Fail-closed generation fixes

- History validation always re-renders stored semantics with the current fixer
- Broken Iris worlds get a refusing generator and a banner instead of vanilla
- A failed enable locks Iris worlds instead of disabling the plugin
- Engine failures fail the chunk instead of skipping objects or features
- Modded engines close after levels unload instead of at server stopping
- Folia maintenance refuses chunks only after players leave the world
- Saved-biome loading defers chunk update passes
- Mixin audit handler names are checked against the compiled mixins
- Teleports wait up to 120 s and report the real failure

adapters/bukkit/nms/v26_3_R1/src/offline/java/art/arcane/iris/probe/HeadlessNativePlatform.java

@@ -15,7 +15,6 @@ import art.arcane.volmlib.nativelib.minecraft26_2.modded.ModdedBlockState;
 import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeBlockResolver;
 import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeRegistryAccess;
 import art.arcane.volmlib.nativelib.v26_3_R1.terrain.NativeGenerationRegistryImpl;
-import art.arcane.volmlib.nativelib.v26_3_R1.terrain.NativeWorldGenerationImpl;
 import art.arcane.volmlib.nativelib.terrain.NativeBiome;
 import art.arcane.volmlib.nativelib.terrain.NativeBlockProperty;
 import art.arcane.volmlib.nativelib.terrain.NativeBlockState;
@@ -49,7 +48,7 @@ final class HeadlessNativePlatform implements IrisPlatform, PlatformRegistries,
                 return access;
             }
             throw new IllegalStateException("Generation registry contract requires loaded native registries");
-        }), "bukkit-generation-registry-v1", new NativeWorldGenerationImpl().generationRendererIdentity());
+        }), "bukkit-generation-registry-v1");
         nativeAccess = new NativeRegistryAccess(new NativeRegistryAccess.Configuration(registries,
                 () -> { throw new UnsupportedOperationException("Headless reloadable registries are not loaded"); },
                 message -> { throw new IllegalStateException("Unavailable native registry: " + message); }));

adapters/bukkit/nms/v26_3_R1/src/test/java/art/arcane/iris/probe/BareMobSpawnHistoryTest.java

@@ -0,0 +1,156 @@
+package art.arcane.iris.probe;
+
+import art.arcane.iris.generation.biome.IrisBiomeCustom;
+import art.arcane.iris.generation.biome.IrisBiomeCustomSpawn;
+import art.arcane.iris.generation.biome.IrisBiomeCustomSpawnType;
+import art.arcane.iris.pack.datapack.v263.DataFixerV263;
+import art.arcane.iris.spi.PlatformGenerationRegistry;
+import art.arcane.iris.world.history.GenerationRegistryContract;
+import art.arcane.iris.world.history.GenerationRegistryContractFactory;
+import art.arcane.volmlib.util.collection.KList;
+import com.google.gson.JsonObject;
+import com.google.gson.JsonParser;
+import org.bukkit.Bukkit;
+import org.junit.AfterClass;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import java.io.File;
+import java.io.IOException;
+import java.util.Map;
+import java.util.Set;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotEquals;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertThrows;
+
+public final class BareMobSpawnHistoryTest {
+    private static final String LEGACY_RENDERER_IDENTITY = "bukkit-v26_3_R1-generated-registry-json-v1";
+    private static final String NATURAL_MOB_SPAWNS = "minecraft:gameplay/natural_mob_spawns";
+    private static final GenerationRegistryContract.PhysicalResourceKey INSTALLED =
+            new GenerationRegistryContract.PhysicalResourceKey(
+                    GenerationRegistryContractFactory.BIOME_REGISTRY,
+                    "iris:biomes/" + "c".repeat(64)
+            );
+    private static HeadlessNativeRegistries loaded;
+    private static PlatformGenerationRegistry registry;
+
+    @BeforeClass
+    public static void installOverlayRendering() throws IOException {
+        assertNull(Bukkit.getServer());
+        loaded = HeadlessNativeRegistries.load(Map.of(
+                "data/iris/worldgen/biome/biomes/" + "c".repeat(64) + ".json",
+                spawningBiome().generateJson(new DataFixerV263())
+        ));
+        registry = new HeadlessNativePlatform(new File("unused-native-platform"), loaded::registries)
+                .generationRegistry();
+    }
+
+    @AfterClass
+    public static void closeRegistries() throws IOException {
+        if (loaded != null) {
+            loaded.close();
+        }
+    }
+
+    @Test
+    public void bareMobSpawnHistoryValidatesAgainstTheInstalledOverlayRendering() throws IOException {
+        GenerationRegistryContract legacy = legacyContract(INSTALLED, spawningBiome());
+        GenerationRegistryContract.GeneratedSource source = legacy.generatedSources().get(INSTALLED);
+        assertEquals(GenerationRegistryContract.FINGERPRINT_SCHEMA_VERSION_ONE, legacy.fingerprintSchema());
+        assertEquals(LEGACY_RENDERER_IDENTITY, source.rendererIdentity());
+        assertNotEquals(
+                JsonParser.parseString(source.sourceJson()),
+                JsonParser.parseString(registry.generatedDefinition(
+                        INSTALLED.registryKey(),
+                        INSTALLED.resourceKey()
+                ).value())
+        );
+
+        GenerationRegistryContract available = GenerationRegistryContractFactory.captureRequiredDefinitions(
+                Set.of(legacy),
+                new DataFixerV263(),
+                registry
+        );
+
+        legacy.requireDefinitionsAvailableIn(available);
+    }
+
+    @Test
+    public void bareMobSpawnHistoryStillRejectsDifferentSemantics() throws IOException {
+        GenerationRegistryContract changed = legacyContract(INSTALLED, spawningBiome().setTemperature(0.2D));
+
+        IOException failure = assertThrows(IOException.class,
+                () -> GenerationRegistryContractFactory.captureRequiredDefinitions(
+                        Set.of(changed),
+                        new DataFixerV263(),
+                        registry
+                ));
+
+        assertEquals("Historical generated registry definition changed for minecraft:worldgen/biome / "
+                + INSTALLED.resourceKey() + ".", failure.getMessage());
+    }
+
+    @Test
+    public void bareMobSpawnHistoryStillRejectsAMissingDefinition() throws IOException {
+        GenerationRegistryContract missing = legacyContract(new GenerationRegistryContract.PhysicalResourceKey(
+                GenerationRegistryContractFactory.BIOME_REGISTRY,
+                "iris:biomes/" + "d".repeat(64)
+        ), spawningBiome());
+
+        assertThrows(IOException.class, () -> GenerationRegistryContractFactory.captureRequiredDefinitions(
+                Set.of(missing),
+                new DataFixerV263(),
+                registry
+        ));
+    }
+
+    private static GenerationRegistryContract legacyContract(
+            GenerationRegistryContract.PhysicalResourceKey key,
+            IrisBiomeCustom biome
+    ) {
+        JsonObject rendered = JsonParser.parseString(biome.generateJson(new DataFixerV263())).getAsJsonObject();
+        JsonObject attributes = rendered.getAsJsonObject("attributes");
+        attributes.add(NATURAL_MOB_SPAWNS, attributes.getAsJsonObject(NATURAL_MOB_SPAWNS).get("argument"));
+        String captured = registry.canonicalDefinition(key.registryKey(), key.resourceKey(), rendered.toString())
+                .value();
+        String semantic = GenerationRegistryContractFactory.customBiomeEffectiveSemanticJson(biome, null);
+        GenerationRegistryContract.GeneratedSource source = new GenerationRegistryContract.GeneratedSource(
+                GenerationRegistryContractFactory.CUSTOM_BIOME_EFFECTIVE_SOURCE_SCHEMA,
+                GenerationRegistryContractFactory.fingerprintCustomBiomeAuthoredDefinition(semantic),
+                semantic,
+                LEGACY_RENDERER_IDENTITY,
+                GenerationRegistryContractFactory.fingerprintDefinition(
+                        key,
+                        PlatformGenerationRegistry.Definition.exactJson(captured),
+                        "generated"
+                ),
+                captured
+        );
+        return GenerationRegistryContract.fromDefinitionsAndGeneratedSources(
+                Map.of(key, GenerationRegistryContractFactory.fingerprintGeneratedSemantic(key, source)),
+                Map.of(key, source)
+        );
+    }
+
+    private static IrisBiomeCustom spawningBiome() {
+        return new IrisBiomeCustom()
+                .setId("tester")
+                .setSpawnRarity(2)
+                .setSpawns(new KList<>(
+                        new IrisBiomeCustomSpawn()
+                                .setType("minecraft:zombie")
+                                .setGroup(IrisBiomeCustomSpawnType.MONSTER)
+                                .setMinCount(2)
+                                .setMaxCount(4)
+                                .setWeight(7),
+                        new IrisBiomeCustomSpawn()
+                                .setType("minecraft:cow")
+                                .setGroup(IrisBiomeCustomSpawnType.CREATURE)
+                                .setMinCount(3)
+                                .setMaxCount(3)
+                                .setWeight(5)
+                ));
+    }
+}

adapters/bukkit/nms/v26_3_R1/src/test/java/art/arcane/iris/probe/HeadlessGenerationRegistryTest.java

@@ -1,7 +1,6 @@
 package art.arcane.iris.probe;
 
 import art.arcane.iris.spi.PlatformGenerationRegistry;
-import art.arcane.volmlib.nativelib.v26_3_R1.terrain.NativeWorldGenerationImpl;
 import net.minecraft.data.registries.VanillaRegistries;
 import org.bukkit.Bukkit;
 import org.junit.Test;
@@ -22,8 +21,6 @@ public final class HeadlessGenerationRegistryTest {
             HeadlessNativeTestRegistries::get);
         PlatformGenerationRegistry registry = platform.generationRegistry();
         assertEquals("bukkit-generation-registry-v1", registry.runtimeIdentity());
-        assertEquals(new NativeWorldGenerationImpl().generationRendererIdentity(),
-                registry.generatedDefinitionRendererIdentity());
         assertEquals(registry.canonicalDefinition("minecraft:worldgen/biome", "iris:native_test", biome),
                 registry.generatedDefinition("minecraft:worldgen/biome", "iris:native_test"));
         assertEquals(registry.canonicalDefinition("minecraft:dimension_type", "iris:native_test", dimension),

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

@@ -0,0 +1,88 @@
+package art.arcane.iris;
+
+import art.arcane.iris.platform.bootstrap.ServerProperties;
+import art.arcane.iris.world.IrisStartupValidation;
+import art.arcane.iris.world.IrisWorldStorage;
+import art.arcane.iris.world.lifecycle.BukkitWorldConfiguration;
+import art.arcane.iris.world.safeguard.GenerationRefusalNotice;
+
+import java.io.File;
+import java.io.IOException;
+import java.util.List;
+
+/**
+ * Keeps a failed enable from handing Iris worlds to the vanilla generator.
+ * <p>
+ * Paper disables a plugin whose onEnable fails, and CraftServer builds every world bukkit.yml points at a disabled
+ * generator plugin with the vanilla generator. On a server with Iris worlds, Iris therefore stays enabled with its
+ * runtime locked: the generator resolver answers every Iris world with a fail-closed generator, which stops the
+ * level before it exists, and the admission listener refuses logins. It only needs IrisStartupValidation and
+ * logging, never a service the failed enable may not have created.
+ */
+final class FailedEnableLock {
+    private FailedEnableLock() {
+    }
+
+    /**
+     * @return true when Iris must stay enabled and locked, false when the failure may disable Iris as before
+     */
+    static boolean engage(Throwable failure, boolean irisWorldsPresent, boolean startupWorldsCreated) {
+        if (!irisWorldsPresent) {
+            return false;
+        }
+        IrisStartupValidation.markRuntimeInvalid("Iris failed to enable: " + GenerationRefusalNotice.summary(failure));
+        List<String> notice = notice(failure, startupWorldsCreated);
+        try {
+            for (String line : notice) {
+                Iris.error(line);
+            }
+            Iris.reportError(failure);
+        } catch (Throwable loggingFailure) {
+            notice.forEach(System.err::println);
+            failure.addSuppressed(loggingFailure);
+            failure.printStackTrace(System.err);
+        }
+        return true;
+    }
+
+    /**
+     * Deferring teardown to the server stop quiesces through the NMS binding and waits for generators Paper closes.
+     * A failed enable may have neither, so it tears down at once even while the server stops.
+     */
+    static boolean defersTeardownToServerStop(boolean enableFailed, boolean serverStopping) {
+        return !enableFailed && serverStopping;
+    }
+
+    /**
+     * @param startupWorldsCreated true when Iris enabled on a running server (a hotload), whose startup worlds
+     *                             already exist, so nothing stops
+     */
+    static List<String> notice(Throwable failure, boolean startupWorldsCreated) {
+        return GenerationRefusalNotice.compose(
+                "Iris failed to enable",
+                GenerationRefusalNotice.causes(failure),
+                List.of(
+                        "Iris stays enabled with a locked runtime so no Iris world falls back to vanilla generation.",
+                        startupWorldsCreated
+                                ? "Every Iris world that is not loaded yet refuses to load; the server keeps running"
+                                + " and no chunks are written for them."
+                                : "Every Iris world refuses to generate: server startup stops before the first one"
+                                + " loads, and no chunks are written.",
+                        "Player logins are refused until this is fixed and the server restarts."
+                ));
+    }
+
+    static boolean irisWorldsPresent() {
+        try {
+            return irisWorldsPresent(IrisWorldStorage.levelRoot(), ServerProperties.BUKKIT_YML);
+        } catch (Throwable unreadable) {
+            Iris.reportError("Could not inspect this server for Iris worlds; treating it as having them.", unreadable);
+            return true;
+        }
+    }
+
+    static boolean irisWorldsPresent(File levelRoot, File bukkitConfiguration) throws IOException {
+        return IrisWorldStorage.hasManagedWorldStorage(levelRoot)
+                || BukkitWorldConfiguration.configuresLoadingIrisWorld(bukkitConfiguration, levelRoot.toPath());
+    }
+}

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

@@ -32,9 +32,9 @@ import art.arcane.iris.world.IrisStartupValidation;
 import art.arcane.iris.world.IrisStartupAdmissionListener;
 import art.arcane.iris.world.BukkitWorldReconciler;
 import art.arcane.iris.world.IrisWorldGeneratorResolver;
-import art.arcane.iris.world.IrisWorldStorage;
 import art.arcane.iris.world.PendingWorldDeleteQueue;
 import art.arcane.iris.world.PendingWorldReplacementManager;
+import art.arcane.iris.world.WorldRefusalReporter;
 import art.arcane.iris.configuration.SettingsHotloadWatch;
 import art.arcane.iris.pack.datapack.ServerConfigurator;
 import art.arcane.iris.pack.datapack.DatapackIngestService;
@@ -200,6 +200,7 @@ public class Iris extends VolmitPlugin implements Listener, ReloadAware {
     private final AtomicBoolean terminalCleanupCompleted = new AtomicBoolean(false);
     private final AtomicBoolean runtimeTeardownFailed = new AtomicBoolean(false);
     private volatile boolean generatorDrainCompleted;
+    private volatile boolean enableFailed;
     private volatile PlaceholderRegistration papiRegistration;
     private volatile IrisPapiListener papiListener;
     private volatile IrisPapiState papiState;
@@ -613,21 +614,7 @@ public class Iris extends VolmitPlugin implements Listener, ReloadAware {
         return plugin == null ? ComponentLog.discriminator("Iris", "&a") : plugin.getTag();
     }
 
-    /**
-     * @return false when the bootstrap was aborted (unsupported server version); the caller
-     * must bail out of onEnable without touching any further setup.
-     */
-    private boolean enable() {
-        if (!INMS.isBound()) {
-            Throwable bindFailure = INMS.bindFailure();
-            Iris.error("Iris cannot start: " + (bindFailure == null
-                    ? "no NMS binding is available for this server version."
-                    : bindFailure.getMessage()));
-            // Deferred one tick: disablePlugin from inside onEnable re-enters onDisable
-            // synchronously and the loader then continues registering the half-enabled plugin.
-            J.s(() -> Bukkit.getPluginManager().disablePlugin(this), 1);
-            return false;
-        }
+    private void enable() {
         EnableTimings timings = new EnableTimings();
         alreadyDrained.set(false);
         postStopFinisherStarted.set(false);
@@ -788,7 +775,6 @@ public class Iris extends VolmitPlugin implements Listener, ReloadAware {
         });
         timings.mark("startupTasks");
         timings.report();
-        return true;
     }
 
     private static final class EnableTimings {
@@ -910,20 +896,25 @@ public class Iris extends VolmitPlugin implements Listener, ReloadAware {
     }
 
     public void onEnable() {
-        IrisPlatforms.bind(new BukkitPlatform());
+        enableFailed = false;
         IrisStartupValidation.begin();
         Bukkit.getPluginManager().registerEvents(new IrisStartupAdmissionListener(), this);
-        Bukkit.getPluginManager().registerEvents(pendingWorldReplacements, this);
-        pendingWorldReplacements.registerPlatformEntryListener();
-        boolean enabled;
         try {
-            enabled = enable();
+            generatorResolver.refusals().attach(this);
+            IrisPlatforms.bind(new BukkitPlatform());
+            Bukkit.getPluginManager().registerEvents(pendingWorldReplacements, this);
+            pendingWorldReplacements.registerPlatformEntryListener();
+            if (!INMS.isBound()) {
+                refuseUnsupportedServer();
+                return;
+            }
+            enable();
         } catch (Throwable failure) {
-            refuseVanillaFallback(failure);
-            throw failure;
-        }
-        if (!enabled) {
-            refuseVanillaFallback(null);
+            if (!FailedEnableLock.engage(failure, FailedEnableLock.irisWorldsPresent(),
+                    generatorResolver.refusals().startupWorldsCreated())) {
+                throw failure;
+            }
+            enableFailed = true;
             return;
         }
         BukkitGuiHost.install();
@@ -939,54 +930,32 @@ public class Iris extends VolmitPlugin implements Listener, ReloadAware {
         reportLockedRuntime();
     }
 
+    private void refuseUnsupportedServer() {
+        Throwable bindFailure = INMS.bindFailure();
+        IllegalStateException failure = new IllegalStateException("Iris cannot start: " + (bindFailure == null
+                ? "no NMS binding is available for this server version."
+                : bindFailure.getMessage()), bindFailure);
+        if (FailedEnableLock.engage(failure, FailedEnableLock.irisWorldsPresent(),
+                generatorResolver.refusals().startupWorldsCreated())) {
+            enableFailed = true;
+            return;
+        }
+        Iris.error(failure.getMessage());
+        // Deferred one tick: disablePlugin from inside onEnable re-enters onDisable
+        // synchronously and the loader then continues registering the half-enabled plugin.
+        J.s(() -> Bukkit.getPluginManager().disablePlugin(this), 1);
+    }
+
     private static void reportLockedRuntime() {
         String denial = IrisStartupValidation.denialReason().orElse(null);
         if (denial == null) {
             return;
         }
-        boolean managedStorage;
-        try {
-            managedStorage = IrisWorldStorage.hasManagedWorldStorage(IrisWorldStorage.levelRoot());
-        } catch (Throwable unavailable) {
-            Iris.reportError("Could not inspect Iris world storage while reporting the locked runtime.", unavailable);
-            managedStorage = false;
-        }
-        for (String line : RuntimeLockNotice.compose(denial, managedStorage)) {
+        for (String line : RuntimeLockNotice.compose(denial, FailedEnableLock.irisWorldsPresent())) {
             Iris.error(line);
         }
     }
 
-    /**
-     * Stops a server whose Iris worlds would otherwise be generated by the vanilla generator.
-     * <p>
-     * A disabled Iris gets no {@code getDefaultWorldGenerator} call at all, so the server falls back to
-     * vanilla for every world bukkit.yml points at Iris and writes vanilla terrain into their region files.
-     * There is no Bukkit API that refuses a world at that point, so the server is stopped instead. This is
-     * damage control, not prevention: level creation runs in the same startup step that enables plugins, so
-     * spawn chunks of the affected worlds can still be written before the stop takes effect. The prevention
-     * lives in IrisBootstrap, which refuses startup before any level is created.
-     */
-    private static void refuseVanillaFallback(Throwable failure) {
-        File levelRoot;
-        try {
-            levelRoot = IrisWorldStorage.levelRoot();
-        } catch (Throwable unavailable) {
-            return;
-        }
-        if (!IrisWorldStorage.hasManagedWorldStorage(levelRoot)) {
-            return;
-        }
-        Iris.error("Iris did not enable and this server has Iris worlds; stopping the server before they generate vanilla terrain.");
-        if (failure != null) {
-            Iris.reportError("Iris enable failed", failure);
-        }
-        try {
-            Bukkit.shutdown();
-        } catch (Throwable unavailable) {
-            Iris.error("Could not stop the server: " + unavailable.getClass().getSimpleName());
-        }
-    }
-
     public BukkitDebugDump debugDump() {
         return debugDump;
     }
@@ -1014,11 +983,11 @@ public class Iris extends VolmitPlugin implements Listener, ReloadAware {
         }
         IrisLanguage.shutdown();
         teardownPapi();
-        boolean serverStopping = IrisToolbelt.isServerStopping();
+        boolean deferToServerStop = FailedEnableLock.defersTeardownToServerStop(enableFailed, IrisToolbelt.isServerStopping());
         boolean restartingAtStartupBoundary = startupBoundaryRestart.get();
         if (restartingAtStartupBoundary) {
             teardownRuntime("startup-boundary-restart", 30L);
-        } else if (serverStopping) {
+        } else if (deferToServerStop) {
             quiesceRuntimeForServerShutdown("onDisable");
             startPostStopFinisher();
         } else {
@@ -1036,7 +1005,7 @@ public class Iris extends VolmitPlugin implements Listener, ReloadAware {
         }
         // super.onDisable() cancels plugin tasks and unregisters every listener.
         super.onDisable();
-        if (!serverStopping || restartingAtStartupBoundary) {
+        if (!deferToServerStop || restartingAtStartupBoundary) {
             finishTerminalCleanup();
         }
     }
@@ -1457,6 +1426,14 @@ public class Iris extends VolmitPlugin implements Listener, ReloadAware {
         return generatorResolver.resolveDefaultWorldGenerator(worldName, id);
     }
 
+    public ChunkGenerator requireWorldGenerator(String worldName, String id) {
+        return generatorResolver.requireWorldGenerator(worldName, id);
+    }
+
+    public WorldRefusalReporter worldRefusals() {
+        return generatorResolver.refusals();
+    }
+
     public void splash() {
         Iris.info("Custom Biomes: " + INMS.get().countCustomBiomes());
         printPacks();

