorded.remove(replacement.levelKey());
+                ModdedIrisLog.error("Iris replacement of {} is configured but the loaded level uses another chunk generator; a mod creates that level while the server runs, so Iris cannot replace it. Remove its dimensionReplacements entry from modded.json",
+                        replacement.levelKey());
+                continue;
+            }
+            ModdedIrisLog.warn("Iris replacement of {} is configured but the level does not generate from {}{}; it stays unapplied",
+                    replacement.levelKey(), replacement.packRef(),
+                    replacement.seed().isPresent() ? " with seed " + replacement.seed().getAsLong() : "");
+        }
+        if (!recorded.equals(state.applied())) {
+            writeState(worldRoot, new State(recorded, state.pending()));
+        }
+        return Map.copyOf(recorded);
+    }
+
+    static synchronized Result reconcile(Request request) throws IOException {
+        Path worldRoot = request.worldRoot();
+        requireReadableConfig(worldRoot, request.configProblems());
+        State state = readState(worldRoot);
+        Map<String, ModdedDimensionReplacement> applied = state.applied();
+        Set<String> refreshed = new TreeSet<>();
+        boolean irisWorldsPending = false;
+        for (String level : state.pending().keySet()) {
+            if (level.startsWith(IRIS_WORLD_NAMESPACE)) {
+                irisWorldsPending = true;
+            } else if (request.configured().containsKey(level)) {
+                refreshed.add(level);
+            }
+        }
+        Set<String> changed = new TreeSet<>(ModdedDimensionReplacements.changedLevels(applied, request.configured()));
+        changed.addAll(refreshed);
+        Map<String, ModdedDimensionReplacement> recorded = new TreeMap<>(applied);
+        Set<String> quarantined = new TreeSet<>();
+        Set<String> adopted = new TreeSet<>();
+        Set<String> unreplaceable = new TreeSet<>();
+        for (String level : changed) {
+            ModdedDimensionReplacement replacement = request.configured().get(level);
+            if (replacement == null) {
+                recorded.remove(level);
+                quarantined.add(level);
+                continue;
+            }
+            if (!request.levels().replaceable(level)) {
+                unreplaceable.add(level);
+                ModdedIrisLog.error(ModdedDimensionReplacements.unreplaceableReason(level, request.levels())
+                        + " Remove its dimensionReplacements entry from modded.json.");
+                continue;
+            }
+            Path storage = replacement.storageFolder(worldRoot);
+            boolean keepHistory = !refreshed.contains(level) && matchingHistorySeed(storage, replacement).isPresent();
+            if (keepHistory) {
+                adopted.add(level);
+            } else if (request.installed().test(replacement)) {
+                quarantined.add(level);
+            } else {
+                refuseOrSkipUninstalled(worldRoot, applied, replacement);
+            }
+        }
+        List<ModdedDimensionRegistryStore.PersistentDimension> registry = irisWorldsPending
+                ? ModdedDimensionRegistryStore.loadWorldRoot(worldRoot)
+                : List.of();
+        Map<String, ModdedDimensionReplacement> replacedWorlds = new TreeMap<>();
+        for (ModdedDimensionReplacement pending : state.pending().values()) {
+            if (!pending.levelKey().startsWith(IRIS_WORLD_NAMESPACE)) {
+                continue;
+            }
+            if (registered(registry, pending.levelKey())) {
+                replacedWorlds.put(pending.levelKey(), pending);
+            } else {
+                ModdedIrisLog.warn("Iris dropped the staged replacement of {}: the Iris world is no longer registered",
+                        pending.levelKey());
+            }
+        }
+        List<Path> sources = new ArrayList<>();
+        for (String level : quarantined) {
+            addChunkData(sources, ModdedDimensionReplacement.storageFolder(worldRoot, level));
+        }
+        for (String level : replacedWorlds.keySet()) {
+            addChunkData(sources, ModdedDimensionReplacement.storageFolder(worldRoot, level));
+        }
+        Path recovery = request.recoveryParent().resolve("replacement-recovery-" + UUID.randomUUID());
+        List<Path> moved = sources.isEmpty() ? List.of() : ModdedWorldQuarantine.move(worldRoot, sources, recovery);
+        if (quarantined.contains(OVERWORLD)) {
+            WorldReplacementEntryGuard.stage(worldRoot, ModdedDimensionReplacement.storageFolder(worldRoot, OVERWORLD),
+                    UUID.randomUUID());
+        }
+        if (!replacedWorlds.isEmpty()) {
+            ModdedDimensionRegistryStore.writeWorldRoot(worldRoot, repointed(registry, replacedWorlds));
+        }
+        State reconciled = new State(recorded, Map.of());
+        if (!reconciled.equals(state)) {
+            writeState(worldRoot, reconciled);
+        }
+        return new Result(Set.copyOf(quarantined), Set.copyOf(adopted), Set.copyOf(replacedWorlds.keySet()),
+                Set.copyOf(unreplaceable), moved.isEmpty() ? null : recovery);
+    }
+
+    public static boolean pending(Path worldRoot, String levelKey, Map<String, ModdedDimensionReplacement> configured)
+            throws IOException {
+        State state = readState(worldRoot);
+        if (state.pending().containsKey(levelKey)) {
+            return true;
+        }
+        ModdedDimensionReplacement replacement = configured.get(levelKey);
+        return replacement != null && !ModdedDimensionReplacements.matches(state.applied().get(levelKey), replacement);
+    }
+
+    public static Optional<ModdedDimensionReplacement> applied(Path worldRoot, String levelKey) throws IOException {
+        return Optional.ofNullable(readState(worldRoot).applied().get(levelKey));
+    }
+
+    public static synchronized void stagePending(Path worldRoot, ModdedDimensionReplacement replacement) throws IOException {
+        if (replacement.seed().isEmpty()) {
+            throw new IllegalArgumentException("A staged replacement needs its effective seed: " + replacement.levelKey());
+        }
+        State state = readState(worldRoot);
+        Map<String, ModdedDimensionReplacement> pending = new TreeMap<>(state.pending());
+        pending.put(replacement.levelKey(), replacement);
+        writeState(worldRoot, new State(state.applied(), pending));
+    }
+
+    public static synchronized boolean cancelPending(Path worldRoot, String levelKey) throws IOException {
+        State state = readState(worldRoot);
+        Map<String, ModdedDimensionReplacement> pending = new TreeMap<>(state.pending());
+        if (pending.remove(levelKey) == null) {
+            return false;
+        }
+        writeState(worldRoot, new State(state.applied(), pending));
+        return true;
+    }
+
+    static boolean hasReplacementRecord(Path worldRoot, String levelKey) throws IOException {
+        return readState(worldRoot).applied().containsKey(levelKey) || hasGenerationHistory(
+                ModdedDimensionReplacement.storageFolder(worldRoot, levelKey));
+    }
+
+    private static Set<String> movedLevels(Result result) {
+        Set<String> levels = new TreeSet<>(result.quarantinedLevels());
+        levels.addAll(result.replacedWorlds());
+        return levels;
+    }
+
+    private static void addChunkData(List<Path> sources, Path storage) {
+        for (String folder : ModdedDimensionStorage.chunkDataFolders()) {
+            sources.add(storage.resolve(folder));
+        }
+    }
+
+    private static boolean registered(List<ModdedDimensionRegistryStore.PersistentDimension> registry, String levelKey) {
+        for (ModdedDimensionRegistryStore.PersistentDimension dimension : registry) {
+            if (dimension.id().equals(levelKey)) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    private static List<ModdedDimensionRegistryStore.PersistentDimension> repointed(
+            List<ModdedDimensionRegistryStore.PersistentDimension> registry,
+            Map<String, ModdedDimensionReplacement> replacedWorlds) {
+        List<ModdedDimensionRegistryStore.PersistentDimension> updated = new ArrayList<>(registry.size());
+        for (ModdedDimensionRegistryStore.PersistentDimension dimension : registry) {
+            ModdedDimensionReplacement replacement = replacedWorlds.get(dimension.id());
+            updated.add(replacement == null ? dimension : new ModdedDimensionRegistryStore.PersistentDimension(
+                    dimension.id(), replacement.pack(), replacement.packDimension(), replacement.seed().getAsLong()));
+        }
+        return updated;
+    }
+
+    private static void refuseOrSkipUninstalled(Path worldRoot, Map<String, ModdedDimensionReplacement> applied,
+                                                ModdedDimensionReplacement replacement) throws IOException {
+        if (applied.containsKey(replacement.levelKey()) || hasGenerationHistory(replacement.storageFolder(worldRoot))) {
+            throw new IOException("Iris refused to switch the replacement of " + replacement.levelKey() + " to "
+                    + replacement.packRef() + ": pack '" + replacement.pack() + "' dimension '" + replacement.packDimension()
+                    + "' is not installed, and the level already has an applied replacement or Iris generation history. Install the pack or restore the previous replacement.");
+        }
+        ModdedIrisLog.error("Iris left {} untouched: its replacement pack '{}' dimension '{}' is not installed",
+                replacement.levelKey(), replacement.pack(), replacement.packDimension());
+    }
+
+    private static boolean hasGenerationHistory(Path storage) {
+        return Files.exists(GenerationHistoryPaths.forDimension(storage).generationRoot(), LinkOption.NOFOLLOW_LINKS);
+    }
+
+    static OptionalLong matchingHistorySeed(Path storage, ModdedDimensionReplacement replacement) throws IOException {
+        if (!hasGenerationHistory(storage)) {
+            return OptionalLong.empty();
+        }
+        GenerationEpoch epoch = GenerationHistory.inspectPacks(storage).manifest().activeEpoch();
+        if (replacement.seed().isPresent() && replacement.seed().getAsLong() != epoch.worldSeed()) {
+            return OptionalLong.empty();
+        }
+        GenerationEpoch.DimensionContract contract = epoch.dimensionContract();
+        if (!contract.dimensionKey().equals(replacement.packDimension())) {
+            return OptionalLong.empty();
+        }
+        Optional<ModdedWorldgenIds.ScopedDimension> scoped = ModdedWorldgenIds.scopedDimensionType(contract.dimensionTypeKey());
+        boolean samePack = scoped.isPresent()
+                ? scoped.get().equals(new ModdedWorldgenIds.ScopedDimension(replacement.pack(), replacement.packDimension()))
+                : aliasMatches(epoch, contract, replacement);
+        return samePack ? OptionalLong.of(epoch.worldSeed()) : OptionalLong.empty();
+    }
+
+    private static boolean aliasMatches(GenerationEpoch epoch, GenerationEpoch.DimensionContract contract,
+                                        ModdedDimensionReplacement replacement) {
+        Set<String> packs = ModdedWorldgenIds.aliasPacks(epoch.registryContract(), contract.dimensionKey());
+        return packs.isEmpty() || packs.contains(replacement.pack());
+    }
+
+    private static Optional<LiveLevel> liveLevel(NativeModdedServer server, String levelKey) {
+        NativeWorld world = server.world(levelKey);
+        if (world == null) {
+            return Optional.empty();
+        }
+        IrisModdedChunkGenerator generator = NativeWorldGenerators.find(world, IrisModdedChunkGenerator.class);
+        if (generator == null) {
+            return Optional.of(new LiveLevel(false, "", 0L));
+        }
+        return Optional.of(new LiveLevel(true, generator.dimensionKey(), generator.visibleBiomeSeed()));
+    }
+
+    private static void requireReadableConfig(Path worldRoot, List<String> configProblems) throws IOException {
+        if (configProblems.isEmpty()) {
+            return;
+        }
+        Path state = worldRoot.resolve(STATE_FILE);
+        if (!Files.exists(state)) {
+            return;
+        }
+        throw new IOException("Iris refused to reconcile dimension replacements because the configured replacements are unreadable while "
+                + state + " records applied replacements: " + String.join("; ", configProblems)
+                + ". Fix the modded config so every replacement entry is valid; Iris never treats an unreadable replacement as removed.");
+    }
+
+    static State readState(Path worldRoot) throws IOException {
+        Path state = worldRoot.resolve(STATE_FILE);
+        if (!Files.isRegularFile(state)) {
+            return State.EMPTY;
+        }
+        JSONObject json = new JSONObject(Files.readString(state, StandardCharsets.UTF_8));
+        return new State(readSection(json, APPLIED, state), readSection(json, PENDING, state));
+    }
+
+    static void writeState(Path worldRoot, State replacements) throws IOException {
+        Path state = worldRoot.resolve(STATE_FILE);
+        Files.createDirectories(state.getParent());
+        JSONObject json = new JSONObject();
+        json.put(APPLIED, section(replacements.applied()));
+        json.put(PENDING, section(replacements.pending()));
+        Path temporary = state.resolveSibling(state.getFileName() + ".tmp-" + UUID.randomUUID());
+        Files.writeString(temporary, json.toString(2), StandardCharsets.UTF_8);
+        try {
+            Files.move(temporary, state, StandardCopyOption.REPLACE_EXISTING, StandardCopyOption.ATOMIC_MOVE);
+        } catch (IOException atomicUnsupported) {
+            Files.move(temporary, state, StandardCopyOption.REPLACE_EXISTING);
+        }
+    }
+
+    private static Map<String, ModdedDimensionReplacement> readSection(JSONObject json, String name, Path state)
+            throws IOException {
+        JSONObject section = json.optJSONObject(name);
+        if (section == null) {
+            return Map.of();
+        }
+        Map<String, ModdedDimensionReplacement> replacements = new TreeMap<>();
+        for (String level : section.keySet()) {
+            try {
+                replacements.put(level, ModdedDimensionReplacement.fromJson(level, section.opt(level)));
+            } catch (IllegalArgumentException invalid) {
+                throw new IOException("Iris could not read replacement '" + level + "' in " + state + ": "
+                        + invalid.getMessage(), invalid);
+            }
+        }
+        return Map.copyOf(replacements);
+    }
+
+    private static JSONObject section(Map<String, ModdedDimensionReplacement> replacements) {
+        JSONObject section = new JSONObject();
+        for (Map.Entry<String, ModdedDimensionReplacement> entry : new TreeMap<>(replacements).entrySet()) {
+            section.put(entry.getKey(), entry.getValue().toJson());
+        }
+        return section;
+    }
+
+    interface LiveLevels {
+        Optional<LiveLevel> level(String levelKey);
+    }
+
+    record LiveLevel(boolean iris, String packRef, long seed) {
+        LiveLevel {
+            Objects.requireNonNull(packRef, "packRef");
+        }
+
+        boolean generates(ModdedDimensionReplacement replacement) {
+            return iris && packRef.equals(replacement.packRef())
+                    && (replacement.seed().isEmpty() || replacement.seed().getAsLong() == seed);
+        }
+    }
+
+    record State(Map<String, ModdedDimensionReplacement> applied, Map<String, ModdedDimensionReplacement> pending) {
+        static final State EMPTY = new State(Map.of(), Map.of());
+
+        State {
+            applied = Map.copyOf(applied);
+            pending = Map.copyOf(pending);
+        }
+    }
+
+    record Request(Path worldRoot, Map<String, ModdedDimensionReplacement> configured, List<String> configProblems,
+                   Predicate<ModdedDimensionReplacement> installed, Path recoveryParent,
+                   ModdedDimensionReplacements.ReplaceableLevels levels) {
+    }
+
+    record Result(Set<String> quarantinedLevels, Set<String> adoptedLevels, Set<String> replacedWorlds,
+                  Set<String> unreplaceableLevels, Path recovery) {
+    }
+}

adapters/modded-common/src/main/java/art/arcane/iris/modded/ModdedStartup.java

@@ -27,6 +27,7 @@ import art.arcane.iris.pack.PackValidationRegistry;
 import art.arcane.iris.pack.PackValidationCache;
 import art.arcane.iris.pack.PackValidationResult;
 import art.arcane.iris.pack.PackValidator;
+import art.arcane.iris.generation.runtime.Engine;
 import art.arcane.iris.modded.command.ModdedPackCommands;
 import art.arcane.iris.spi.IrisPlatforms;
 import art.arcane.iris.world.safeguard.GenerationRefusalNotice;
@@ -39,19 +40,29 @@ import java.util.List;
 import java.util.Map;
 import java.util.concurrent.CopyOnWriteArrayList;
 import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicReference;
 
 public final class ModdedStartup {
     private static final int COMPAT_BOOT_KEY_CAP = 3;
     private static final AtomicBoolean PREPARED = new AtomicBoolean(false);
     private static final AtomicBoolean STARTED = new AtomicBoolean(false);
+    private static final AtomicBoolean RESTORE_BEGUN = new AtomicBoolean(false);
+    private static final AtomicReference<ModdedDimensionInjection<ModdedWorldEngines.PreparedPack, ModdedDimensionManager.PendingInjection, Engine>> RESTORE =
+            new AtomicReference<>();
     private static final List<String> DIMENSION_FAILURES = new CopyOnWriteArrayList<>();
 
     private ModdedStartup() {
     }
 
     public static void reset() {
+        ModdedDimensionInjection<ModdedWorldEngines.PreparedPack, ModdedDimensionManager.PendingInjection, Engine> restore =
+                RESTORE.getAndSet(null);
+        if (restore != null) {
+            restore.close();
+        }
         PREPARED.set(false);
         STARTED.set(false);
+        RESTORE_BEGUN.set(false);
         DIMENSION_FAILURES.clear();
     }
 
@@ -62,6 +73,24 @@ public final class ModdedStartup {
         validateAllPacks();
     }
 
+    public static void prepareDimensionRestore(NativeModdedServer server) {
+        if (server == null || !RESTORE_BEGUN.compareAndSet(false, true)) {
+            return;
+        }
+        List<ModdedDimensionRegistryStore.PersistentDimension> dimensions =
+                ModdedDimensionRegistryStore.loadForStartup(server);
+        if (dimensions.isEmpty()) {
+            return;
+        }
+        long startedAt = System.currentTimeMillis();
+        ModdedDimensionInjection<ModdedWorldEngines.PreparedPack, ModdedDimensionManager.PendingInjection, Engine> restore =
+                ModdedDimensionInjection.start(dimensions, new PersistentRestoreSteps(server));
+        RESTORE.set(restore);
+        restore.awaitPreparations();
+        ModdedIrisLog.info("Iris prepared {} persistent dimension(s) during world load in {}ms",
+                dimensions.size(), System.currentTimeMillis() - startedAt);
+    }
+
     /**
      * Boot trigger for the forced datapack. Runs on its own daemon thread rather than the Iris scheduler:
      * ModdedEngineBootstrap.start clears the async queue at SERVER_STARTING, which would silently drop this
@@ -91,7 +120,6 @@ public final class ModdedStartup {
         }
         ModdedForcedDatapack.verifyInjected();
         ModdedMixinAudit.runOnce();
-        reinjectPersistentDimensions(server);
 
         ModdedScheduler scheduler = ModdedEngineBootstrap.schedulerOrNull();
         if (scheduler == null) {
@@ -219,38 +247,46 @@ public final class ModdedStartup {
     }
 
     static void reinjectPersistentDimensions(NativeModdedServer server) {
-        List<ModdedDimensionRegistryStore.PersistentDimension> dimensions =
-                ModdedDimensionRegistryStore.loadForStartup(server);
-        if (dimensions.isEmpty()) {
+        prepareDimensionRestore(server);
+        ModdedDimensionInjection<ModdedWorldEngines.PreparedPack, ModdedDimensionManager.PendingInjection, Engine> restore =
+                RESTORE.getAndSet(null);
+        if (restore == null) {
             return;
         }
+        finishDimensionRestore(restore);
+    }
+
+    static void finishDimensionRestore(ModdedDimensionInjection<?, ?, ?> restore) {
+        long startedAt = System.currentTimeMillis();
+        List<ModdedDimensionInjection.Result> results;
+        try (restore) {
+            results = restore.finish();
+        }
+        long waited = System.currentTimeMillis() - startedAt;
         int injected = 0;
         int index = 0;
-        long startedAt = System.currentTimeMillis();
-        for (ModdedDimensionRegistryStore.PersistentDimension dimension : dimensions) {
+        OutOfMemoryError outOfMemory = null;
+        for (ModdedDimensionInjection.Result result : results) {
             index++;
-            long dimensionStartedAt = System.currentTimeMillis();
-            try {
-                ModdedDimensionManager.restorePersistent(
-                        server,
-                        dimension.id(),
-                        dimension.pack(),
-                        dimension.dimension(),
-                        dimension.seed()
-                );
+            ModdedDimensionRegistryStore.PersistentDimension dimension = result.dimension();
+            Throwable failure = result.failure();
+            if (failure == null) {
                 injected++;
-                ModdedIrisLog.info("Iris re-injected {}/{} '{}' (pack={} dim={}) in {}ms",
-                        index, dimensions.size(), dimension.id(), dimension.pack(), dimension.dimension(),
-                        System.currentTimeMillis() - dimensionStartedAt);
-            } catch (Throwable e) {
-                reportDimensionFailure(dimension, e);
-                if (e instanceof OutOfMemoryError outOfMemory) {
-                    throw outOfMemory;
-                }
+                ModdedIrisLog.info("Iris re-injected {}/{} '{}' (pack={} dim={}): prepared {}ms, engine {}ms",
+                        index, results.size(), dimension.id(), dimension.pack(), dimension.dimension(),
+                        result.preparedMillis(), result.builtMillis());
+                continue;
+            }
+            reportDimensionFailure(dimension, failure);
+            if (failure instanceof OutOfMemoryError fatal && outOfMemory == null) {
+                outOfMemory = fatal;
             }
         }
-        ModdedIrisLog.info("Iris re-injected {}/{} persistent dimension(s) at startup in {}ms",
-                injected, dimensions.size(), System.currentTimeMillis() - startedAt);
+        ModdedIrisLog.info("Iris re-injected {}/{} persistent dimension(s) at startup; server thread waited {}ms",
+                injected, results.size(), waited);
+        if (outOfMemory != null) {
+            throw outOfMemory;
+        }
     }
 
     private static void reportDimensionFailure(ModdedDimensionRegistryStore.PersistentDimension dimension, Throwable failure) {
@@ -304,4 +340,44 @@ public final class ModdedStartup {
         }
     }
 