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

@@ -13,6 +13,7 @@ import art.arcane.iris.pack.datapack.DataVersion;
 import io.papermc.paper.ServerBuildInfo;
 import art.arcane.iris.pack.DefaultPackBootstrapProvisioner.ProvisionResult;
 import art.arcane.iris.platform.bootstrap.SlimJar;
+import art.arcane.iris.world.safeguard.GenerationRefusalNotice;
 import io.papermc.paper.plugin.bootstrap.BootstrapContext;
 import io.papermc.paper.plugin.bootstrap.PluginBootstrap;
 import io.papermc.paper.plugin.lifecycle.event.LifecycleEvent;
@@ -21,6 +22,7 @@ import io.papermc.paper.plugin.lifecycle.event.types.LifecycleEvents;
 
 import java.io.IOException;
 import java.nio.file.Path;
+import java.util.ArrayList;
 import java.util.List;
 import java.util.function.Consumer;
 
@@ -112,16 +114,18 @@ public final class IrisBootstrap implements PluginBootstrap {
      * Stops startup when a world the server is about to load carries Iris storage Iris cannot generate from.
      * <p>
      * The server enumerates levels from {@code <levelRoot>/dimensions/<namespace>/<key>} on disk, so a world
-     * whose folder is present is going to be loaded whatever Iris does; and CraftBukkit swallows whatever
-     * {@code getDefaultWorldGenerator} throws and falls back to the vanilla generator, which writes vanilla
-     * terrain straight into that world's region files. A pack snapshot that has gone missing therefore has
-     * to be found here, before any level is created, exactly as a corrupt {@code dimensions/<id>.json} is.
+     * whose folder is present is going to be loaded whatever Iris does. The generator resolver answers a world
+     * it cannot generate with a fail-closed generator, which stops startup at that world's own level creation,
+     * after the levels before it have loaded. A pack snapshot that has gone missing is found here instead,
+     * before any level is created, exactly as a corrupt {@code dimensions/<id>.json} is. An Iris world in a
+     * vanilla slot whose bukkit.yml entry no longer names Iris stops startup too: CraftServer would build it
+     * with the vanilla generator without ever asking Iris.
      * <p>
      * A world with no folder at all is not a startup failure: nothing enumerates it, nothing loads it, and
      * its bukkit.yml and Multiverse entries are what make restoring the folder a complete recovery. Neither
      * is a folder that holds no pack snapshot and no world data - {@link #quarantineWorthlessHusks} has
      * already moved those out of the dimensions tree, and one that survives it (a Spigot-layout world folder,
-     * or a move that failed) owns nothing a vanilla generator could destroy. Both are only reported.
+     * or a move that failed) owns nothing to lose. Both are only reported here.
      */
     static void requireUsableWorldStorage(BukkitStartupPaths startupPaths) throws IOException {
         Path levelRoot = startupPaths.levelRoot();
@@ -135,6 +139,7 @@ public final class IrisBootstrap implements PluginBootstrap {
                 levelRoot
         );
         StringBuilder unusable = new StringBuilder();
+        StringBuilder unbound = new StringBuilder();
         for (IrisWorldStorageEntry entry : entries) {
             switch (entry.state()) {
                 case PRESENT -> {
@@ -152,15 +157,29 @@ public final class IrisBootstrap implements PluginBootstrap {
                         .append(": ")
                         .append(entry.detail() == null ? "storage is unusable" : entry.detail())
                         .append(')');
+                case UNBOUND -> unbound.append(unbound.isEmpty() ? "" : "; ")
+                        .append(entry.configuredWorldName())
+                        .append(" (")
+                        .append(entry.storagePath())
+                        .append("): set worlds.")
+                        .append(entry.configuredWorldName())
+                        .append(".generator to Iris:<pack> in bukkit.yml, or move the folder aside to start a new"
+                                + " vanilla world there");
             }
         }
-        if (unusable.isEmpty()) {
-            return;
+        List<String> refusals = new ArrayList<>(2);
+        if (!unusable.isEmpty()) {
+            refusals.add("Iris world storage is unusable and the server would generate vanilla terrain over it: "
+                    + unusable + ". Restore each world folder from a backup, or move it aside; a world with no"
+                    + " folder is reported and skipped, and the server starts.");
+        }
+        if (!unbound.isEmpty()) {
+            refusals.add("Iris worlds in vanilla slots are not bound to Iris, so the server would generate vanilla"
+                    + " terrain into them: " + unbound + ".");
+        }
+        if (!refusals.isEmpty()) {
+            throw new IllegalStateException(String.join(" ", refusals));
         }
-        throw new IllegalStateException("Iris world storage is unusable and the server would generate vanilla"
-                + " terrain over it: " + unusable
-                + ". Restore each world folder from a backup, or move it aside; a world with no folder is"
-                + " reported and skipped, and the server starts.");
     }
 
     static void armStartupFailure(BootstrapContext context, Throwable failure) {
@@ -175,17 +194,30 @@ public final class IrisBootstrap implements PluginBootstrap {
         context.getLifecycleManager().registerEventHandler(eventType, event -> {
             throw new IllegalStateException("Iris bootstrap did not establish safe world-generation state.", failure);
         });
+        List<String> notice = startupRefusalNotice(failure);
         try {
-            context.getLogger().error(
-                    "Iris bootstrap failed; registry and world startup will be stopped at datapack discovery.",
-                    failure
-            );
+            for (String line : notice) {
+                context.getLogger().error(line);
+            }
+            context.getLogger().warn("Iris bootstrap failure", failure);
         } catch (Throwable loggingFailure) {
+            notice.forEach(System.err::println);
             failure.addSuppressed(loggingFailure);
             failure.printStackTrace(System.err);
         }
     }
 
+    static List<String> startupRefusalNotice(Throwable failure) {
+        return GenerationRefusalNotice.compose(
+                "Iris stopped server startup before any world loads",
+                GenerationRefusalNotice.causes(failure),
+                List.of(
+                        "Startup stops at datapack discovery: no world loads and no chunks are written.",
+                        "Fix the cause, then start the server again. Paper's --safeMode hint does not apply:"
+                                + " Iris worlds must not load without Iris."
+                ));
+    }
+
     private static ProvisionResult provision(BootstrapContext context, BukkitStartupPaths startupPaths) {
         try {
             return DefaultPackBootstrapProvisioner.provision(new BootstrapRequest(

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

@@ -511,7 +511,9 @@ public class CommandIris implements DirectorExecutor {
             return;
         }
         PlatformChunkGenerator generator = IrisToolbelt.access(world);
-        IrisToolbelt.beginWorldMaintenance(world, "world-unload", true);
+        // Maintenance that forbids mantle stages refuses every chunk, and Folia treats a refused chunk as a chunk
+        // system failure, so it starts only once no player is left to request one.
+        AtomicBoolean maintenanceEntered = new AtomicBoolean(false);
         try {
             AtomicBoolean terminalTimeout = new AtomicBoolean(false);
             CompletableFuture<Boolean> sequence = IrisToolbelt.evacuateAsync(world)
@@ -523,6 +525,8 @@ public class CommandIris implements DirectorExecutor {
                         if (!Boolean.TRUE.equals(evacuated)) {
                             return CompletableFuture.completedFuture(false);
                         }
+                        IrisToolbelt.beginWorldMaintenance(world, "world-unload", true);
+                        maintenanceEntered.set(true);
                         return WorldLifecycleService.get().unloadAsync(world, true);
                     })
                     .thenCompose(unloaded -> {
@@ -537,7 +541,9 @@ public class CommandIris implements DirectorExecutor {
                     });
             guardUnloadCompletion(sequence, terminalTimeout, world.getName())
                     .whenComplete((unloaded, throwable) -> {
-                        IrisToolbelt.endWorldMaintenance(world, "world-unload", true);
+                        if (maintenanceEntered.get()) {
+                            IrisToolbelt.endWorldMaintenance(world, "world-unload", true);
+                        }
                         lease.close();
                         Runnable response = () -> reportUnloadResult(responseSender, world, unloaded, throwable);
                         if (responseSender.isPlayer() && J.runEntity(responseSender.player(), response)) {
@@ -546,7 +552,9 @@ public class CommandIris implements DirectorExecutor {
                         J.s(response);
                     });
         } catch (Exception e) {
-            IrisToolbelt.endWorldMaintenance(world, "world-unload", true);
+            if (maintenanceEntered.get()) {
+                IrisToolbelt.endWorldMaintenance(world, "world-unload", true);
+            }
             lease.close();
             responseSender.sendMessage(IrisLanguage.text(BukkitCommandMessagesExtended.COMMAND_IRIS_FAILED_UNLOAD_WORLD_3, MessageArgument.untrusted("value", String.valueOf(e.getMessage()))));
             Iris.reportError("Failed to unload world \"" + world.getName() + "\".", e);

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

@@ -722,19 +722,30 @@ public final class BukkitWorldReconciler {
             return WorldIdentity.resolve(worldKey);
         }
 
+        /**
+         * A world Iris cannot resolve is refused like one CraftServer asked for, with the banner and operator notice,
+         * then fails this load only.
+         */
         @Override
         public CompletableFuture<World> createWorld(NamespacedKey worldKey, String dimension, Long seed) {
+            String configuredWorldName = worldKey.toString();
+            ChunkGenerator generator;
+            IrisDimension irisDimension;
             try {
-                String logicalWorldName = IrisWorldStorage.logicalName(worldKey);
-                String configuredWorldName = configuredWorldName(worldKey);
-                Iris.info("Loading World: %s | Generator: %s", logicalWorldName, dimension);
-                ChunkGenerator generator = plugin.getDefaultWorldGenerator(configuredWorldName, dimension);
-                IrisDimension irisDimension = IrisWorldGeneratorResolver.loadDimension(configuredWorldName, dimension);
+                configuredWorldName = configuredWorldName(worldKey);
+                Iris.info("Loading World: %s | Generator: %s", IrisWorldStorage.logicalName(worldKey), dimension);
+                generator = plugin.requireWorldGenerator(configuredWorldName, dimension);
+                irisDimension = IrisWorldGeneratorResolver.loadDimension(configuredWorldName, dimension);
                 if (generator == null || irisDimension == null) {
                     throw new IllegalStateException("Could not resolve the Iris generator or dimension \"" + dimension + "\".");
                 }
-
-                Iris.info(C.LIGHT_PURPLE + "Preparing Spawn for " + logicalWorldName + " using Iris:" + dimension + "...");
+            } catch (Throwable refusal) {
+                plugin.worldRefusals().report(configuredWorldName, worldKey, refusal);
+                return CompletableFuture.failedFuture(refusal);
+            }
+            try {
+                Iris.info(C.LIGHT_PURPLE + "Preparing Spawn for " + IrisWorldStorage.logicalName(worldKey)
+                        + " using Iris:" + dimension + "...");
                 WorldCreator creator = WorldCreatorCompat.ofPersistentKey(worldKey)
                         .generator(generator)
                         .environment(BukkitEnvironment.from(irisDimension.getEnvironment()));

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

@@ -18,6 +18,7 @@
 
 package art.arcane.iris.world;
 
+import art.arcane.iris.world.safeguard.GenerationRefusalNotice;
 import org.bukkit.HeightMap;
 import org.bukkit.Location;
 import org.bukkit.World;
@@ -48,6 +49,20 @@ final class IrisFailClosedChunkGenerator extends ChunkGenerator {
                 + "' remains locked: " + denialReason);
     }
 
+    /**
+     * Built on the way back to CraftServer, which turns any throw into the vanilla generator, so a cause that cannot
+     * be summarized is named by its type instead.
+     */
+    static IrisFailClosedChunkGenerator refused(String worldName, Throwable failure) {
+        String reason;
+        try {
+            reason = GenerationRefusalNotice.summary(failure);
+        } catch (Throwable unreadable) {
+            reason = failure.getClass().getName();
+        }
+        return new IrisFailClosedChunkGenerator("Iris refuses to generate '" + worldName + "': " + reason);
+    }
+
     @Override
     public void generateNoise(@NotNull WorldInfo worldInfo, @NotNull Random random, int x, int z, @NotNull ChunkData chunkData) {
         throw refusal();

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

@@ -73,6 +73,7 @@ import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.function.Supplier;
+import java.util.stream.Stream;
 
 /**
  * Pack validation, dimension lookup, and the world generator / biome provider resolution that the
@@ -90,6 +91,7 @@ public final class IrisWorldGeneratorResolver {
     private final AtomicBoolean externalContentRefreshQueued = new AtomicBoolean();
     private final AtomicBoolean externalContentRefreshRequested = new AtomicBoolean();
     private final Map<Path, PendingSnapshot> pendingSnapshots = new ConcurrentHashMap<>();
+    private final WorldRefusalReporter refusals = new WorldRefusalReporter();
 
     public IrisWorldGeneratorResolver(VolmitPlugin plugin) {
         this.plugin = plugin;
@@ -480,12 +482,28 @@ public final class IrisWorldGeneratorResolver {
         return fallback.get();
     }
 
+    /**
+     * The generator CraftServer asks for. Paper turns a throw or a null here into the vanilla generator, so every
+     * request aimed at an Iris world gets a generator back: the Iris one, or a fail-closed one that refuses to let
+     * the level be created. Only the PlotSquared discovery sentinel, which is never created, gets null.
+     */
     @Nullable
     public ChunkGenerator resolveDefaultWorldGenerator(String worldName, @Nullable String id) {
         if (isPlotSquaredGeneratorDiscoveryProbe(worldName, id)) {
             Iris.debug("Ignoring PlotSquared generator discovery probe");
             return null;
         }
+        try {
+            return requireWorldGenerator(worldName, id);
+        } catch (Throwable failure) {
+            return refuseWorld(worldName, failure);
+        }
+    }
+
+    /**
+     * Resolution for Iris' own loads, which report a failure per world instead of handing it to CraftServer.
+     */
+    public ChunkGenerator requireWorldGenerator(String worldName, @Nullable String id) {
         if (isGeneratorDiscoveryProbe(worldName, id)) {
             Iris.debug("Generator discovery probe for loaded world " + worldName);
             return IrisFailClosedChunkGenerator.discoveryProbe(worldName);
@@ -505,21 +523,37 @@ public final class IrisWorldGeneratorResolver {
             return startupLock;
         }
         Iris.debug("Default World Generator Called for " + worldName + " using ID: " + id);
-        if (id == null || id.isEmpty()) id = IrisSettings.get().getGenerator().getDefaultWorldType();
-        Iris.debug("Generator ID: " + id + " requested by bukkit/plugin");
+        String dimension = id == null || id.isEmpty() ? IrisSettings.get().getGenerator().getDefaultWorldType() : id;
+        Iris.debug("Generator ID: " + dimension + " requested by bukkit/plugin");
 
         File levelRoot = IrisWorldStorage.levelRoot();
         NamespacedKey worldKey = configuredWorldKey(worldName, levelRoot.getName(), levelRoot);
         requireWorldKeyAvailable(worldName, worldKey);
         requireOwnedWorld(worldName, levelRoot, worldKey);
+        return resolveFrozenWorldGenerator(worldName, dimension);
+    }
 
+    public WorldRefusalReporter refusals() {
+        return refusals;
+    }
+
+    private ChunkGenerator refuseWorld(String worldName, Throwable failure) {
+        refusals.report(worldName, refusalKey(worldName), failure);
         try {
-            return resolveFrozenWorldGenerator(worldName, id);
-        } catch (RuntimeException failure) {
-            Iris.reportError("Refusing to load configured Iris world '" + worldName
-                    + "' because its frozen world-local pack snapshot could not be used.", failure);
-            Bukkit.shutdown();
-            throw failure;
+            Iris.reportError(failure);
+        } catch (Throwable loggingFailure) {
+            System.err.println("[Iris] Could not log the refusal of '" + worldName + "': "
+                    + loggingFailure.getClass().getName());
+        }
+        return IrisFailClosedChunkGenerator.refused(worldName, failure);
+    }
+
+    @Nullable
+    private static NamespacedKey refusalKey(String worldName) {
+        try {
+            return messageWorldKey(worldName, IrisWorldStorage.levelRoot().getName());
+        } catch (Throwable unresolved) {
+            return null;
         }
     }
 
@@ -588,12 +622,56 @@ public final class IrisWorldGeneratorResolver {
             return;
         }
         NamespacedKey messageKey = messageWorldKey(worldName, levelRoot.getName());
+        if (!IRIS_DIMENSION_NAMESPACE.equals(messageKey.getNamespace())) {
+            if (dimensionRoot != null && IrisWorldStorage.holdsIrisContent(dimensionRoot.toPath())) {
+                throw new IllegalStateException("'" + worldName + "' (" + messageKey + ") is an Iris world whose"
+                        + " generation history is missing from "
+                        + GenerationHistoryPaths.forDimension(dimensionRoot.toPath()).generationRoot()
+                        + ", so Iris cannot generate it. Restore that folder from a backup. Keep worlds." + worldName
+                        + ".generator in bukkit.yml: without it the server generates vanilla terrain into this world.");
+            }
+            // Only bukkit.yml binds a vanilla slot at startup, and the refusal stops startup, so no command can run
+            // until that binding is gone.
+            throw new IllegalStateException("'" + worldName + "' (" + messageKey
+                    + ") is a vanilla world slot with no Iris world storage, so Iris cannot generate it."
+                    + " Remove worlds." + worldName + ".generator from bukkit.yml"
+                    + leftoverLevelDataRemoval(levelRoot)
+                    + ", start the server, then run /iris replace " + messageKey
+                    + " type=<pack> to replace it with Iris on the next restart.");
+        }
         throw new IllegalStateException("'" + worldName + "' (" + messageKey
                 + ") has no Iris world storage, so Iris cannot generate it."
                 + " Create Iris worlds with /iris create " + IrisWorldStorage.logicalName(messageKey)
                 + " type=<pack>; Iris registers them with Multiverse itself.");
     }
 
+    /**
+     * A start refused before the level's overworld existed still leaves level.dat behind, and vanilla cannot start
+     * from a level.dat without world generation settings. A level that holds no chunks loses nothing to its removal.
+     */
+    private static String leftoverLevelDataRemoval(File levelRoot) {
+        Path level = levelRoot.toPath();
+        Path overworld = level.resolve("dimensions").resolve("minecraft").resolve("overworld");
+        if (Files.exists(overworld.resolve("data").resolve("minecraft").resolve("world_gen_settings.dat"),
+                LinkOption.NOFOLLOW_LINKS)
+                || hasEntries(overworld.resolve("region"))
+                || hasEntries(level.resolve("region"))) {
+            return "";
+        }
+        return " and delete " + level.resolve("level.dat") + " (this level has no chunks and was never created)";
+    }
+
+    private static boolean hasEntries(Path directory) {
+        if (!Files.isDirectory(directory, LinkOption.NOFOLLOW_LINKS)) {
+            return false;
+        }
+        try (Stream<Path> entries = Files.list(directory)) {
+            return entries.findAny().isPresent();
+        } catch (IOException unreadable) {
+            return true;
+        }
+    }
+
     private static boolean hasGenerationStorage(File dimensionRoot) {
         GenerationHistoryPaths paths = GenerationHistoryPaths.forDimension(dimensionRoot.toPath());
         return Files.isDirectory(paths.generationRoot(), LinkOption.NOFOLLOW_LINKS)

adapters/bukkit/plugin/src/main/java/art/arcane/iris/world/WorldRefusalReporter.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.world;
+
+import art.arcane.iris.Iris;
+import art.arcane.iris.localization.C;
+import art.arcane.iris.world.safeguard.GenerationRefusalNotice;
+import art.arcane.volmlib.util.bukkit.WorldIdentity;
+import org.bukkit.Bukkit;
+import org.bukkit.NamespacedKey;
+import org.bukkit.entity.Player;
+import org.bukkit.event.EventHandler;
+import org.bukkit.event.EventPriority;
+import org.bukkit.event.Listener;
+import org.bukkit.event.player.PlayerJoinEvent;
+import org.bukkit.event.world.WorldLoadEvent;
+import org.bukkit.plugin.Plugin;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.ConcurrentSkipListMap;
+
+/**
+ * Reports Iris worlds that refused to generate: a console banner that says what the refusal does to the server, and
+ * an operator notice on join for as long as the world stays unloaded, since the banner scrolls away.
+ */
+public final class WorldRefusalReporter implements Listener {
+    private static final String UNRESOLVED_KEY = "unresolved key";
+
+    private final Map<String, String> operatorNotices = new ConcurrentSkipListMap<>();
+    private volatile boolean startupWorldsCreated;
+
+    /**
+     * Iris enabled on a running server (a hotload) finds the startup worlds already loaded.
+     */
+    public void attach(Plugin plugin) {
+        if (!Bukkit.getWorlds().isEmpty()) {
+            startupWorldsCreated = true;
+        }
+        Bukkit.getPluginManager().registerEvents(this, plugin);
+    }
+
+    /**
+     * Paper creates every startup level before it prepares any, and preparing one fires the first WorldLoadEvent.
+     * A generator asked for after that belongs to a runtime create, which fails only its caller.
+     */
+    public boolean startupWorldsCreated() {
+        return startupWorldsCreated;
+    }
+
+    @EventHandler(priority = EventPriority.MONITOR)
+    public void onWorldLoad(WorldLoadEvent event) {
+        startupWorldsCreated = true;
+        try {
+            operatorNotices.remove(WorldIdentity.key(event.getWorld()).toString());
+        } catch (RuntimeException unkeyed) {
+            Iris.debug("Loaded world " + event.getWorld().getName() + " has no key to clear a refusal notice by");
+        }
+    }
+
+    @EventHandler(priority = EventPriority.MONITOR)
+    public void onPlayerJoin(PlayerJoinEvent event) {
+        if (operatorNotices.isEmpty()) {
+            return;
+        }
+        Player player = event.getPlayer();
+        if (!player.isOp() && !player.hasPermission("iris.all")) {
+            return;
+        }
+        for (String notice : operatorNotices.values()) {
+            player.sendMessage(C.RED + notice);
+        }
+    }
+
+    /**
+     * Never throws: the caller is handing CraftServer a fail-closed generator or failing a load, and a reporting
+     * failure must not turn either into something else.
+     */
+    public void report(String worldName, @Nullable NamespacedKey worldKey, Throwable failure) {
+        String key = worldKey == null ? UNRESOLVED_KEY : worldKey.toString();
+        try {
+            for (String line : notice(worldName, key, failure, startupWorldsCreated)) {
+                Iris.error(line);
+            }
+            operatorNotices.put(worldKey == null ? worldName : key, "Iris world '" + worldName + "' (" + key
+                    + ") did not load and refuses to generate: " + GenerationRefusalNotice.summary(failure));
+        } catch (Throwable reportingFailure) {
+            System.err.println("[Iris] Iris refused to generate world '" + worldName + "' (" + key
+                    + "); the refusal could not be reported: " + reportingFailure.getClass().getName());
+        }
+    }
+
+    static List<String> notice(String worldName, String worldKey, Throwable failure, boolean startupWorldsCreated) {
+        return GenerationRefusalNotice.compose(
+                "Iris refused to generate world '" + worldName + "' (" + worldKey + ")",
+                GenerationRefusalNotice.causes(failure),
+                List.of(
+                        "Iris does not generate this world and does not let vanilla or any other generator"
+                                + " write it; no chunks are written.",
+                        startupWorldsCreated
+                                ? "The world does not load; the server keeps running. Fix the cause, then load it again."
+                                : "Server startup stops before this world loads. Fix the cause, then start the server again."
+                ));
+    }
+}

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

@@ -189,7 +189,7 @@ public final class BukkitEnginePlatformHooks implements EnginePlatformHooks {
     }
 
     @Override
-    public boolean shouldBypassMantleStages(Engine engine) {
+    public boolean shouldRefuseGeneration(Engine engine) {
         if (!J.isFolia() || !engine.getWorld().hasPlatformWorld()) {
             return false;
         }

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

@@ -0,0 +1,244 @@
+package art.arcane.iris;
+
+import art.arcane.iris.platform.bukkit.nms.INMS;
+import art.arcane.iris.spi.IrisPlatform;
+import art.arcane.iris.spi.IrisPlatforms;
+import art.arcane.iris.world.IrisStartupAdmissionListener;
+import art.arcane.iris.world.IrisStartupValidation;
+import art.arcane.iris.world.IrisWorldGeneratorResolver;
+import art.arcane.iris.world.PendingWorldReplacementManager;
+import art.arcane.iris.world.task.J;
+import com.destroystokyo.paper.profile.PlayerProfile;
+import org.bukkit.Bukkit;
+import org.bukkit.configuration.file.YamlConfiguration;
+import org.bukkit.event.player.AsyncPlayerPreLoginEvent;
+import org.bukkit.generator.ChunkGenerator;
+import org.bukkit.generator.WorldInfo;
+import org.bukkit.plugin.PluginManager;
+import org.junit.After;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.TemporaryFolder;
+import org.mockito.MockedStatic;
+
+import java.io.File;
+import java.lang.reflect.Field;
+import java.net.InetAddress;
+import java.util.List;
+import java.util.UUID;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
+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.Mockito.CALLS_REAL_METHODS;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.mockStatic;
+import static org.mockito.Mockito.never;
+
+/**
+ * Paper disables a plugin whose onEnable throws, and CraftServer then builds every world bukkit.yml points at a
+ * disabled generator plugin with the vanilla generator. A failed enable on a server with Iris worlds therefore has
+ * to leave Iris enabled and locked instead.
+ */
+public class FailedEnableLockTest {
+    @Rule
+    public TemporaryFolder temporaryFolder = new TemporaryFolder();
+
+    @After
+    public void disableValidation() {
+        IrisStartupValidation.disable();
+        IrisPlatforms.unbind();
+    }
+
+    @Test
+    public void enableFailureWithIrisWorldsLocksTheRuntimeInsteadOfDisablingIris() throws Exception {
+        IrisStartupValidation.begin();
+        IllegalStateException failure = new IllegalStateException("service graph exploded");
+
+        try (MockedStatic<Bukkit> bukkit = mockStatic(Bukkit.class);
+             MockedStatic<Iris> iris = mockStatic(Iris.class)) {
+            assertTrue(FailedEnableLock.engage(failure, true, false));
+
+            String denial = IrisStartupValidation.denialReason().orElseThrow();
+            assertTrue(denial, denial.contains("service graph exploded"));
+
+            ChunkGenerator generator = new IrisWorldGeneratorResolver(null)
+                    .resolveDefaultWorldGenerator("world", "overworld");
+            assertNotNull("a null generator is the vanilla generator", generator);
+            IllegalStateException refusal = assertThrows(IllegalStateException.class,
+                    () -> generator.getDefaultBiomeProvider(mock(WorldInfo.class)));
+            assertTrue(refusal.getMessage(), refusal.getMessage().contains("service graph exploded"));
+            bukkit.verify(Bukkit::shutdown, never());
+        }
+
+        AsyncPlayerPreLoginEvent login = new AsyncPlayerPreLoginEvent(
+                "LockedTest", InetAddress.getLoopbackAddress(), UUID.randomUUID(), false, mock(PlayerProfile.class));
+        new IrisStartupAdmissionListener().onAsyncPlayerPreLogin(login);
+        assertEquals(AsyncPlayerPreLoginEvent.Result.KICK_OTHER, login.getLoginResult());
+    }
+
+    @Test
+    public void enableFailureWithoutIrisWorldsLeavesIrisToBeDisabled() {
+        IrisStartupValidation.begin();
+
+        try (MockedStatic<Iris> iris = mockStatic(Iris.class)) {
+            assertFalse(FailedEnableLock.engage(new IllegalStateException("service graph exploded"), false, false));
+        }
+
+        String denial = IrisStartupValidation.denialReason().orElseThrow();
+        assertFalse(denial, denial.contains("service graph exploded"));
+    }
+
+    @Test
+    public void noticeSaysIrisStaysLockedAndWhatThatBlocks() {
+        String notice = String.join("\n", FailedEnableLock.notice(
+                new IllegalStateException("outer", new IllegalArgumentException("inner")), false));
+
+        assertTrue(notice, notice.contains("Iris failed to enable"));
+        assertTrue(notice, notice.contains("outer"));
+        assertTrue(notice, notice.contains("inner"));
+        assertTrue(notice, notice.contains("vanilla"));
+        assertTrue(notice, notice.contains("startup stops"));
+        assertTrue(notice, notice.contains("logins"));
+    }
+
+    /**
+     * A hotload enables Iris on a running server whose startup worlds already exist, so nothing stops.
+     */
+    @Test
+    public void noticeAfterStartupWorldsExistSaysTheServerKeepsRunning() {
+        String notice = String.join("\n", FailedEnableLock.notice(new IllegalStateException("outer"), true));
+
+        assertFalse(notice, notice.contains("startup stops"));
+        assertTrue(notice, notice.contains("keeps running"));
+    }
+
+    /**
+     * IrisPlatforms.bind refuses a second platform, which is a real way for enable to throw. It has to throw inside
+     * the guarded region, and the throw must not reach Paper.
+     */
+    @Test
+    public void onEnableKeepsIrisEnabledAndLockedWhenEnableThrowsOnAServerWithIrisWorlds() throws Exception {
+        IrisPlatforms.bind(mock(IrisPlatform.class));
+        Iris plugin = plugin();
+
+        try (EnableFixture fixture = new EnableFixture(true)) {
+            plugin.onEnable();
+
+            String denial = IrisStartupValidation.denialReason().orElseThrow();
+            assertTrue(denial, denial.contains("already bound"));
+            ChunkGenerator generator = plugin.getDefaultWorldGenerator("world", "overworld");
+            assertNotNull("a null generator is the vanilla generator", generator);
+            IllegalStateException refusal = assertThrows(IllegalStateException.class,
+                    () -> generator.getDefaultBiomeProvider(mock(WorldInfo.class)));
+            assertTrue(refusal.getMessage(), refusal.getMessage().contains("already bound"));
+            fixture.bukkit.verify(Bukkit::shutdown, never());
+        }
+    }
+
+    @Test
+    public void onEnableStillThrowsToPaperWhenTheServerHasNoIrisWorlds() throws Exception {
+        IrisPlatforms.bind(mock(IrisPlatform.class));
+        Iris plugin = plugin();
+
+        try (EnableFixture fixture = new EnableFixture(false)) {
+            IllegalStateException failure = assertThrows(IllegalStateException.class, plugin::onEnable);
+            assertTrue(failure.getMessage(), failure.getMessage().contains("already bound"));
+        }
+    }
+
+    @Test
+    public void anUnsupportedServerWithIrisWorldsLocksInsteadOfDisablingIris() throws Exception {
+        Iris plugin = plugin();
+        set(plugin, "pendingWorldReplacements", mock(PendingWorldReplacementManager.class));
+
+        try (EnableFixture fixture = new EnableFixture(true);
+             MockedStatic<INMS> nms = mockStatic(INMS.class);
+             MockedStatic<J> scheduler = mockStatic(J.class)) {
+            nms.when(INMS::isBound).thenReturn(false);
+            nms.when(INMS::bindFailure).thenReturn(new IllegalStateException("no NMS binding for 26.9"));
+
+            plugin.onEnable();
+
+            String denial = IrisStartupValidation.denialReason().orElseThrow();
+            assertTrue(denial, denial.contains("no NMS binding for 26.9"));
+            scheduler.verify(() -> J.s(any(Runnable.class), anyInt()), never());
+        }
+    }
+
+    /**
+     * Deferring to the server stop quiesces through the NMS binding and waits for generators a failed enable never
+     * made, so a failed enable tears down at once even while the server stops.
+     */
+    @Test
+    public void aFailedEnableNeverDefersItsTeardownToTheServerStop() {
+        assertFalse(FailedEnableLock.defersTeardownToServerStop(true, true));
+        assertFalse(FailedEnableLock.defersTeardownToServerStop(true, false));
+        assertTrue(FailedEnableLock.defersTeardownToServerStop(false, true));
+        assertFalse(FailedEnableLock.defersTeardownToServerStop(false, false));
+    }
+
+    @Test
+    public void irisWorldsAreManagedStorageOrABukkitBindingForAWorldThatLoads() throws Exception {
+        File levelRoot = temporaryFolder.newFolder("level", "world");
+        File bukkit = new File(temporaryFolder.getRoot(), "bukkit.yml");
+
+        assertFalse(FailedEnableLock.irisWorldsPresent(levelRoot, bukkit));
+
+        YamlConfiguration yaml = new YamlConfiguration();
+        yaml.set("worlds.removed_iris_world.generator", "Iris:overworld");
+        yaml.save(bukkit);
+        assertFalse("a leftover entry for a world that never loads", FailedEnableLock.irisWorldsPresent(levelRoot, bukkit));
+
+        yaml.set("worlds.world.generator", "Iris:overworld");
+        yaml.save(bukkit);
+        assertTrue("an Iris overworld lives in a vanilla slot", FailedEnableLock.irisWorldsPresent(levelRoot, bukkit));
+
+        assertTrue(bukkit.delete());
+        assertTrue(new File(levelRoot, "dimensions/iris/moon").mkdirs());
+        assertTrue(FailedEnableLock.irisWorldsPresent(levelRoot, bukkit));
+    }
+
+    /**
+     * Paper builds plugins through its class loader, so the plugin under test is the real class with its fields
+     * set by hand: the resolver getDefaultWorldGenerator delegates to, and whatever enable touches before failing.
+     */
+    private static Iris plugin() throws Exception {
+        Iris plugin = mock(Iris.class, CALLS_REAL_METHODS);
+        set(plugin, "generatorResolver", new IrisWorldGeneratorResolver(plugin));
+        return plugin;
+    }
+
+    private static void set(Iris plugin, String name, Object value) throws Exception {
+        Field field = Iris.class.getDeclaredField(name);
+        field.setAccessible(true);
+        field.set(plugin, value);
+    }
+
+    /**
+     * irisWorldsPresent reads the real server.properties, which a test has none of, so the answer is set here.
+     */
+    private static final class EnableFixture implements AutoCloseable {
+        private final MockedStatic<Bukkit> bukkit = mockStatic(Bukkit.class);
+        private final MockedStatic<Iris> iris = mockStatic(Iris.class);
+        private final MockedStatic<FailedEnableLock> lock = mockStatic(FailedEnableLock.class, CALLS_REAL_METHODS);
+
+        private EnableFixture(boolean irisWorlds) {
+            PluginManager plugins = mock(PluginManager.class);
+            bukkit.when(Bukkit::getPluginManager).thenReturn(plugins);
+            bukkit.when(Bukkit::getWorlds).thenReturn(List.of());
+            lock.when(FailedEnableLock::irisWorldsPresent).thenReturn(irisWorlds);
+        }
+
+        @Override
+        public void close() {
+            lock.close();
+            iris.close();
+            bukkit.close();
+        }
+    }
+}

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

@@ -8,10 +8,16 @@ import io.papermc.paper.plugin.lifecycle.event.handler.configuration.LifecycleEv
 import io.papermc.paper.plugin.lifecycle.event.types.LifecycleEventType;
 import net.kyori.adventure.text.logger.slf4j.ComponentLogger;
 import org.junit.Test;
+import org.mockito.ArgumentCaptor;
+
+import java.io.IOException;
 
 import static org.junit.Assert.assertSame;
 import static org.junit.Assert.assertThrows;
+import static org.junit.Assert.assertTrue;
+import static org.mockito.Mockito.atLeastOnce;
 import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
 public class IrisBootstrapFailureContractTest {
@@ -32,6 +38,27 @@ public class IrisBootstrapFailureContractTest {
         assertSame(cause, failure.getCause());
     }
 
+    @Test
+    public void bootstrapFailureIsReportedWithTheRefusalBanner() {
+        BootstrapContext context = mock(BootstrapContext.class);
+        ComponentLogger logger = mock(ComponentLogger.class);
+        when(context.getLogger()).thenReturn(logger);
+        when(context.getLifecycleManager()).thenReturn(new CapturingLifecycleManager());
+        IllegalStateException failure = new IllegalStateException("Iris world storage is unusable",
+                new IOException("Invalid generation manifest: manifest.json"));
+
+        IrisBootstrap.armStartupFailure(context, failure, lifecycleEventType());
+
+        ArgumentCaptor<String> lines = ArgumentCaptor.forClass(String.class);
+        verify(logger, atLeastOnce()).error(lines.capture());
+        String banner = String.join("\n", lines.getAllValues());
+        assertTrue(banner, banner.startsWith("=".repeat(78)));
+        assertTrue(banner, banner.contains("Cause: Iris world storage is unusable"));
+        assertTrue(banner, banner.contains("Caused by: Invalid generation manifest: manifest.json"));
+        assertTrue(banner, banner.contains("no chunks are written"));
+        assertTrue(banner, banner.contains("--safeMode"));
+    }
+
     @SuppressWarnings("unchecked")
     private static LifecycleEventType<BootstrapContext, LifecycleEvent, ?> lifecycleEventType() {
         return (LifecycleEventType<BootstrapContext, LifecycleEvent, ?>) mock(LifecycleEventType.class);

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

@@ -175,6 +175,81 @@ public class IrisBootstrapWorldStorageContractTest {
         assertFalse(MissingWorldStorageLog.hasWarned("world_iris_moon"));
     }
 
+    /**
+     * A vanilla slot that holds an Iris world is generated from its history like any Iris world, so a broken
+     * history stops startup before the level exists instead of reaching the level-load refusal.
+     */
+    @Test
+    public void startupIsRefusedWhenABoundVanillaSlotLostItsGenerationHistory() throws Exception {
+        Path serverRoot = temporaryFolder.newFolder("broken-overworld-server").toPath();
+        Files.createDirectories(serverRoot.resolve("world/dimensions/minecraft/overworld/iris/engine-data"));
+        Files.createDirectories(serverRoot.resolve("world/dimensions/minecraft/overworld/region"));
+        Files.writeString(serverRoot.resolve("world/dimensions/minecraft/overworld/region/r.0.0.mca"), "terrain");
+        writeServerProperties(serverRoot);
+        writeBukkitWorlds(serverRoot, "world");
+
+        IllegalStateException failure = assertThrows(
+                IllegalStateException.class,
+                () -> IrisBootstrap.requireUsableWorldStorage(startupPaths(serverRoot)));
+
+        assertTrue(failure.getMessage(),
+                failure.getMessage().contains(serverRoot.toRealPath().resolve("world/dimensions/minecraft/overworld")
+                        .toString()));
+        assertTrue(failure.getMessage(), failure.getMessage().contains("generation history"));
+        assertFalse(failure.getMessage(), failure.getMessage().contains("Remove worlds."));
+    }
+
+    @Test
+    public void unusableStorageNamesWhyTheHistoryCannotBeRead() throws Exception {
+        Path serverRoot = temporaryFolder.newFolder("cut-history-server").toPath();
+        Path generation = serverRoot.resolve("world/dimensions/minecraft/overworld/iris/generation");
+        Files.createDirectories(generation);
+        Files.writeString(generation.resolve("manifest.json"), "{\"schema\":1,\"epochs\":[{\"id", StandardCharsets.UTF_8);
+        writeServerProperties(serverRoot);
+        writeBukkitWorlds(serverRoot, "world");
+
+        IllegalStateException failure = assertThrows(
+                IllegalStateException.class,
+                () -> IrisBootstrap.requireUsableWorldStorage(startupPaths(serverRoot)));
+
+        assertTrue(failure.getMessage(), failure.getMessage().contains("Invalid generation manifest"));
+        assertFalse(failure.getMessage(), failure.getMessage().contains("\n"));
+    }
+
+    /**
+     * Without its bukkit.yml binding the server builds an Iris world in a vanilla slot with the vanilla generator,
+     * which writes vanilla terrain into it.
+     */
+    @Test
+    public void startupIsRefusedWhenAnIrisWorldInAVanillaSlotLostItsBinding() throws Exception {
+        Path serverRoot = temporaryFolder.newFolder("unbound-overworld-server").toPath();
+        Files.createDirectories(serverRoot.resolve("world/dimensions/minecraft/overworld/iris/pack"));
+        writeServerProperties(serverRoot);
+        writeBukkitWorlds(serverRoot);
+
+        IllegalStateException failure = assertThrows(
+                IllegalStateException.class,
+                () -> IrisBootstrap.requireUsableWorldStorage(startupPaths(serverRoot)));
+
+        assertTrue(failure.getMessage(), failure.getMessage().contains("worlds.world.generator"));
+        assertTrue(failure.getMessage(),
+                failure.getMessage().contains(serverRoot.toRealPath().resolve("world/dimensions/minecraft/overworld")
+                        .toString()));
+    }
+
+    @Test
+    public void startupContinuesForVanillaSlotsWithoutIrisContent() throws Exception {
+        Path serverRoot = temporaryFolder.newFolder("vanilla-server").toPath();
+        Files.createDirectories(serverRoot.resolve("world/dimensions/minecraft/overworld/region"));
+        Files.writeString(serverRoot.resolve("world/dimensions/minecraft/overworld/region/r.0.0.mca"), "terrain");
+        Files.createDirectories(serverRoot.resolve("world/dimensions/minecraft/the_nether/iris"));
+        Files.writeString(serverRoot.resolve("world/dimensions/minecraft/the_nether/iris/.DS_Store"), "finder");
+        writeServerProperties(serverRoot);
+        writeBukkitWorlds(serverRoot);
+
+        IrisBootstrap.requireUsableWorldStorage(startupPaths(serverRoot));
+    }
+
     private static BukkitStartupPaths startupPaths(Path serverRoot) throws Exception {
         return BukkitStartupPaths.resolve(serverRoot, new String[0]);
     }

adapters/bukkit/plugin/src/test/java/art/arcane/iris/world/BukkitWorldReconcilerRuntimeTest.java

@@ -11,12 +11,14 @@ import art.arcane.iris.world.history.GenerationHistory;
 import art.arcane.iris.world.history.GenerationHistoryPaths;
 import art.arcane.iris.world.history.GenerationHistoryRuntimeRouter;
 import art.arcane.iris.world.history.GenerationManifest;
+import java.io.File;
 import java.io.IOException;
 import java.lang.reflect.Constructor;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.Optional;
 import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ExecutionException;
 import org.bukkit.Bukkit;
 import org.bukkit.NamespacedKey;
 import org.bukkit.World;
@@ -26,9 +28,11 @@ import org.junit.rules.TemporaryFolder;
 import org.mockito.MockedStatic;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertSame;
 import static org.junit.Assert.assertThrows;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.mockStatic;
+import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
 public class BukkitWorldReconcilerRuntimeTest {
@@ -95,6 +99,33 @@ public class BukkitWorldReconcilerRuntimeTest {
         }
     }
 
+    /**
+     * The startup reconcile and /iris load create worlds through the backend, so a world Iris refuses there needs
+     * the same banner and operator notice as one CraftServer asked for.
+     */
+    @Test
+    public void aRefusedReconcilerCreateIsReportedAsARefusal() throws Exception {
+        NamespacedKey key = new NamespacedKey("iris", "probe");
+        IllegalStateException refusal = new IllegalStateException("Iris generation history is unusable at /srv/probe.");
+        Iris plugin = mock(Iris.class);
+        WorldRefusalReporter refusals = mock(WorldRefusalReporter.class);
+        when(plugin.worldRefusals()).thenReturn(refusals);
+        when(plugin.requireWorldGenerator("world_iris_probe", "overworld")).thenThrow(refusal);
+
+        try (MockedStatic<Iris> iris = mockStatic(Iris.class);
+             MockedStatic<IrisWorldStorage> storage = mockStatic(IrisWorldStorage.class)) {
+            storage.when(IrisWorldStorage::levelRoot).thenReturn(new File("world"));
+            storage.when(() -> IrisWorldStorage.configuredWorldName(key, "world")).thenReturn("world_iris_probe");
+            storage.when(() -> IrisWorldStorage.logicalName(key)).thenReturn("probe");
+
+            CompletableFuture<World> created = backend(plugin).createWorld(key, "overworld", 1337L);
+
+            ExecutionException failure = assertThrows(ExecutionException.class, created::get);
+            assertSame(refusal, failure.getCause());
+            verify(refusals).report("world_iris_probe", key, refusal);
+        }
+    }
+
     private RuntimeFixture fixture() throws Exception {
         Path container = temporaryFolder.newFolder().toPath();
         Path root = container.resolve("world/dimensions/iris/probe");
@@ -134,11 +165,14 @@ public class BukkitWorldReconcilerRuntimeTest {
         when(dimension.getLoadKey()).thenReturn("overworld");
         when(engine.getData()).thenReturn(data);
         when(data.getDataFolder()).thenReturn(pack.toFile());
+        return new RuntimeFixture(backend(mock(Iris.class)), world, key, generator, engine, history, root, pack);
+    }
+
+    private static BukkitWorldReconciler.Backend backend(Iris plugin) throws Exception {
         Class<?> backendClass = Class.forName(BukkitWorldReconciler.class.getName() + "$BukkitBackend");
         Constructor<?> constructor = backendClass.getDeclaredConstructor(Iris.class);
         constructor.setAccessible(true);
-        BukkitWorldReconciler.Backend backend = (BukkitWorldReconciler.Backend) constructor.newInstance(mock(Iris.class));
-        return new RuntimeFixture(backend, world, key, generator, engine, history, root, pack);
+        return (BukkitWorldReconciler.Backend) constructor.newInstance(plugin);
     }
 
     private record RuntimeFixture(BukkitWorldReconciler.Backend backend, World world, NamespacedKey key,

adapters/bukkit/plugin/src/test/java/art/arcane/iris/world/IrisFailClosedChunkGeneratorTest.java