+    private record PersistentRestoreSteps(NativeModdedServer server)
+            implements ModdedDimensionInjection.Steps<ModdedWorldEngines.PreparedPack, ModdedDimensionManager.PendingInjection, Engine> {
+        @Override
+        public ModdedWorldEngines.PreparedPack prepare(ModdedDimensionRegistryStore.PersistentDimension dimension) {
+            return ModdedWorldEngines.preparePersistent(server, dimension);
+        }
+
+        @Override
+        public ModdedDimensionManager.PendingInjection begin(
+                ModdedDimensionRegistryStore.PersistentDimension dimension,
+                ModdedWorldEngines.PreparedPack prepared
+        ) {
+            return ModdedDimensionManager.beginInjection(
+                    server, dimension, prepared.active(), ModdedGenerationMode.PERSISTENT_RESTORE);
+        }
+
+        @Override
+        public Engine build(ModdedDimensionManager.PendingInjection level, ModdedWorldEngines.PreparedPack prepared) {
+            if (level.present()) {
+                prepared.close();
+                return null;
+            }
+            return ModdedWorldEngines.createPrepared(level.handle().level(), level.handle().seed(), prepared);
+        }
+
+        @Override
+        public void complete(ModdedDimensionManager.PendingInjection level, Engine engine) {
+            ModdedDimensionManager.completeInjection(server, level, engine);
+        }
+
+        @Override
+        public void abandon(ModdedDimensionManager.PendingInjection level, Engine engine, Throwable failure) {
+            ModdedDimensionManager.abandonInjection(server, level, engine, failure);
+        }
+
+        @Override
+        public void discard(ModdedWorldEngines.PreparedPack prepared) {
+            prepared.close();
+        }
+    }
 }

adapters/modded-common/src/main/java/art/arcane/iris/modded/ModdedWorldEngines.java

@@ -20,6 +20,7 @@ package art.arcane.iris.modded;
 
 import art.arcane.volmlib.nativelib.terrain.NativeWorld;
 
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeDimensionRuntime;
 import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeModdedServer;
 import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeWorldDimensions;
 import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeWorldGenerators;
@@ -31,6 +32,7 @@ import art.arcane.iris.generation.runtime.IrisEngine;
 import art.arcane.iris.generation.runtime.Engine;
 import art.arcane.iris.generation.runtime.EngineTarget;
 import art.arcane.iris.world.history.GenerationActivation;
+import art.arcane.iris.world.history.GenerationAdmission;
 import art.arcane.iris.world.history.GenerationEpoch;
 import art.arcane.iris.world.history.GenerationEpochContractFactory;
 import art.arcane.iris.world.history.GenerationHistory;
@@ -48,8 +50,10 @@ import java.io.File;
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.List;
 import java.util.Map;
 import java.util.Objects;
+import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
 
 public final class ModdedWorldEngines {
@@ -91,6 +95,19 @@ public final class ModdedWorldEngines {
         }
     }
 
+    static List<String> evictUnpublished(NativeModdedServer server, Set<String> levelKeys) {
+        List<String> evicted = new ArrayList<>();
+        for (NativeWorld level : new ArrayList<>(ENGINES.keySet())) {
+            if (!levelKeys.contains(level.name())
+                    || NativeDimensionRuntime.sameWorld(server.world(level.name()), level)) {
+                continue;
+            }
+            evict(level);
+            evicted.add(level.name());
+        }
+        return evicted;
+    }
+
     static void evictOrThrow(NativeWorld level) {
         Engine[] removed = new Engine[1];
         ENGINES.computeIfPresent(level, (NativeWorld ignored, Engine current) -> {
@@ -128,6 +145,60 @@ public final class ModdedWorldEngines {
         });
     }
 
+    static PreparedPack preparePersistent(
+            NativeModdedServer server,
+            ModdedDimensionRegistryStore.PersistentDimension dimension
+    ) {
+        ModdedEngineBootstrap.bind();
+        return prepared(ModdedGenerationHistoryStorage.prepareRestore(
+                server,
+                dimension.id(),
+                dimension.pack(),
+                dimension.dimension(),
+                dimension.seed()
+        ));
+    }
+
+    static PreparedPack prepareCreated(
+            NativeModdedServer server,
+            ModdedDimensionRegistryStore.PersistentDimension dimension
+    ) {
+        ModdedEngineBootstrap.bind();
+        return prepared(ModdedGenerationHistoryStorage.prepareCreate(
+                server,
+                dimension.id(),
+                dimension.pack(),
+                dimension.dimension(),
+                dimension.seed()
+        ));
+    }
+
+    private static PreparedPack prepared(ModdedGenerationHistoryStorage.PreparedHistory prepared) {
+        try {
+            ModdedDimensionMetadata.warmConfiguredPack(prepared.active().packRoot().toFile(), prepared.active().dimensionKey());
+            return new PreparedPack(prepared.active(), prepared.lease(), loadPack(prepared.active()));
+        } catch (RuntimeException | Error failure) {
+            prepared.lease().close();
+            throw failure;
+        }
+    }
+
+    static Engine createPrepared(NativeWorld level, long seedOverride, PreparedPack prepared) {
+        ModdedEngineBootstrap.bind();
+        long seed = seedOverride == Long.MIN_VALUE ? level.seed() : seedOverride;
+        try (prepared) {
+            return attachHistoryEngine(level, seed, prepared.active(), prepared.take());
+        } catch (IOException failure) {
+            throw new IllegalStateException("Iris generation history could not initialize runtime routing for '"
+                    + level.name() + "'.", failure);
+        }
+    }
+
+    static void installPrepared(NativeWorld level, Engine engine) {
+        applyWorldBoundary(level, engine);
+        installReplacement(level, engine);
+    }
+
     static void closeUnregistered(Engine engine) {
         close(engine);
         ENGINES.entrySet().removeIf((Map.Entry<NativeWorld, Engine> entry) -> entry.getValue() == engine);
@@ -142,9 +213,13 @@ public final class ModdedWorldEngines {
             ModdedGenerationMode generationMode
     ) {
         Engine engine = create(level, pack, dimensionKey, seedOverride, generationMode);
+        applyWorldBoundary(level, engine);
+        return engine;
+    }
+
+    private static void applyWorldBoundary(NativeWorld level, Engine engine) {
         try {
             engine.getPlatformHooks().applyWorldBoundary(engine);
-            return engine;
         } catch (Throwable failure) {
             try {
                 close(engine);
@@ -197,57 +272,63 @@ public final class ModdedWorldEngines {
         GenerationHistory history = opened.history();
         try (GenerationAdmission.RuntimeLease startupAdmission = history.retainRuntime()) {
             history.prepareCurrentGenerator(IrisSettings.get().getGenerator().getGenerationTransitionWidthBlocks());
-            opened = ModdedGenerationHistoryStorage.resolveActive(history);
-            long openedActivationId = history.activeActivation().activationId();
-            IrisEngine candidate = buildEngine(level, seed, opened);
-            boolean ready = false;
-            try {
-                GenerationHistoryRuntimeRouter router = candidate.attachGenerationHistory(
+            ModdedGenerationHistoryStorage.ActivePack active = ModdedGenerationHistoryStorage.resolveActive(history, null);
+            return attachHistoryEngine(level, seed, active, loadPack(active));
+        }
+    }
+
+    private static IrisEngine attachHistoryEngine(
+            NativeWorld level,
+            long seed,
+            ModdedGenerationHistoryStorage.ActivePack active,
+            LoadedPack loaded
+    ) throws IOException {
+        GenerationHistory history = active.history();
+        long openedActivationId = history.activeActivation().activationId();
+        IrisEngine candidate = buildEngine(level, seed, active, loaded);
+        boolean ready = false;
+        try {
+            GenerationHistoryRuntimeRouter router = candidate.attachGenerationHistory(
+                    history,
+                    IrisBoundarySignatureSampler.INSTANCE,
+                    IrisSettings.get().getGenerator().getGenerationTransitionWidthBlocks()
+            );
+            router.preloadActiveRuntimes();
+            if (history.activeActivation().activationId() != openedActivationId) {
+                close(candidate);
+                ModdedGenerationHistoryStorage.ActivePack promoted =
+                        ModdedGenerationHistoryStorage.resolveActive(history, null);
+                candidate = buildEngine(level, seed, promoted, loadPack(promoted));
+                router = GenerationHistoryRuntimeRouter.attach(
+                        candidate,
                         history,
-                        IrisBoundarySignatureSampler.INSTANCE,
-                        IrisSettings.get().getGenerator().getGenerationTransitionWidthBlocks()
+                        IrisBoundarySignatureSampler.INSTANCE
                 );
                 router.preloadActiveRuntimes();
-                if (history.activeActivation().activationId() != openedActivationId) {
-                    close(candidate);
-                    ModdedGenerationHistoryStorage.ActivePack promoted =
-                            ModdedGenerationHistoryStorage.resolveActive(history);
-                    candidate = buildEngine(level, seed, promoted);
-                    router = GenerationHistoryRuntimeRouter.attach(
-                            candidate,
-                            history,
-                            IrisBoundarySignatureSampler.INSTANCE
-                    );
-                    router.preloadActiveRuntimes();
-                }
-                requireReady(candidate, level, ModdedGenerationMode.PERSISTENT_RESTORE);
-                ready = true;
-                ModdedIrisLog.info("Iris engine up for {}: pack={} dim={} seed={} height={}..{} activation={}",
-                        level.name(),
-                        candidate.getData().getDataFolder().getAbsolutePath(),
-                        candidate.getDimension().getLoadKey(),
-                        seed,
-                        candidate.getDimension().getMinHeight(),
-                        candidate.getDimension().getMaxHeight(),
-                        history.activeActivation().activationId());
-                return candidate;
-            } finally {
-                if (!ready) {
-                    close(candidate);
-                }
+            }
+            requireReady(candidate, level, ModdedGenerationMode.PERSISTENT_RESTORE);
+            ready = true;
+            ModdedIrisLog.info("Iris engine up for {}: pack={} dim={} seed={} height={}..{} activation={}",
+                    level.name(),
+                    candidate.getData().getDataFolder().getAbsolutePath(),
+                    candidate.getDimension().getLoadKey(),
+                    seed,
+                    candidate.getDimension().getMinHeight(),
+                    candidate.getDimension().getMaxHeight(),
+                    history.activeActivation().activationId());
+            return candidate;
+        } finally {
+            if (!ready) {
+                close(candidate);
             }
         }
     }
 
-    private static IrisEngine buildEngine(
-            NativeWorld level,
-            long seed,
-            ModdedGenerationHistoryStorage.ActivePack active
-    ) throws IOException {
+    private static LoadedPack loadPack(ModdedGenerationHistoryStorage.ActivePack active) {
         File packDir = active.packRoot().toFile();
         PackValidationRegistry.requireLoadable(active.packRoot());
         IrisData data = IrisData.openRuntime(packDir);
-        boolean runtimeOwnsData = false;
+        boolean loaded = false;
         try {
             IrisDimension dimension = data.getDimensionLoader().load(active.dimensionKey());
             if (dimension == null) {
@@ -256,7 +337,26 @@ public final class ModdedWorldEngines {
                 throw new IllegalStateException("Iris dimension '" + active.dimensionKey()
                         + "' missing from immutable pack " + packDir.getAbsolutePath());
             }
+            data.generationPackFingerprint();
+            loaded = true;
+            return new LoadedPack(data, dimension);
+        } finally {
+            if (!loaded) {
+                data.close();
+            }
+        }
+    }
 
+    private static IrisEngine buildEngine(
+            NativeWorld level,
+            long seed,
+            ModdedGenerationHistoryStorage.ActivePack active,
+            LoadedPack loaded
+    ) throws IOException {
+        IrisData data = loaded.data();
+        IrisDimension dimension = loaded.dimension();
+        boolean runtimeOwnsData = false;
+        try {
             validateDimensionContract(active.dimensionContract(), dimension, level);
             File worldFolder = NativeModdedServer.forWorld(level).dimensionFolder(level.name()).toFile();
             IrisWorld world = buildWorld(level, seed, dimension, worldFolder);
@@ -391,6 +491,15 @@ public final class ModdedWorldEngines {
                 (actualType.maximumHeight() - actualType.minimumHeight()),
                 actualType.logicalHeight());
         String runtimeName = "Modded level '" + level.name() + "'";
+        if (dimension.hasBorrowedDimensionType()) {
+            if (!recorded.dimensionTypeKey().equals(dimension.getBorrowedDimensionType().trim())) {
+                throw new IllegalStateException("Immutable Iris dimension contract for '" + level.name()
+                        + "' records dimension type " + recorded.dimensionTypeKey() + ", but its pack borrows "
+                        + dimension.getBorrowedDimensionType().trim() + ".");
+            }
+            expected.requireBorrowedFit(runtimeName, actual);
+            return;
+        }
         expected.requireExact(runtimeName, actual);
         expected.requireHeight(runtimeName, level.minHeight(), (level.maxHeight() - level.minHeight()));
     }
@@ -419,6 +528,55 @@ public final class ModdedWorldEngines {
         }
     }
 
+    private record LoadedPack(IrisData data, IrisDimension dimension) {
+        private LoadedPack {
+            data = Objects.requireNonNull(data, "data");
+            dimension = Objects.requireNonNull(dimension, "dimension");
+        }
+    }
+
+    static final class PreparedPack implements AutoCloseable {
+        private final ModdedGenerationHistoryStorage.ActivePack active;
+        private final GenerationAdmission.RuntimeLease lease;
+        private LoadedPack loaded;
+
+        private PreparedPack(
+                ModdedGenerationHistoryStorage.ActivePack active,
+                GenerationAdmission.RuntimeLease lease,
+                LoadedPack loaded
+        ) {
+            this.active = Objects.requireNonNull(active, "active");
+            this.lease = Objects.requireNonNull(lease, "lease");
+            this.loaded = Objects.requireNonNull(loaded, "loaded");
+        }
+
+        ModdedGenerationHistoryStorage.ActivePack active() {
+            return active;
+        }
+
+        private synchronized LoadedPack take() {
+            LoadedPack taken = loaded;
+            if (taken == null) {
+                throw new IllegalStateException("Iris prepared pack for " + active.packRoot() + " was already used");
+            }
+            loaded = null;
+            return taken;
+        }
+
+        @Override
+        public synchronized void close() {
+            LoadedPack unused = loaded;
+            loaded = null;
+            try {
+                if (unused != null) {
+                    unused.data().close();
+                }
+            } finally {
+                lease.close();
+            }
+        }
+    }
+
     public static void shutdown() {
         Throwable failure = null;
         for (Map.Entry<NativeWorld, Engine> entry : new ArrayList<>(ENGINES.entrySet())) {

adapters/modded-common/src/main/java/art/arcane/iris/modded/ModdedWorldQuarantine.java

@@ -0,0 +1,73 @@
+/*
+ * Iris is a World Generator for Minecraft Servers
+ * Copyright (c) 2026 Arcane Arts (Volmit Software)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package art.arcane.iris.modded;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.ArrayList;
+import java.util.List;
+
+final class ModdedWorldQuarantine {
+    private ModdedWorldQuarantine() {
+    }
+
+    static List<Path> move(Path worldRoot, List<Path> sources, Path recovery) throws IOException {
+        List<Path> moved = new ArrayList<>(sources.size());
+        try {
+            for (Path source : sources) {
+                moveOne(worldRoot, source, recovery, moved);
+            }
+        } catch (IOException failure) {
+            rollback(worldRoot, recovery, moved, failure);
+            throw failure;
+        }
+        if (moved.isEmpty()) {
+            Files.deleteIfExists(recovery);
+        }
+        return List.copyOf(moved);
+    }
+
+    private static void moveOne(Path worldRoot, Path source, Path recovery, List<Path> moved) throws IOException {
+        if (!Files.exists(source)) {
+            return;
+        }
+        Path relative = worldRoot.relativize(source);
+        if (relative.isAbsolute() || relative.startsWith("..")) {
+            throw new IOException("Iris refuses to quarantine " + source + " outside the world " + worldRoot);
+        }
+        Path target = recovery.resolve(relative);
+        Files.createDirectories(target.getParent());
+        Files.move(source, target);
+        moved.add(relative);
+    }
+
+    private static void rollback(Path worldRoot, Path recovery, List<Path> moved, IOException failure) {
+        for (int index = moved.size() - 1; index >= 0; index--) {
+            Path relative = moved.get(index);
+            Path rollbackTarget = worldRoot.resolve(relative);
+            try {
+                Files.createDirectories(rollbackTarget.getParent());
+                Files.move(recovery.resolve(relative), rollbackTarget);
+            } catch (IOException rollbackFailure) {
+                failure.addSuppressed(rollbackFailure);
+            }
+        }
+    }
+}

adapters/modded-common/src/main/java/art/arcane/iris/modded/ModdedWorldgenIds.java

@@ -1,12 +1,18 @@
 package art.arcane.iris.modded;
 
 import art.arcane.iris.generation.runtime.Engine;
+import art.arcane.iris.generation.terrain.IrisDimension;
+import art.arcane.iris.world.history.GenerationRegistryContract;
+import art.arcane.iris.world.history.GenerationRegistryContract.PhysicalResourceKey;
+import art.arcane.iris.world.history.GenerationRegistryContractFactory;
 
 import java.nio.charset.StandardCharsets;
 import java.util.HexFormat;
 import java.util.List;
 import java.util.Locale;
 import java.util.Optional;
+import java.util.Set;
+import java.util.TreeSet;
 
 public final class ModdedWorldgenIds {
     private static final String NAMESPACE = "irisworldgen";
@@ -22,6 +28,12 @@ public final class ModdedWorldgenIds {
         return NAMESPACE + ":" + scopedPath(pack, dimension) + "/dimension_type";
     }
 
+    public static String dimensionTypeRef(String pack, IrisDimension dimension) {
+        return dimension.hasBorrowedDimensionType()
+                ? dimension.getBorrowedDimensionType().trim()
+                : dimensionTypeRef(pack, dimension.getLoadKey());
+    }
+
     public static String biomePathPrefix(String pack, String dimension) {
         return scopedPath(pack, dimension) + "/biomes";
     }
@@ -61,6 +73,41 @@ public final class ModdedWorldgenIds {
         return Optional.of(new ScopedDimension(pack, dimension));
     }
 
+    static Set<String> aliasPacks(GenerationRegistryContract contract, String dimension) {
+        Set<String> packs = new TreeSet<>();
+        for (PhysicalResourceKey key : contract.definitions().keySet()) {
+            if (!GenerationRegistryContractFactory.BIOME_REGISTRY.equals(key.registryKey())) {
+                continue;
+            }
+            Optional<ScopedDimension> scoped = scopedBiome(key.resourceKey());
+            if (scoped.isPresent() && scoped.get().dimension().equals(dimension)) {
+                packs.add(scoped.get().pack());
+            }
+        }
+        return packs;
+    }
+
+    static Optional<ScopedDimension> scopedBiome(String biomeRef) {
+        String prefix = NAMESPACE + ":";
+        if (biomeRef == null || !biomeRef.startsWith(prefix)) {
+            return Optional.empty();
+        }
+        String[] parts = biomeRef.substring(prefix.length()).split("/", 6);
+        if (parts.length != 6
+                || !"packs".equals(parts[0])
+                || !"dimensions".equals(parts[2])
+                || !"biomes".equals(parts[4])
+                || parts[5].isEmpty()) {
+            return Optional.empty();
+        }
+        String pack = decode(parts[1]);
+        String dimension = decode(parts[3]);
+        if (pack == null || dimension == null) {
+            return Optional.empty();
+        }
+        return Optional.of(new ScopedDimension(pack, dimension));
+    }
+
     public static String displayName(String presetPath) {
         String[] parts = presetPath.split("/");
         if (parts.length != 5 || !"packs".equals(parts[0])

adapters/modded-common/src/main/java/art/arcane/iris/modded/WorldCheckDimensionContract.java

@@ -22,6 +22,7 @@ package art.arcane.iris.modded;
 import art.arcane.iris.pack.datapack.DataVersion;
 import art.arcane.iris.generation.terrain.IrisDimension;
 import art.arcane.volmlib.util.json.JSONObject;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeWorldDimensions;
 import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeWorldInspection;
 import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeWorldInspection.Dimension;
 import art.arcane.volmlib.nativelib.terrain.NativeWorld;
@@ -34,6 +35,9 @@ final class WorldCheckDimensionContract {
     static boolean checkDimensionType(NativeWorld level, IrisModdedChunkGenerator generator) {
         try {
             IrisDimension dimension = generator.commandEngine().getDimension();
+            if (dimension.hasBorrowedDimensionType()) {
+                return checkBorrowedDimensionType(level, dimension);
+            }
             Dimension expected = expectedDimensionContract(dimension);
             Dimension actual = new NativeWorldInspection(level).dimension();
             boolean pass = matchesDimensionContract(level.minHeight(), (level.maxHeight() - level.minHeight()), expected, actual);
@@ -54,6 +58,24 @@ final class WorldCheckDimensionContract {
         }
     }
 
+    private static boolean checkBorrowedDimensionType(NativeWorld level, IrisDimension dimension) {
+        String borrowed = dimension.getBorrowedDimensionType().trim();
+        String actualKey = NativeWorldDimensions.settings(level).key();
+        boolean pass = borrowed.equals(actualKey)
+                && dimension.getMinHeight() == level.minHeight()
+                && dimension.getMaxHeight() <= level.maxHeight();
+        String detail = "borrowed=" + borrowed + ",actual=" + actualKey
+                + ",packRange=" + dimension.getMinHeight() + ".." + dimension.getMaxHeight()
+                + ",levelRange=" + level.minHeight() + ".." + level.maxHeight();
+        WorldCheckPredicates.qaEvent("dimension_type", dimension.getLoadKey(), pass, detail);
+        if (!pass) {
+            ModdedIrisLog.error("[worldcheck] borrowed dimension type mismatch for {}: {}", dimension.getLoadKey(), detail);
+        } else {
+            ModdedIrisLog.info("[worldcheck] borrowed dimension type contract: {}", detail);
+        }
+        return pass;
+    }
+
     static Dimension expectedDimensionContract(IrisDimension dimension) {
         JSONObject json = new JSONObject(dimension.getDimensionType().toJson(DataVersion.getRuntime().get()));
         return new Dimension(
@@ -64,7 +86,8 @@ final class WorldCheckDimensionContract {
                 (float) json.getDouble("ambient_light"),
                 json.getBoolean("has_skylight"),
                 json.getBoolean("has_ceiling"),
-                json.getBoolean("has_ender_dragon_fight"),
+                json.has("has_ender_dragon_fight") ? json.getBoolean("has_ender_dragon_fight")
+                        : "minecraft:the_end".equals(json.optString("effects")),
                 json.getInt("monster_spawn_block_light_limit"));
     }
 

adapters/modded-common/src/main/java/art/arcane/iris/modded/catalog/CatalogCaptureContext.java

@@ -0,0 +1,32 @@
+/*
+ * Iris is a World Generator for Minecraft Servers
+ * Copyright (c) 2026 Arcane Arts (Volmit Software)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package art.arcane.iris.modded.catalog;
+
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeModMetadata;
+
+import java.util.List;
+import java.util.Objects;
+
+public record CatalogCaptureContext(String minecraftVersion, String platform, long capturedAtEpochMillis, List<NativeModMetadata> mods) {
+    public CatalogCaptureContext {
+        Objects.requireNonNull(minecraftVersion, "minecraftVersion");
+        Objects.requireNonNull(platform, "platform");
+        mods = List.copyOf(Objects.requireNonNull(mods, "mods"));
+    }
+}

adapters/modded-common/src/main/java/art/arcane/iris/modded/catalog/ModdedWorldgenCatalogs.java

@@ -0,0 +1,167 @@
+/*
+ * Iris is a World Generator for Minecraft Servers
+ * Copyright (c) 2026 Arcane Arts (Volmit Software)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package art.arcane.iris.modded.catalog;
+
+import art.arcane.iris.modded.ModdedEngineBootstrap;
+import art.arcane.iris.modded.ModdedIrisLog;
+import art.arcane.iris.pack.ingest.catalog.WorldgenCatalog;
+import art.arcane.iris.pack.ingest.catalog.WorldgenCatalogStore;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeModdedLoader;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeModdedServer;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeWorldgenScan;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeWorldgenSnapshot;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeWorldgenSnapshot.EncodeFailures;
+
+import java.io.IOException;
+import java.io.UncheckedIOException;
+import java.nio.file.Path;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicReference;
+
+public final class ModdedWorldgenCatalogs {
+    private static final AtomicReference<WorldgenCatalog> LATEST = new AtomicReference<>();
+    private static final AtomicReference<CompletableFuture<CaptureResult>> RUNNING = new AtomicReference<>();
+
+    private ModdedWorldgenCatalogs() {
+    }
+
+    public static Optional<WorldgenCatalog> latest() {
+        return Optional.ofNullable(LATEST.get());
+    }
+
+    public static Path catalogFile() {
+        return ModdedEngineBootstrap.loader().configDir().resolve("irisworldgen").resolve("catalog")
+                .resolve(WorldgenCatalogStore.FILE_NAME);
+    }
+
+    public static CompletableFuture<CaptureResult> capture(NativeModdedServer server) {
+        Objects.requireNonNull(server, "server");
+        return capture(() -> scan(server));
+    }
+
+    static CompletableFuture<CaptureResult> capture(CaptureScan scan) {
+        CompletableFuture<CaptureResult> pending = new CompletableFuture<>();
+        CompletableFuture<CaptureResult> running = RUNNING.compareAndExchange(null, pending);
+        if (running != null) {
+            return running;
+        }
+        CaptureWork work;
+        try {
+            work = scan.scan();
+        } catch (Throwable failure) {
+            ModdedIrisLog.error("Iris could not read the worldgen registries for the catalog", failure);
+            finish(pending, null, failure);
+            rethrowIfVirtualMachineError(failure);
+            return pending;
+        }
+        Thread worker = new Thread(() -> complete(work, pending), "Iris Worldgen Catalog");
+        worker.setDaemon(true);
+        worker.start();
+        return pending;
+    }
+
+    private static CaptureWork scan(NativeModdedServer server) {
+        long startedAt = System.nanoTime();
+        NativeModdedLoader loader = ModdedEngineBootstrap.loader();
+        NativeWorldgenScan scan = NativeWorldgenScan.scan(server, loader);
+        CatalogCaptureContext context = new CatalogCaptureContext(loader.minecraftVersion(), loader.platformName(),
+                System.currentTimeMillis(), loader.mods());
+        PendingCapture capture = new PendingCapture(scan, context, catalogFile(), startedAt, elapsedMillis(startedAt));
+        return () -> encodeAndWrite(capture);
+    }
+
+    private static void complete(CaptureWork work, CompletableFuture<CaptureResult> pending) {
+        try {
+            finish(pending, work.run(), null);
+        } catch (IOException failure) {
+            ModdedIrisLog.error("Iris could not write the worldgen catalog", failure);
+            finish(pending, null, new UncheckedIOException(failure));
+        } catch (Throwable failure) {
+            ModdedIrisLog.error("Iris could not build the worldgen catalog", failure);
+            finish(pending, null, failure);
+            rethrowIfVirtualMachineError(failure);
+        }
+    }
+
+    private static CaptureResult encodeAndWrite(PendingCapture capture) throws IOException {
+        NativeWorldgenSnapshot snapshot = capture.scan().encode();
+        WorldgenCatalog catalog = WorldgenCatalogAssembler.assemble(snapshot, capture.context());
+        WorldgenCatalogStore.write(capture.file(), catalog);
+        LATEST.set(catalog);
+        CaptureResult result = new CaptureResult(catalog, capture.file(), elapsedMillis(capture.startedAt()));
+        ModdedIrisLog.info("Iris worldgen catalog: {} namespaces, {} biomes, {} placed features, {} structures, "
+                        + "{} dimension types, {} level stems -> {} ({}ms server thread, {}ms total)",
+                catalog.namespaces().size(), catalog.biomes().size(), catalog.placedFeatures().size(),
+                catalog.structures().size(), catalog.dimensionTypes().size(), catalog.levelStems().size(),
+                capture.file(), capture.scanMillis(), result.millis());
+        reportEncodeFailures(snapshot.failures());
+        return result;
+    }
+
+    private static void reportEncodeFailures(EncodeFailures failures) {
+        if (failures.count() == 0) {
+            return;
+        }
+        String first = failures.samples().isEmpty() ? "" : failures.samples().getFirst();
+        if (failures.firstException() != null) {
+            ModdedIrisLog.warn("Iris worldgen catalog left {} entries without JSON; first: {}", failures.count(), first,
+                    failures.firstException());
+            return;
+        }
+        ModdedIrisLog.warn("Iris worldgen catalog left {} entries without JSON; first: {}", failures.count(), first);
+    }
+
+    private static void finish(CompletableFuture<CaptureResult> pending, CaptureResult result, Throwable failure) {
+        RUNNING.compareAndSet(pending, null);
+        if (failure != null) {
+            pending.completeExceptionally(failure);
+            return;
+        }
+        pending.complete(result);
+    }
+
+    private static void rethrowIfVirtualMachineError(Throwable failure) {
+        if (failure instanceof VirtualMachineError virtualMachineError) {
+            throw virtualMachineError;
+        }
+    }
+
+    private static long elapsedMillis(long startedAt) {
+        return TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - startedAt);
+    }
+
+    public record CaptureResult(WorldgenCatalog catalog, Path file, long millis) {
+    }
+
+    @FunctionalInterface
+    interface CaptureScan {
+        CaptureWork scan();
+    }
+
+    @FunctionalInterface
+    interface CaptureWork {
+        CaptureResult run() throws IOException;
+    }
+
+    private record PendingCapture(NativeWorldgenScan scan, CatalogCaptureContext context, Path file, long startedAt, long scanMillis) {
+    }
+}

adapters/modded-common/src/main/java/art/arcane/iris/modded/catalog/WorldgenCatalogAssembler.java

@@ -0,0 +1,192 @@
+/*
+ * Iris is a World Generator for Minecraft Servers
+ * Copyright (c) 2026 Arcane Arts (Volmit Software)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package art.arcane.iris.modded.catalog;
+
+import art.arcane.iris.pack.ingest.catalog.CatalogBiome;
+import art.arcane.iris.pack.ingest.catalog.CatalogDimensionType;
+import art.arcane.iris.pack.ingest.catalog.CatalogLevelStem;
+import art.arcane.iris.pack.ingest.catalog.CatalogNamespace;
+import art.arcane.iris.pack.ingest.catalog.CatalogPlacedFeature;
+import art.arcane.iris.pack.ingest.catalog.CatalogSpawn;
+import art.arcane.iris.pack.ingest.catalog.CatalogStructure;
+import art.arcane.iris.pack.ingest.catalog.WorldgenCatalog;
+import art.arcane.iris.pack.ingest.catalog.WorldgenCatalogFingerprint;
+import art.arcane.iris.pack.ingest.catalog.WorldgenCatalogIndex;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeModMetadata;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeWorldgenSnapshot;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeWorldgenSnapshot.WorldgenBiome;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeWorldgenSnapshot.WorldgenDimensionType;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeWorldgenSnapshot.WorldgenLevelStem;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeWorldgenSnapshot.WorldgenPlacedFeature;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeWorldgenSnapshot.WorldgenSpawn;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeWorldgenSnapshot.WorldgenStructure;
+
+import com.google.gson.JsonElement;
+import com.google.gson.JsonObject;
+
+import java.util.ArrayList;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Set;
+import java.util.TreeMap;
+import java.util.TreeSet;
+
+public final class WorldgenCatalogAssembler {
+    private static final String MINECRAFT = "minecraft";
+
+    private WorldgenCatalogAssembler() {
+    }
+
+    public static WorldgenCatalog assemble(NativeWorldgenSnapshot snapshot, CatalogCaptureContext context) {
+        Objects.requireNonNull(snapshot, "snapshot");
+        Objects.requireNonNull(context, "context");
+        List<CatalogBiome> biomes = biomes(snapshot.biomes());
+        List<CatalogPlacedFeature> placedFeatures = placedFeatures(snapshot.placedFeatures());
+        List<CatalogStructure> structures = structures(snapshot.structures());
+        List<CatalogDimensionType> dimensionTypes = dimensionTypes(snapshot.dimensionTypes());
+        List<CatalogLevelStem> levelStems = levelStems(snapshot.levelStems());
+        Map<String, List<String>> blockTags = referencedBlockTags(placedFeatures, snapshot.blockTags());
+        Map<String, List<String>> registryKeys = new LinkedHashMap<>();
+        registryKeys.put("biome", biomes.stream().map(CatalogBiome::key).toList());
+        registryKeys.put("placed_feature", placedFeatures.stream().map(CatalogPlacedFeature::key).toList());
+        registryKeys.put("structure", structures.stream().map(CatalogStructure::key).toList());
+        registryKeys.put("dimension_type", dimensionTypes.stream().map(CatalogDimensionType::key).toList());
+        registryKeys.put("level_stem", levelStems.stream().map(CatalogLevelStem::key).toList());
+        registryKeys.put("block_tag", List.copyOf(blockTags.keySet()));
+        List<CatalogNamespace> namespaces = namespaces(registryKeys, context);
+        return new WorldgenCatalog(WorldgenCatalog.FORMAT, context.minecraftVersion(), context.platform(),
+                context.capturedAtEpochMillis(), WorldgenCatalogFingerprint.of(namespaces, registryKeys), namespaces,
+                biomes, placedFeatures, structures, dimensionTypes, levelStems, blockTags);
+    }
+
+    private static Map<String, List<String>> referencedBlockTags(List<CatalogPlacedFeature> features,
+                                                                 Map<String, List<String>> available) {
+        Set<String> referenced = new TreeSet<>();
+        for (CatalogPlacedFeature feature : features) {
+            collectTagMatches(feature.config(), referenced);
+        }
+        Map<String, List<String>> tags = new TreeMap<>();
+        for (String tag : referenced) {
+            List<String> members = available.get(tag);
+            if (members != null) {
+                tags.put(tag, members);
+            }
+        }
+        return tags;
+    }
+
+    private static void collectTagMatches(JsonElement element, Set<String> tags) {
+        if (element == null || element.isJsonNull() || element.isJsonPrimitive()) {
+            return;
+        }
+        if (element.isJsonArray()) {
+            for (JsonElement entry : element.getAsJsonArray()) {
+                collectTagMatches(entry, tags);
+            }
+            return;
+        }
+        JsonObject object = element.getAsJsonObject();
+        JsonElement predicate = object.get("predicate_type");
+        JsonElement tag = object.get("tag");
+        if (predicate != null && predicate.isJsonPrimitive() && predicate.getAsString().endsWith("tag_match")
+                && tag != null && tag.isJsonPrimitive()) {
+            String key = tag.getAsString();
+            tags.add(key.contains(":") ? key : MINECRAFT + ":" + key);
+        }
+        for (Map.Entry<String, JsonElement> entry : object.entrySet()) {
+            collectTagMatches(entry.getValue(), tags);
+        }
+    }
+
+    private static List<CatalogNamespace> namespaces(Map<String, List<String>> registryKeys, CatalogCaptureContext context) {
+        Map<String, CatalogNamespace> namespaces = new TreeMap<>();
+        for (NativeModMetadata mod : context.mods()) {
+            namespaces.put(mod.id(), new CatalogNamespace(mod.id(), mod.displayName(), mod.version()));
+        }
+        for (List<String> keys : registryKeys.values()) {
+            for (String key : keys) {
+                String namespace = WorldgenCatalogIndex.namespaceOf(key);
+                if (!namespaces.containsKey(namespace)) {
+                    namespaces.put(namespace, fallbackNamespace(namespace, context));
+                }
+            }
+        }
+        if (!namespaces.containsKey(MINECRAFT)) {
+            namespaces.put(MINECRAFT, fallbackNamespace(MINECRAFT, context));
+        }
+        return List.copyOf(namespaces.values());
+    }
+
+    private static CatalogNamespace fallbackNamespace(String namespace, CatalogCaptureContext context) {
+        if (MINECRAFT.equals(namespace)) {
+            return new CatalogNamespace(MINECRAFT, "Minecraft", context.minecraftVersion());
+        }
+        return new CatalogNamespace(namespace, namespace, "");
+    }
+
+    private static List<CatalogBiome> biomes(List<WorldgenBiome> biomes) {
+        List<CatalogBiome> result = new ArrayList<>(biomes.size());
+        for (WorldgenBiome biome : biomes) {
+            List<CatalogSpawn> spawns = new ArrayList<>(biome.spawns().size());
+            for (WorldgenSpawn spawn : biome.spawns()) {
+                spawns.add(new CatalogSpawn(spawn.category(), spawn.entity(), spawn.weight(), spawn.minCount(), spawn.maxCount()));
+            }
+            result.add(new CatalogBiome(biome.key(), biome.temperature(), biome.downfall(), biome.hasPrecipitation(),
+                    biome.tags(), biome.featureSteps(), spawns, biome.definition()));
+        }
+        return result;
+    }
+
+    private static List<CatalogPlacedFeature> placedFeatures(List<WorldgenPlacedFeature> features) {
+        List<CatalogPlacedFeature> result = new ArrayList<>(features.size());
+        for (WorldgenPlacedFeature feature : features) {
+            result.add(new CatalogPlacedFeature(feature.key(), feature.feature(), feature.featureType(),
+                    feature.config(), feature.placement()));
+        }
+        return result;
+    }
+
+    private static List<CatalogStructure> structures(List<WorldgenStructure> structures) {
+        List<CatalogStructure> result = new ArrayList<>(structures.size());
+        for (WorldgenStructure structure : structures) {
+            result.add(new CatalogStructure(structure.key(), structure.type(), structure.step(),
+                    structure.terrainAdaptation(), structure.biomeTag(), structure.biomes(), structure.structureSets()));
+        }
+        return result;
+    }
+
+    private static List<CatalogDimensionType> dimensionTypes(List<WorldgenDimensionType> types) {
+        List<CatalogDimensionType> result = new ArrayList<>(types.size());
+        for (WorldgenDimensionType type : types) {
+            result.add(new CatalogDimensionType(type.key(), type.minY(), type.height(), type.logicalHeight(), type.definition()));
+        }
+        return result;
+    }
+
+    private static List<CatalogLevelStem> levelStems(List<WorldgenLevelStem> stems) {
+        List<CatalogLevelStem> result = new ArrayList<>(stems.size());
+        for (WorldgenLevelStem stem : stems) {
+            result.add(new CatalogLevelStem(stem.key(), stem.dimensionType(), stem.generatorType(),
+                    stem.biomeSourceType(), stem.generator()));
+        }
+        return result;
+    }
+}

adapters/modded-common/src/main/java/art/arcane/iris/modded/catalog/WorldgenCatalogSummary.java