@@ -0,0 +1,77 @@
+package art.arcane.iris.world;
+
+import org.bukkit.World;
+import org.bukkit.generator.ChunkGenerator;
+import org.bukkit.generator.WorldInfo;
+import org.junit.Test;
+
+import java.io.IOException;
+import java.util.List;
+import java.util.Random;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertThrows;
+import static org.junit.Assert.assertTrue;
+import static org.mockito.Mockito.mock;
+
+/**
+ * Paper 26.3 asks a plugin generator for its biome provider in MinecraftServer.createLevel and
+ * CraftServer.createWorld before the level exists, outside any catch. A throw there is the only thing that stops a
+ * broken Iris world from being created at all, so every fail-closed generator must keep throwing from it.
+ */
+public class IrisFailClosedChunkGeneratorTest {
+    @Test
+    public void everyFailClosedGeneratorRefusesTheBiomeProviderBeforeTheLevelExists() {
+        List<ChunkGenerator> generators = List.of(
+                IrisFailClosedChunkGenerator.discoveryProbe("world"),
+                IrisFailClosedChunkGenerator.startupLock("world", "locked for a test"),
+                IrisFailClosedChunkGenerator.refused("world", new IllegalStateException("history drifted")));
+
+        for (ChunkGenerator generator : generators) {
+            IllegalStateException refusal = assertThrows(
+                    IllegalStateException.class,
+                    () -> generator.getDefaultBiomeProvider(mock(WorldInfo.class)));
+            assertTrue(refusal.getMessage(), refusal.getMessage().contains("'world'"));
+            assertThrows(IllegalStateException.class, () -> generator.getDefaultPopulators(mock(World.class)));
+            assertThrows(IllegalStateException.class,
+                    () -> generator.getFixedSpawnLocation(mock(World.class), new Random()));
+            assertFalse(generator.shouldGenerateNoise());
+        }
+    }
+
+    @Test
+    public void refusalCarriesTheWholeCauseChain() {
+        IllegalStateException failure = new IllegalStateException("Iris generation history is unusable at /srv/moon.",
+                new IOException("Historical generated registry definition changed"));
+
+        IllegalStateException refusal = assertThrows(
+                IllegalStateException.class,
+                () -> IrisFailClosedChunkGenerator.refused("world_iris_moon", failure)
+                        .getDefaultBiomeProvider(mock(WorldInfo.class)));
+
+        assertTrue(refusal.getMessage(), refusal.getMessage().contains("world_iris_moon"));
+        assertTrue(refusal.getMessage(), refusal.getMessage().contains("generation history is unusable"));
+        assertTrue(refusal.getMessage(), refusal.getMessage().contains("registry definition changed"));
+    }
+
+    /**
+     * The refusal is built on the way back to CraftServer, which turns any throw into the vanilla generator, so an
+     * unreadable cause still has to produce a generator.
+     */
+    @Test
+    public void aCauseWhoseMessageCannotBeReadStillRefuses() {
+        IllegalStateException unreadable = new IllegalStateException() {
+            @Override
+            public String getMessage() {
+                throw new UnsupportedOperationException("message unavailable");
+            }
+        };
+
+        ChunkGenerator generator = IrisFailClosedChunkGenerator.refused("world_iris_moon", unreadable);
+
+        IllegalStateException refusal = assertThrows(
+                IllegalStateException.class,
+                () -> generator.getDefaultBiomeProvider(mock(WorldInfo.class)));
+        assertTrue(refusal.getMessage(), refusal.getMessage().contains("world_iris_moon"));
+    }
+}

adapters/bukkit/plugin/src/test/java/art/arcane/iris/world/IrisWorldGeneratorResolverTest.java

@@ -24,6 +24,7 @@ import org.bukkit.generator.WorldInfo;
 import org.mockito.MockedStatic;
 
 import java.io.File;
+import java.io.IOException;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.nio.file.Path;
@@ -256,18 +257,12 @@ public class IrisWorldGeneratorResolverTest {
 
         try (MockedStatic<Bukkit> bukkit = mockStatic(Bukkit.class);
              MockedStatic<Iris> iris = mockStatic(Iris.class)) {
-            Server server = mock(Server.class);
-            when(server.getLevelDirectory()).thenReturn(levelRoot.toPath());
-            bukkit.when(Bukkit::getServer).thenReturn(server);
-            bukkit.when(Bukkit::getWorldContainer).thenReturn(worldContainer);
-            bukkit.when(Bukkit::getWorlds).thenReturn(List.of());
+            mockServer(bukkit, worldContainer, levelRoot, List.of());
 
-            IllegalStateException failure = assertThrows(
-                    IllegalStateException.class,
-                    () -> new IrisWorldGeneratorResolver(null)
-                            .resolveDefaultWorldGenerator("CheckingPlotSquaredGenerator", "overworld"));
+            String refusal = assertFailsClosed(() -> new IrisWorldGeneratorResolver(null)
+                    .resolveDefaultWorldGenerator("CheckingPlotSquaredGenerator", "overworld"));
 
-            assertTrue(failure.getMessage(), failure.getMessage().contains("CheckingPlotSquaredGenerator"));
+            assertTrue(refusal, refusal.contains("CheckingPlotSquaredGenerator"));
             bukkit.verify(Bukkit::shutdown, never());
         }
     }
@@ -382,32 +377,26 @@ public class IrisWorldGeneratorResolverTest {
     }
 
     @Test
-    public void externalCreateWithoutIrisStorageThrowsWithoutShutdown() throws Exception {
+    public void externalCreateWithoutIrisStorageFailsClosedWithoutShutdown() throws Exception {
         File worldContainer = temporaryFolder.newFolder("external-create");
         File levelRoot = new File(worldContainer, "world");
         assertTrue(levelRoot.mkdirs());
 
         try (MockedStatic<Bukkit> bukkit = mockStatic(Bukkit.class);
              MockedStatic<Iris> iris = mockStatic(Iris.class)) {
-            Server server = mock(Server.class);
-            when(server.getLevelDirectory()).thenReturn(levelRoot.toPath());
-            bukkit.when(Bukkit::getServer).thenReturn(server);
-            bukkit.when(Bukkit::getWorldContainer).thenReturn(worldContainer);
-            bukkit.when(Bukkit::getWorlds).thenReturn(List.of());
+            mockServer(bukkit, worldContainer, levelRoot, List.of());
 
-            IllegalStateException failure = assertThrows(
-                    IllegalStateException.class,
-                    () -> new IrisWorldGeneratorResolver(null)
-                            .resolveDefaultWorldGenerator("mvtest", "overworld"));
+            String refusal = assertFailsClosed(() -> new IrisWorldGeneratorResolver(null)
+                    .resolveDefaultWorldGenerator("mvtest", "overworld"));
 
-            assertTrue(failure.getMessage(), failure.getMessage().contains("mvtest"));
-            assertTrue(failure.getMessage(), failure.getMessage().contains("/iris create"));
+            assertTrue(refusal, refusal.contains("mvtest"));
+            assertTrue(refusal, refusal.contains("/iris create"));
             bukkit.verify(Bukkit::shutdown, never());
         }
     }
 
     @Test
-    public void ownedIrisWorldWithUnusableSnapshotStillStopsTheServer() throws Exception {
+    public void ownedIrisWorldWithUnusableSnapshotFailsClosedWithoutShutdown() throws Exception {
         File worldContainer = temporaryFolder.newFolder("owned-broken");
         File levelRoot = new File(worldContainer, "world");
         assertTrue(levelRoot.mkdirs());
@@ -415,46 +404,162 @@ public class IrisWorldGeneratorResolverTest {
 
         try (MockedStatic<Bukkit> bukkit = mockStatic(Bukkit.class);
              MockedStatic<Iris> iris = mockStatic(Iris.class)) {
-            Server server = mock(Server.class);
-            when(server.getLevelDirectory()).thenReturn(levelRoot.toPath());
-            bukkit.when(Bukkit::getServer).thenReturn(server);
-            bukkit.when(Bukkit::getWorldContainer).thenReturn(worldContainer);
-            bukkit.when(Bukkit::getWorlds).thenReturn(List.of());
+            mockServer(bukkit, worldContainer, levelRoot, List.of());
 
-            assertThrows(
-                    IllegalStateException.class,
-                    () -> new IrisWorldGeneratorResolver(null)
-                            .resolveDefaultWorldGenerator("world_iris_moon", "overworld"));
+            String refusal = assertFailsClosed(() -> new IrisWorldGeneratorResolver(null)
+                    .resolveDefaultWorldGenerator("world_iris_moon", "overworld"));
 
-            bukkit.verify(Bukkit::shutdown);
+            assertTrue(refusal, refusal.contains("world_iris_moon"));
+            bukkit.verify(Bukkit::shutdown, never());
+        }
+    }
+
+    /**
+     * The tester's failure: a world whose generation history no longer matches the live registries. CraftServer
+     * turns a throw here into the vanilla generator, so the history failure has to come back as a generator that
+     * refuses to create the level.
+     */
+    @Test
+    public void unusableGenerationHistoryFailsClosedWithoutShutdown() throws Exception {
+        File worldContainer = temporaryFolder.newFolder("history-broken").getCanonicalFile();
+        File levelRoot = new File(worldContainer, "world");
+        File dimensionRoot = new File(levelRoot, "dimensions/iris/moon");
+        assertTrue(new File(dimensionRoot, "iris/generation").mkdirs());
+
+        try (MockedStatic<Bukkit> bukkit = mockStatic(Bukkit.class);
+             MockedStatic<Iris> iris = mockStatic(Iris.class);
+             MockedStatic<IrisWorlds> worlds = mockStatic(IrisWorlds.class)) {
+            mockServer(bukkit, worldContainer, levelRoot, List.of());
+            worlds.when(() -> IrisWorlds.readBukkitWorldSeed("moon")).thenReturn(1337L);
+
+            String refusal = assertFailsClosed(() -> new IrisWorldGeneratorResolver(null)
+                    .resolveDefaultWorldGenerator("moon", "overworld"));
+
+            assertTrue(refusal, refusal.contains("'moon'"));
+            assertTrue(refusal, refusal.contains("generation history is unusable"));
+            bukkit.verify(Bukkit::shutdown, never());
         }
     }
 
     @Test
-    public void vanillaDimensionSlotWithoutFrozenPackIsNotOwned() throws Exception {
+    public void internalLoadsGetTheResolutionFailureWithoutShutdown() throws Exception {
+        File worldContainer = temporaryFolder.newFolder("internal-load").getCanonicalFile();
+        File levelRoot = new File(worldContainer, "world");
+        File dimensionRoot = new File(levelRoot, "dimensions/iris/moon");
+        assertTrue(new File(dimensionRoot, "iris/generation").mkdirs());
+
+        try (MockedStatic<Bukkit> bukkit = mockStatic(Bukkit.class);
+             MockedStatic<Iris> iris = mockStatic(Iris.class);
+             MockedStatic<IrisWorlds> worlds = mockStatic(IrisWorlds.class)) {
+            mockServer(bukkit, worldContainer, levelRoot, List.of());
+            worlds.when(() -> IrisWorlds.readBukkitWorldSeed("moon")).thenReturn(1337L);
+
+            IllegalStateException failure = assertThrows(
+                    IllegalStateException.class,
+                    () -> new IrisWorldGeneratorResolver(null).requireWorldGenerator("moon", "overworld"));
+
+            assertTrue(failure.getMessage(), failure.getMessage().contains("generation history is unusable"));
+            bukkit.verify(Bukkit::shutdown, never());
+            iris.verify(() -> Iris.error(any(String.class), any(Object[].class)), never());
+        }
+    }
+
+    /**
+     * A vanilla slot bound to Iris in bukkit.yml with no Iris storage stops startup, so no command can run until the
+     * binding is gone. /iris create is for new worlds anyway; a vanilla slot is taken over with /iris replace.
+     */
+    @Test
+    public void vanillaDimensionSlotWithoutFrozenPackFailsClosed() throws Exception {
         File worldContainer = temporaryFolder.newFolder("vanilla-slot");
         File levelRoot = new File(worldContainer, "world");
         assertTrue(new File(levelRoot, "dimensions/minecraft/the_nether").mkdirs());
 
         try (MockedStatic<Bukkit> bukkit = mockStatic(Bukkit.class);
              MockedStatic<Iris> iris = mockStatic(Iris.class)) {
-            Server server = mock(Server.class);
-            when(server.getLevelDirectory()).thenReturn(levelRoot.toPath());
-            bukkit.when(Bukkit::getServer).thenReturn(server);
-            bukkit.when(Bukkit::getWorldContainer).thenReturn(worldContainer);
-            bukkit.when(Bukkit::getWorlds).thenReturn(List.of());
+            mockServer(bukkit, worldContainer, levelRoot, List.of());
 
-            IllegalStateException failure = assertThrows(
-                    IllegalStateException.class,
-                    () -> new IrisWorldGeneratorResolver(null)
-                            .resolveDefaultWorldGenerator("world_nether", "overworld"));
+            String refusal = assertFailsClosed(() -> new IrisWorldGeneratorResolver(null)
+                    .resolveDefaultWorldGenerator("world_nether", "overworld"));
 
-            assertTrue(failure.getMessage(), failure.getMessage().contains("minecraft:the_nether"));
-            assertTrue(failure.getMessage(), failure.getMessage().contains("/iris create"));
+            assertTrue(refusal, refusal.contains("minecraft:the_nether"));
+            assertTrue(refusal, refusal.contains("worlds.world_nether.generator"));
+            assertTrue(refusal, refusal.contains("bukkit.yml"));
+            assertTrue(refusal, refusal.contains("/iris replace minecraft:the_nether type=<pack>"));
+            assertFalse(refusal, refusal.contains("/iris create"));
             bukkit.verify(Bukkit::shutdown, never());
         }
     }
 
+    /**
+     * The fix for a vanilla slot bound to Iris is removing the binding. Given for an Iris world whose history is
+     * gone, that fix loads the world under the vanilla generator, which writes vanilla terrain into it.
+     */
+    @Test
+    public void vanillaSlotHoldingAnIrisWorldKeepsItsBindingAndPointsAtTheHistory() throws Exception {
+        File worldContainer = temporaryFolder.newFolder("iris-in-vanilla-slot");
+        File levelRoot = new File(worldContainer, "world");
+        File dimensionRoot = new File(levelRoot, "dimensions/minecraft/overworld");
+        assertTrue(new File(dimensionRoot, "iris/engine-data").mkdirs());
+        assertTrue(new File(dimensionRoot, "data/minecraft").mkdirs());
+        assertTrue(new File(dimensionRoot, "data/minecraft/world_gen_settings.dat").createNewFile());
+
+        try (MockedStatic<Bukkit> bukkit = mockStatic(Bukkit.class);
+             MockedStatic<Iris> iris = mockStatic(Iris.class)) {
+            mockServer(bukkit, worldContainer, levelRoot, List.of());
+
+            String refusal = assertFailsClosed(() -> new IrisWorldGeneratorResolver(null)
+                    .resolveDefaultWorldGenerator("world", "overworld"));
+
+            assertTrue(refusal, refusal.contains("minecraft:overworld"));
+            assertTrue(refusal, refusal.contains("is an Iris world"));
+            assertTrue(refusal, refusal.contains(new File(dimensionRoot, "iris/generation").getPath()));
+            assertFalse(refusal, refusal.contains("Remove worlds.world.generator"));
+            assertFalse(refusal, refusal.contains("/iris replace"));
+        }
+    }
+
+    /**
+     * A start refused before the overworld existed still leaves level.dat behind, and vanilla cannot start from a
+     * level.dat that has no world generation settings next to it.
+     */
+    @Test
+    public void vanillaSlotRefusalOnANeverCreatedLevelNamesTheLeftoverLevelDat() throws Exception {
+        File worldContainer = temporaryFolder.newFolder("never-created");
+        File levelRoot = new File(worldContainer, "world");
+        assertTrue(levelRoot.mkdirs());
+
+        try (MockedStatic<Bukkit> bukkit = mockStatic(Bukkit.class);
+             MockedStatic<Iris> iris = mockStatic(Iris.class)) {
+            mockServer(bukkit, worldContainer, levelRoot, List.of());
+
+            String refusal = assertFailsClosed(() -> new IrisWorldGeneratorResolver(null)
+                    .resolveDefaultWorldGenerator("world", "overworld"));
+
+            assertTrue(refusal, refusal.contains("Remove worlds.world.generator"));
+            assertTrue(refusal, refusal.contains(new File(levelRoot, "level.dat").getPath()));
+        }
+    }
+
+    @Test
+    public void vanillaSlotRefusalOnAnExistingLevelLeavesLevelDatAlone() throws Exception {
+        File worldContainer = temporaryFolder.newFolder("existing-vanilla");
+        File levelRoot = new File(worldContainer, "world");
+        File settings = new File(levelRoot, "dimensions/minecraft/overworld/data/minecraft/world_gen_settings.dat");
+        assertTrue(settings.getParentFile().mkdirs());
+        assertTrue(settings.createNewFile());
+
+        try (MockedStatic<Bukkit> bukkit = mockStatic(Bukkit.class);
+             MockedStatic<Iris> iris = mockStatic(Iris.class)) {
+            mockServer(bukkit, worldContainer, levelRoot, List.of());
+
+            String refusal = assertFailsClosed(() -> new IrisWorldGeneratorResolver(null)
+                    .resolveDefaultWorldGenerator("world", "overworld"));
+
+            assertTrue(refusal, refusal.contains("Remove worlds.world.generator"));
+            assertFalse(refusal, refusal.contains("level.dat"));
+        }
+    }
+
     @Test
     public void alreadyLoadedIrisKeyIsRefusedBeforeAnyEngineCanStart() throws Exception {
         File worldContainer = temporaryFolder.newFolder("duplicate-key");
@@ -468,23 +573,39 @@ public class IrisWorldGeneratorResolverTest {
 
         try (MockedStatic<Bukkit> bukkit = mockStatic(Bukkit.class);
              MockedStatic<Iris> iris = mockStatic(Iris.class)) {
-            Server server = mock(Server.class);
-            when(server.getLevelDirectory()).thenReturn(levelRoot.toPath());
-            bukkit.when(Bukkit::getServer).thenReturn(server);
-            bukkit.when(Bukkit::getWorldContainer).thenReturn(worldContainer);
-            bukkit.when(Bukkit::getWorlds).thenReturn(List.of(loaded));
+            mockServer(bukkit, worldContainer, levelRoot, List.of(loaded));
 
-            IllegalStateException failure = assertThrows(
-                    IllegalStateException.class,
-                    () -> new IrisWorldGeneratorResolver(null)
-                            .resolveDefaultWorldGenerator("irisworld", "overworld"));
+            String refusal = assertFailsClosed(() -> new IrisWorldGeneratorResolver(null)
+                    .resolveDefaultWorldGenerator("irisworld", "overworld"));
 
-            assertTrue(failure.getMessage(), failure.getMessage().contains("iris:irisworld"));
-            assertTrue(failure.getMessage(), failure.getMessage().contains("world_iris_irisworld"));
+            assertTrue(refusal, refusal.contains("iris:irisworld"));
+            assertTrue(refusal, refusal.contains("world_iris_irisworld"));
             bukkit.verify(Bukkit::shutdown, never());
         }
     }
 
+    private static void mockServer(MockedStatic<Bukkit> bukkit, File worldContainer, File levelRoot, List<World> worlds) {
+        Server server = mock(Server.class);
+        when(server.getLevelDirectory()).thenReturn(levelRoot.toPath());
+        bukkit.when(Bukkit::getServer).thenReturn(server);
+        bukkit.when(Bukkit::getWorldContainer).thenReturn(worldContainer);
+        bukkit.when(Bukkit::getWorlds).thenReturn(worlds);
+    }
+
+    /**
+     * Resolves through CraftServer's fallback and proves the result is Iris' refusal rather than vanilla: Paper
+     * calls getDefaultBiomeProvider before the level exists, and that throw is what stops the level being created.
+     */
+    private static String assertFailsClosed(Supplier<ChunkGenerator> resolution) {
+        ChunkGenerator vanillaFallback = mock(ChunkGenerator.class);
+        ChunkGenerator selected = craftBukkitGeneratorOrFallback(resolution, vanillaFallback);
+        assertNotSame(vanillaFallback, selected);
+        IllegalStateException refusal = assertThrows(
+                IllegalStateException.class,
+                () -> selected.getDefaultBiomeProvider(mock(WorldInfo.class)));
+        return refusal.getMessage();
+    }
+
     private static void writeValidPack(Path packRoot) throws Exception {
         Files.createDirectories(packRoot.resolve("dimensions"));
         Files.createDirectories(packRoot.resolve("regions"));

adapters/bukkit/plugin/src/test/java/art/arcane/iris/world/WorldRefusalReporterTest.java