@@ -0,0 +1,173 @@
+/*
+ * Iris is a World Generator for Minecraft Servers
+ * Copyright (c) 2026 Arcane Arts (Volmit Software)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package art.arcane.iris.modded.catalog;
+
+import art.arcane.iris.pack.ingest.catalog.CatalogBiome;
+import art.arcane.iris.pack.ingest.catalog.CatalogDimensionType;
+import art.arcane.iris.pack.ingest.catalog.CatalogLevelStem;
+import art.arcane.iris.pack.ingest.catalog.CatalogNamespace;
+import art.arcane.iris.pack.ingest.catalog.CatalogPlacedFeature;
+import art.arcane.iris.pack.ingest.catalog.CatalogStructure;
+import art.arcane.iris.pack.ingest.catalog.WorldgenCatalog;
+import art.arcane.iris.pack.ingest.catalog.WorldgenCatalogIndex;
+
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.TreeMap;
+import java.util.function.Function;
+
+public final class WorldgenCatalogSummary {
+    private static final String VANILLA_PREFIX = "minecraft:";
+
+    private WorldgenCatalogSummary() {
+    }
+
+    public static List<NamespaceSummary> namespaces(WorldgenCatalog catalog) {
+        Map<String, Builder> builders = new TreeMap<>();
+        for (CatalogNamespace namespace : catalog.namespaces()) {
+            builders.put(namespace.namespace(), new Builder(namespace));
+        }
+        collect(builders, catalog.biomes(), CatalogBiome::key, Builder::biomes);
+        collect(builders, catalog.placedFeatures(), CatalogPlacedFeature::key, Builder::placedFeatures);
+        collect(builders, catalog.structures(), CatalogStructure::key, Builder::structures);
+        collect(builders, catalog.dimensionTypes(), CatalogDimensionType::key, Builder::dimensionTypes);
+        collect(builders, catalog.levelStems(), CatalogLevelStem::key, Builder::levelStems);
+        for (CatalogPlacedFeature feature : catalog.placedFeatures()) {
+            builder(builders, WorldgenCatalogIndex.namespaceOf(feature.key())).featureTypes()
+                    .merge(feature.featureType(), 1, Integer::sum);
+        }
+        List<NamespaceSummary> summaries = new ArrayList<>(builders.size());
+        for (Builder builder : builders.values()) {
+            summaries.add(builder.build());
+        }
+        return summaries;
+    }
+
+    public static Optional<NamespaceSummary> namespace(WorldgenCatalog catalog, String namespace) {
+        for (NamespaceSummary summary : namespaces(catalog)) {
+            if (summary.namespace().namespace().equals(namespace)) {
+                return Optional.of(summary);
+            }
+        }
+        return Optional.empty();
+    }
+
+    public static String featureTypes(List<TypeCount> types, int limit) {
+        List<String> labels = new ArrayList<>(Math.min(types.size(), limit));
+        for (int index = 0; index < types.size() && index < limit; index++) {
+            TypeCount type = types.get(index);
+            labels.add(shortType(type.type()) + " " + type.count());
+        }
+        return withRemainder(String.join(", ", labels), types.size() - labels.size());
+    }
+
+    public static String limited(List<String> keys, String namespace, int limit) {
+        List<String> labels = new ArrayList<>(Math.min(keys.size(), limit));
+        String ownPrefix = namespace + ":";
+        for (int index = 0; index < keys.size() && index < limit; index++) {
+            String key = keys.get(index);
+            labels.add(key.startsWith(ownPrefix) ? key.substring(ownPrefix.length()) : key);
+        }
+        return withRemainder(String.join(", ", labels), keys.size() - labels.size());
+    }
+
+    private static String shortType(String type) {
+        return type.startsWith(VANILLA_PREFIX) ? type.substring(VANILLA_PREFIX.length()) : type;
+    }
+
+    private static String withRemainder(String joined, int remainder) {
+        return remainder > 0 ? joined + " (+" + remainder + " more)" : joined;
+    }
+
+    private static <T> void collect(Map<String, Builder> builders, List<T> entries, Function<T, String> key,
+                                    Function<Builder, List<String>> target) {
+        for (T entry : entries) {
+            String entryKey = key.apply(entry);
+            target.apply(builder(builders, WorldgenCatalogIndex.namespaceOf(entryKey))).add(entryKey);
+        }
+    }
+
+    private static Builder builder(Map<String, Builder> builders, String namespace) {
+        return builders.computeIfAbsent(namespace, (String missing) -> new Builder(new CatalogNamespace(missing, missing, "")));
+    }
+
+    public record TypeCount(String type, int count) {
+        public TypeCount {
+            Objects.requireNonNull(type, "type");
+        }
+    }
+
+    public record NamespaceSummary(
+            CatalogNamespace namespace,
+            List<String> biomes,
+            List<String> placedFeatures,
+            List<TypeCount> featureTypes,
+            List<String> structures,
+            List<String> dimensionTypes,
+            List<String> levelStems) {
+        public NamespaceSummary {
+            Objects.requireNonNull(namespace, "namespace");
+            biomes = List.copyOf(biomes);
+            placedFeatures = List.copyOf(placedFeatures);
+            featureTypes = List.copyOf(featureTypes);
+            structures = List.copyOf(structures);
+            dimensionTypes = List.copyOf(dimensionTypes);
+            levelStems = List.copyOf(levelStems);
+        }
+
+        public boolean hasContent() {
+            return !biomes.isEmpty() || !placedFeatures.isEmpty() || !structures.isEmpty()
+                    || !dimensionTypes.isEmpty() || !levelStems.isEmpty();
+        }
+    }
+
+    private record Builder(
+            CatalogNamespace namespace,
+            List<String> biomes,
+            List<String> placedFeatures,
+            Map<String, Integer> featureTypes,
+            List<String> structures,
+            List<String> dimensionTypes,
+            List<String> levelStems) {
+        private Builder(CatalogNamespace namespace) {
+            this(namespace, new ArrayList<>(), new ArrayList<>(), new TreeMap<>(), new ArrayList<>(), new ArrayList<>(),
+                    new ArrayList<>());
+        }
+
+        private NamespaceSummary build() {
+            List<TypeCount> types = new ArrayList<>(featureTypes.size());
+            for (Map.Entry<String, Integer> entry : featureTypes.entrySet()) {
+                types.add(new TypeCount(entry.getKey(), entry.getValue()));
+            }
+            types.sort(Comparator.comparingInt(TypeCount::count).reversed().thenComparing(TypeCount::type));
+            return new NamespaceSummary(namespace, sorted(biomes), sorted(placedFeatures), types, sorted(structures),
+                    sorted(dimensionTypes), sorted(levelStems));
+        }
+
+        private static List<String> sorted(List<String> keys) {
+            List<String> copy = new ArrayList<>(keys);
+            copy.sort(null);
+            return copy;
+        }
+    }
+}

adapters/modded-common/src/main/java/art/arcane/iris/modded/command/IrisModdedCommands.java

@@ -294,16 +294,14 @@ public final class IrisModdedCommands {
             }
             Engine engine = irisGenerator.engineIfBound();
             if (engine == null) {
-                lines.add(irisIdentity + ": pack=" + irisGenerator.dimensionKey()
-                        + " world=" + dimensionId + " (engine not started yet)");
+                lines.add(dimensionId + ": pack=" + irisGenerator.dimensionKey() + " (engine not started yet)");
                 continue;
             }
             String featureStatus = irisGenerator.importedFeaturesStatus();
-            lines.add(irisIdentity + ": pack=" + engine.getDimension().getLoadKey()
-                    + " world=" + dimensionId
-                    + (showSeed ? " seed=" + level.seed() : "")
+            lines.add(dimensionId + ": pack=" + engine.getDimension().getLoadKey()
+                    + (showSeed ? " seed=" + engine.getWorld().getRawWorldSeed() : "")
                     + " height=" + engine.getMinHeight() + ".." + engine.getMaxHeight()
-                    + " generated=" + engine.getGenerated()
+                    + " generated=" + engine.getEngineData().getStatistics().getChunksGenerated()
                     + (featureStatus == null ? "" : " importedFeatures=" + featureStatus)
                     + " data=" + engine.getData().getDataFolder().getName());
         }
@@ -329,7 +327,7 @@ public final class IrisModdedCommands {
             fail(source, IrisLanguage.plain(ModdedCommandMessages.IRIS_MODDED_COMMANDS_THIS_DIMENSION_IS_NOT_GENERATED_BY_IRIS_14));
             return 0;
         }
-        ok(source, IrisLanguage.plain(ModdedCommandMessages.IRIS_MODDED_COMMANDS_WORLD_SEED, MessageArgument.untrusted("value", level.seed())));
+        ok(source, IrisLanguage.plain(ModdedCommandMessages.IRIS_MODDED_COMMANDS_WORLD_SEED, MessageArgument.untrusted("value", engine.getWorld().getRawWorldSeed())));
         ok(source, IrisLanguage.plain(ModdedCommandMessages.IRIS_MODDED_COMMANDS_ENGINE_SEED_MIXED, MessageArgument.untrusted("value", engine.getSeedManager().getSeed()), MessageArgument.untrusted("value2", engine.getSeedManager().getFullMixedSeed())));
         return 1;
     }

adapters/modded-common/src/main/java/art/arcane/iris/modded/command/ModIngestArguments.java

@@ -0,0 +1,154 @@
+/*
+ * Iris is a World Generator for Minecraft Servers
+ * Copyright (c) 2026 Arcane Arts (Volmit Software)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package art.arcane.iris.modded.command;
+
+import java.util.HashMap;
+import java.util.LinkedHashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Set;
+import java.util.regex.Pattern;
+
+record ModIngestArguments(String sourcePack, String targetPack, String dimension, Set<String> namespaces,
+                          Set<String> excludedRegions, boolean replace) {
+    static final List<String> OPTION_SUGGESTIONS = List.of("dimension=", "namespaces=", "excludeRegions=", "replace=true");
+    private static final Pattern PACK = Pattern.compile("[A-Za-z0-9_.-]+");
+    private static final Pattern TARGET_PACK = Pattern.compile("[A-Za-z0-9_-]+");
+    private static final Pattern DIMENSION = Pattern.compile("[A-Za-z0-9_/.-]+");
+    private static final Pattern NAMESPACE = Pattern.compile("[a-z0-9_.-]+");
+    private static final Pattern REGION = Pattern.compile("[A-Za-z0-9_/.-]+");
+    private static final String DIMENSION_KEY = "dimension";
+    private static final String NAMESPACES_KEY = "namespaces";
+    private static final String REPLACE_KEY = "replace";
+    private static final String EXCLUDE_REGIONS_KEY = "excludeRegions";
+
+    ModIngestArguments {
+        Objects.requireNonNull(sourcePack, "sourcePack");
+        Objects.requireNonNull(targetPack, "targetPack");
+        Objects.requireNonNull(dimension, "dimension");
+        namespaces = Set.copyOf(Objects.requireNonNull(namespaces, "namespaces"));
+        excludedRegions = Set.copyOf(Objects.requireNonNull(excludedRegions, "excludedRegions"));
+    }
+
+    static ModIngestArguments parse(String raw) {
+        String trimmed = raw == null ? "" : raw.trim();
+        String[] tokens = trimmed.isEmpty() ? new String[0] : trimmed.split("\\s+");
+        String source = null;
+        String target = null;
+        Map<String, String> options = new HashMap<>(4);
+        for (String token : tokens) {
+            int equals = token.indexOf('=');
+            if (equals < 0) {
+                if (source == null) {
+                    source = token;
+                } else if (target == null) {
+                    target = token;
+                } else {
+                    throw new IllegalArgumentException("unexpected argument '" + token + "'");
+                }
+                continue;
+            }
+            String key = token.substring(0, equals);
+            if (!key.equals(DIMENSION_KEY) && !key.equals(NAMESPACES_KEY) && !key.equals(REPLACE_KEY)
+                    && !key.equals(EXCLUDE_REGIONS_KEY)) {
+                throw new IllegalArgumentException("unknown option '" + key + "'");
+            }
+            if (options.putIfAbsent(key, token.substring(equals + 1)) != null) {
+                throw new IllegalArgumentException("option '" + key + "' given twice");
+            }
+        }
+        if (source == null) {
+            throw new IllegalArgumentException("missing source pack");
+        }
+        if (target == null) {
+            throw new IllegalArgumentException("missing target pack");
+        }
+        requirePack(source);
+        requirePack(target);
+        if (!TARGET_PACK.matcher(target).matches()) {
+            throw new IllegalArgumentException("invalid target pack name '" + target + "'");
+        }
+        if (source.equals(target)) {
+            throw new IllegalArgumentException("source and target must be different packs");
+        }
+        String dimension = options.getOrDefault(DIMENSION_KEY, source);
+        if (!DIMENSION.matcher(dimension).matches() || dimension.contains("..")) {
+            throw new IllegalArgumentException("invalid dimension key '" + dimension + "'");
+        }
+        return new ModIngestArguments(source, target, dimension, namespaces(options.get(NAMESPACES_KEY)),
+                regions(options.get(EXCLUDE_REGIONS_KEY)), replace(options.get(REPLACE_KEY)));
+    }
+
+    private static void requirePack(String pack) {
+        if (!PACK.matcher(pack).matches() || pack.contains("..")) {
+            throw new IllegalArgumentException("invalid pack name '" + pack + "'");
+        }
+    }
+
+    private static Set<String> namespaces(String raw) {
+        if (raw == null) {
+            return Set.of();
+        }
+        Set<String> namespaces = new LinkedHashSet<>();
+        for (String part : raw.split(",")) {
+            if (part.isEmpty()) {
+                continue;
+            }
+            if (!NAMESPACE.matcher(part).matches()) {
+                throw new IllegalArgumentException("invalid namespace '" + part + "'");
+            }
+            namespaces.add(part);
+        }
+        if (namespaces.isEmpty()) {
+            throw new IllegalArgumentException("namespaces must not be empty");
+        }
+        return namespaces;
+    }
+
+    private static Set<String> regions(String raw) {
+        if (raw == null) {
+            return Set.of();
+        }
+        Set<String> regions = new LinkedHashSet<>();
+        for (String part : raw.split(",")) {
+            if (part.isEmpty()) {
+                continue;
+            }
+            if (!REGION.matcher(part).matches() || part.contains("..")) {
+                throw new IllegalArgumentException("invalid region '" + part + "'");
+            }
+            regions.add(part);
+        }
+        if (regions.isEmpty()) {
+            throw new IllegalArgumentException("excludeRegions must not be empty");
+        }
+        return regions;
+    }
+
+    private static boolean replace(String raw) {
+        if (raw == null || raw.equals("false")) {
+            return false;
+        }
+        if (raw.equals("true")) {
+            return true;
+        }
+        throw new IllegalArgumentException("replace must be true or false");
+    }
+}

adapters/modded-common/src/main/java/art/arcane/iris/modded/command/ModdedCatalogCommands.java

@@ -0,0 +1,313 @@
+/*
+ * Iris is a World Generator for Minecraft Servers
+ * Copyright (c) 2026 Arcane Arts (Volmit Software)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package art.arcane.iris.modded.command;
+
+import art.arcane.iris.localization.IrisLanguage;
+import art.arcane.iris.modded.ModdedIrisLog;
+import art.arcane.iris.modded.catalog.ModdedWorldgenCatalogs;
+import art.arcane.iris.modded.catalog.ModdedWorldgenCatalogs.CaptureResult;
+import art.arcane.iris.modded.catalog.WorldgenCatalogSummary;
+import art.arcane.iris.modded.catalog.WorldgenCatalogSummary.NamespaceSummary;
+import art.arcane.iris.modded.localization.ModdedCatalogMessages;
+import art.arcane.iris.pack.PackDirectoryResolver;
+import art.arcane.iris.pack.ingest.ModIngestReport;
+import art.arcane.iris.pack.ingest.ModIngestRequest;
+import art.arcane.iris.pack.ingest.ModIngester;
+import art.arcane.iris.pack.ingest.catalog.WorldgenCatalog;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeCommandRegistration;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeCommandSource;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeModdedServer;
+import art.arcane.volmlib.util.localization.MessageArgument;
+import com.mojang.brigadier.arguments.StringArgumentType;
+import com.mojang.brigadier.builder.LiteralArgumentBuilder;
+import com.mojang.brigadier.context.CommandContext;
+import com.mojang.brigadier.suggestion.SuggestionProvider;
+import com.mojang.brigadier.suggestion.Suggestions;
+import com.mojang.brigadier.suggestion.SuggestionsBuilder;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.file.FileAlreadyExistsException;
+import java.nio.file.Path;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Optional;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CompletionException;
+import java.util.concurrent.atomic.AtomicReference;
+import java.util.function.Predicate;
+
+final class ModdedCatalogCommands {
+    private static final Predicate<NativeCommandSource> GATE = NativeCommandRegistration.GAMEMASTERS;
+    private static final int LIST_FEATURE_TYPES = 3;
+    private static final int DETAIL_LIMIT = 24;
+    private static final String NONE = "-";
+    private static final AtomicReference<NamespaceCache> NAMESPACE_CACHE = new AtomicReference<>();
+    private static final SuggestionProvider<NativeCommandSource> NAMESPACES = (CommandContext<NativeCommandSource> context,
+                                                                             SuggestionsBuilder builder) ->
+            NativeCommandRegistration.suggest(contentNamespaces(), builder);
+    private static final SuggestionProvider<NativeCommandSource> INGEST_ARGUMENTS = ModdedCatalogCommands::suggestIngestArguments;
+
+    private ModdedCatalogCommands() {
+    }
+
+    static LiteralArgumentBuilder<NativeCommandSource> catalogTree() {
+        return NativeCommandRegistration.literal("catalog").requires(GATE)
+                .executes(ModdedCommandTree.localized((CommandContext<NativeCommandSource> context) -> list(context.getSource())))
+                .then(NativeCommandRegistration.literal("refresh")
+                        .executes(ModdedCommandTree.localized((CommandContext<NativeCommandSource> context) -> refresh(context.getSource()))))
+                .then(NativeCommandRegistration.argument("namespace", StringArgumentType.word()).suggests(NAMESPACES)
+                        .executes(ModdedCommandTree.localized((CommandContext<NativeCommandSource> context) ->
+                                detail(context.getSource(), StringArgumentType.getString(context, "namespace")))));
+    }
+
+    static LiteralArgumentBuilder<NativeCommandSource> ingestTree() {
+        return NativeCommandRegistration.literal("ingest").requires(GATE)
+                .executes(ModdedCommandTree.localized((CommandContext<NativeCommandSource> context) -> ModdedCommandHelp.send(context.getSource(), "ingest")))
+                .then(NativeCommandRegistration.literal("mods")
+                        .executes(ModdedCommandTree.localized((CommandContext<NativeCommandSource> context) -> ingest(context.getSource(), "")))
+                        .then(NativeCommandRegistration.argument("arguments", StringArgumentType.greedyString()).suggests(INGEST_ARGUMENTS)
+                                .executes(ModdedCommandTree.localized((CommandContext<NativeCommandSource> context) ->
+                                        ingest(context.getSource(), StringArgumentType.getString(context, "arguments"))))));
+    }
+
+    private static int list(NativeCommandSource source) {
+        Optional<WorldgenCatalog> latest = ModdedWorldgenCatalogs.latest();
+        if (latest.isEmpty()) {
+            IrisModdedCommands.fail(source, IrisLanguage.plain(ModdedCatalogMessages.MISSING));
+            return 0;
+        }
+        WorldgenCatalog catalog = latest.get();
+        IrisModdedCommands.ok(source, IrisLanguage.plain(ModdedCatalogMessages.HEADER,
+                MessageArgument.untrusted("name", catalog.platform()),
+                MessageArgument.untrusted("version", catalog.minecraftVersion()),
+                MessageArgument.untrusted("count", catalog.namespaces().size()),
+                MessageArgument.untrusted("value", catalog.biomes().size()),
+                MessageArgument.untrusted("value2", catalog.placedFeatures().size()),
+                MessageArgument.untrusted("value3", catalog.structures().size()),
+                MessageArgument.untrusted("value4", catalog.dimensionTypes().size()),
+                MessageArgument.untrusted("value5", catalog.levelStems().size())));
+        int quiet = 0;
+        for (NamespaceSummary summary : WorldgenCatalogSummary.namespaces(catalog)) {
+            if (!summary.hasContent()) {
+                quiet++;
+                continue;
+            }
+            IrisModdedCommands.ok(source, namespaceLine(summary));
+        }
+        if (quiet > 0) {
+            IrisModdedCommands.ok(source, IrisLanguage.plain(ModdedCatalogMessages.QUIET, MessageArgument.untrusted("count", quiet)));
+        }
+        return 1;
+    }
+
+    private static int detail(NativeCommandSource source, String namespace) {
+        Optional<WorldgenCatalog> latest = ModdedWorldgenCatalogs.latest();
+        if (latest.isEmpty()) {
+            IrisModdedCommands.fail(source, IrisLanguage.plain(ModdedCatalogMessages.MISSING));
+            return 0;
+        }
+        Optional<NamespaceSummary> found = WorldgenCatalogSummary.namespace(latest.get(), namespace);
+        if (found.isEmpty() || !found.get().hasContent()) {
+            IrisModdedCommands.fail(source, IrisLanguage.plain(ModdedCatalogMessages.UNKNOWN_NAMESPACE,
+                    MessageArgument.untrusted("name", namespace)));
+            return 0;
+        }
+        NamespaceSummary summary = found.get();
+        IrisModdedCommands.ok(source, namespaceLine(summary));
+        if (!summary.biomes().isEmpty()) {
+            IrisModdedCommands.ok(source, IrisLanguage.plain(ModdedCatalogMessages.DETAIL_BIOMES,
+                    MessageArgument.untrusted("count", summary.biomes().size()),
+                    MessageArgument.untrusted("value", WorldgenCatalogSummary.limited(summary.biomes(), namespace, DETAIL_LIMIT))));
+        }
+        if (!summary.placedFeatures().isEmpty()) {
+            IrisModdedCommands.ok(source, IrisLanguage.plain(ModdedCatalogMessages.DETAIL_FEATURES,
+                    MessageArgument.untrusted("count", summary.placedFeatures().size()),
+                    MessageArgument.untrusted("value", WorldgenCatalogSummary.featureTypes(summary.featureTypes(), DETAIL_LIMIT))));
+        }
+        if (!summary.structures().isEmpty()) {
+            IrisModdedCommands.ok(source, IrisLanguage.plain(ModdedCatalogMessages.DETAIL_STRUCTURES,
+                    MessageArgument.untrusted("count", summary.structures().size()),
+                    MessageArgument.untrusted("value", WorldgenCatalogSummary.limited(summary.structures(), namespace, DETAIL_LIMIT))));
+        }
+        if (!summary.dimensionTypes().isEmpty() || !summary.levelStems().isEmpty()) {
+            IrisModdedCommands.ok(source, IrisLanguage.plain(ModdedCatalogMessages.DETAIL_DIMENSIONS,
+                    MessageArgument.untrusted("value", orNone(WorldgenCatalogSummary.limited(summary.dimensionTypes(), namespace, DETAIL_LIMIT))),
+                    MessageArgument.untrusted("value2", orNone(WorldgenCatalogSummary.limited(summary.levelStems(), namespace, DETAIL_LIMIT)))));
+        }
+        return 1;
+    }
+
+    private static int refresh(NativeCommandSource source) {
+        NativeModdedServer server = source.server();
+        IrisModdedCommands.ok(source, IrisLanguage.plain(ModdedCatalogMessages.REFRESHING));
+        ModdedWorldgenCatalogs.capture(server).whenComplete((CaptureResult result, Throwable failure) ->
+                source.execute(() -> reportRefresh(source, result, failure)));
+        return 1;
+    }
+
+    private static void reportRefresh(NativeCommandSource source, CaptureResult result, Throwable failure) {
+        if (failure != null) {
+            IrisModdedCommands.fail(source, IrisLanguage.plain(ModdedCatalogMessages.REFRESH_FAILED,
+                    MessageArgument.untrusted("reason", reason(failure))));
+            return;
+        }
+        IrisModdedCommands.ok(source, IrisLanguage.plain(ModdedCatalogMessages.REFRESHED,
+                MessageArgument.untrusted("duration", result.millis() + " ms"),
+                MessageArgument.untrusted("path", result.file().toString())));
+    }
+
+    private static int ingest(NativeCommandSource source, String raw) {
+        ModIngestArguments arguments;
+        try {
+            arguments = ModIngestArguments.parse(raw);
+        } catch (IllegalArgumentException invalid) {
+            IrisModdedCommands.fail(source, IrisLanguage.plain(ModdedCatalogMessages.INGEST_INVALID,
+                    MessageArgument.untrusted("reason", invalid.getMessage())));
+            return 0;
+        }
+        Optional<WorldgenCatalog> catalog = ModdedWorldgenCatalogs.latest();
+        if (catalog.isEmpty()) {
+            IrisModdedCommands.fail(source, IrisLanguage.plain(ModdedCatalogMessages.MISSING));
+            return 0;
+        }
+        File packsRoot = ModdedPackCommands.packsRoot();
+        File sourcePack = PackDirectoryResolver.resolveExisting(packsRoot, arguments.sourcePack());
+        if (sourcePack == null) {
+            IrisModdedCommands.fail(source, IrisLanguage.plain(ModdedCatalogMessages.INGEST_PACK_MISSING,
+                    MessageArgument.untrusted("pack", arguments.sourcePack()),
+                    MessageArgument.untrusted("path", packsRoot.getAbsolutePath())));
+            return 0;
+        }
+        Path targetPack = packsRoot.toPath().toAbsolutePath().normalize().resolve(arguments.targetPack());
+        ModIngestRequest request = new ModIngestRequest(sourcePack.toPath(), targetPack, arguments.dimension(),
+                catalog.get(), arguments.namespaces(), arguments.excludedRegions(), arguments.replace());
+        IrisModdedCommands.ok(source, IrisLanguage.plain(ModdedCatalogMessages.INGEST_STARTED,
+                MessageArgument.untrusted("source", arguments.sourcePack()),
+                MessageArgument.untrusted("target", arguments.targetPack()),
+                MessageArgument.untrusted("dimension", arguments.dimension())));
+        Thread worker = new Thread(() -> runIngest(source, request), "Iris Mod Ingest");
+        worker.setDaemon(true);
+        worker.start();
+        return 1;
+    }
+
+    private static void runIngest(NativeCommandSource source, ModIngestRequest request) {
+        try {
+            ModIngestReport report = ModIngester.ingest(request);
+            source.execute(() -> reportIngest(source, report));
+        } catch (FileAlreadyExistsException exists) {
+            source.execute(() -> IrisModdedCommands.fail(source, IrisLanguage.plain(ModdedCatalogMessages.INGEST_TARGET_EXISTS,
+                    MessageArgument.untrusted("target", request.targetPack().getFileName().toString()))));
+        } catch (IOException | RuntimeException failure) {
+            ModdedIrisLog.error("Iris mod ingest into " + request.targetPack() + " failed", failure);
+            String reason = reason(failure);
+            source.execute(() -> IrisModdedCommands.fail(source, IrisLanguage.plain(ModdedCatalogMessages.INGEST_FAILED,
+                    MessageArgument.untrusted("reason", reason))));
+        }
+    }
+
+    private static void reportIngest(NativeCommandSource source, ModIngestReport report) {
+        for (String line : report.summaryLines()) {
+            IrisModdedCommands.ok(source, IrisLanguage.plain(ModdedCatalogMessages.INGEST_LINE, MessageArgument.untrusted("summary", line)));
+        }
+        IrisModdedCommands.ok(source, IrisLanguage.plain(ModdedCatalogMessages.INGEST_COMPLETE,
+                MessageArgument.untrusted("path", report.targetPack().toString())));
+    }
+
+    private static String namespaceLine(NamespaceSummary summary) {
+        String version = summary.namespace().version().isEmpty() ? NONE : summary.namespace().version();
+        return IrisLanguage.plain(ModdedCatalogMessages.NAMESPACE,
+                MessageArgument.untrusted("name", summary.namespace().namespace()),
+                MessageArgument.untrusted("version", version),
+                MessageArgument.untrusted("value", summary.biomes().size()),
+                MessageArgument.untrusted("value2", summary.placedFeatures().size()),
+                MessageArgument.untrusted("detail", orNone(WorldgenCatalogSummary.featureTypes(summary.featureTypes(), LIST_FEATURE_TYPES))),
+                MessageArgument.untrusted("value3", summary.structures().size()),
+                MessageArgument.untrusted("value4", summary.dimensionTypes().size()),
+                MessageArgument.untrusted("value5", summary.levelStems().size()));
+    }
+
+    private static String orNone(String value) {
+        return value.isEmpty() ? NONE : value;
+    }
+
+    private static String reason(Throwable failure) {
+        Throwable cause = failure instanceof CompletionException && failure.getCause() != null ? failure.getCause() : failure;
+        String message = cause.getMessage();
+        return message == null || message.isBlank() ? cause.getClass().getSimpleName() : message;
+    }
+
+    private static List<String> contentNamespaces() {
+        Optional<WorldgenCatalog> latest = ModdedWorldgenCatalogs.latest();
+        if (latest.isEmpty()) {
+            return List.of();
+        }
+        NamespaceCache cached = NAMESPACE_CACHE.get();
+        if (cached != null && cached.catalog() == latest.get()) {
+            return cached.namespaces();
+        }
+        List<String> namespaces = new ArrayList<>();
+        for (NamespaceSummary summary : WorldgenCatalogSummary.namespaces(latest.get())) {
+            if (summary.hasContent()) {
+                namespaces.add(summary.namespace().namespace());
+            }
+        }
+        NamespaceCache created = new NamespaceCache(latest.get(), List.copyOf(namespaces));
+        NAMESPACE_CACHE.set(created);
+        return created.namespaces();
+    }
+
+    private static CompletableFuture<Suggestions> suggestIngestArguments(CommandContext<NativeCommandSource> context,
+                                                                         SuggestionsBuilder builder) {
+        String remaining = builder.getRemaining();
+        int lastSpace = remaining.lastIndexOf(' ');
+        int bareArguments = 0;
+        List<String> usedOptions = new ArrayList<>(3);
+        for (String token : remaining.substring(0, Math.max(0, lastSpace)).trim().split("\\s+")) {
+            if (token.isEmpty()) {
+                continue;
+            }
+            int equals = token.indexOf('=');
+            if (equals < 0) {
+                bareArguments++;
+            } else {
+                usedOptions.add(token.substring(0, equals + 1));
+            }
+        }
+        SuggestionsBuilder current = builder.createOffset(builder.getStart() + lastSpace + 1);
+        if (bareArguments < 2) {
+            List<String> packs = new ArrayList<>();
+            for (File pack : PackDirectoryResolver.listVisiblePackDirectories(ModdedPackCommands.packsRoot())) {
+                packs.add(pack.getName());
+            }
+            return NativeCommandRegistration.suggest(packs, current);
+        }
+        List<String> options = new ArrayList<>(ModIngestArguments.OPTION_SUGGESTIONS.size());
+        for (String option : ModIngestArguments.OPTION_SUGGESTIONS) {
+            if (!usedOptions.contains(option.substring(0, option.indexOf('=') + 1))) {
+                options.add(option);
+            }
+        }
+        return NativeCommandRegistration.suggest(options, current);
+    }
+
+    private record NamespaceCache(WorldgenCatalog catalog, List<String> namespaces) {
+    }
+}

adapters/modded-common/src/main/java/art/arcane/iris/modded/command/ModdedCommandHelp.java

@@ -18,8 +18,10 @@
 
 package art.arcane.iris.modded.command;
 
+import art.arcane.iris.localization.DirectorCommandMessages;
 import art.arcane.iris.localization.IrisLanguage;
 import art.arcane.iris.localization.IrisMessages;
+import art.arcane.iris.modded.localization.ModdedCatalogMessages;
 import art.arcane.iris.modded.localization.ModdedHelpMessages;
 import art.arcane.volmlib.util.director.help.DirectorHelpMessages;
 import art.arcane.volmlib.util.localization.MessageArgument;
@@ -68,6 +70,8 @@ final class ModdedCommandHelp {
                 Entry.command("debug", "", ModdedHelpMessages.COMMAND_DEBUG_TOGGLE_IRIS_DEBUG_LOGGING_AND_SAVE_SETTINGS_JSON),
                 Entry.command("reload", "", ModdedHelpMessages.COMMAND_RELOAD_RELOAD_SETTINGS_JSON_ALSO_HOTLOADED_AUTOMATICALLY_EVERY_3S),
                 Entry.command("download", "<pack=overworld|pack=underworld|link=<zip-url>> [overwrite=true]", ModdedHelpMessages.COMMAND_DOWNLOAD_DOWNLOAD_A_PACK_PROJECT, "dl"),
+                Entry.command("catalog", "[namespace|refresh]", ModdedCatalogMessages.HELP_CATALOG),
+                Entry.group("ingest", ModdedCatalogMessages.HELP_INGEST),
                 Entry.command("metrics", "", ModdedHelpMessages.COMMAND_METRICS_PRINT_GENERATION_METRICS_FOR_YOUR_CURRENT_IRIS_DIMENSION, "measure"),
                 Entry.command("regen", "[radius]", ModdedHelpMessages.COMMAND_REGEN_DELETE_AND_REGENERATE_NEARBY_CHUNKS_IN_PLACE, "rg"),
                 Entry.group("pregen", ModdedHelpMessages.GROUP_PREGEN_PREGENERATE_AN_IRIS_DIMENSION, "pregenerate"),
@@ -76,6 +80,7 @@ final class ModdedCommandHelp {
                 Entry.group("object", ModdedHelpMessages.GROUP_OBJECT_OBJECT_WAND_SAVE_PASTE_ANALYZE_AND_UNDO_TOOLS, "o"),
                 Entry.group("edit", ModdedHelpMessages.GROUP_EDIT_OPEN_PACK_BIOME_REGION_AND_DIMENSION_JSON_FILES_IN_YOUR_DESKTOP_EDITOR),
                 Entry.command("create", "<name> [pack|pack:dimensionKey] [seed]", ModdedHelpMessages.COMMAND_CREATE_CREATE_AND_INJECT_A_PERSISTENT_IRIS_DIMENSION_QUOTE_PACK_DIMENSIONKEY_TO_PICK, "c"),
+                Entry.command("replace", "<target> [type=<pack|pack:dimensionKey|off>] [seed=<seed>]", DirectorCommandMessages.COMMAND_IRIS_PARAM_REPLACE_EXACT_EXISTING_WORLD_SLOT_NEXT_RESTART, "override", "overwrite"),
                 Entry.command("height", "", ModdedHelpMessages.COMMAND_HEIGHT_PRINT_WORLD_HEIGHT),
                 Entry.command("worlds", "", ModdedHelpMessages.COMMAND_WORLDS_LIST_WORLD_ACCESS, "accesslist"),
                 Entry.group("studio", ModdedHelpMessages.GROUP_STUDIO_PACK_PROJECT_CREATION_PACKAGING_AND_REPORTS, "std", "s"),
@@ -165,6 +170,9 @@ final class ModdedCommandHelp {
                 Entry.command("compat", "[pack]", ModdedHelpMessages.COMMAND_COMPAT_SHOW_CONTENT_THAT_CANNOT_GENERATE_ON_THIS_MINECRAFT_VERSION, "cp")
         ));
         SECTIONS.put("pk", SECTIONS.get("pack"));
+        SECTIONS.put("ingest", List.of(
+                Entry.command("mods", "<source> <target> [dimension=<key>] [namespaces=<a,b>] [excludeRegions=<a,b>] [replace=true]", ModdedCatalogMessages.HELP_INGEST_MODS)
+        ));
         SECTIONS.put("world", List.of(
                 Entry.command("enable", "<dimension> <pack|pack:dimensionKey> [seed|random]", ModdedHelpMessages.COMMAND_ENABLE_CREATE_AND_INJECT_A_PERSISTENT_IRIS_DIMENSION_AT_RUNTIME_DOWNLOADS_THE_PACK, "create"),
                 Entry.command("replace-overworld", "<pack|pack:dimensionKey> [seed|random]", ModdedHelpMessages.COMMAND_REPLACE_OVERWORLD_INJECT_AN_IRIS_PRIMARY_WORLD_AND_ROUTE_PLAYERS_THERE_INSTEAD_OF_THE),

adapters/modded-common/src/main/java/art/arcane/iris/modded/command/ModdedCommandTree.java

@@ -114,6 +114,9 @@ final class ModdedCommandTree {
         root.then(downloadTree("download"));
         root.then(downloadTree("dl"));
 
+        root.then(ModdedCatalogCommands.catalogTree());
+        root.then(ModdedCatalogCommands.ingestTree());
+
         root.then(metricsTree("metrics"));
         root.then(metricsTree("measure"));
 
@@ -135,6 +138,9 @@ final class ModdedCommandTree {
 
         root.then(createTree("create"));
         root.then(createTree("c"));
+        root.then(ModdedReplaceCommands.tree("replace"));
+        root.then(ModdedReplaceCommands.tree("override"));
+        root.then(ModdedReplaceCommands.tree("overwrite"));
 
         root.then(ModdedStudioCommands.tree("studio"));
         root.then(ModdedStudioCommands.tree("std"));

adapters/modded-common/src/main/java/art/arcane/iris/modded/command/ModdedDatapackCommands.java

@@ -163,6 +163,9 @@ public final class ModdedDatapackCommands {
                 continue;
             }
             IrisDimension dimension = engine.getDimension();
+            if (dimension.hasBorrowedDimensionType()) {
+                continue;
+            }
             String json;
             try {
                 json = dimension.getDimensionType().toJson(DataVersion.getRuntime().get());

adapters/modded-common/src/main/java/art/arcane/iris/modded/command/ModdedPregenMethod.java

@@ -114,15 +114,9 @@ public final class ModdedPregenMethod implements PregeneratorMethod {
     @Override
     public void close() {
         try {
-            if (!sync) {
-                try {
-                    semaphore.tryAcquire(maxInFlight, 5, TimeUnit.SECONDS);
-                } catch (InterruptedException e) {
-                    Thread.currentThread().interrupt();
-                }
-            }
-            ModdedIrisLog.info("Iris modded pregen done: dim={} completed={} peakInFlight={} finalLimit={}",
-                    runtime.worldIdentity(), completed.get(), inFlightPeak.get(), adaptiveLimit.get());
+            awaitPendingChunks();
+            ModdedIrisLog.info("Iris modded pregen closing: dim={} completed={} pending={} peakInFlight={} finalLimit={}",
+                    runtime.worldIdentity(), completed.get(), inFlight.get(), inFlightPeak.get(), adaptiveLimit.get());
             try {
                 engine.syncGenerationHistory();
             } catch (RuntimeException e) {
@@ -180,6 +174,39 @@ public final class ModdedPregenMethod implements PregeneratorMethod {
                 || queuedFinalSave.get() != null;
     }
 
+    private void awaitPendingChunks() {
+        if (sync || runtime.isServerThread()) {
+            return;
+        }
+        long deadline = System.nanoTime() + TimeUnit.SECONDS.toNanos(timeoutSeconds)
+                + TimeUnit.MILLISECONDS.toNanos(FINAL_SAVE_TIMEOUT_MILLIS);
+        boolean interrupted = false;
+        try {
+            while (inFlight.get() > 0) {
+                if (finalSaveOnServerThread.get() || !runtime.isRunning()) {
+                    return;
+                }
+                if (System.nanoTime() >= deadline) {
+                    throw new IllegalStateException("Iris pregen chunk callbacks did not finish for "
+                            + runtime.worldIdentity() + ": " + inFlight.get() + " pending");
+                }
+                try {
+                    synchronized (permitMonitor) {
+                        if (inFlight.get() > 0) {
+                            permitMonitor.wait(FINAL_SAVE_POLL_MILLIS);
+                        }
+                    }
+                } catch (InterruptedException ignored) {
+                    interrupted = true;
+                }
+            }
+        } finally {
+            if (interrupted) {
+                Thread.currentThread().interrupt();
+            }
+        }
+    }
+
     private void saveLevel(boolean wait) {
         if (wait) {
             saveFinalLevel();
@@ -237,30 +264,36 @@ public final class ModdedPregenMethod implements PregeneratorMethod {
 
     private void awaitFinalSave(FinalSaveRequest request) {
         long deadline = System.nanoTime() + TimeUnit.MILLISECONDS.toNanos(FINAL_SAVE_TIMEOUT_MILLIS);
-        while (true) {
-            if (deferFinalSaveIfRequested()) {
-                return;
+        boolean interrupted = false;
+        try {
+            while (true) {
+                if (deferFinalSaveIfRequested()) {
+                    return;
+                }
+                long remainingNanos = deadline - System.nanoTime();
+                if (remainingNanos <= 0L) {
+                    ModdedIrisLog.warn("Iris pregen level save did not complete in time for {}", runtime.worldIdentity());
+                    return;
+                }
+                long waitMillis = Math.max(1L, Math.min(FINAL_SAVE_POLL_MILLIS,
+                        TimeUnit.NANOSECONDS.toMillis(remainingNanos)));
+                try {
+                    request.completion().get(waitMillis, TimeUnit.MILLISECONDS);
+                    return;
+                } catch (InterruptedException ignored) {
+                    interrupted = true;
+                } catch (TimeoutException e) {
+                    continue;
+                } catch (ExecutionException e) {
+                    Throwable cause = e.getCause() == null ? e : e.getCause();
+                    ModdedIrisLog.error("Iris pregen level save failed for {}", runtime.worldIdentity(), cause);
+                    throw new IllegalStateException("Iris pregen level save failed for "
+                            + runtime.worldIdentity(), cause);
+                }
             }
-            long remainingNanos = deadline - System.nanoTime();
-            if (remainingNanos <= 0L) {
-                ModdedIrisLog.warn("Iris pregen level save did not complete in time for {}", runtime.worldIdentity());
-                return;
-            }
-            long waitMillis = Math.max(1L, Math.min(FINAL_SAVE_POLL_MILLIS,
-                    TimeUnit.NANOSECONDS.toMillis(remainingNanos)));
-            try {
-                request.completion().get(waitMillis, TimeUnit.MILLISECONDS);
-                return;
-            } catch (InterruptedException e) {
+        } finally {
+            if (interrupted) {
                 Thread.currentThread().interrupt();
-                return;
-            } catch (TimeoutException e) {
-                continue;
-            } catch (ExecutionException e) {
-                Throwable cause = e.getCause() == null ? e : e.getCause();
-                ModdedIrisLog.error("Iris pregen level save failed for {}", runtime.worldIdentity(), cause);
-                throw new IllegalStateException("Iris pregen level save failed for "
-                        + runtime.worldIdentity(), cause);
             }
         }
     }

adapters/modded-common/src/main/java/art/arcane/iris/modded/command/ModdedReplaceArguments.java