@@ -0,0 +1,145 @@
+package art.arcane.iris.world;
+
+import art.arcane.iris.Iris;
+import net.kyori.adventure.text.Component;
+import org.bukkit.Bukkit;
+import org.bukkit.NamespacedKey;
+import org.bukkit.World;
+import org.bukkit.entity.Player;
+import org.bukkit.event.player.PlayerJoinEvent;
+import org.bukkit.event.world.WorldLoadEvent;
+import org.bukkit.plugin.Plugin;
+import org.bukkit.plugin.PluginManager;
+import org.junit.Test;
+import org.mockito.MockedStatic;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.anyString;
+import static org.mockito.ArgumentMatchers.contains;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.mockStatic;
+import static org.mockito.Mockito.never;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+/**
+ * Whether a refused world stops startup depends on who asked for it: Paper's startup level creation aborts the
+ * server, a runtime create only fails its caller. The banner must not claim the wrong one.
+ */
+public class WorldRefusalReporterTest {
+    private static final NamespacedKey MOON = new NamespacedKey("iris", "moon");
+
+    @Test
+    public void aRefusalBeforeAnyWorldLoadedSaysStartupStops() {
+        String banner = reportAndCapture(new WorldRefusalReporter());
+
+        assertTrue(banner, banner.contains("'moon'"));
+        assertTrue(banner, banner.contains("iris:moon"));
+        assertTrue(banner, banner.contains("Iris generation history is unusable at /srv/moon."));
+        assertTrue(banner, banner.contains("Historical generated registry definition changed for iris:biomes/abc"));
+        assertTrue(banner, banner.contains("no chunks"));
+        assertTrue(banner, banner.contains("startup stops"));
+    }
+
+    /**
+     * Paper creates every startup level before it prepares any, and preparing one fires the first WorldLoadEvent.
+     * A plugin enabling at POSTWORLD creates its worlds after that, before the first tick, and the server keeps
+     * running when that create fails.
+     */
+    @Test
+    public void aRefusalAfterTheFirstWorldLoadSaysTheServerKeepsRunning() {
+        WorldRefusalReporter reporter = new WorldRefusalReporter();
+        reporter.onWorldLoad(new WorldLoadEvent(world(NamespacedKey.minecraft("overworld"))));
+
+        String banner = reportAndCapture(reporter);
+
+        assertTrue(banner, banner.contains("keeps running"));
+        assertFalse(banner, banner.contains("startup stops"));
+    }
+
+    @Test
+    public void irisEnabledAfterWorldsExistTreatsEveryRefusalAsRuntime() {
+        WorldRefusalReporter reporter = new WorldRefusalReporter();
+        Plugin plugin = mock(Plugin.class);
+        PluginManager plugins = mock(PluginManager.class);
+        World overworld = world(NamespacedKey.minecraft("overworld"));
+
+        try (MockedStatic<Bukkit> bukkit = mockStatic(Bukkit.class)) {
+            bukkit.when(Bukkit::getWorlds).thenReturn(List.of(overworld));
+            bukkit.when(Bukkit::getPluginManager).thenReturn(plugins);
+
+            reporter.attach(plugin);
+        }
+
+        assertTrue(reporter.startupWorldsCreated());
+        verify(plugins).registerEvents(reporter, plugin);
+        String banner = reportAndCapture(reporter);
+        assertTrue(banner, banner.contains("keeps running"));
+    }
+
+    @Test
+    public void operatorsHearAboutARefusedWorldOnJoinUntilItLoads() {
+        WorldRefusalReporter reporter = new WorldRefusalReporter();
+        reportAndCapture(reporter);
+        Player operator = player(true);
+        Player member = player(false);
+
+        reporter.onPlayerJoin(new PlayerJoinEvent(operator, Component.empty()));
+        reporter.onPlayerJoin(new PlayerJoinEvent(member, Component.empty()));
+
+        verify(operator).sendMessage(contains("iris:moon"));
+        verify(member, never()).sendMessage(anyString());
+
+        reporter.onWorldLoad(new WorldLoadEvent(world(MOON)));
+        Player later = player(true);
+        reporter.onPlayerJoin(new PlayerJoinEvent(later, Component.empty()));
+        verify(later, never()).sendMessage(anyString());
+    }
+
+    @Test
+    public void aFailureWhileReportingNeverEscapes() {
+        Throwable unreadable = new IllegalStateException() {
+            @Override
+            public String getMessage() {
+                throw new UnsupportedOperationException("message unavailable");
+            }
+        };
+
+        try (MockedStatic<Iris> iris = mockStatic(Iris.class)) {
+            new WorldRefusalReporter().report("moon", MOON, unreadable);
+        }
+    }
+
+    private static String reportAndCapture(WorldRefusalReporter reporter) {
+        IllegalStateException failure = new IllegalStateException("Iris generation history is unusable at /srv/moon.",
+                new IOException("Historical generated registry definition changed for iris:biomes/abc"));
+        List<String> lines = new ArrayList<>();
+        try (MockedStatic<Iris> iris = mockStatic(Iris.class)) {
+            iris.when(() -> Iris.error(anyString(), any(Object[].class))).thenAnswer(invocation -> {
+                lines.add(invocation.getArgument(0, String.class));
+                return null;
+            });
+            reporter.report("moon", MOON, failure);
+        }
+        return String.join("\n", lines);
+    }
+
+    private static World world(NamespacedKey key) {
+        World world = mock(World.class);
+        when(world.getKey()).thenReturn(key);
+        when(world.getName()).thenReturn(key.getKey());
+        return world;
+    }
+
+    private static Player player(boolean operator) {
+        Player player = mock(Player.class);
+        when(player.isOp()).thenReturn(operator);
+        return player;
+    }
+}

adapters/fabric/src/main/java/art/arcane/iris/fabric/IrisFabricBootstrap.java

@@ -17,6 +17,7 @@ public final class IrisFabricBootstrap implements ModInitializer {
     public void onInitialize() {
         NativeFabricLoader loader = new NativeFabricLoader(new NativeLoaderOptions(
                 "irisworldgen", "treefeller", ModdedTreeFellerService::runBreakProbe));
+        loader.captureOriginalBiomes();
         NativeChunkGeneratorDefinition generator = IrisModdedChunkGenerator.DEFINITION;
         NativeFabricPackSources.bind(ModdedForcedDatapack::repositorySource);
         ModdedEngineBootstrap.bootCommon(loader, "Fabric", () -> NativeFabricBootstrap.registerGenerator(generator));

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

@@ -0,0 +1,108 @@
+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.Identifier;
+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.WorldCarver;
+import net.minecraft.world.level.levelgen.feature.Feature;
+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\":{\"water_color\":\"#3f76e4\"},\"carvers\":[],\"features\":[]}";
+
+    @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, Identifier.parse("iris:modded_ore")),
+                new PlacedFeature(Holder.direct(mock(Feature.class)), List.of()),
+                RegistrationInfo.BUILT_IN);
+        features.freeze();
+        MappedRegistry<WorldCarver> carvers = new MappedRegistry<>(Registries.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, Identifier.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()));
+    }
+
+    /**
+     * What a Fabric biome modification that adds an ore does: it replaces the feature list of the registered biome's
+     * own generation settings.
+     */
+    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));
+    }
+
+    /**
+     * What a Fabric weather modification does: it replaces the registered biome's climate settings.
+     */
+    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/src/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.Identifier;
+import net.minecraft.resources.RegistryOps;
+import net.minecraft.resources.ResourceKey;
+import net.minecraft.server.Bootstrap;
+import net.minecraft.world.attribute.EnvironmentAttributes;
+import net.minecraft.world.attribute.modifier.MobSpawnSettingsModifier;
+import net.minecraft.world.entity.EntityTypes;
+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.WorldCarver;
+import net.minecraft.world.level.levelgen.feature.Feature;
+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\":[]}";
+
+    @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(Feature.class)), List.of()),
+                RegistrationInfo.BUILT_IN);
+        features.freeze();
+        MappedRegistry<WorldCarver> carvers = new MappedRegistry<>(Registries.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().getBaseTemperature(), 0.0F);
+        assertEquals(0x102030, biome.value().getWaterColor() & 0xFFFFFF);
+        assertTrue(biome.value().getGenerationSettings().hasFeature(ore.value()));
+        assertTrue(biome.value().getAttributes().contains(EnvironmentAttributes.NATURAL_MOB_SPAWNS));
+        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.climateSettings().setTemperature(0.1F);
+            builder.effects().waterColor(0x102030);
+            builder.attributes().modify(EnvironmentAttributes.NATURAL_MOB_SPAWNS, MobSpawnSettingsModifier.overlay(),
+                    new MobSpawnSettings.Builder().addSpawn(EntityTypes.ZOMBIE, 5, 1, 2).build());
+            builder.generationSettings().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

@@ -59,6 +59,7 @@ import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeGeneratorContext;
 import art.arcane.volmlib.nativelib.terrain.NativeWorld;
 
 import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeModdedStructureStage;
+import art.arcane.iris.world.safeguard.GenerationRefusalNotice;
 import art.arcane.iris.structure.nativegen.NativeStructureOwnershipRecord;
 
 import art.arcane.iris.structure.nativegen.IrisStructurePolicy;
@@ -72,6 +73,7 @@ import art.arcane.iris.pack.loading.IrisData;
 import art.arcane.iris.pack.PackValidationRegistry;
 import art.arcane.iris.generation.runtime.IrisEngine;
 import art.arcane.iris.generation.runtime.Engine;
+import art.arcane.iris.generation.runtime.GenerationFailures;
 import art.arcane.iris.generation.runtime.GenerationSessionException;
 import art.arcane.iris.generation.runtime.GenerationSessionLease;
 import art.arcane.iris.structure.nativegen.NativeFeatureGenerationPolicy;
@@ -454,11 +456,14 @@ public final class IrisModdedChunkGenerator implements NativeGeneratorOwner, Nat
 
     private Engine bindEngine(NativeWorld level) {
         requireBindingAllowed();
+        // A recorded failure stands until repoint or unbind resets the binding; re-running the bind would repeat the
+        // history verification on every chunk call and fail the same way.
+        engineBinding.throwIfFailed(dimensionKey);
         try {
             requireGlobalStructureGeneration(
                     NativeModdedServer.forWorld(level).generateStructures(), dimensionKey);
         } catch (RuntimeException error) {
-            engineBinding.fail(error);
+            recordBindFailure(level, error);
             throw error;
         }
         // Cache the owning level so hot paths never scan the level map to find themselves.
@@ -500,7 +505,7 @@ public final class IrisModdedChunkGenerator implements NativeGeneratorOwner, Nat
                 engineBinding.complete(created);
                 return created;
             } catch (Throwable error) {
-                engineBinding.fail(error);
+                recordBindFailure(level, error);
                 if (error instanceof RuntimeException runtimeException) {
                     throw runtimeException;
                 }
@@ -512,6 +517,31 @@ public final class IrisModdedChunkGenerator implements NativeGeneratorOwner, Nat
         }
     }
 
+    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)) {
+            ModdedIrisLog.warn("Iris bind of {} ({}) stopped with its runtime: {}", level.name(), dimensionKey,
+                    error.toString());
+            return;
+        }
+        engineBinding.fail(error);
+        for (String line : bindFailureNotice(level.name(), dimensionKey, error)) {
+            ModdedIrisLog.error(line);
+        }
+    }
+
+    static List<String> bindFailureNotice(String levelName, String dimensionKey, Throwable failure) {
+        return GenerationRefusalNotice.compose(
+                "Iris refused to generate " + levelName + " (generator " + dimensionKey + ")",
+                GenerationRefusalNotice.causes(failure),
+                List.of(
+                        "Iris does not generate this level and does not let vanilla or any other generator"
+                                + " write it; no chunks are written.",
+                        "A startup level stops the server; a runtime dimension stays unloaded."
+                                + " Fix the cause, then start the server again."
+                ));
+    }
+
     private void requireCompletedShutdown(Engine current) {
         if (current == null || !current.isClosing() || current.isClosed()) {
             return;
@@ -565,21 +595,11 @@ public final class IrisModdedChunkGenerator implements NativeGeneratorOwner, Nat
         }
     }
 
-    Engine engineOrNull() {
-        requireBindingAllowed();
-        Engine cached = engine;
-        requireCompletedShutdown(cached);
-        if (cached != null && !cached.isClosed()) {
-            return cached;
-        }
-        try {
-            return engine();
-        } catch (Throwable ignored) {
-            return null;
-        }
-    }
-
-    Engine structureEngineOrNull() {
+    /**
+     * Null only while no level uses this generator (world creation screens, codec validation). A bound level whose
+     * engine is refused, unloading or stopping throws, so no stage can mistake it for an unbound generator.
+     */
+    Engine boundEngineOrNull() {
         requireBindingAllowed();
         engineBinding.throwIfFailed(dimensionKey);
         Engine cached = engine;
@@ -984,7 +1004,7 @@ public final class IrisModdedChunkGenerator implements NativeGeneratorOwner, Nat
     @Override
     public <H, S> NativeModdedBiomePolicy<H, S> biomePolicy(NativeBiomeSourceAccess<H, S> source) {
         ModdedBiomePolicy<H, S> policy = new ModdedBiomePolicy<>(source);
-        policy.bind(new ModdedBiomePolicy.RuntimeCallbacks(this::structureEngineOrNull, this::awaitStructureEngine,
+        policy.bind(new ModdedBiomePolicy.RuntimeCallbacks(this::boundEngineOrNull, this::awaitStructureEngine,
                 this::allowsGenerationHistoryBypass, this::configuredStructureBiomeKeys,
                 IrisModdedChunkGenerator::retainedBiomeKeys, this::visibleBiomeSeed));
         return policy;

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

@@ -266,7 +266,7 @@ final class ModdedBiomePolicy<H, S> implements NativeModdedBiomePolicy<H, S> {
 
     @Override
     public H getNoiseBiome(int quartX, int quartY, int quartZ, S sampler) {
-        Engine engine = engineOrNull();
+        Engine engine = boundEngineOrNull();
         if (engine == null) {
             return access.serializedNoise(quartX, quartY, quartZ, sampler);
         }
@@ -288,7 +288,7 @@ final class ModdedBiomePolicy<H, S> implements NativeModdedBiomePolicy<H, S> {
 
     @Override
     public NativeBiomeSourcePolicy.BiomeLocation<H> findClosestBiome3d(ClosestQuery<H, S> query) {
-        Engine engine = engineOrNull();
+        Engine engine = boundEngineOrNull();
         if (engine == null) {
             return query.unboundFallback().get();
         }
@@ -355,7 +355,7 @@ final class ModdedBiomePolicy<H, S> implements NativeModdedBiomePolicy<H, S> {
     }
 
     public H getVisibleNoiseBiome(int quartX, int quartY, int quartZ, S sampler) {
-        Engine engine = engineOrNull();
+        Engine engine = boundEngineOrNull();
         if (engine == null) {
             return access.serializedNoise(quartX, quartY, quartZ, sampler);
         }
@@ -411,7 +411,7 @@ final class ModdedBiomePolicy<H, S> implements NativeModdedBiomePolicy<H, S> {
     }
 
     public H getVisibleSurfaceBiome(int blockX, int blockZ) {
-        Engine engine = engineOrNull();
+        Engine engine = boundEngineOrNull();
         if (engine == null) {
             return null;
         }
@@ -420,15 +420,15 @@ final class ModdedBiomePolicy<H, S> implements NativeModdedBiomePolicy<H, S> {
         try (historyScope) {
             GenerationSessionLease lease = tryAcquireGenerationLease(engine, "modded_surface_spawn_biome");
             if (lease == null) {
-                return null;
+                throw new IllegalStateException("Iris surface spawn biome lookup was rejected during an engine transition");
             }
             try (lease; IrisContext.Scope ignored = IrisContext.open(engine, lease.sessionId(), null)) {
                 if (!isReady(engine)) {
-                    return null;
+                    throw new IllegalStateException("Iris surface spawn biome lookup has no active engine runtime");
                 }
                 NativeBiomeSourceAccess.RegistryView<H> registry = biomeRegistry();
                 if (registry == null) {
-                    return null;
+                    throw new IllegalStateException("Iris surface spawn biome lookup has no biome registry");
                 }
                 int quartX = ((blockX) >> 2);
                 int quartZ = ((blockZ) >> 2);
@@ -463,7 +463,7 @@ final class ModdedBiomePolicy<H, S> implements NativeModdedBiomePolicy<H, S> {
     }
 
     public boolean isStructureReachable(Iterable<H> biomes) {
-        Engine engine = engineOrNull();
+        Engine engine = boundEngineOrNull();
         if (engine == null) {
             return isStructureReachable(biomes, possibleStructureBiomeKeys());
         }
@@ -494,7 +494,7 @@ final class ModdedBiomePolicy<H, S> implements NativeModdedBiomePolicy<H, S> {
         int radius = query.radius();
         S sampler = query.sampler();
         int minQuartY = ((y - radius) >> 2);
-        Engine engine = engineOrNull();
+        Engine engine = boundEngineOrNull();
         if (engine == null) {
             return query.fallback().get();
         }
@@ -874,7 +874,7 @@ final class ModdedBiomePolicy<H, S> implements NativeModdedBiomePolicy<H, S> {
         return engine != null && !engine.isClosed() && engine.getComplex() != null;
     }
 
-    private Engine engineOrNull() {
+    private Engine boundEngineOrNull() {
         RuntimeCallbacks current = runtime;
         return current == null ? null : current.currentEngine().get();
     }

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

@@ -79,6 +79,8 @@ import art.arcane.iris.spi.IrisServices;
 import art.arcane.iris.generation.concurrent.MultiBurst;
 
 import java.util.ArrayDeque;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicBoolean;
 
 public final class ModdedEngineBootstrap {
     private static final String[] CORE_SELF_TEST_CLASSES = {
@@ -87,12 +89,17 @@ public final class ModdedEngineBootstrap {
         "art.arcane.iris.pack.loading.IrisData"
     };
     private static final Object LOCK = new Object();
+    private static final Object STOP_LOCK = new Object();
+    private static final AtomicBoolean EXIT_FLUSH_REGISTERED = new AtomicBoolean();
+    private static final long EXIT_FLUSH_SERVER_WAIT_SECONDS = 30L;
     private static final ModdedServiceManager UNBOUND_SERVICE_MANAGER = new ModdedServiceManager();
     private static volatile NativeModdedLoader loader;
     private static volatile BoundRuntime runtime;
     private static volatile NativeModdedServer currentServer;
     private static volatile NativeModdedServer spawnCaptureServer;
     private static volatile boolean initialSpawnWasDefault;
+    private static volatile boolean stoppedPending;
+    private static volatile Thread stoppingThread;
 
     private ModdedEngineBootstrap() {
     }
@@ -119,10 +126,12 @@ public final class ModdedEngineBootstrap {
     }
 
     public static void start(NativeModdedServer server) {
+        finishPreviousServer("server start");
+        registerExitFlush();
         captureInitialSpawn(server);
         currentServer = server;
         bind();
-        // Pair of the stop() burst-pools stage. Load-bearing on integrated servers: once
+        // Pair of the stopped() burst-pools stage. Load-bearing on integrated servers: once
         // closed, MultiBurst falls back to a same-thread executor, so a second world load
         // without reopen() would silently run every burst inline.
         MultiBurst.burst.reopen();
@@ -150,6 +159,7 @@ public final class ModdedEngineBootstrap {
     }
 
     public static void serverAboutToStart(NativeModdedServer server) {
+        finishPreviousServer("server start");
         captureInitialSpawn(server);
         ModdedStartup.prepareForStartup();
     }
@@ -180,20 +190,16 @@ public final class ModdedEngineBootstrap {
         try {
             generator.unbindEngine(world);
         } catch (Throwable exception) {
+            // Never propagate into the loader's unload loop: a throw there skips closing every later level. A
+            // runtime dimension removal retries the eviction itself and fails with the retained mapping.
             ModdedIrisLog.error("Iris engine unload failed for {}", world.name(), exception);
-            if (exception instanceof RuntimeException runtimeException) {
-                throw runtimeException;
-            }
-            if (exception instanceof Error fatalError) {
-                throw fatalError;
-            }
-            throw new IllegalStateException("Iris engine unload failed for "
-                    + world.name(), exception);
         }
     }
 
     public static void stop() {
         NativeModdedServer stoppingServer = currentServer;
+        stoppingThread = Thread.currentThread();
+        stoppedPending = true;
         Throwable failure = null;
         failure = runStopStage(failure, "pack downloads", IrisModdedCommands::shutdownDownloads);
         failure = runStopStage(failure, "world check", () -> ModdedWorldCheck.serverStopped(stoppingServer));
@@ -205,6 +211,62 @@ public final class ModdedEngineBootstrap {
         failure = runStopStage(failure, "studio commands", ModdedStudioCommands::clear);
         failure = runStopStage(failure, "gui host", ModdedGuiHost::clear);
         failure = runStopStage(failure, "services", () -> services().disableAll());
+        reportStopFailure("stopping", failure);
+    }
+
+    /**
+     * The loaders still drain queued chunk generation after server stopping and only close levels afterwards, so
+     * engines, their mantle and generation history, and the generation pools stay open until the server stopped.
+     * Engines of unloaded levels are already closed by {@link #levelUnloaded}; this closes whatever remains.
+     * Fabric fires it at the tail of stopServer, so a throw there skips it: the next server start or the JVM
+     * exit runs it instead.
+     */
+    public static void stopped() {
+        synchronized (STOP_LOCK) {
+            stoppedPending = false;
+            stoppingThread = null;
+            closeStoppedServer();
+        }
+    }
+
+    private static void finishPreviousServer(String trigger) {
+        synchronized (STOP_LOCK) {
+            if (!stoppedPending) {
+                return;
+            }
+            ModdedIrisLog.warn("Iris closing the engines the previous server left open ({})", trigger);
+            stopped();
+        }
+    }
+
+    private static void registerExitFlush() {
+        if (EXIT_FLUSH_REGISTERED.compareAndSet(false, true)) {
+            Runtime.getRuntime().addShutdownHook(new Thread(ModdedEngineBootstrap::flushAtExit, "Iris Exit Flush"));
+        }
+    }
+
+    private static void flushAtExit() {
+        if (!stoppedPending) {
+            return;
+        }
+        Thread serverThread = stoppingThread;
+        if (serverThread != null && serverThread != Thread.currentThread()) {
+            try {
+                serverThread.join(TimeUnit.SECONDS.toMillis(EXIT_FLUSH_SERVER_WAIT_SECONDS));
+            } catch (InterruptedException interrupted) {
+                Thread.currentThread().interrupt();
+                return;
+            }
+            if (serverThread.isAlive()) {
+                ModdedIrisLog.warn("Iris skipped its exit flush: the server thread is still stopping");
+                return;
+            }
+        }
+        finishPreviousServer("JVM exit");
+    }
+
+    private static void closeStoppedServer() {
+        Throwable failure = null;
         failure = runStopStage(failure, "world engines", ModdedWorldEngines::shutdown);
         failure = runStopStage(failure, "primary world router", ModdedPrimaryWorldRouter::clear);
         failure = runStopStage(failure, "dimension manager", ModdedDimensionManager::clear);
@@ -226,10 +288,14 @@ public final class ModdedEngineBootstrap {
             spawnCaptureServer = null;
             initialSpawnWasDefault = false;
         });
+        reportStopFailure("stopped", failure);
+    }
+
+    private static void reportStopFailure(String phase, Throwable failure) {
         if (failure != null) {
             // The shutdown path must not propagate: propagating aborts the remaining loader stop handlers and
             // can leave the level unsaved. Every stage already logged its own failure.
-            ModdedIrisLog.error("Iris modded shutdown completed with failures", failure);
+            ModdedIrisLog.error("Iris modded shutdown ({}) completed with failures", phase, failure);
         }
     }
 