@@ -0,0 +1,113 @@
+/*
+ * Iris is a World Generator for Minecraft Servers
+ * Copyright (c) 2026 Arcane Arts (Volmit Software)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package art.arcane.iris.modded.command;
+
+import art.arcane.iris.modded.ModdedDimensionReplacement;
+
+import java.util.List;
+import java.util.Locale;
+import java.util.Map;
+import java.util.OptionalLong;
+
+record ModdedReplaceArguments(String target, String type, OptionalLong seed, boolean off) {
+    static final String DEFAULT_TYPE = "default";
+    static final String OFF = "off";
+    static final String PRESERVE_SEED = "preserve";
+    private static final String TARGET = "target";
+    private static final String TYPE = "type";
+    private static final String SEED = "seed";
+    private static final List<String> POSITIONAL = List.of(TARGET, TYPE, SEED);
+    private static final Map<String, String> KEYS = Map.of(
+            TARGET, TARGET,
+            "world-name", TARGET,
+            TYPE, TYPE,
+            "dimension", TYPE,
+            "pack", TYPE,
+            SEED, SEED,
+            "s", SEED
+    );
+
+    static ModdedReplaceArguments parse(String raw) {
+        String input = raw == null ? "" : raw.trim();
+        String[] values = new String[POSITIONAL.size()];
+        String[] tokens = input.isEmpty() ? new String[0] : input.split("\\s+");
+        for (String token : tokens) {
+            int equals = token.indexOf('=');
+            if (equals < 0) {
+                continue;
+            }
+            String key = KEYS.get(token.substring(0, equals).toLowerCase(Locale.ROOT));
+            if (key == null) {
+                throw new IllegalArgumentException("Unknown argument '" + token.substring(0, equals)
+                        + "'. Use target=, type=, or seed=.");
+            }
+            String value = token.substring(equals + 1);
+            if (value.isEmpty()) {
+                throw new IllegalArgumentException("Argument " + key + "= needs a value.");
+            }
+            int index = POSITIONAL.indexOf(key);
+            if (values[index] != null) {
+                throw new IllegalArgumentException("Argument " + key + " was given more than once.");
+            }
+            values[index] = value;
+        }
+        for (String token : tokens) {
+            if (token.indexOf('=') >= 0) {
+                continue;
+            }
+            int index = nextUnset(values);
+            if (index < 0) {
+                throw new IllegalArgumentException("Unexpected argument '" + token
+                        + "'. Usage: /iris replace <target> [type=<pack|pack:dimensionKey|off>] [seed=<seed>]");
+            }
+            values[index] = token;
+        }
+        if (values[0] == null) {
+            throw new IllegalArgumentException("Missing target. Usage: /iris replace <target> [type=<pack|pack:dimensionKey|off>] [seed=<seed>]");
+        }
+        String type = values[1] == null ? DEFAULT_TYPE : values[1];
+        boolean off = OFF.equalsIgnoreCase(type);
+        if (off && values[2] != null) {
+            throw new IllegalArgumentException("Turning a replacement off takes no seed.");
+        }
+        return new ModdedReplaceArguments(values[0], type, parseSeed(values[2]), off);
+    }
+
+    private static int nextUnset(String[] values) {
+        for (int index = 0; index < values.length; index++) {
+            if (values[index] == null) {
+                return index;
+            }
+        }
+        return -1;
+    }
+
+    private static OptionalLong parseSeed(String raw) {
+        if (raw == null || PRESERVE_SEED.equalsIgnoreCase(raw)) {
+            return OptionalLong.empty();
+        }
+        long seed;
+        try {
+            seed = Long.parseLong(raw);
+        } catch (NumberFormatException failure) {
+            throw new IllegalArgumentException("Seed must be a signed 64-bit integer");
+        }
+        return OptionalLong.of(ModdedDimensionReplacement.requireUsableSeed(seed));
+    }
+}

adapters/modded-common/src/main/java/art/arcane/iris/modded/command/ModdedReplaceCommands.java

@@ -0,0 +1,370 @@
+/*
+ * Iris is a World Generator for Minecraft Servers
+ * Copyright (c) 2026 Arcane Arts (Volmit Software)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package art.arcane.iris.modded.command;
+
+import art.arcane.iris.configuration.IrisSettings;
+import art.arcane.iris.generation.terrain.IrisDimension;
+import art.arcane.iris.localization.BukkitCommandMessagesExtended;
+import art.arcane.iris.localization.IrisLanguage;
+import art.arcane.iris.modded.ModdedDimensionRegistryStore;
+import art.arcane.iris.modded.ModdedDimensionReplacement;
+import art.arcane.iris.modded.ModdedDimensionReplacements;
+import art.arcane.iris.modded.ModdedEngineBootstrap;
+import art.arcane.iris.modded.ModdedForcedDatapack;
+import art.arcane.iris.modded.ModdedIrisLog;
+import art.arcane.iris.modded.ModdedModConfig;
+import art.arcane.iris.modded.ModdedReplacementReconciler;
+import art.arcane.iris.modded.catalog.ModdedWorldgenCatalogs;
+import art.arcane.iris.modded.localization.ModdedCommandMessages;
+import art.arcane.iris.pack.PackDirectoryResolver;
+import art.arcane.iris.pack.PackDownloader;
+import art.arcane.iris.pack.ingest.catalog.WorldgenCatalog;
+import art.arcane.iris.pack.loading.IrisData;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeCommandRegistration;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeCommandSource;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeModdedServer;
+import art.arcane.volmlib.nativelib.terrain.NativeWorld;
+import art.arcane.volmlib.util.localization.MessageArgument;
+import com.mojang.brigadier.arguments.StringArgumentType;
+import com.mojang.brigadier.builder.LiteralArgumentBuilder;
+import com.mojang.brigadier.context.CommandContext;
+import com.mojang.brigadier.exceptions.CommandSyntaxException;
+import com.mojang.brigadier.suggestion.Suggestions;
+import com.mojang.brigadier.suggestion.SuggestionsBuilder;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.stream.Stream;
+import java.util.concurrent.CompletableFuture;
+import java.util.function.Predicate;
+
+final class ModdedReplaceCommands {
+    private static final Predicate<NativeCommandSource> GATE = NativeCommandRegistration.GAMEMASTERS;
+    private static final String ARGUMENTS = "arguments";
+    private static final String MISSING_TARGET = "/iris replace requires an existing exact world slot; use /iris create for a new world.";
+    private static final String STAGE_FAILURE = "Could not stage the world replacement: ";
+    private static final List<String> TARGET_NAMES = List.of("main", "nether", "end");
+    private static final List<String> KEYS = List.of("target=", "type=", "seed=");
+
+    private ModdedReplaceCommands() {
+    }
+
+    static LiteralArgumentBuilder<NativeCommandSource> tree(String name) {
+        return NativeCommandRegistration.literal(name).requires(GATE)
+                .then(NativeCommandRegistration.argument(ARGUMENTS, StringArgumentType.greedyString())
+                        .suggests(ModdedReplaceCommands::suggest)
+                        .executes(ModdedCommandTree.localized((CommandContext<NativeCommandSource> context) -> replace(
+                                context.getSource(),
+                                StringArgumentType.getString(context, ARGUMENTS)))));
+    }
+
+    private static int replace(NativeCommandSource source, String raw) {
+        NativeModdedServer server = source.server();
+        ModdedReplaceArguments arguments;
+        ModdedReplaceTarget target;
+        try {
+            arguments = ModdedReplaceArguments.parse(raw);
+            target = ModdedReplaceTarget.resolve(arguments.target(), levelName(server));
+        } catch (IllegalArgumentException invalid) {
+            IrisModdedCommands.fail(source, invalid.getMessage());
+            return 0;
+        }
+        if (ModdedEngineBootstrap.loader().clientEnvironment()) {
+            IrisModdedCommands.fail(source, "Iris replaces dimensions only on dedicated servers.");
+            return 0;
+        }
+        if (arguments.off()) {
+            return turnOff(source, server, target);
+        }
+        String resolvedType = arguments.type().equalsIgnoreCase(ModdedReplaceArguments.DEFAULT_TYPE)
+                ? IrisSettings.get().getGenerator().getDefaultWorldType()
+                : arguments.type();
+        String pack = packOf(resolvedType);
+        IrisDimension dimension = installedDimension(pack, packDimensionOf(resolvedType));
+        if (dimension == null) {
+            reportDimensionNotFound(source, resolvedType);
+            return 0;
+        }
+        if (ModdedWorldCommands.blockIfPackBroken(source, target.levelKey(), pack)) {
+            return 0;
+        }
+        try {
+            ModdedReplaceTarget.requireCompatibleEnvironment(target.kind(), dimension.getEnvironment());
+            ModdedDimensionReplacement requested = ModdedDimensionReplacements.canonical(
+                    ModdedDimensionReplacement.parse(target.levelKey(), resolvedType, arguments.seed()),
+                    ModdedPackCommands.packsRoot().toPath());
+            ModdedDimensionReplacement staged = target.kind() == ModdedReplaceTarget.Kind.IRIS_WORLD
+                    ? stageIrisWorld(server, requested)
+                    : stageLevel(server, requested);
+            String seedDetail = arguments.seed().isEmpty()
+                    ? " preserving seed " + staged.seed().getAsLong()
+                    : " using seed " + staged.seed().getAsLong();
+            IrisModdedCommands.ok(source, "Staged Iris replacement for " + staged.levelKey() + seedDetail
+                    + ". Restart once to publish it. On that restart the current terrain of the dimension moves to "
+                    + "a replacement-recovery folder under config/irisworldgen; player data stays in the save.");
+            return 1;
+        } catch (IllegalArgumentException rejected) {
+            IrisModdedCommands.fail(source, STAGE_FAILURE + rejected.getMessage());
+            return 0;
+        } catch (IOException | RuntimeException failure) {
+            ModdedIrisLog.error("Iris failed to stage the world replacement for {}", target.levelKey(), failure);
+            IrisModdedCommands.fail(source, STAGE_FAILURE + IrisLanguage.errorDetail(failure));
+            return 0;
+        }
+    }
+
+    private static ModdedDimensionReplacement stageLevel(NativeModdedServer server, ModdedDimensionReplacement requested)
+            throws IOException {
+        NativeWorld level = server.world(requested.levelKey());
+        if (level == null) {
+            throw new IllegalArgumentException(MISSING_TARGET);
+        }
+        Path worldRoot = server.root();
+        requireReplaceableLevel(worldRoot, requested.levelKey());
+        requireNothingPending(worldRoot, requested.levelKey());
+        long seed = requested.seed().orElse(ModdedReplacementReconciler.applied(worldRoot, requested.levelKey())
+                .map((ModdedDimensionReplacement applied) -> applied.seed().getAsLong())
+                .orElse(level.seed()));
+        ModdedDimensionReplacement staged = requested.withSeed(seed);
+        ModdedReplacementReconciler.stagePending(worldRoot, staged);
+        try {
+            if (ModdedModConfig.setDimensionReplacement(staged)) {
+                ModdedForcedDatapack.scheduleRegeneration("dimension replacement of " + staged.levelKey());
+            }
+        } catch (RuntimeException failure) {
+            ModdedReplacementReconciler.cancelPending(worldRoot, staged.levelKey());
+            throw failure;
+        }
+        return staged;
+    }
+
+    private static ModdedDimensionReplacement stageIrisWorld(NativeModdedServer server, ModdedDimensionReplacement requested)
+            throws IOException {
+        ModdedDimensionRegistryStore.PersistentDimension registered =
+                ModdedDimensionRegistryStore.get(server, requested.levelKey());
+        if (registered == null) {
+            throw new IllegalArgumentException(MISSING_TARGET);
+        }
+        Path worldRoot = server.root();
+        requireNothingPending(worldRoot, requested.levelKey());
+        ModdedDimensionReplacement staged = requested.withSeed(requested.seed().orElse(registered.seed()));
+        ModdedReplacementReconciler.stagePending(worldRoot, staged);
+        return staged;
+    }
+
+    private static void requireReplaceableLevel(Path worldRoot, String levelKey) throws IOException {
+        Optional<WorldgenCatalog> catalog = ModdedWorldgenCatalogs.latest();
+        Set<String> applied = ModdedReplacementReconciler.applied(worldRoot, levelKey).isPresent()
+                ? Set.of(levelKey)
+                : Set.of();
+        ModdedDimensionReplacements.ReplaceableLevels levels = catalog.isEmpty()
+                ? ModdedDimensionReplacements.ReplaceableLevels.unknown()
+                : ModdedDimensionReplacements.ReplaceableLevels.of(catalog.get().levelStems(), applied);
+        if (levels.replaceable(levelKey)) {
+            return;
+        }
+        if (!levels.known()) {
+            throw new IllegalArgumentException(IrisLanguage.plain(
+                    ModdedCommandMessages.MODDED_WORLD_COMMANDS_REPLACE_REGISTRY_NOT_READY));
+        }
+        throw new IllegalArgumentException(IrisLanguage.plain(
+                ModdedCommandMessages.MODDED_WORLD_COMMANDS_REPLACE_RUNTIME_LEVEL,
+                MessageArgument.untrusted("dimensionId", levelKey)));
+    }
+
+    private static void requireNothingPending(Path worldRoot, String levelKey) throws IOException {
+        Map<String, ModdedDimensionReplacement> configured = ModdedModConfig.get().dimensionReplacements();
+        if (ModdedReplacementReconciler.pending(worldRoot, levelKey, configured)) {
+            throw new IllegalArgumentException("A replacement is already pending for " + levelKey + ".");
+        }
+    }
+
+    private static int turnOff(NativeCommandSource source, NativeModdedServer server, ModdedReplaceTarget target) {
+        String levelKey = target.levelKey();
+        try {
+            Path worldRoot = server.root();
+            boolean cancelled = ModdedReplacementReconciler.cancelPending(worldRoot, levelKey);
+            boolean applied = target.kind() != ModdedReplaceTarget.Kind.IRIS_WORLD
+                    && ModdedReplacementReconciler.applied(worldRoot, levelKey).isPresent();
+            boolean cleared = target.kind() != ModdedReplaceTarget.Kind.IRIS_WORLD
+                    && ModdedModConfig.clearDimensionReplacement(levelKey);
+            if (cleared) {
+                ModdedForcedDatapack.scheduleRegeneration("dimension replacement of " + levelKey + " turned off");
+            }
+            if (cleared && applied) {
+                IrisModdedCommands.ok(source, "Turned off the Iris replacement of " + levelKey
+                        + ". Restart once to return the dimension to its own generator; its Iris terrain moves to "
+                        + "a replacement-recovery folder under config/irisworldgen.");
+                return 1;
+            }
+            if (cleared || cancelled) {
+                IrisModdedCommands.ok(source, "Cancelled the staged Iris replacement of " + levelKey + ".");
+                return 1;
+            }
+            if (applied) {
+                IrisModdedCommands.ok(source, "The Iris replacement of " + levelKey
+                        + " is already turned off. Restart once to return the dimension to its own generator.");
+                return 1;
+            }
+            IrisModdedCommands.fail(source, "No Iris replacement is staged or applied for " + levelKey + ".");
+            return 0;
+        } catch (IOException | RuntimeException failure) {
+            ModdedIrisLog.error("Iris failed to turn off the replacement of {}", levelKey, failure);
+            IrisModdedCommands.fail(source, "Could not turn off the world replacement: " + IrisLanguage.errorDetail(failure));
+            return 0;
+        }
+    }
+
+    private static String levelName(NativeModdedServer server) {
+        Path levelFolder = server.root().toAbsolutePath().normalize().getFileName();
+        return levelFolder == null ? "" : levelFolder.toString();
+    }
+
+    private static IrisDimension installedDimension(String pack, String packDimension) {
+        if (!pack.matches("[A-Za-z0-9_.-]+") || pack.contains("..")
+                || !packDimension.matches("[A-Za-z0-9_/.-]+") || packDimension.contains("..")) {
+            return null;
+        }
+        File packFolder = new File(ModdedPackCommands.packsRoot(), pack);
+        if (!packFolder.isDirectory()) {
+            return null;
+        }
+        return IrisData.get(packFolder).getDimensionLoader().load(packDimension);
+    }
+
+    private static void reportDimensionNotFound(NativeCommandSource source, String resolvedType) {
+        IrisModdedCommands.fail(source, IrisLanguage.plain(
+                BukkitCommandMessagesExtended.COMMAND_IRIS_DIMENSION_NOT_FOUND,
+                MessageArgument.untrusted("dimension", resolvedType)));
+        List<String> installed = installedTypes(ModdedPackCommands.packsRoot());
+        if (!installed.isEmpty()) {
+            IrisModdedCommands.fail(source, IrisLanguage.plain(
+                    ModdedCommandMessages.MODDED_WORLD_COMMANDS_REPLACE_INSTALLED_TYPES,
+                    MessageArgument.untrusted("value", String.join(", ", installed))));
+        }
+        IrisModdedCommands.fail(source, IrisLanguage.plain(
+                BukkitCommandMessagesExtended.COMMAND_IRIS_INSTALL_PACK_AND_RESTART,
+                MessageArgument.untrusted("command", PackDownloader.downloadCommandFor(packOf(resolvedType)))));
+    }
+
+    static List<String> installedTypes(File packsRoot) {
+        Set<String> types = new TreeSet<>();
+        for (File pack : PackDirectoryResolver.listVisiblePackDirectories(packsRoot)) {
+            List<String> dimensionKeys = dimensionKeys(pack.toPath().resolve("dimensions"));
+            if (dimensionKeys.isEmpty()) {
+                continue;
+            }
+            types.add(pack.getName());
+            for (String dimensionKey : dimensionKeys) {
+                if (!dimensionKey.equals(pack.getName())) {
+                    types.add(pack.getName() + ":" + dimensionKey);
+                }
+            }
+        }
+        return List.copyOf(types);
+    }
+
+    private static List<String> dimensionKeys(Path dimensions) {
+        if (!Files.isDirectory(dimensions)) {
+            return List.of();
+        }
+        List<String> keys = new ArrayList<>();
+        try (Stream<Path> files = Files.walk(dimensions)) {
+            for (Path file : files.filter(Files::isRegularFile).toList()) {
+                String relative = dimensions.relativize(file).toString().replace(File.separatorChar, '/');
+                if (relative.endsWith(".json")) {
+                    keys.add(relative.substring(0, relative.length() - ".json".length()));
+                }
+            }
+        } catch (IOException | RuntimeException unreadable) {
+            ModdedIrisLog.warn("Iris could not list the dimensions of pack folder {}", dimensions.getParent(), unreadable);
+        }
+        return keys;
+    }
+
+    private static String packOf(String type) {
+        String value = type.trim();
+        int colon = value.indexOf(':');
+        return colon >= 0 ? value.substring(0, colon) : value;
+    }
+
+    private static String packDimensionOf(String type) {
+        String value = type.trim();
+        int colon = value.indexOf(':');
+        return colon >= 0 ? value.substring(colon + 1) : value;
+    }
+
+    private static CompletableFuture<Suggestions> suggest(CommandContext<NativeCommandSource> context,
+                                                          SuggestionsBuilder builder) throws CommandSyntaxException {
+        String remaining = builder.getRemaining();
+        int tokenStart = remaining.lastIndexOf(' ') + 1;
+        String token = remaining.substring(tokenStart);
+        int positional = 0;
+        for (String previous : remaining.substring(0, tokenStart).trim().split("\\s+")) {
+            if (!previous.isEmpty() && previous.indexOf('=') < 0) {
+                positional++;
+            }
+        }
+        int equals = token.indexOf('=');
+        if (equals >= 0) {
+            String key = token.substring(0, equals);
+            SuggestionsBuilder valueBuilder = builder.createOffset(builder.getStart() + tokenStart + equals + 1);
+            return switch (key) {
+                case "target", "world-name" -> NativeCommandRegistration.suggest(targetNames(context.getSource()), valueBuilder);
+                case "type", "dimension", "pack" -> typeSuggestions(context, valueBuilder);
+                default -> builder.buildFuture();
+            };
+        }
+        SuggestionsBuilder tokenBuilder = builder.createOffset(builder.getStart() + tokenStart);
+        if (positional == 0) {
+            List<String> targets = new ArrayList<>(targetNames(context.getSource()));
+            targets.addAll(KEYS);
+            return NativeCommandRegistration.suggest(targets, tokenBuilder);
+        }
+        if (positional == 1) {
+            return typeSuggestions(context, tokenBuilder);
+        }
+        return NativeCommandRegistration.suggest(List.of(ModdedReplaceArguments.PRESERVE_SEED), tokenBuilder);
+    }
+
+    private static CompletableFuture<Suggestions> typeSuggestions(CommandContext<NativeCommandSource> context,
+                                                                  SuggestionsBuilder builder)
+            throws CommandSyntaxException {
+        if (ModdedReplaceArguments.OFF.startsWith(builder.getRemainingLowerCase())) {
+            builder.suggest(ModdedReplaceArguments.OFF);
+        }
+        return ModdedCommandSuggestions.PACK_NAMES.getSuggestions(context, builder);
+    }
+
+    private static List<String> targetNames(NativeCommandSource source) {
+        List<String> names = new ArrayList<>(TARGET_NAMES);
+        for (NativeWorld level : source.server().worlds()) {
+            names.add(level.name());
+        }
+        return names;
+    }
+}

adapters/modded-common/src/main/java/art/arcane/iris/modded/command/ModdedReplaceTarget.java

@@ -0,0 +1,122 @@
+/*
+ * Iris is a World Generator for Minecraft Servers
+ * Copyright (c) 2026 Arcane Arts (Volmit Software)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package art.arcane.iris.modded.command;
+
+import art.arcane.iris.modded.ModdedDimensionReplacement;
+import art.arcane.iris.world.IrisEnvironment;
+
+import java.util.Locale;
+import java.util.Objects;
+
+record ModdedReplaceTarget(String levelKey, Kind kind) {
+    static final String IRIS_WORLD_NAMESPACE = "irisworldgen";
+    private static final String PAPER_IRIS_NAMESPACE = "iris";
+    private static final String OVERWORLD = "minecraft:overworld";
+    private static final String NETHER = "minecraft:the_nether";
+    private static final String END = "minecraft:the_end";
+
+    ModdedReplaceTarget {
+        Objects.requireNonNull(levelKey, "levelKey");
+        Objects.requireNonNull(kind, "kind");
+    }
+
+    static ModdedReplaceTarget resolve(String requestedName, String levelName) {
+        String requested = requestedName == null ? "" : requestedName.trim();
+        if (requested.isEmpty()) {
+            throw new IllegalArgumentException("World name cannot be empty.");
+        }
+        String normalized = requested.toLowerCase(Locale.ENGLISH);
+        if (normalized.contains(":")) {
+            return exact(normalized, requestedName);
+        }
+        if (requested.contains("/") || requested.contains("\\") || requested.contains("..")) {
+            throw new IllegalArgumentException("World name must be a safe single path segment.");
+        }
+        String configuredLevelName = levelName == null ? "" : levelName.trim();
+        if (!configuredLevelName.isEmpty()) {
+            if (requested.equalsIgnoreCase(configuredLevelName)) {
+                return of(OVERWORLD);
+            }
+            if (requested.equalsIgnoreCase(configuredLevelName + "_nether")) {
+                return of(NETHER);
+            }
+            if (requested.equalsIgnoreCase(configuredLevelName + "_the_end")) {
+                return of(END);
+            }
+        }
+        return switch (normalized) {
+            case "main", "overworld" -> of(OVERWORLD);
+            case "nether", "the_nether" -> of(NETHER);
+            case "end", "the_end" -> of(END);
+            default -> of(IRIS_WORLD_NAMESPACE + ":" + normalized.replace(' ', '_'));
+        };
+    }
+
+    static void requireCompatibleEnvironment(Kind kind, IrisEnvironment environment) {
+        IrisEnvironment expected = kind.environment();
+        if (expected != null && environment != expected) {
+            throw new IllegalArgumentException("The " + kind.slotName() + " slot requires a pack environment of "
+                    + expected.name() + ".");
+        }
+    }
+
+    private static ModdedReplaceTarget exact(String normalized, String requestedName) {
+        int separator = normalized.indexOf(':');
+        if (separator == 0 || separator == normalized.length() - 1 || separator != normalized.lastIndexOf(':')) {
+            throw new IllegalArgumentException("World identifier is invalid: " + requestedName);
+        }
+        String namespace = normalized.substring(0, separator);
+        String path = normalized.substring(separator + 1);
+        String levelKey = PAPER_IRIS_NAMESPACE.equals(namespace) ? IRIS_WORLD_NAMESPACE + ":" + path : normalized;
+        return of(levelKey);
+    }
+
+    private static ModdedReplaceTarget of(String levelKey) {
+        String level = ModdedDimensionReplacement.requireLevelKey(levelKey);
+        Kind kind = switch (level) {
+            case OVERWORLD -> Kind.VANILLA_OVERWORLD;
+            case NETHER -> Kind.VANILLA_NETHER;
+            case END -> Kind.VANILLA_END;
+            default -> level.startsWith(IRIS_WORLD_NAMESPACE + ":") ? Kind.IRIS_WORLD : Kind.DIMENSION;
+        };
+        return new ModdedReplaceTarget(level, kind);
+    }
+
+    enum Kind {
+        VANILLA_OVERWORLD(IrisEnvironment.NORMAL),
+        VANILLA_NETHER(IrisEnvironment.NETHER),
+        VANILLA_END(IrisEnvironment.THE_END),
+        IRIS_WORLD(null),
+        DIMENSION(null);
+
+        private final IrisEnvironment environment;
+
+        Kind(IrisEnvironment environment) {
+            this.environment = environment;
+        }
+
+        IrisEnvironment environment() {
+            return environment;
+        }
+
+        String slotName() {
+            return name().toLowerCase(Locale.ENGLISH);
+        }
+    }
+}

adapters/modded-common/src/main/java/art/arcane/iris/modded/command/ModdedWorldCommands.java

@@ -26,6 +26,8 @@ import art.arcane.iris.generation.terrain.IrisDimension;
 import art.arcane.iris.modded.IrisModdedChunkGenerator;
 import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeWorldGenerators;
 import art.arcane.iris.modded.MainWorldService;
+import art.arcane.iris.modded.MissingPackDimensionException;
+import art.arcane.iris.modded.ModdedDimensionCreations;
 import art.arcane.iris.modded.ModdedDimensionManager;
 import art.arcane.iris.modded.ModdedEngineBootstrap;
 import art.arcane.iris.modded.ModdedModConfig;
@@ -47,12 +49,16 @@ import java.io.File;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Locale;
+import java.util.UUID;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CompletionException;
 import java.util.concurrent.ThreadLocalRandom;
 import java.util.function.Predicate;
 
 import art.arcane.iris.localization.IrisLanguage;
 import art.arcane.iris.modded.localization.ModdedCommandMessages;
 import art.arcane.iris.localization.RuntimeUiMessages;
+import art.arcane.volmlib.util.localization.LanguageAudience;
 import art.arcane.volmlib.util.localization.MessageArgument;
 public final class ModdedWorldCommands {
     private static final Predicate<NativeCommandSource> GATE = NativeCommandRegistration.GAMEMASTERS;
@@ -193,24 +199,75 @@ public final class ModdedWorldCommands {
     }
 
     private static int enableInstalled(NativeCommandSource source, NativeModdedServer server, String dimensionId, String pack, String packDimension, long seed) {
-        if (blockIfPackBroken(source, dimensionId, pack)) {
-            return 0;
+        return create(source, server, new CreationRequest(dimensionId, pack, packDimension, seed), ModdedWorldCommands::reportWorldCreation);
+    }
+
+    private static int create(NativeCommandSource source, NativeModdedServer server, CreationRequest request, CreationReport report) {
+        CompletableFuture<Void> creation = ModdedDimensionCreations.create(
+                server, request.dimensionId(), request.pack(), request.packDimension(), request.seed());
+        if (creation.isDone()) {
+            Throwable failure = creation.isCompletedExceptionally() ? creation.exceptionNow() : null;
+            report.report(source, request, failure);
+            return failure == null ? 1 : 0;
         }
-        if (!loadPackDimension(source, pack, packDimension)) {
-            return 0;
-        }
-        try {
-            ModdedDimensionManager.createPersistent(server, dimensionId, pack, packDimension, seed);
-        } catch (Throwable e) {
-            ModdedIrisLog.error("Iris world injection failed for {} (pack={} dim={})", dimensionId, pack, packDimension, e);
-            IrisModdedCommands.fail(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_WORLD_COMMANDS_FAILED_INJECT_IRIS_WORLD, MessageArgument.untrusted("dimensionId", dimensionId), MessageArgument.untrusted("value", e.getClass().getSimpleName()), MessageArgument.trusted("errorMessage", IrisLanguage.errorDetail(e))));
-            return 0;
-        }
-        IrisModdedCommands.ok(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_WORLD_COMMANDS_CREATED_IRIS_WORLD_FROM_PACK_DIMENSION_SEED, MessageArgument.untrusted("dimensionId", dimensionId), MessageArgument.untrusted("pack", pack), MessageArgument.untrusted("packDimension", packDimension), MessageArgument.untrusted("seed", seed)));
-        IrisModdedCommands.ok(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_WORLD_COMMANDS_IT_IS_LIVE_NOW_RE_INJECTED_ON_EVERY_STARTUP_TELEPORT));
+        IrisModdedCommands.ok(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_WORLD_COMMANDS_CREATING_IRIS_WORLD_IN_BACKGROUND, MessageArgument.untrusted("dimensionId", request.dimensionId()), MessageArgument.untrusted("pack", request.pack()), MessageArgument.untrusted("packDimension", request.packDimension()), MessageArgument.untrusted("seed", request.seed())));
+        UUID audience = source.playerId();
+        creation.whenComplete((Void ignored, Throwable failure) -> server.execute(
+                () -> LanguageAudience.run(audience, () -> report.report(source, request, failure))));
         return 1;
     }
 
+    private static void reportWorldCreation(NativeCommandSource source, CreationRequest request, Throwable failure) {
+        Throwable cause = creationCause(failure);
+        if (cause == null) {
+            IrisModdedCommands.ok(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_WORLD_COMMANDS_CREATED_IRIS_WORLD_FROM_PACK_DIMENSION_SEED, MessageArgument.untrusted("dimensionId", request.dimensionId()), MessageArgument.untrusted("pack", request.pack()), MessageArgument.untrusted("packDimension", request.packDimension()), MessageArgument.untrusted("seed", request.seed())));
+            IrisModdedCommands.ok(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_WORLD_COMMANDS_IT_IS_LIVE_NOW_RE_INJECTED_ON_EVERY_STARTUP_TELEPORT));
+            return;
+        }
+        if (reportPackRefusal(source, request, cause)) {
+            return;
+        }
+        ModdedIrisLog.error("Iris world injection failed for {} (pack={} dim={})", request.dimensionId(), request.pack(), request.packDimension(), cause);
+        IrisModdedCommands.fail(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_WORLD_COMMANDS_FAILED_INJECT_IRIS_WORLD, MessageArgument.untrusted("dimensionId", request.dimensionId()), MessageArgument.untrusted("value", cause.getClass().getSimpleName()), MessageArgument.trusted("errorMessage", IrisLanguage.errorDetail(cause))));
+    }
+
+    private static void reportPrimaryCreation(NativeCommandSource source, CreationRequest request, Throwable failure) {
+        Throwable cause = creationCause(failure);
+        if (cause == null) {
+            ModdedModConfig.setPrimaryWorld(request.dimensionId());
+            ModdedPrimaryWorldRouter.clear();
+            IrisModdedCommands.ok(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_WORLD_COMMANDS_IRIS_PRIMARY_WORLD_SET_PACK_DIMENSION_SEED, MessageArgument.untrusted("dimensionId", request.dimensionId()), MessageArgument.untrusted("pack", request.pack()), MessageArgument.untrusted("packDimension", request.packDimension()), MessageArgument.untrusted("seed", request.seed())));
+            IrisModdedCommands.ok(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_WORLD_COMMANDS_VANILLA_OVERWORLD_GENERATOR_CANNOT_BE_HOT_SWAPPED_SO_THIS_DOES));
+            IrisModdedCommands.ok(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_WORLD_COMMANDS_INSTEAD_IS_NOW_CONFIGURED_PRIMARY_WORLD_PLAYERS_VANILLA_OVERWORLD_ARE, MessageArgument.untrusted("dimensionId", request.dimensionId())));
+            return;
+        }
+        if (reportPackRefusal(source, request, cause)) {
+            return;
+        }
+        ModdedIrisLog.error("Iris primary world injection failed for {} (pack={} dim={})", request.dimensionId(), request.pack(), request.packDimension(), cause);
+        IrisModdedCommands.fail(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_WORLD_COMMANDS_FAILED_INJECT_IRIS_PRIMARY_WORLD, MessageArgument.untrusted("value", cause.getClass().getSimpleName()), MessageArgument.trusted("errorMessage", IrisLanguage.errorDetail(cause))));
+    }
+
+    private static boolean reportPackRefusal(NativeCommandSource source, CreationRequest request, Throwable cause) {
+        if (cause instanceof BrokenPackException broken) {
+            reportBrokenPack(source, request.dimensionId(), request.pack(), broken);
+            return true;
+        }
+        if (cause instanceof MissingPackDimensionException missing) {
+            IrisModdedCommands.fail(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_WORLD_COMMANDS_PACK_DOES_NOT_CONTAIN_DIMENSIONS_JSON, MessageArgument.untrusted("pack", missing.pack()), MessageArgument.untrusted("packDimension", missing.dimensionKey())));
+            return true;
+        }
+        return false;
+    }
+
+    private static Throwable creationCause(Throwable failure) {
+        Throwable cause = failure;
+        while (cause instanceof CompletionException && cause.getCause() != null) {
+            cause = cause.getCause();
+        }
+        return cause;
+    }
+
     private static int update(NativeCommandSource source, String targetDimension, String packRaw) {
         String dimensionId;
         try {
@@ -265,25 +322,12 @@ public final class ModdedWorldCommands {
             return 0;
         }
         String dimensionId = DEFAULT_NAMESPACE + ":primary";
-        if (blockIfPackBroken(source, dimensionId, pack)) {
+        File packFolder = new File(ModdedPackCommands.packsRoot(), pack);
+        if (!packFolder.isDirectory()) {
+            IrisModdedCommands.fail(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_WORLD_COMMANDS_PACK_WAS_NOT_FOUND_UNDER, MessageArgument.untrusted("pack", pack), MessageArgument.untrusted("value", ModdedPackCommands.packsRoot().getAbsolutePath())));
             return 0;
         }
-        if (!loadPackDimension(source, pack, packDimension)) {
-            return 0;
-        }
-        try {
-            ModdedDimensionManager.createPersistent(server, dimensionId, pack, packDimension, seed);
-        } catch (Throwable e) {
-            ModdedIrisLog.error("Iris primary world injection failed for {} (pack={} dim={})", dimensionId, pack, packDimension, e);
-            IrisModdedCommands.fail(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_WORLD_COMMANDS_FAILED_INJECT_IRIS_PRIMARY_WORLD, MessageArgument.untrusted("value", e.getClass().getSimpleName()), MessageArgument.trusted("errorMessage", IrisLanguage.errorDetail(e))));
-            return 0;
-        }
-        ModdedModConfig.setPrimaryWorld(dimensionId);
-        ModdedPrimaryWorldRouter.clear();
-        IrisModdedCommands.ok(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_WORLD_COMMANDS_IRIS_PRIMARY_WORLD_SET_PACK_DIMENSION_SEED, MessageArgument.untrusted("dimensionId", dimensionId), MessageArgument.untrusted("pack", pack), MessageArgument.untrusted("packDimension", packDimension), MessageArgument.untrusted("seed", seed)));
-        IrisModdedCommands.ok(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_WORLD_COMMANDS_VANILLA_OVERWORLD_GENERATOR_CANNOT_BE_HOT_SWAPPED_SO_THIS_DOES));
-        IrisModdedCommands.ok(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_WORLD_COMMANDS_INSTEAD_IS_NOW_CONFIGURED_PRIMARY_WORLD_PLAYERS_VANILLA_OVERWORLD_ARE, MessageArgument.untrusted("dimensionId", dimensionId)));
-        return 1;
+        return create(source, server, new CreationRequest(dimensionId, pack, packDimension, seed), ModdedWorldCommands::reportPrimaryCreation);
     }
 
     private static int clearMainWorld(NativeCommandSource source) {
@@ -363,20 +407,24 @@ public final class ModdedWorldCommands {
         return 1;
     }
 
-    private static boolean blockIfPackBroken(NativeCommandSource source, String dimensionId, String pack) {
+    static boolean blockIfPackBroken(NativeCommandSource source, String dimensionId, String pack) {
         try {
             ModdedStartup.requirePackForWorldCreation(pack);
             return false;
         } catch (BrokenPackException e) {
-            IrisModdedCommands.fail(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_WORLD_COMMANDS_REFUSING_CREATE_WORLD_USING_PACK_BECAUSE_REQUIRED_VALIDATION_FAILED, MessageArgument.untrusted("dimensionId", dimensionId), MessageArgument.untrusted("pack", pack)));
-            for (String reason : e.getReasons()) {
-                IrisModdedCommands.fail(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_WORLD_COMMANDS_MESSAGE, MessageArgument.untrusted("reason", reason)));
-            }
-            IrisModdedCommands.fail(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_WORLD_COMMANDS_FIX_PACK_RUN_IRIS_PACK_VALIDATE_REVALIDATE, MessageArgument.untrusted("pack", pack)));
+            reportBrokenPack(source, dimensionId, pack, e);
             return true;
         }
     }
 
+    private static void reportBrokenPack(NativeCommandSource source, String dimensionId, String pack, BrokenPackException broken) {
+        IrisModdedCommands.fail(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_WORLD_COMMANDS_REFUSING_CREATE_WORLD_USING_PACK_BECAUSE_REQUIRED_VALIDATION_FAILED, MessageArgument.untrusted("dimensionId", dimensionId), MessageArgument.untrusted("pack", pack)));
+        for (String reason : broken.getReasons()) {
+            IrisModdedCommands.fail(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_WORLD_COMMANDS_MESSAGE, MessageArgument.untrusted("reason", reason)));
+        }
+        IrisModdedCommands.fail(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_WORLD_COMMANDS_FIX_PACK_RUN_IRIS_PACK_VALIDATE_REVALIDATE, MessageArgument.untrusted("pack", pack)));
+    }
+
     private static boolean loadPackDimension(NativeCommandSource source, String pack, String packDimension) {
         File packFolder = new File(ModdedPackCommands.packsRoot(), pack);
         if (!packFolder.isDirectory()) {
@@ -532,4 +580,12 @@ public final class ModdedWorldCommands {
         }
         return namespace + ":" + path;
     }
+
+    @FunctionalInterface
+    private interface CreationReport {
+        void report(NativeCommandSource source, CreationRequest request, Throwable failure);
+    }
+
+    private record CreationRequest(String dimensionId, String pack, String packDimension, long seed) {
+    }
 }

adapters/modded-common/src/main/java/art/arcane/iris/modded/localization/ModdedCatalogMessages.java