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

@@ -314,12 +314,13 @@ public final class ModdedForcedDatapack {
         } catch (NoSuchAlgorithmException missing) {
             throw new IllegalStateException("SHA-256 is unavailable", missing);
         }
+        DataVersion dataVersion = DataVersion.getRuntime();
         digest.update((HASH_SALT + '|' + ModdedEngineBootstrap.loader().platformName()
-                + '|' + DataVersion.V26_3.getPackFormat() + '\n').getBytes(StandardCharsets.UTF_8));
+                + '|' + dataVersion.getPackFormat() + '\n').getBytes(StandardCharsets.UTF_8));
         String inputFingerprint = IrisDatapackCompiler.computeInputFingerprint(
                 compilationPackRoots(),
                 List.of(),
-                DataVersion.V26_3.get(),
+                dataVersion.get(),
                 false
         );
         digest.update(inputFingerprint.getBytes(StandardCharsets.UTF_8));
@@ -328,7 +329,7 @@ public final class ModdedForcedDatapack {
 
     private static void writeStagedPack(Path stagingDirectory) throws IOException {
         Map<String, KSet<String>> seenBiomes = new LinkedHashMap<>();
-        IDataFixer fixer = DataVersion.V26_3.get();
+        IDataFixer fixer = DataVersion.getRuntime().get();
 
         int packCount = 0;
         KList<String> presetIds = new KList<>();
@@ -679,7 +680,7 @@ public final class ModdedForcedDatapack {
     }
 
     static void writePackMeta(Path packDirectory) throws IOException {
-        int packFormat = DataVersion.V26_3.getPackFormat();
+        int packFormat = DataVersion.getRuntime().getPackFormat();
         String json = "{\n"
                 + "  \"pack\": {\n"
                 + "    \"description\": \"Iris world generation biomes and dimension types for installed packs.\",\n"

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

@@ -9,12 +9,10 @@ import java.util.Objects;
 final class ModdedGenerationRegistry implements PlatformGenerationRegistry {
     private final NativeGenerationRegistry nativeRegistry;
     private final String runtimeIdentity;
-    private final String rendererIdentity;
 
-    ModdedGenerationRegistry(NativeGenerationRegistry nativeRegistry, Identity identity) {
+    ModdedGenerationRegistry(NativeGenerationRegistry nativeRegistry, String runtimeIdentity) {
         this.nativeRegistry = Objects.requireNonNull(nativeRegistry, "nativeRegistry");
-        this.runtimeIdentity = requireText(identity.runtime(), "runtimeIdentity");
-        this.rendererIdentity = requireText(identity.renderer(), "rendererIdentity");
+        this.runtimeIdentity = requireText(runtimeIdentity, "runtimeIdentity");
     }
 
     @Override
@@ -22,11 +20,6 @@ final class ModdedGenerationRegistry implements PlatformGenerationRegistry {
         return runtimeIdentity;
     }
 
-    @Override
-    public String generatedDefinitionRendererIdentity() {
-        return rendererIdentity;
-    }
-
     @Override
     public String customBiomeResourceKey(String identitySha256) {
         return PlatformGenerationRegistry.contentAddressedCustomBiomeResourceKey(identitySha256);
@@ -75,7 +68,4 @@ final class ModdedGenerationRegistry implements PlatformGenerationRegistry {
         }
         return required;
     }
-
-    record Identity(String runtime, String renderer) {
-    }
 }

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

@@ -25,6 +25,8 @@ import art.arcane.volmlib.nativelib.terrain.feature.NativeFeatureTable;
 import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeModdedImportedFeatures;
 
 import art.arcane.iris.generation.runtime.Engine;
+import art.arcane.iris.generation.runtime.GenerationClosedException;
+import art.arcane.iris.generation.runtime.GenerationFailures;
 import art.arcane.iris.generation.runtime.GenerationSessionLease;
 import art.arcane.iris.structure.nativegen.NativeFeatureGenerationPolicy;
 import art.arcane.iris.structure.nativegen.IrisImportedFeatureControl;
@@ -95,10 +97,12 @@ final class ModdedImportedFeatureStage implements NativeModdedGeneratorPolicy.Fe
      * the per-step feature lists and {@code BiomeFilter}'s hasFeature gate both see real features for a biome
      * whose datapack JSON declares none by design. Real registry biomes pass straight through.
      *
-     * <p>With {@code importedFeatures} disabled there is no table and this is vanilla's default getter.
+     * <p>With {@code importedFeatures} disabled there is no table and this is vanilla's default getter. So is an
+     * unbound generator, which only world creation and codec validation ask. A bound generator whose engine is
+     * refused or stopping throws: BiomeFilter would otherwise drop every imported feature of a custom biome.
      */
     public NativeFeatureTable currentTable() {
-        Engine engine = generator == null ? null : generator.engineOrNull();
+        Engine engine = generator == null ? null : generator.boundEngineOrNull();
         return engine == null ? null : featureTables.get(engine.getCacheID());
     }
 
@@ -111,8 +115,15 @@ final class ModdedImportedFeatureStage implements NativeModdedGeneratorPolicy.Fe
      * the build itself is serialized because {@code applyBiomeDecoration} calls this from every worldgen
      * thread, and two threads that both found the stage unprepared would each run {@code FeatureSorter}, whose
      * cycle detection is the expensive part. Waiting here is safe: this caller holds no generator monitor.
+     * A sealed runtime keeps the table it already settled but cannot build one, and decorating without it
+     * would persist a chunk with no imported features, so it fails the chunk instead.
      */
     public void prepare(Engine engine) {
+        if ((engine.isClosed() || engine.isClosing())
+                && !settled(engine.getCacheID(), biomeSource.packGeneration())) {
+            throw new GenerationClosedException("Iris imported features cannot prepare runtime "
+                    + engine.getCacheID() + " while its engine is closing.");
+        }
         prepare(engine, true);
     }
 
@@ -127,7 +138,7 @@ final class ModdedImportedFeatureStage implements NativeModdedGeneratorPolicy.Fe
     }
 
     private void prepare(Engine engine, boolean waitForBuild) {
-        if (engine == null || engine.isClosed() || engine.isClosing()) {
+        if (engine.isClosed() || engine.isClosing()) {
             return;
         }
         int runtimeIdentity = engine.getCacheID();
@@ -163,6 +174,7 @@ final class ModdedImportedFeatureStage implements NativeModdedGeneratorPolicy.Fe
         try {
             control = NativeFeatureGenerationPolicy.control(engine);
         } catch (RuntimeException error) {
+            GenerationFailures.rethrowEngineFailure(error);
             ModdedIrisLog.error("Iris could not read importedFeatures for this dimension; features off: {}",
                     error.toString(), error);
             markInert(runtimeIdentity, generation);
@@ -177,6 +189,7 @@ final class ModdedImportedFeatureStage implements NativeModdedGeneratorPolicy.Fe
              IrisContext.Scope ignored = IrisContext.open(engine, lease.sessionId(), null)) {
             built = nativeFeatures.buildTable(new ModdedImportedFeaturePolicy(engine), control, generation);
         } catch (Throwable error) {
+            GenerationFailures.rethrowEngineFailure(error);
             ModdedIrisLog.error("Iris importedFeatures is off for {}: feature table construction failed: {}",
                     dimensionKey(engine), error.toString(), error);
             markInert(runtimeIdentity, generation);
@@ -201,17 +214,24 @@ final class ModdedImportedFeatureStage implements NativeModdedGeneratorPolicy.Fe
         inertGenerations.put(runtimeIdentity, generation);
     }
 
+    /**
+     * Null only for a runtime whose features are settled off. A table retired or superseded since this chunk's
+     * prepare fails the chunk: skipping the pass would persist it without imported features.
+     */
     public NativeFeatureTable placementTable(Engine engine) {
         int runtimeIdentity = engine.getCacheID();
+        long generation = biomeSource.packGeneration();
         NativeFeatureTable table = featureTables.get(runtimeIdentity);
-        if (table == null) {
+        if (table == null && Long.valueOf(generation).equals(inertGenerations.get(runtimeIdentity))) {
             WorldCheckFeaturePlacement.recordFeaturesOff();
             return null;
         }
-        if (table.generation() != biomeSource.packGeneration()) {
-            featureTables.remove(runtimeIdentity, table);
-            inertGenerations.remove(runtimeIdentity);
-            return null;
+        if (table == null || table.generation() != generation) {
+            if (table != null) {
+                featureTables.remove(runtimeIdentity, table);
+            }
+            throw new GenerationClosedException("Iris imported feature table for runtime " + runtimeIdentity
+                    + " was retired before decoration.");
         }
         return generator == null ? null : table;
     }

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

@@ -16,6 +16,7 @@ public final class ModdedLifecycleCallbacks {
                 ModdedEngineBootstrap::start,
                 ModdedEngineBootstrap::serverStarted,
                 ModdedEngineBootstrap::stop,
+                ModdedEngineBootstrap::stopped,
                 ModdedEngineBootstrap::levelLoaded,
                 ModdedEngineBootstrap::levelUnloaded,
                 ModdedProtocolHandler::onPlayerJoin,

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

@@ -40,29 +40,31 @@ import java.util.function.BooleanSupplier;
  * references and is safe on a dedicated server.
  */
 public final class ModdedMixinAudit {
+    private static final String ENTITY_CONFIG = "volmlib.entity.mixins.json";
+    private static final String CLIENT_CONFIG = "volmlib.client.mixins.json";
     private static final AtomicBoolean AUDITED = new AtomicBoolean(false);
 
-    private static final List<ExpectedMixin> EXPECTED = List.of(
-            new ExpectedMixin("EntityPersistenceMixin", "entity",
+    static final List<ExpectedMixin> EXPECTED = List.of(
+            new ExpectedMixin(ENTITY_CONFIG, "EntityPersistenceMixin",
                     NativeMixinTarget.ENTITY, "iris$applyGeneratedPersistence",
                     false, NativeMixinFlags::entityPersistenceRan),
-            new ExpectedMixin("LivingEntityLootMixin", "entity",
+            new ExpectedMixin(ENTITY_CONFIG, "LivingEntityLootMixin",
                     NativeMixinTarget.LIVING_ENTITY, "iris$replaceBaseLoot",
                     false, NativeMixinFlags::livingEntityLootRan),
-            new ExpectedMixin("MobAwarenessMixin", "entity",
+            new ExpectedMixin(ENTITY_CONFIG, "MobAwarenessMixin",
                     NativeMixinTarget.MOB, "iris$tickUnawareMob",
                     false, NativeMixinFlags::mobAwarenessRan),
-            new ExpectedMixin("StructureTemplatePaletteConcurrencyMixin", "common",
+            new ExpectedMixin(ENTITY_CONFIG, "StructureTemplatePaletteConcurrencyMixin",
                     NativeMixinTarget.STRUCTURE_PALETTE,
                     "iris$installConcurrentBlockCache",
                     false, NativeMixinFlags::structureTemplatePaletteRan),
-            new ExpectedMixin("NativeWorldOpenFlowsMixin", "client",
+            new ExpectedMixin(CLIENT_CONFIG, "NativeWorldOpenFlowsMixin",
                     NativeMixinTarget.WORLD_OPEN_FLOWS,
-                    "iris$openWorldCheckWorldStemCompatibility",
+                    "volmlib$openWorldCheckWorldStemCompatibility",
                     true, NativeMixinFlags::worldOpenFlowsRan),
-            new ExpectedMixin("NativeWorldTypeEntryMixin", "client",
+            new ExpectedMixin(CLIENT_CONFIG, "NativeWorldTypeEntryMixin",
                     NativeMixinTarget.WORLD_TYPE_ENTRY,
-                    "iris$describePreset",
+                    "volmlib$describePreset",
                     true, NativeMixinFlags::worldTypeEntryRan));
 
     private ModdedMixinAudit() {
@@ -90,7 +92,7 @@ public final class ModdedMixinAudit {
             if (isApplied(expected)) {
                 applied.add(expected.mixinName() + (expected.ran().getAsBoolean() ? "" : " (not yet exercised)"));
             } else {
-                missing.add(expected.config() + '/' + expected.mixinName() + " -> " + expected.targetClass());
+                missing.add(expected.config() + '/' + expected.mixinName() + " -> " + expected.targetClass().className());
             }
         }
         if (missing.isEmpty()) {
@@ -119,7 +121,7 @@ public final class ModdedMixinAudit {
         }
     }
 
-    private record ExpectedMixin(String mixinName, String config, NativeMixinTarget targetClass, String handlerMethod,
-                                 boolean clientOnly, BooleanSupplier ran) {
+    record ExpectedMixin(String config, String mixinName, NativeMixinTarget targetClass, String handlerMethod,
+                         boolean clientOnly, BooleanSupplier ran) {
     }
 }

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

@@ -61,7 +61,7 @@ public final class ModdedPlatform implements IrisPlatform {
         this.loader = loader;
         this.registries = new ModdedRegistries(
                 NativeModdedServer.registryAccess(ModdedEngineBootstrap::currentServer, ModdedRegistries::warnNotReady),
-                ModdedPlatform::generationRegistry);
+                () -> generationRegistry(loader));
         this.scheduler = new ModdedScheduler();
         this.structureHooks = new ModdedStructureHooks(ModdedEngineBootstrap::currentServer);
         this.biomeWriter = new ModdedBiomeWriter(new NativeBiomeRegistry(ModdedEngineBootstrap::currentServer, "minecraft:plains"));
@@ -352,13 +352,12 @@ public final class ModdedPlatform implements IrisPlatform {
         }
     }
 
-    private static PlatformGenerationRegistry generationRegistry() {
+    private static PlatformGenerationRegistry generationRegistry(NativeModdedLoader loader) {
         if (ModdedEngineBootstrap.currentServer() == null) {
             throw new IllegalStateException("Minecraft server is not ready for generation registry capture.");
         }
-        return new ModdedGenerationRegistry(NativeModdedServer.registryDefinitions(ModdedEngineBootstrap::currentServer),
-                new ModdedGenerationRegistry.Identity("modded-generation-registry-v1",
-                        "modded-generated-registry-json-v1|minecraft:" + BuildConstants.MINECRAFT_VERSION));
+        return new ModdedGenerationRegistry(NativeModdedServer.registryDefinitions(ModdedEngineBootstrap::currentServer, loader),
+                "modded-generation-registry-v1");
     }
 
 }

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

@@ -18,15 +18,17 @@
 
 package art.arcane.iris.modded;
 
+import art.arcane.iris.world.safeguard.GenerationRefusalNotice;
 import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeModdedServer;
 import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeWorldTeleport;
 import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeDimensionRuntime;
 import art.arcane.volmlib.nativelib.terrain.NativeWorld;
 import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeProtocolPlayer;
 
+import java.util.ArrayList;
+import java.util.List;
 import java.util.Set;
 import java.util.UUID;
-import java.util.concurrent.TimeUnit;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.ConcurrentHashMap;
 
@@ -36,6 +38,8 @@ public final class ModdedPrimaryWorldRouter {
     private static final Set<UUID> routed = ConcurrentHashMap.newKeySet();
     private static final Set<UUID> inFlight = ConcurrentHashMap.newKeySet();
     private static int tickCounter = 0;
+    private static volatile String loginRefusal;
+    private static volatile String absentPrimary;
 
     private ModdedPrimaryWorldRouter() {
     }
@@ -43,6 +47,8 @@ public final class ModdedPrimaryWorldRouter {
     public static void clear() {
         routed.clear();
         inFlight.clear();
+        loginRefusal = null;
+        absentPrimary = null;
     }
 
     /**
@@ -56,6 +62,20 @@ public final class ModdedPrimaryWorldRouter {
         }
     }
 
+    /**
+     * Disconnects a joining player while the configured primary world is missing.
+     *
+     * @return true when the player was refused
+     */
+    public static boolean refuseIfUnavailable(NativeProtocolPlayer player) {
+        String refusal = loginRefusal;
+        if (refusal == null || player == null) {
+            return false;
+        }
+        player.disconnect(refusal);
+        return true;
+    }
+
     public static void tick(NativeModdedServer server) {
         if (server == null) {
             return;
@@ -68,17 +88,23 @@ public final class ModdedPrimaryWorldRouter {
 
         ModdedModConfig config = ModdedModConfig.get();
         if (!config.routePlayersToPrimaryWorld()) {
+            loginRefusal = null;
             return;
         }
         String primary = config.primaryWorld();
         if (primary.isBlank()) {
+            loginRefusal = null;
             return;
         }
 
         NativeWorld target = ModdedDimensionManager.level(server, primary);
         if (target == null) {
+            if (ModdedStartup.dimensionsRestored()) {
+                judgeMissingPrimary(server, primary);
+            }
             return;
         }
+        loginRefusal = null;
         NativeWorld overworld = server.overworld();
         if (NativeDimensionRuntime.sameWorld(target, overworld)) {
             return;
@@ -97,7 +123,7 @@ public final class ModdedPrimaryWorldRouter {
             try {
                 CompletableFuture<Boolean> teleport = NativeWorldTeleport.teleport(player,
                         new NativeWorldTeleport.Destination(server, target, player.x(), Double.MIN_VALUE, player.z(),
-                                System.nanoTime() + TimeUnit.SECONDS.toNanos(10)));
+                                ModdedTeleportDeadline.fromNow()));
                 teleport.whenComplete((success, failure) -> {
                     inFlight.remove(id);
                     if (Boolean.TRUE.equals(success) && failure == null) {
@@ -115,4 +141,62 @@ public final class ModdedPrimaryWorldRouter {
             }
         });
     }
+
+    /**
+     * primaryWorld is instance-wide but the dimension it names belongs to one save. Only a save whose registry lists
+     * it expected it here, so only that save has a primary world that failed to load.
+     */
+    private static void judgeMissingPrimary(NativeModdedServer server, String primary) {
+        if (loginRefusal == null && primary.equals(absentPrimary)) {
+            return;
+        }
+        if (loginRefusal == null && !expectedInThisSave(server, primary)) {
+            absentPrimary = primary;
+            ModdedIrisLog.warn("Iris primary world '" + primary + "' from config/irisworldgen/modded.json does not"
+                    + " exist in this save, so players are not routed. Create it here with /iris world replace-overworld"
+                    + " <pack> or clear primaryWorld.");
+            return;
+        }
+        refuseLogins(server, primary);
+    }
+
+    private static boolean expectedInThisSave(NativeModdedServer server, String primary) {
+        try {
+            return ModdedDimensionRegistryStore.get(server, primary) != null;
+        } catch (RuntimeException unreadable) {
+            ModdedIrisLog.error("Iris could not read this save's dimension registry to judge primary world '"
+                    + primary + "'", unreadable);
+            return true;
+        }
+    }
+
+    /**
+     * Players left in the overworld would generate the terrain the primary Iris world was configured to replace, so a
+     * primary world this save expected and did not load refuses every player instead.
+     */
+    private static void refuseLogins(NativeModdedServer server, String primary) {
+        String refusal = "Iris primary world '" + primary + "' is not loaded, so this server refuses players."
+                + " An operator has to check the server console.";
+        if (loginRefusal == null) {
+            for (String line : GenerationRefusalNotice.compose(
+                    "Iris refused player logins: primary world '" + primary + "' is not loaded",
+                    List.of("routePlayersToPrimaryWorld sends players to '" + primary
+                            + "', which this save's dimension registry expects but did not load at startup."),
+                    List.of(
+                            "Players are disconnected instead of playing in the overworld, so no chunks are"
+                                    + " written there.",
+                            "Fix the dimension (see the Iris errors above) or clear primaryWorld in"
+                                    + " config/irisworldgen/modded.json, then start the server again."
+                    ))) {
+                ModdedIrisLog.error(line);
+            }
+        }
+        loginRefusal = refusal;
+        List<NativeProtocolPlayer> online = new ArrayList<>();
+        // Disconnecting removes the player from the list being walked, so collect first.
+        server.forEachPlayer(online::add);
+        for (NativeProtocolPlayer player : online) {
+            player.disconnect(refusal);
+        }
+    }
 }

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

@@ -123,11 +123,11 @@ public final class ModdedProtocolHandler {
     }
 
     public static void onPlayerJoin(NativeProtocolPlayer player) {
-        if (player == null) {
+        if (player == null || ModdedPrimaryWorldRouter.refuseIfUnavailable(player)) {
             return;
         }
         String sessionId = sessionId(player);
-        ModdedStartup.warnPackFailuresTo(player);
+        ModdedStartup.warnStartupFailuresTo(player);
         IrisSessionRegistry current = registry;
         ModdedProtocolTransport currentTransport = transport;
         if (current == null || currentTransport == null) {

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

@@ -195,7 +195,8 @@ public final class ModdedScheduler implements PlatformScheduler {
         mainQueue.clear();
         delayedQueue.clear();
         mainThread = null;
-        // Shutdown stage that always runs (ModdedEngineBootstrap.stop): release the level snapshot with it.
+        // Runs from ModdedEngineBootstrap.stopped, or its fallback at the next server start or JVM exit when the
+        // loader skipped it: release the level snapshot with it.
         ModdedServerLevels.forget();
     }
 

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

@@ -26,6 +26,7 @@ import art.arcane.iris.pack.PackValidationResult;
 import art.arcane.iris.pack.PackValidator;
 import art.arcane.iris.modded.command.ModdedPackCommands;
 import art.arcane.iris.spi.IrisPlatforms;
+import art.arcane.iris.world.safeguard.GenerationRefusalNotice;
 import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeModdedServer;
 import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeProtocolPlayer;
 
@@ -36,6 +37,7 @@ import java.nio.file.Path;
 import java.nio.file.attribute.BasicFileAttributes;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.CopyOnWriteArrayList;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.stream.Stream;
 
@@ -43,6 +45,7 @@ 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 List<String> DIMENSION_FAILURES = new CopyOnWriteArrayList<>();
 
     private ModdedStartup() {
     }
@@ -50,6 +53,7 @@ public final class ModdedStartup {
     public static void reset() {
         PREPARED.set(false);
         STARTED.set(false);
+        DIMENSION_FAILURES.clear();
     }
 
     public static void prepareForStartup() {
@@ -208,7 +212,7 @@ public final class ModdedStartup {
         }
     }
 
-    private static void reinjectPersistentDimensions(NativeModdedServer server) {
+    static void reinjectPersistentDimensions(NativeModdedServer server) {
         List<ModdedDimensionRegistryStore.PersistentDimension> dimensions =
                 ModdedDimensionRegistryStore.loadForStartup(server);
         if (dimensions.isEmpty()) {
@@ -233,7 +237,7 @@ public final class ModdedStartup {
                         index, dimensions.size(), dimension.id(), dimension.pack(), dimension.dimension(),
                         System.currentTimeMillis() - dimensionStartedAt);
             } catch (Throwable e) {
-                ModdedIrisLog.error("Iris failed to re-inject persistent dimension '{}' (pack={} dim={} seed={})", dimension.id(), dimension.pack(), dimension.dimension(), dimension.seed(), e);
+                reportDimensionFailure(dimension, e);
                 if (e instanceof OutOfMemoryError outOfMemory) {
                     throw outOfMemory;
                 }
@@ -243,6 +247,25 @@ public final class ModdedStartup {
                 injected, dimensions.size(), System.currentTimeMillis() - startedAt);
     }
 
+    private static void reportDimensionFailure(ModdedDimensionRegistryStore.PersistentDimension dimension, Throwable failure) {
+        List<String> notice = GenerationRefusalNotice.compose(
+                "Iris refused to load dimension '" + dimension.id() + "' (pack=" + dimension.pack()
+                        + " dim=" + dimension.dimension() + " seed=" + dimension.seed() + ")",
+                GenerationRefusalNotice.causes(failure),
+                List.of(
+                        "Iris does not generate this dimension and does not let vanilla or any other generator"
+                                + " write it; no chunks are written.",
+                        "It stays unloaded. Fix the cause, then start the server again."
+                ));
+        for (String line : notice) {
+            ModdedIrisLog.error(line);
+        }
+        ModdedIrisLog.error("Iris failed to re-inject persistent dimension '{}' (pack={} dim={} seed={})",
+                dimension.id(), dimension.pack(), dimension.dimension(), dimension.seed(), failure);
+        DIMENSION_FAILURES.add("Iris dimension '" + dimension.id() + "' did not load and refuses to generate: "
+                + GenerationRefusalNotice.summary(failure));
+    }
+
     private static long newestModificationMillis(Path root) {
         long newest = 0L;
         try (Stream<Path> walk = Files.walk(root)) {
@@ -261,13 +284,24 @@ public final class ModdedStartup {
     }
 
     /**
-     * SP-6: a pack excluded by validation is otherwise only visible in the console. Tell the operators who
-     * can actually act on it when they join.
+     * True once the first tick with a player list has re-injected the persistent dimensions. Before that a runtime
+     * dimension that is not loaded yet is still on its way.
      */
-    public static void warnPackFailuresTo(NativeProtocolPlayer player) {
+    public static boolean dimensionsRestored() {
+        return STARTED.get();
+    }
+
+    /**
+     * SP-6: a pack excluded by validation or a persistent dimension that did not load is otherwise only visible in
+     * the console. Tell the operators who can actually act on it when they join.
+     */
+    public static void warnStartupFailuresTo(NativeProtocolPlayer player) {
         if (player == null || !player.isGameMaster()) {
             return;
         }
+        for (String failure : DIMENSION_FAILURES) {
+            player.sendMessage(failure);
+        }
         for (Map.Entry<String, PackValidationResult> entry : PackValidationRegistry.snapshot().entrySet()) {
             PackValidationResult result = entry.getValue();
             if (result == null || result.isLoadable()) {

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

@@ -0,0 +1,37 @@
+/*
+ * 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.concurrent.TimeUnit;
+
+/**
+ * Deadline for a teleport that waits on its destination chunk. The first chunk of a cold dimension also loads the
+ * pack and binds the engine; the deadline only bounds a destination whose chunk never completes (a refusing
+ * generator or a removed dimension).
+ */
+public final class ModdedTeleportDeadline {
+    private static final long DEADLINE_SECONDS = 120L;
+
+    private ModdedTeleportDeadline() {
+    }
+
+    public static long fromNow() {
+        return System.nanoTime() + TimeUnit.SECONDS.toNanos(DEADLINE_SECONDS);
+    }
+}

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

@@ -426,9 +426,9 @@ public final class ModdedWorldEngines {
             Engine engine = entry.getValue();
             try {
                 // Latch the generator's unloading flag BEFORE closing (unbindEngine sets it,
-                // then evicts): chunk-system drain work running after this stage would
-                // otherwise see a closed engine and silently rebuild a fresh engine + Mantle
-                // that no teardown stage ever closes, writing plates after the final save.
+                // then evicts): late chunk work would otherwise see a closed engine and
+                // silently rebuild a fresh engine + Mantle that no teardown stage ever
+                // closes, writing plates after the final save.
                 IrisModdedChunkGenerator generator = NativeWorldGenerators.find(level, IrisModdedChunkGenerator.class);
                 if (generator != null) {
                     generator.unbindEngine(level);

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

@@ -55,7 +55,7 @@ final class WorldCheckDimensionContract {
     }
 
     static Dimension expectedDimensionContract(IrisDimension dimension) {
-        JSONObject json = new JSONObject(dimension.getDimensionType().toJson(DataVersion.V26_3.get()));
+        JSONObject json = new JSONObject(dimension.getDimensionType().toJson(DataVersion.getRuntime().get()));
         return new Dimension(
                 json.getInt("min_y"),
                 json.getInt("height"),

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

@@ -36,6 +36,7 @@ import art.arcane.iris.modded.ModdedEngineBootstrap;
 import art.arcane.iris.modded.ModdedForcedDatapack;
 import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeModdedLoader;
 import art.arcane.iris.modded.ModdedScheduler;
+import art.arcane.iris.modded.ModdedTeleportDeadline;
 import art.arcane.iris.modded.ModdedWorldgenIds;
 import art.arcane.iris.spi.IrisLogging;
 import art.arcane.volmlib.util.collection.KMap;
@@ -60,6 +61,7 @@ import java.util.Locale;
 import java.util.Map;
 import java.util.TreeMap;
 import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CompletionException;
 import java.util.concurrent.TimeUnit;
 
 import art.arcane.volmlib.util.localization.MessageArgument;
@@ -133,7 +135,7 @@ public final class IrisModdedCommands {
         NativeModdedServer server = source.server();
         CompletableFuture<Boolean> teleport = NativeWorldTeleport.teleport(player, new NativeWorldTeleport.Destination(
                 server, ModdedDimensionManager.level(server, dimensionId), 8.5D, Double.MIN_VALUE, 8.5D,
-                System.nanoTime() + TimeUnit.SECONDS.toNanos(10L)));
+                ModdedTeleportDeadline.fromNow()));
         teleport.whenComplete((success, failure) -> {
             if (Boolean.TRUE.equals(success) && failure == null) {
                 return;
@@ -142,14 +144,42 @@ public final class IrisModdedCommands {
                 ModdedIrisLog.error("Iris teleport into '{}' failed for {}",
                         dimensionId, player.id(), failure);
             }
-            server.execute(() -> fail(source, IrisLanguage.plain(
-                    ModdedCommandMessages.IRIS_MODDED_COMMANDS_TELEPORT_FAILED_DIMENSION_IS_NOT_LOADED,
-                    MessageArgument.untrusted("dimensionId", dimensionId))));
+            server.execute(() -> fail(source, teleportFailure(dimensionId, player.name(), failure,
+                    ModdedDimensionManager.level(server, dimensionId) != null, server.player(player.id()) != null)));
         });
         ok(source, IrisLanguage.plain(ModdedCommandMessages.IRIS_MODDED_COMMANDS_TELEPORTING, MessageArgument.untrusted("value", player.name()), MessageArgument.untrusted("dimensionId", dimensionId)));
         return 1;
     }
 
+    static String teleportFailure(String dimensionId, String playerName, Throwable failure,
+                                  boolean dimensionLoaded, boolean playerOnline) {
+        if (failure != null) {
+            return IrisLanguage.plain(ModdedCommandMessages.IRIS_MODDED_COMMANDS_TELEPORT_FAILED_REASON,
+                    MessageArgument.untrusted("dimensionId", dimensionId),
+                    MessageArgument.untrusted("reason", failureReason(failure)));
+        }
+        if (!dimensionLoaded) {
+            return IrisLanguage.plain(ModdedCommandMessages.IRIS_MODDED_COMMANDS_TELEPORT_FAILED_DIMENSION_IS_NOT_LOADED,
+                    MessageArgument.untrusted("dimensionId", dimensionId));
+        }
+        if (!playerOnline) {
+            return IrisLanguage.plain(ModdedCommandMessages.IRIS_MODDED_COMMANDS_TELEPORT_CANCELLED_PLAYER_OFFLINE,
+                    MessageArgument.untrusted("dimensionId", dimensionId),
+                    MessageArgument.untrusted("value", playerName));
+        }
+        return IrisLanguage.plain(ModdedCommandMessages.IRIS_MODDED_COMMANDS_TELEPORT_REFUSED,
+                MessageArgument.untrusted("dimensionId", dimensionId));
+    }
+
+    private static String failureReason(Throwable failure) {
+        Throwable cause = failure;
+        while (cause instanceof CompletionException && cause.getCause() != null) {
+            cause = cause.getCause();
+        }
+        String message = cause.getMessage();
+        return message == null || message.isBlank() ? cause.getClass().getSimpleName() : message;
+    }
+
     static int evacuate(NativeCommandSource source, NativeWorld target) {
         NativeModdedServer server = source.server();
         NativeWorld level = target != null ? target : source.world();

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

@@ -165,7 +165,7 @@ public final class ModdedDatapackCommands {
             IrisDimension dimension = engine.getDimension();
             String json;
             try {
-                json = dimension.getDimensionType().toJson(DataVersion.V26_3.get());
+                json = dimension.getDimensionType().toJson(DataVersion.getRuntime().get());
             } catch (Throwable e) {
                 ModdedIrisLog.error("Iris dimension type generation failed for {}", dimension.getLoadKey(), e);
                 IrisModdedCommands.fail(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_DATAPACK_COMMANDS_DIMENSION_TYPE_GENERATION_FAILED, MessageArgument.untrusted("value", level.name()), MessageArgument.untrusted("value2", String.valueOf(e.getMessage()))));
@@ -187,7 +187,7 @@ public final class ModdedDatapackCommands {
         }
 
         File mcmeta = new File(worldDatapacksFolder(server), WORLD_PACK_NAME + "/pack.mcmeta");
-        int packFormat = DataVersion.V26_3.getPackFormat();
+        int packFormat = DataVersion.getRuntime().getPackFormat();
         String meta = "{\n"
                 + "  \"pack\": {\n"
                 + "    \"description\": \"Iris dimension types derived from the installed Iris packs.\",\n"

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

@@ -25,6 +25,7 @@ import art.arcane.iris.generation.runtime.IrisComplex;
 import art.arcane.iris.generation.runtime.Engine;
 import art.arcane.iris.studio.render.RenderType;
 import art.arcane.iris.modded.ModdedIrisLog;
+import art.arcane.iris.modded.ModdedTeleportDeadline;
 
 import java.awt.Desktop;
 import java.io.File;
@@ -32,7 +33,6 @@ import java.util.List;
 import java.util.Optional;
 import art.arcane.volmlib.nativelib.view.WorldView;
 import java.util.UUID;
-import java.util.concurrent.TimeUnit;
 import java.util.function.Consumer;
 
 public final class ModdedVisionOverlay implements GuiOverlay {
@@ -63,8 +63,7 @@ public final class ModdedVisionOverlay implements GuiOverlay {
         world.execute(() -> {
             int surfaceY = engine.getMinHeight() + engine.getHeight(blockX, blockZ, false) + 2;
             Optional<WorldView.TeleportOperation> operation = world.teleport(opener,
-                    new WorldView.Destination(blockX + 0.5D, surfaceY, blockZ + 0.5D,
-                            System.nanoTime() + TimeUnit.SECONDS.toNanos(10L)));
+                    new WorldView.Destination(blockX + 0.5D, surfaceY, blockZ + 0.5D, ModdedTeleportDeadline.fromNow()));
             if (operation.isEmpty()) {
                 return;
             }

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

@@ -71,6 +71,18 @@ public final class ModdedCommandMessages {
             "iris.modded.irismoddedcommands.teleport_failed_dimension_is_not_loaded",
             "Teleport failed: dimension " + "{dimensionId}" + " is not loaded."
     );
+    public static final TextKey IRIS_MODDED_COMMANDS_TELEPORT_FAILED_REASON = TextKey.of(
+            "iris.modded.irismoddedcommands.teleport_failed_reason",
+            "Teleport into " + "{dimensionId}" + " failed: " + "{reason}"
+    );
+    public static final TextKey IRIS_MODDED_COMMANDS_TELEPORT_CANCELLED_PLAYER_OFFLINE = TextKey.of(
+            "iris.modded.irismoddedcommands.teleport_cancelled_player_offline",
+            "Teleport into " + "{dimensionId}" + " cancelled: " + "{value}" + " is no longer online."
+    );
+    public static final TextKey IRIS_MODDED_COMMANDS_TELEPORT_REFUSED = TextKey.of(
+            "iris.modded.irismoddedcommands.teleport_refused",
+            "Teleport into " + "{dimensionId}" + " was refused by the server."
+    );
     public static final TextKey IRIS_MODDED_COMMANDS_TELEPORTING = TextKey.of(
             "iris.modded.irismoddedcommands.teleporting",
             "Teleporting " + "{value}" + " to " + "{dimensionId}" + "..."
@@ -1266,6 +1278,9 @@ public final class ModdedCommandMessages {
             IRIS_MODDED_COMMANDS_CONSOLE_MUST_NAME_PLAYER_IRIS_TP_DIMENSION_PLAYER,
             IRIS_MODDED_COMMANDS_IS_NOT_GENERATED_BY_IRIS,
             IRIS_MODDED_COMMANDS_TELEPORT_FAILED_DIMENSION_IS_NOT_LOADED,
+            IRIS_MODDED_COMMANDS_TELEPORT_FAILED_REASON,
+            IRIS_MODDED_COMMANDS_TELEPORT_CANCELLED_PLAYER_OFFLINE,
+            IRIS_MODDED_COMMANDS_TELEPORT_REFUSED,
             IRIS_MODDED_COMMANDS_TELEPORTING,
             IRIS_MODDED_COMMANDS_IS_NOT_GENERATED_BY_IRIS_2,
             IRIS_MODDED_COMMANDS_CANNOT_EVACUATE_PRIMARY_WORLD_THERE_IS_NOWHERE_SEND_PLAYERS,

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

@@ -30,6 +30,7 @@ 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;
@@ -38,6 +39,7 @@ import art.arcane.iris.modded.ModdedTileData;
 import art.arcane.iris.modded.api.ModdedCustomContentRegistry;
 import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeBlockPlacement;
 import art.arcane.iris.spi.IrisLogging;
+import art.arcane.iris.world.history.SavedBiomeUnavailableException;
 import art.arcane.iris.world.storage.matter.TileWrapper;
 import art.arcane.volmlib.util.mantle.flag.MantleFlag;
 import art.arcane.volmlib.util.mantle.runtime.Mantle;
@@ -47,6 +49,7 @@ import art.arcane.volmlib.util.matter.MatterCavern;
 import art.arcane.volmlib.util.matter.MatterUpdate;
 import art.arcane.volmlib.util.scheduling.PrecisionStopwatch;
 import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeModdedServer;
+import it.unimi.dsi.fastutil.ints.IntArrayList;
 
 import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
@@ -149,7 +152,7 @@ public final class ModdedChunkUpdateService implements ModdedTickableService {
             int centerZ = player.z() >> 4;
             for (int dx = -PLAYER_CHUNK_RADIUS; dx <= PLAYER_CHUNK_RADIUS; dx++) {
                 for (int dz = -PLAYER_CHUNK_RADIUS; dz <= PLAYER_CHUNK_RADIUS; dz++) {
-                    updateChunk(engine, level, centerX + dx, centerZ + dz);
+                    updatePassChunk(engine, level, centerX + dx, centerZ + dz);
                 }
             }
         });
@@ -157,15 +160,29 @@ public final class ModdedChunkUpdateService implements ModdedTickableService {
 
     private void updateForcedChunks(Engine engine, NativeWorld level) {
         new NativeWorldMaintenance(level).forEachForcedChunk(chunkKey ->
-                updateChunk(engine, level, (int) chunkKey, (int) (chunkKey >> 32)));
+                updatePassChunk(engine, level, (int) chunkKey, (int) (chunkKey >> 32)));
     }
 
     public void updateRegeneratedChunk(Engine engine, NativeWorld level, int chunkX, int chunkZ) {
         updateChunk(engine, level, chunkX, chunkZ, false);
     }
 
-    private void updateChunk(Engine engine, NativeWorld level, int chunkX, int chunkZ) {
-        updateChunk(engine, level, chunkX, chunkZ, true);
+    /**
+     * One chunk of a level pass. A failed chunk keeps its flags and retries on a later pass without stopping the
+     * chunks after it; only a closed engine ends the level's pass.
+     */
+    private void updatePassChunk(Engine engine, NativeWorld level, int chunkX, int chunkZ) {
+        try {
+            updateChunk(engine, level, chunkX, chunkZ, true);
+        } catch (Throwable failure) {
+            if (engine.isClosed() || engine.getMantle().getMantle().isClosed()) {
+                throw failure;
+            }
+            if (IrisLogging.errorOnce("chunk-update:" + level.name() + ":" + chunkX + "," + chunkZ + ":" + failure,
+                    "Iris chunk update failed at " + chunkX + "," + chunkZ + " in " + level.name() + ", retrying each pass: " + failure)) {
+                IrisLogging.reportError(failure);
+            }
+        }
     }
 
     private void updateChunk(Engine engine, NativeWorld level, int chunkX, int chunkZ, boolean requireNeighbors) {
@@ -195,6 +212,11 @@ public final class ModdedChunkUpdateService implements ModdedTickableService {
                 chunk.raiseFlagUnchecked(MantleFlag.CUSTOM, () -> runCustomPass(engine, level, chunkX, chunkZ, chunk));
                 chunk.raiseFlagUnchecked(MantleFlag.UPDATE, () -> runUpdatePass(engine, level, chunkX, chunkZ, chunk));
             });
+        } catch (SavedBiomeUnavailableException unavailable) {
+            if (!unavailable.isLoading() || unavailable.getSuppressed().length != 0) {
+                throw unavailable;
+            }
+            IrisLogging.debug("Iris chunk update deferred at " + chunkX + "," + chunkZ + ": saved biomes loading");
         } finally {
             chunk.release();
         }
@@ -315,15 +337,40 @@ public final class ModdedChunkUpdateService implements ModdedTickableService {
             }
         }
 
-        chunk.iterate(MatterUpdate.class, (Integer x, Integer yf, Integer z, MatterUpdate v) -> {
-            if (v != null && v.isUpdate()) {
-                update(engine, level, x, yf + minHeight, z, baseX, baseZ, chunk);
-            }
-        });
+        IntArrayList completed = new IntArrayList();
+        try {
+            chunk.iterate(MatterUpdate.class, (Integer x, Integer yf, Integer z, MatterUpdate v) -> {
+                if (v != null && v.isUpdate()) {
+                    update(engine, level, x, yf + minHeight, z, baseX, baseZ, chunk);
+                    completed.add((yf << 8) | ((x & 15) << 4) | (z & 15));
+                }
+            });
+        } catch (RuntimeException | Error failure) {
+            forgetCompletedUpdates(chunk, completed, failure);
+            throw failure;
+        }
         chunk.deleteSlices(MatterUpdate.class);
         engine.getMetrics().getUpdates().put(stopwatch.getMilliseconds());
     }
 
+    private static void forgetCompletedUpdates(MantleChunk<Matter> chunk, IntArrayList completed, Throwable failure) {
+        try {
+            for (int index = 0; index < completed.size(); index++) {
+                int position = completed.getInt(index);
+                int y = position >>> 8;
+                Matter section = chunk.get(y >> 4);
+                if (section != null && section.hasSlice(MatterUpdate.class)) {
+                    section.<MatterUpdate>getSlice(MatterUpdate.class)
+                            .set((position >> 4) & 15, y & 15, position & 15, null);
+                }
+            }
+        } catch (RuntimeException | Error cleanupFailure) {
+            if (cleanupFailure != failure) {
+                failure.addSuppressed(cleanupFailure);
+            }
+        }
+    }
+
     private void update(Engine engine, NativeWorld level, int x, int y, int z, int baseX, int baseZ, MantleChunk<Matter> chunk) {
         if (y < level.minHeight() || y >= level.maxHeight() - 1) {
             return;
@@ -337,7 +384,12 @@ public final class ModdedChunkUpdateService implements ModdedTickableService {
             }
             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);
             }
         } else {