@@ -0,0 +1,150 @@
+/*
+ * Iris is a World Generator for Minecraft Servers
+ * Copyright (c) 2026 Arcane Arts (Volmit Software)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package art.arcane.iris.modded.localization;
+
+import art.arcane.volmlib.util.localization.MessageKey;
+import art.arcane.volmlib.util.localization.TextKey;
+
+import java.util.List;
+
+public final class ModdedCatalogMessages {
+    public static final TextKey MISSING = TextKey.of(
+            "iris.modded.catalog.missing",
+            "No worldgen catalog has been captured yet. Run /iris catalog refresh."
+    );
+    public static final TextKey HEADER = TextKey.of(
+            "iris.modded.catalog.header",
+            "Worldgen catalog ({name} {version}): {count} namespaces, {value} biomes, {value2} placed features, "
+                    + "{value3} structures, {value4} dimension types, {value5} level stems"
+    );
+    public static final TextKey NAMESPACE = TextKey.of(
+            "iris.modded.catalog.namespace",
+            "{name} {version}: {value} biomes, {value2} placed features ({detail}), {value3} structures, "
+                    + "{value4} dimension types, {value5} level stems"
+    );
+    public static final TextKey QUIET = TextKey.of(
+            "iris.modded.catalog.quiet",
+            "{count} more loaded mods have no worldgen content."
+    );
+    public static final TextKey UNKNOWN_NAMESPACE = TextKey.of(
+            "iris.modded.catalog.unknown_namespace",
+            "The worldgen catalog has no content from namespace {name}."
+    );
+    public static final TextKey DETAIL_BIOMES = TextKey.of(
+            "iris.modded.catalog.detail_biomes",
+            "Biomes ({count}): {value}"
+    );
+    public static final TextKey DETAIL_FEATURES = TextKey.of(
+            "iris.modded.catalog.detail_features",
+            "Placed features by type ({count}): {value}"
+    );
+    public static final TextKey DETAIL_STRUCTURES = TextKey.of(
+            "iris.modded.catalog.detail_structures",
+            "Structures ({count}): {value}"
+    );
+    public static final TextKey DETAIL_DIMENSIONS = TextKey.of(
+            "iris.modded.catalog.detail_dimensions",
+            "Dimension types: {value}; level stems: {value2}"
+    );
+    public static final TextKey REFRESHING = TextKey.of(
+            "iris.modded.catalog.refreshing",
+            "Capturing the worldgen catalog..."
+    );
+    public static final TextKey REFRESHED = TextKey.of(
+            "iris.modded.catalog.refreshed",
+            "Worldgen catalog captured in {duration}: {path}"
+    );
+    public static final TextKey REFRESH_FAILED = TextKey.of(
+            "iris.modded.catalog.refresh_failed",
+            "Worldgen catalog capture failed: {reason}"
+    );
+    public static final TextKey INGEST_INVALID = TextKey.of(
+            "iris.modded.catalog.ingest_invalid",
+            "Invalid arguments: {reason}. Usage: /iris ingest mods <source> <target> [dimension=<key>] "
+                    + "[namespaces=<a,b>] [excludeRegions=<a,b>] [replace=true]"
+    );
+    public static final TextKey INGEST_PACK_MISSING = TextKey.of(
+            "iris.modded.catalog.ingest_pack_missing",
+            "Pack '{pack}' was not found under {path}."
+    );
+    public static final TextKey INGEST_STARTED = TextKey.of(
+            "iris.modded.catalog.ingest_started",
+            "Ingesting mod worldgen from '{source}' into '{target}' (dimension {dimension})..."
+    );
+    public static final TextKey INGEST_FAILED = TextKey.of(
+            "iris.modded.catalog.ingest_failed",
+            "Mod ingest failed: {reason}"
+    );
+    public static final TextKey INGEST_TARGET_EXISTS = TextKey.of(
+            "iris.modded.catalog.ingest_target_exists",
+            "Target pack '{target}' already exists. Add replace=true to overwrite it."
+    );
+    public static final TextKey INGEST_LINE = TextKey.of(
+            "iris.modded.catalog.ingest_line",
+            "  {summary}"
+    );
+    public static final TextKey INGEST_COMPLETE = TextKey.of(
+            "iris.modded.catalog.ingest_complete",
+            "Mod ingest finished: {path}"
+    );
+    public static final TextKey HELP_CATALOG = TextKey.of(
+            "iris.modded.help.entry.command.catalog",
+            "List the worldgen content of loaded mods, show one namespace, or capture it again"
+    );
+    public static final TextKey HELP_INGEST = TextKey.of(
+            "iris.modded.help.entry.group.ingest",
+            "Build Iris packs from the worldgen content of loaded mods"
+    );
+    public static final TextKey HELP_INGEST_MODS = TextKey.of(
+            "iris.modded.help.entry.command.ingest_mods",
+            "Copy a source pack into a new target pack and adopt the worldgen of loaded mods"
+    );
+
+    private static final List<MessageKey> KEYS = List.of(
+            MISSING,
+            HEADER,
+            NAMESPACE,
+            QUIET,
+            UNKNOWN_NAMESPACE,
+            DETAIL_BIOMES,
+            DETAIL_FEATURES,
+            DETAIL_STRUCTURES,
+            DETAIL_DIMENSIONS,
+            REFRESHING,
+            REFRESHED,
+            REFRESH_FAILED,
+            INGEST_INVALID,
+            INGEST_PACK_MISSING,
+            INGEST_STARTED,
+            INGEST_FAILED,
+            INGEST_TARGET_EXISTS,
+            INGEST_LINE,
+            INGEST_COMPLETE,
+            HELP_CATALOG,
+            HELP_INGEST,
+            HELP_INGEST_MODS
+    );
+
+    private ModdedCatalogMessages() {
+    }
+
+    public static List<MessageKey> keys() {
+        return KEYS;
+    }
+}

adapters/modded-common/src/main/java/art/arcane/iris/modded/localization/ModdedCommandMessages.java

@@ -1124,6 +1124,10 @@ public final class ModdedCommandMessages {
             "iris.modded.moddedworldcommands.failed_inject_iris_world",
             "Failed to inject Iris world '" + "{dimensionId}" + "': " + "{value}" + "{errorMessage}"
     );
+    public static final TextKey MODDED_WORLD_COMMANDS_CREATING_IRIS_WORLD_IN_BACKGROUND = TextKey.of(
+            "iris.modded.moddedworldcommands.creating_iris_world_in_background",
+            "Creating Iris world " + "{dimensionId}" + " from pack '" + "{pack}" + "' dimension '" + "{packDimension}" + "' (seed " + "{seed}" + ") in the background. You will be told when it is live."
+    );
     public static final TextKey MODDED_WORLD_COMMANDS_CREATED_IRIS_WORLD_FROM_PACK_DIMENSION_SEED = TextKey.of(
             "iris.modded.moddedworldcommands.created_iris_world_from_pack_dimension_seed",
             "Created Iris world " + "{dimensionId}" + " from pack '" + "{pack}" + "' dimension '" + "{packDimension}" + "' (seed " + "{seed}" + ")."
@@ -1260,6 +1264,18 @@ public final class ModdedCommandMessages {
             "iris.modded.moddedworldcommands.use_iris_world_create_name_pack_inject_one_without_restarting",
             "Use /iris world create <name> <pack> to inject one without restarting."
     );
+    public static final TextKey MODDED_WORLD_COMMANDS_REPLACE_RUNTIME_LEVEL = TextKey.of(
+            "iris.modded.moddedworldcommands.replace_runtime_level",
+            "{dimensionId}" + " is created by a mod while the server runs and is not defined as a dimension, so Iris cannot replace it."
+    );
+    public static final TextKey MODDED_WORLD_COMMANDS_REPLACE_REGISTRY_NOT_READY = TextKey.of(
+            "iris.modded.moddedworldcommands.replace_registry_not_ready",
+            "Iris is still reading this server's dimensions. Try again in a moment."
+    );
+    public static final TextKey MODDED_WORLD_COMMANDS_REPLACE_INSTALLED_TYPES = TextKey.of(
+            "iris.modded.moddedworldcommands.replace_installed_types",
+            "Installed packs: " + "{value}"
+    );
 
     private static final List<MessageKey> KEYS = List.of(
             IRIS_MODDED_COMMANDS_THIS_DIMENSION_IS_NOT_GENERATED_BY_IRIS,
@@ -1541,6 +1557,7 @@ public final class ModdedCommandMessages {
             MODDED_STUDIO_COMMANDS_REGION_SAMPLING_FAILED,
             MODDED_WORLD_COMMANDS_REQUIRED_PACK_IS_NOT_INSTALLED_INSTALL_THEN_RESTART,
             MODDED_WORLD_COMMANDS_FAILED_INJECT_IRIS_WORLD,
+            MODDED_WORLD_COMMANDS_CREATING_IRIS_WORLD_IN_BACKGROUND,
             MODDED_WORLD_COMMANDS_CREATED_IRIS_WORLD_FROM_PACK_DIMENSION_SEED,
             MODDED_WORLD_COMMANDS_IT_IS_LIVE_NOW_RE_INJECTED_ON_EVERY_STARTUP_TELEPORT,
             MODDED_WORLD_COMMANDS_FAILED_INJECT_IRIS_PRIMARY_WORLD,
@@ -1574,7 +1591,10 @@ public final class ModdedCommandMessages {
             MODDED_WORLD_COMMANDS_NO_IRIS_DIMENSIONS_ARE_CURRENTLY_LOADED_CREATE_ONE_WITH_IRIS,
             MODDED_WORLD_COMMANDS_LOADED_IRIS_DIMENSIONS,
             MODDED_WORLD_COMMANDS_MESSAGE_2,
-            MODDED_WORLD_COMMANDS_USE_IRIS_WORLD_CREATE_NAME_PACK_INJECT_ONE_WITHOUT_RESTARTING
+            MODDED_WORLD_COMMANDS_USE_IRIS_WORLD_CREATE_NAME_PACK_INJECT_ONE_WITHOUT_RESTARTING,
+            MODDED_WORLD_COMMANDS_REPLACE_RUNTIME_LEVEL,
+            MODDED_WORLD_COMMANDS_REPLACE_REGISTRY_NOT_READY,
+            MODDED_WORLD_COMMANDS_REPLACE_INSTALLED_TYPES
     );
 
     private ModdedCommandMessages() {

adapters/modded-common/src/main/java/art/arcane/iris/modded/localization/ModdedMessageContributor.java

@@ -12,6 +12,7 @@ public final class ModdedMessageContributor implements IrisMessageContributor {
         List<MessageKey> keys = new ArrayList<>();
         keys.addAll(ModdedCommandMessages.keys());
         keys.addAll(ModdedHelpMessages.keys());
+        keys.addAll(ModdedCatalogMessages.keys());
         keys.addAll(ClientUiMessages.keys());
         return List.copyOf(keys);
     }

adapters/modded-common/src/main/java/art/arcane/iris/modded/service/ModdedChunkUpdateService.java

@@ -30,7 +30,6 @@ import art.arcane.iris.studio.view.PregeneratorJob;
 import art.arcane.iris.integration.Identifier;
 import art.arcane.iris.generation.cache.Cache;
 import art.arcane.iris.generation.runtime.Engine;
-import art.arcane.iris.generation.runtime.GenerationFailures;
 import art.arcane.iris.generation.block.TileData;
 import art.arcane.iris.modded.IrisModdedChunkGenerator;
 import art.arcane.iris.modded.ModdedBlockResolution;
@@ -382,16 +381,7 @@ public final class ModdedChunkUpdateService implements ModdedTickableService {
             if (!state.isStorageChest()) {
                 return;
             }
-            try {
-                ModdedLootApplier.apply(engine, level, pos, state, chunk);
-            } catch (SavedBiomeUnavailableException unavailable) {
-                GenerationFailures.rethrowEngineFailure(unavailable);
-                IrisLogging.warnOnce("chunk-update-loot:" + level.name() + ":" + unavailable.getMessage(),
-                        "Iris left the container at " + pos + " in " + level.name() + " without loot: " + unavailable.getMessage());
-            } catch (Throwable e) {
-                GenerationFailures.rethrowEngineFailure(e);
-                IrisLogging.reportError(e);
-            }
+            ModdedLootApplier.apply(engine, level, pos, state, chunk);
         } else {
             NativeWorldMaintenance.refresh(level, pos);
         }

adapters/modded-common/src/test/java/art/arcane/iris/modded/IrisModLanguageAssetsTest.java

@@ -74,7 +74,8 @@ public class IrisModLanguageAssetsTest {
     private Set<String> resourceFiles() throws Exception {
         URL resource = IrisModLanguageAssetsTest.class.getClassLoader().getResource(ROOT + "en_us.json");
         assertNotNull("Missing English mod language resource", resource);
-        assertEquals("Mod language resources must resolve to a directory on disk", "file", resource.getProtocol());
+        assertTrue("Mod language resources must resolve to a directory, got " + resource,
+                resource.getProtocol().equals("file") || resource.getProtocol().equals("union"));
         Path directory = Path.of(resource.toURI()).getParent();
         try (Stream<Path> paths = Files.list(directory)) {
             return paths

adapters/modded-common/src/test/java/art/arcane/iris/modded/ModdedBiomePolicyTest.java

@@ -6,11 +6,17 @@ import art.arcane.iris.generation.runtime.DimensionStackLayout;
 import art.arcane.iris.generation.terrain.IrisDimension;
 import art.arcane.iris.generation.subterrain.IrisSubterrainFeature;
 import art.arcane.iris.pack.loading.IrisData;
+import art.arcane.iris.pack.loading.ResourceLoader;
+import art.arcane.iris.generation.terrain.IrisRegion;
 import art.arcane.volmlib.util.collection.KList;
 import art.arcane.iris.generation.runtime.GenerationSessionException;
 import art.arcane.iris.generation.runtime.GenerationSessionLease;
 import art.arcane.iris.generation.runtime.IrisComplex;
+import art.arcane.iris.generation.runtime.IrisEngine;
+import art.arcane.iris.world.history.GenerationHistoryRuntimeRouter;
 import art.arcane.volmlib.nativelib.terrain.NativeBiomeSourceAccess;
+import art.arcane.volmlib.nativelib.terrain.NativeBiomeSourcePolicy;
+import art.arcane.volmlib.nativelib.terrain.NativeModdedBiomePolicy;
 import art.arcane.volmlib.util.stream.ProceduralStream;
 import art.arcane.volmlib.util.stream.interpolation.Interpolated;
 import org.junit.Test;
@@ -20,7 +26,9 @@ import java.io.File;
 import java.lang.reflect.Field;
 import java.lang.reflect.Method;
 import java.util.List;
+import java.util.Optional;
 import java.util.Set;
+import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Consumer;
 
@@ -29,8 +37,12 @@ import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertSame;
 import static org.junit.Assert.assertThrows;
 import static org.junit.Assert.assertTrue;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.anyInt;
 import static org.mockito.ArgumentMatchers.anyString;
 import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.verifyNoInteractions;
 import static org.mockito.Mockito.when;
 
@@ -140,6 +152,92 @@ public class ModdedBiomePolicyTest {
         assertThrows(IllegalStateException.class, () -> boundTo(unready).getVisibleSurfaceBiome(8, 8));
     }
 
+    /**
+     * Vanilla /locate biome samples a 6400 block radius every 32 blocks. Each Iris surface sample needs the column's
+     * terrain height, so the search may only resolve columns whose region and biome streams can hold the target, and
+     * it must answer with the visible biome a chunk is filled with.
+     */
+    @Test
+    public void locateResolvesVisibleBiomesOnlyInColumnsThatCanHoldTheTarget() throws Exception {
+        BiomeToken mirage = new BiomeToken("terralith:mirage_isles");
+        BiomeToken plains = new BiomeToken("minecraft:plains");
+        IrisBiome isles = new IrisBiome().setDerivative("terralith:mirage_isles");
+        isles.setLoadKey("isles");
+        IrisBiome meadow = new IrisBiome().setDerivative("minecraft:plains");
+        meadow.setLoadKey("meadow");
+        IrisRegion main = new IrisRegion().setLandBiomes(new KList<>("meadow"));
+        main.setLoadKey("main");
+        IrisRegion archipelago = new IrisRegion().setLandBiomes(new KList<>("isles"));
+        archipelago.setLoadKey("archipelago");
+        IrisDimension dimension = mock(IrisDimension.class);
+        when(dimension.getReachableBiomes(any())).thenReturn(new KList<>(meadow, isles));
+        when(dimension.getAllRegions(any())).thenReturn(new KList<>(main, archipelago));
+        when(dimension.getCarving()).thenReturn(new KList<>());
+        when(dimension.getSubterrainFeatures()).thenReturn(new KList<>());
+        @SuppressWarnings("unchecked")
+        ResourceLoader<IrisBiome> biomes = (ResourceLoader<IrisBiome>) mock(ResourceLoader.class);
+        when(biomes.load("meadow")).thenReturn(meadow);
+        when(biomes.load("isles")).thenReturn(isles);
+        IrisData data = mock(IrisData.class);
+        when(data.getDataFolder()).thenReturn(new File("synthetic-pack"));
+        when(data.getBiomeLoader()).thenReturn(biomes);
+        when(data.physicalBiomeResourceKey(any(), anyString())).thenAnswer(invocation -> invocation.getArgument(1));
+        IrisComplex complex = mock(IrisComplex.class);
+        when(complex.getRegionStream()).thenReturn(ProceduralStream.of(
+                (x, z) -> x >= 4096D ? archipelago : main, Interpolated.of(value -> 0D, value -> main)));
+        when(complex.getLandBiomeStream()).thenReturn(ProceduralStream.of(
+                (x, z) -> x >= 4096D ? isles : meadow, Interpolated.of(value -> 0D, value -> meadow)));
+        when(complex.getSeaBiomeStream()).thenReturn(ProceduralStream.of(
+                (x, z) -> meadow, Interpolated.of(value -> 0D, value -> meadow)));
+        when(complex.getShoreBiomeStream()).thenReturn(ProceduralStream.of(
+                (x, z) -> meadow, Interpolated.of(value -> 0D, value -> meadow)));
+        when(complex.historicalPhysicalBiomeKeyAt(anyInt(), anyInt(), anyInt())).thenReturn(Optional.empty());
+        GenerationHistoryRuntimeRouter router = mock(GenerationHistoryRuntimeRouter.class);
+        GenerationHistoryRuntimeRouter.CoordinateScope scope = mock(GenerationHistoryRuntimeRouter.CoordinateScope.class);
+        when(router.openCoordinateScope(anyInt(), anyInt())).thenReturn(scope);
+        IrisEngine engine = mock(IrisEngine.class);
+        when(engine.getGenerationHistoryRuntimeRouter()).thenReturn(Optional.of(router));
+        when(engine.getDimension()).thenReturn(dimension);
+        when(engine.getData()).thenReturn(data);
+        when(engine.getComplex()).thenReturn(complex);
+        when(engine.getMinHeight()).thenReturn(-64);
+        when(engine.getCacheID()).thenReturn(1);
+        when(engine.acquireGenerationLease(anyString())).thenReturn(GenerationSessionLease.noop());
+        when(engine.answersFromNaturalTerrain(anyInt(), anyInt())).thenReturn(true);
+        AtomicInteger heightSamples = new AtomicInteger();
+        when(engine.getHostSurfaceBiome(anyInt(), anyInt())).thenAnswer(invocation -> {
+            heightSamples.incrementAndGet();
+            return invocation.<Integer>getArgument(0) >= 4096 ? isles : meadow;
+        });
+        ModdedBiomePolicy<BiomeToken, Object> policy = new ModdedBiomePolicy<>(
+                new Access(new ArrayList<>(List.of(plains, mirage))));
+        policy.bind(new ModdedBiomePolicy.RuntimeCallbacks(() -> engine, () -> engine, bound -> false,
+                () -> Set.of(plains.key(), mirage.key()), bound -> Set.of(), () -> 0L));
+        int[] columns = {0, 1024, 2048, 3072, 4096, 5120};
+
+        NativeBiomeSourcePolicy.BiomeLocation<BiomeToken> found = policy.findClosestBiome3d(
+                new NativeModdedBiomePolicy.ClosestQuery<>(mirage::equals, null,
+                        () -> {
+                            throw new AssertionError("A bound engine must not use the unbound search");
+                        },
+                        (candidates, resolver) -> {
+                            for (int x : columns) {
+                                NativeBiomeSourcePolicy.Column<BiomeToken> column = resolver.resolve(x, 0);
+                                BiomeToken biome = column.sample(100);
+                                if (candidates.contains(biome)) {
+                                    return new NativeBiomeSourcePolicy.BiomeLocation<>(x, 100, 0, biome);
+                                }
+                            }
+                            return null;
+                        }));
+
+        assertEquals(new NativeBiomeSourcePolicy.BiomeLocation<>(4096, 100, 0, mirage), found);
+        assertEquals(1, heightSamples.get());
+        verify(router).openCoordinateScope(4096, 0);
+        verify(router, times(1)).openCoordinateScope(anyInt(), anyInt());
+        verify(scope).close();
+    }
+
     private static ModdedBiomePolicy<BiomeToken, Object> boundTo(Engine engine) {
         ModdedBiomePolicy<BiomeToken, Object> policy = new ModdedBiomePolicy<>(new Access(new ArrayList<>()));
         policy.bind(new ModdedBiomePolicy.RuntimeCallbacks(() -> engine, () -> engine, bound -> true,