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

@@ -0,0 +1,170 @@
+package art.arcane.iris.modded;
+
+import art.arcane.iris.generation.runtime.Engine;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeModdedChunkGenerator;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeModdedServer;
+import art.arcane.volmlib.nativelib.terrain.NativeWorld;
+import art.arcane.volmlib.util.mantle.MantleClosedException;
+import net.minecraft.SharedConstants;
+import net.minecraft.server.Bootstrap;
+import net.minecraft.server.level.ServerChunkCache;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.world.level.chunk.ChunkGenerator;
+import org.junit.BeforeClass;
+import org.junit.Test;
+import org.mockito.MockedStatic;
+
+import java.io.IOException;
+import java.lang.reflect.Field;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicBoolean;
+
+import static org.junit.Assert.assertNotSame;
+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.anyLong;
+import static org.mockito.ArgumentMatchers.anyString;
+import static org.mockito.ArgumentMatchers.argThat;
+import static org.mockito.ArgumentMatchers.eq;
+import static org.mockito.Mockito.CALLS_REAL_METHODS;
+import static org.mockito.Mockito.doNothing;
+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.when;
+
+/**
+ * A level whose Iris generator cannot bind must crash its own creation, never fall through to another generator,
+ * and every later chunk call must fail fast on the recorded failure instead of re-running the whole bind
+ * (history verification included) on every worker thread.
+ */
+public class ModdedBindFailureTest {
+    @BeforeClass
+    public static void bootstrap() {
+        SharedConstants.tryDetectVersion();
+        Bootstrap.bootStrap();
+    }
+
+    @Test
+    public void aRecordedBindFailureIsReportedOnceAndRethrownWithoutBindingAgain() throws Exception {
+        IrisModdedChunkGenerator generator = generator("overworld:overworld");
+        NativeWorld level = level(generator, "minecraft:overworld");
+        field("boundLevel").set(generator, level);
+        NativeModdedServer server = mock(NativeModdedServer.class);
+        when(server.generateStructures()).thenReturn(false);
+
+        try (MockedStatic<NativeModdedServer> servers = mockStatic(NativeModdedServer.class);
+             MockedStatic<ModdedIrisLog> log = mockStatic(ModdedIrisLog.class)) {
+            servers.when(() -> NativeModdedServer.forWorld(level)).thenReturn(server);
+
+            IllegalStateException recorded = assertThrows(IllegalStateException.class, () -> generator.bindLevel(level));
+            IllegalStateException second = assertThrows(IllegalStateException.class, generator::engine);
+            IllegalStateException third = assertThrows(IllegalStateException.class, () -> generator.bindLevel(level));
+
+            assertSame(recorded, second.getCause());
+            assertSame(recorded, third.getCause());
+            servers.verify(() -> NativeModdedServer.forWorld(level), times(1));
+            log.verify(() -> ModdedIrisLog.error(argThat((String line) -> line != null && line.startsWith("Cause: ")
+                    && line.contains("generate-structures=false"))), times(1));
+        }
+    }
+
+    /**
+     * A bind that fails because the runtime is stopping (level unload, quit to title, server stop) says nothing about
+     * the world: it fails the chunk that asked, but the next bind tries again and no refusal is announced.
+     */
+    @Test
+    public void aShutdownFailureDuringBindIsNeitherRememberedNorAnnouncedAsARefusal() throws Exception {
+        IrisModdedChunkGenerator generator = generator("overworld:overworld");
+        NativeWorld level = level(generator, "minecraft:overworld");
+        field("boundLevel").set(generator, level);
+        NativeModdedServer server = mock(NativeModdedServer.class);
+        when(server.generateStructures()).thenReturn(true);
+        MantleClosedException closed = new MantleClosedException("Tectonic Plate is closed!");
+
+        try (MockedStatic<NativeModdedServer> servers = mockStatic(NativeModdedServer.class);
+             MockedStatic<ModdedWorldEngines> engines = mockStatic(ModdedWorldEngines.class);
+             MockedStatic<ModdedIrisLog> log = mockStatic(ModdedIrisLog.class)) {
+            servers.when(() -> NativeModdedServer.forWorld(level)).thenReturn(server);
+            engines.when(() -> ModdedWorldEngines.get(eq(level), any(), any(), anyLong(), any())).thenThrow(closed);
+
+            assertSame(closed, assertThrows(MantleClosedException.class, generator::engine));
+            assertSame(closed, assertThrows(MantleClosedException.class, generator::engine));
+
+            engines.verify(() -> ModdedWorldEngines.get(eq(level), any(), any(), anyLong(), any()), times(2));
+            log.verify(() -> ModdedIrisLog.error(anyString()), never());
+        }
+    }
+
+    /**
+     * Unloading a level resets its binding, so a refusal recorded in one load never carries into the next load of the
+     * same generator (a runtime dimension removal that rolls back, or a level loaded again in the same JVM).
+     */
+    @Test
+    public void aRecordedRefusalDoesNotOutliveTheUnloadOfItsLevel() throws Exception {
+        IrisModdedChunkGenerator generator = generator("overworld:overworld");
+        NativeWorld level = level(generator, "minecraft:overworld");
+        doNothing().when((NativeModdedChunkGenerator<?, ?, ?>) field("nativeGenerator").get(generator)).clearCaches();
+        field("importedFeatures").set(generator, mock(ModdedImportedFeatureStage.class));
+        field("announced").set(generator, new AtomicBoolean());
+        NativeModdedServer server = mock(NativeModdedServer.class);
+        when(server.generateStructures()).thenReturn(false);
+
+        try (MockedStatic<NativeModdedServer> servers = mockStatic(NativeModdedServer.class);
+             MockedStatic<ModdedWorldEngines> engines = mockStatic(ModdedWorldEngines.class);
+             MockedStatic<ModdedIrisLog> log = mockStatic(ModdedIrisLog.class)) {
+            servers.when(() -> NativeModdedServer.forWorld(level)).thenReturn(server);
+
+            IllegalStateException first = assertThrows(IllegalStateException.class, () -> generator.bindLevel(level));
+            generator.unbindEngine(level);
+            IllegalStateException second = assertThrows(IllegalStateException.class, () -> generator.bindLevel(level));
+
+            assertNotSame(first, second.getCause());
+            servers.verify(() -> NativeModdedServer.forWorld(level), times(2));
+            engines.verify(() -> ModdedWorldEngines.evictOrThrow(level));
+        }
+    }
+
+    @Test
+    public void bindFailureNoticeNamesTheLevelTheCauseAndThatNothingGenerates() {
+        String notice = String.join("\n", IrisModdedChunkGenerator.bindFailureNotice(
+                "minecraft:overworld",
+                "overworld:overworld",
+                new IllegalStateException("Iris generation history is unusable for 'minecraft:overworld'",
+                        new IOException("Historical generated registry definition changed"))));
+
+        assertTrue(notice, notice.contains("minecraft:overworld"));
+        assertTrue(notice, notice.contains("overworld:overworld"));
+        assertTrue(notice, notice.contains("generation history is unusable"));
+        assertTrue(notice, notice.contains("registry definition changed"));
+        assertTrue(notice, notice.contains("no chunks"));
+    }
+
+    private static IrisModdedChunkGenerator generator(String dimensionKey) throws ReflectiveOperationException {
+        IrisModdedChunkGenerator generator = mock(IrisModdedChunkGenerator.class, CALLS_REAL_METHODS);
+        field("nativeGenerator").set(generator, mock(NativeModdedChunkGenerator.class, CALLS_REAL_METHODS));
+        field("engineBinding").set(generator, new ModdedEngineBinding<Engine>(1L, TimeUnit.SECONDS));
+        field("dimensionKey").set(generator, dimensionKey);
+        return generator;
+    }
+
+    private static NativeWorld level(IrisModdedChunkGenerator generator, String name) throws ReflectiveOperationException {
+        NativeWorld level = mock(NativeWorld.class);
+        ServerLevel handle = mock(ServerLevel.class);
+        ServerChunkCache chunkSource = mock(ServerChunkCache.class);
+        when(level.nativeHandle()).thenReturn(handle);
+        when(level.name()).thenReturn(name);
+        when(handle.getChunkSource()).thenReturn(chunkSource);
+        when(chunkSource.getGenerator()).thenReturn((ChunkGenerator) field("nativeGenerator").get(generator));
+        return level;
+    }
+
+    private static Field field(String name) throws NoSuchFieldException {
+        Field field = IrisModdedChunkGenerator.class.getDeclaredField(name);
+        field.setAccessible(true);
+        return field;
+    }
+}

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

@@ -2,6 +2,7 @@ package art.arcane.iris.modded;
 
 import art.arcane.iris.generation.biome.IrisBiome;
 import art.arcane.iris.generation.runtime.Engine;
+import art.arcane.iris.generation.runtime.GenerationSessionException;
 import art.arcane.iris.generation.runtime.GenerationSessionLease;
 import art.arcane.iris.generation.runtime.IrisComplex;
 import art.arcane.volmlib.nativelib.terrain.NativeBiomeSourceAccess;
@@ -84,6 +85,29 @@ public class ModdedBiomePolicyTest {
         assertSame(forest, policy.requiredStructureBiome(6000, -30, -6000, null));
     }
 
+    /**
+     * Stacked initial mob spawning asks for the visible surface biome. A null answer made it spawn from the chunk's
+     * top biome instead, so a sealed or unready engine has to fail the chunk.
+     */
+    @Test
+    public void surfaceSpawnBiomeRefusesAnEngineInTransitionInsteadOfAnsweringNothing() throws Exception {
+        Engine sealed = mock(Engine.class);
+        when(sealed.isClosing()).thenReturn(true);
+        when(sealed.acquireGenerationLease(anyString())).thenThrow(new GenerationSessionException("sealed", true));
+        Engine unready = mock(Engine.class);
+        when(unready.acquireGenerationLease(anyString())).thenReturn(GenerationSessionLease.noop());
+
+        assertThrows(IllegalStateException.class, () -> boundTo(sealed).getVisibleSurfaceBiome(8, 8));
+        assertThrows(IllegalStateException.class, () -> boundTo(unready).getVisibleSurfaceBiome(8, 8));
+    }
+
+    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,
+                Set::of, bound -> Set.of(), () -> 0L));
+        return policy;
+    }
+
     private static ModdedBiomePolicy<BiomeToken, Object> policy(List<BiomeToken> entries,
                                                                AtomicReference<Set<String>> configured) {
         ModdedBiomePolicy<BiomeToken, Object> policy = new ModdedBiomePolicy<>(new Access(entries));

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

@@ -0,0 +1,111 @@
+package art.arcane.iris.modded;
+
+import art.arcane.iris.configuration.IrisSettings;
+import art.arcane.iris.generation.concurrent.MultiBurst;
+import art.arcane.iris.generation.runtime.Engine;
+import art.arcane.iris.modded.command.IrisModdedCommands;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeModdedServer;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeServerSpawn;
+import art.arcane.volmlib.nativelib.terrain.NativeWorld;
+import net.minecraft.SharedConstants;
+import net.minecraft.server.Bootstrap;
+import net.minecraft.server.level.ServerChunkCache;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.world.level.chunk.ChunkGenerator;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.BeforeClass;
+import org.junit.Test;
+import org.mockito.MockedConstruction;
+import org.mockito.MockedStatic;
+
+import java.util.concurrent.Callable;
+import java.util.concurrent.TimeUnit;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotSame;
+import static org.junit.Assert.assertSame;
+import static org.junit.Assert.assertTrue;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.mockConstruction;
+import static org.mockito.Mockito.mockStatic;
+import static org.mockito.Mockito.never;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+public class ModdedEngineBootstrapShutdownTest {
+    private IrisSettings previousSettings;
+
+    @BeforeClass
+    public static void bootstrap() {
+        SharedConstants.tryDetectVersion();
+        Bootstrap.bootStrap();
+    }
+
+    @Before
+    public void openRuntime() {
+        previousSettings = IrisSettings.settings;
+        IrisSettings.settings = new IrisSettings();
+        reopenBurstPools();
+    }
+
+    @After
+    public void restoreRuntime() {
+        reopenBurstPools();
+        IrisModdedCommands.openDownloadAdmission();
+        IrisSettings.settings = previousSettings;
+    }
+
+    @Test
+    public void serverStoppingKeepsEnginesAndWorkersOpenUntilServerStopped() throws Exception {
+        NativeWorld level = level();
+        Engine engine = mock(Engine.class);
+        ModdedWorldEngines.installReplacement(level, engine);
+        Callable<Thread> worker = Thread::currentThread;
+
+        ModdedEngineBootstrap.stop();
+
+        verify(engine, never()).close();
+        assertTrue(ModdedWorldEngines.activeEngines().contains(engine));
+        assertNotSame(Thread.currentThread(), MultiBurst.burst.submit(worker).get(10L, TimeUnit.SECONDS));
+
+        ModdedEngineBootstrap.stopped();
+
+        verify(engine).close();
+        assertFalse(ModdedWorldEngines.activeEngines().contains(engine));
+        assertSame(Thread.currentThread(), MultiBurst.burst.submit(worker).get(10L, TimeUnit.SECONDS));
+    }
+
+    @Test
+    public void nextServerStartClosesTheEnginesOfAServerThatNeverReachedStopped() {
+        NativeWorld level = level();
+        Engine engine = mock(Engine.class);
+        ModdedWorldEngines.installReplacement(level, engine);
+        ModdedEngineBootstrap.stop();
+
+        try (MockedStatic<ModdedStartup> startup = mockStatic(ModdedStartup.class);
+             MockedConstruction<NativeServerSpawn> spawn = mockConstruction(NativeServerSpawn.class)) {
+            ModdedEngineBootstrap.serverAboutToStart(mock(NativeModdedServer.class));
+        }
+
+        verify(engine).close();
+        assertFalse(ModdedWorldEngines.activeEngines().contains(engine));
+    }
+
+    private static NativeWorld level() {
+        ServerLevel serverLevel = mock(ServerLevel.class);
+        ServerChunkCache chunks = mock(ServerChunkCache.class);
+        when(serverLevel.getChunkSource()).thenReturn(chunks);
+        when(chunks.getGenerator()).thenReturn(mock(ChunkGenerator.class));
+        NativeWorld level = mock(NativeWorld.class);
+        when(level.nativeHandle()).thenReturn(serverLevel);
+        when(level.name()).thenReturn("example:shutdown");
+        return level;
+    }
+
+    private static void reopenBurstPools() {
+        MultiBurst.burst.reopen();
+        MultiBurst.hydrology.reopen();
+        MultiBurst.ioBurst.reopen();
+    }
+}

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

@@ -20,6 +20,7 @@ package art.arcane.iris.modded;
 
 import art.arcane.volmlib.util.collection.KSet;
 import art.arcane.volmlib.util.json.JSONObject;
+import art.arcane.iris.pack.datapack.DataVersion;
 import art.arcane.iris.pack.datapack.v1217.DataFixerV1217;
 import art.arcane.iris.world.history.GenerationEpochContractFactory;
 import art.arcane.iris.world.history.GenerationRegistryContract;
@@ -27,6 +28,8 @@ import art.arcane.iris.world.history.GenerationRegistryContractFactory;
 import art.arcane.iris.generation.biome.IrisCustomBiomeAliasResolver;
 import art.arcane.iris.generation.terrain.IrisDimension;
 import art.arcane.iris.generation.terrain.IrisDimensionType;
+import art.arcane.iris.spi.IrisPlatform;
+import art.arcane.iris.spi.IrisPlatforms;
 import art.arcane.iris.spi.PlatformGenerationRegistry;
 import java.lang.reflect.Constructor;
 import java.util.Set;
@@ -48,6 +51,8 @@ import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotSame;
 import static org.junit.Assert.assertThrows;
 import static org.junit.Assert.assertTrue;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
 
 public class ModdedForcedDatapackTest {
     @Test
@@ -65,6 +70,29 @@ public class ModdedForcedDatapackTest {
         }
     }
 
+    @Test
+    public void metadataFollowsTheRuntimeDataVersionThatValidationUses() throws IOException {
+        IrisPlatform previous = IrisPlatforms.getOrNull();
+        IrisPlatform runtime = mock(IrisPlatform.class);
+        when(runtime.minecraftVersion()).thenReturn("26.2");
+        Path packDirectory = Files.createTempDirectory("iris-modded-runtime-pack-format");
+        IrisPlatforms.unbind();
+        IrisPlatforms.bind(runtime);
+        try {
+            ModdedForcedDatapack.writePackMeta(packDirectory);
+            JSONObject pack = new JSONObject(Files.readString(packDirectory.resolve("pack.mcmeta")))
+                    .getJSONObject("pack");
+            assertEquals(DataVersion.getRuntime().getPackFormat(), pack.getInt("pack_format"));
+            assertEquals(DataVersion.V26_2.getPackFormat(), pack.getInt("pack_format"));
+        } finally {
+            IrisPlatforms.unbind();
+            if (previous != null) {
+                IrisPlatforms.bind(previous);
+            }
+            deleteTree(packDirectory);
+        }
+    }
+
     @Test
     public void retainedDimensionSourceRendersBeforeNativeRegistryExists() throws Exception {
         DataFixerV1217 fixer = new DataFixerV1217();

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

@@ -3,6 +3,7 @@ package art.arcane.iris.modded;
 import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeFeatureBiomeSource;
 
 import art.arcane.iris.generation.runtime.Engine;
+import art.arcane.iris.generation.runtime.GenerationClosedException;
 import art.arcane.iris.generation.terrain.IrisDimension;
 import art.arcane.iris.structure.nativegen.IrisImportedFeatureControl;
 import org.junit.Test;
@@ -11,6 +12,9 @@ import net.minecraft.SharedConstants;
 import net.minecraft.server.Bootstrap;
 
 import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertSame;
+import static org.junit.Assert.assertThrows;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.never;
 import static org.mockito.Mockito.spy;
@@ -56,17 +60,78 @@ public class ModdedImportedFeatureStageTest {
     }
 
     @Test
-    public void closingRuntimeDoesNotBuildFeatureTables() {
+    public void aSealedRuntimeWithoutASettledTableRefusesDecorationInsteadOfSkippingFeatures() {
         NativeFeatureBiomeSource source = mock(NativeFeatureBiomeSource.class);
+        when(source.packGeneration()).thenReturn(1L);
         Engine engine = mock(Engine.class);
+        when(engine.getCacheID()).thenReturn(7);
         when(engine.isClosing()).thenReturn(true);
         ModdedImportedFeatureStage stage = new ModdedImportedFeatureStage(source);
 
-        stage.prepare(engine);
         stage.prepareWithoutWaiting(engine);
+        assertThrows(GenerationClosedException.class, () -> stage.prepare(engine));
 
-        verify(source, never()).packGeneration();
         verify(engine, never()).getDimension();
         assertFalse(stage.active());
     }
+
+    @Test
+    public void aSealedRuntimeKeepsDecoratingWithTheTableItAlreadySettled() {
+        NativeFeatureBiomeSource source = mock(NativeFeatureBiomeSource.class);
+        when(source.packGeneration()).thenReturn(1L);
+        Engine engine = disabledFeatures(7);
+        ModdedImportedFeatureStage stage = new ModdedImportedFeatureStage(source);
+        stage.bind(mock(IrisModdedChunkGenerator.class));
+        stage.prepare(engine);
+
+        when(engine.isClosing()).thenReturn(true);
+        stage.prepare(engine);
+
+        assertNull(stage.placementTable(engine));
+    }
+
+    @Test
+    public void aTableRetiredBetweenPrepareAndPlacementFailsTheChunk() {
+        NativeFeatureBiomeSource source = mock(NativeFeatureBiomeSource.class);
+        when(source.packGeneration()).thenReturn(1L);
+        Engine engine = disabledFeatures(7);
+        ModdedImportedFeatureStage stage = new ModdedImportedFeatureStage(source);
+        stage.bind(mock(IrisModdedChunkGenerator.class));
+
+        stage.prepare(engine);
+        stage.evictRuntime(7);
+        assertThrows(GenerationClosedException.class, () -> stage.placementTable(engine));
+
+        stage.prepare(engine);
+        when(source.packGeneration()).thenReturn(2L);
+        assertThrows(GenerationClosedException.class, () -> stage.placementTable(engine));
+    }
+
+    @Test
+    public void anUnboundGeneratorAnswersVanillaGenerationSettings() {
+        IrisModdedChunkGenerator generator = mock(IrisModdedChunkGenerator.class);
+        when(generator.boundEngineOrNull()).thenReturn(null);
+        ModdedImportedFeatureStage stage = new ModdedImportedFeatureStage(mock(NativeFeatureBiomeSource.class));
+        stage.bind(generator);
+
+        assertNull(stage.currentTable());
+    }
+
+    @Test
+    public void aFailedBindFailsTheGenerationSettingsInsteadOfDroppingImportedFeatures() {
+        IllegalStateException refused = new IllegalStateException("Iris generator 'overworld:overworld' failed to bind");
+        IrisModdedChunkGenerator generator = mock(IrisModdedChunkGenerator.class);
+        when(generator.boundEngineOrNull()).thenThrow(refused);
+        ModdedImportedFeatureStage stage = new ModdedImportedFeatureStage(mock(NativeFeatureBiomeSource.class));
+        stage.bind(generator);
+
+        assertSame(refused, assertThrows(IllegalStateException.class, stage::currentTable));
+    }
+
+    private static Engine disabledFeatures(int runtimeIdentity) {
+        Engine engine = mock(Engine.class);
+        when(engine.getDimension()).thenReturn(new IrisDimension().setImportedFeatures(new IrisImportedFeatureControl()));
+        when(engine.getCacheID()).thenReturn(runtimeIdentity);
+        return engine;
+    }
 }

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

@@ -0,0 +1,194 @@
+package art.arcane.iris.modded;
+
+import com.google.gson.JsonArray;
+import com.google.gson.JsonElement;
+import com.google.gson.JsonObject;
+import com.google.gson.JsonParser;
+import org.junit.Assume;
+import org.junit.Test;
+import org.objectweb.asm.AnnotationVisitor;
+import org.objectweb.asm.ClassReader;
+import org.objectweb.asm.ClassVisitor;
+import org.objectweb.asm.MethodVisitor;
+import org.objectweb.asm.Opcodes;
+import org.objectweb.asm.Type;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.nio.charset.StandardCharsets;
+import java.util.LinkedHashMap;
+import java.util.LinkedHashSet;
+import java.util.Map;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertTrue;
+
+public class ModdedMixinAuditTest {
+    private static final String MIXIN_ANNOTATION = "Lorg/spongepowered/asm/mixin/Mixin;";
+    private static final Set<String> INJECTOR_ANNOTATIONS = Set.of(
+            "Lorg/spongepowered/asm/mixin/injection/Inject;",
+            "Lorg/spongepowered/asm/mixin/injection/Redirect;",
+            "Lorg/spongepowered/asm/mixin/injection/ModifyArg;",
+            "Lorg/spongepowered/asm/mixin/injection/ModifyArgs;",
+            "Lorg/spongepowered/asm/mixin/injection/ModifyVariable;",
+            "Lorg/spongepowered/asm/mixin/injection/ModifyConstant;");
+    private static final Pattern NEOFORGE_MIXIN_CONFIG = Pattern.compile(
+            "\\[\\[mixins]]\\s*config\\s*=\\s*\"([^\"]+)\"");
+    // One applied mixin per config proves the config was registered, which is all the audit detects.
+    private static final Set<String> UNAUDITED = Set.of(
+            "volmlib.entity.mixins.json/WorldGenerationWriteGuardMixin",
+            "volmlib.entity.mixins.json/ChunkMapTerrainReceiptAccess",
+            "volmlib.entity.mixins.json/ChunkTerrainReceiptMixin",
+            "volmlib.entity.mixins.json/LevelChunkTerrainReceiptMixin",
+            "volmlib.entity.mixins.json/SerializableTerrainReceiptMixin",
+            "volmlib.fabric.mixins.json/BlockItemMixin",
+            "volmlib.fabric.mixins.json/BlockMixin",
+            "volmlib.fabric.mixins.json/PackRepositoryMixin");
+
+    @Test
+    public void everyExpectedHandlerIsAnInjectorDeclaredByItsMixin() throws IOException {
+        for (ModdedMixinAudit.ExpectedMixin expected : ModdedMixinAudit.EXPECTED) {
+            MixinConfig config = MixinConfig.read(expected.config());
+            String section = config.sections().get(expected.mixinName());
+            assertNotNull(expected.config() + " does not list " + expected.mixinName(), section);
+            assertEquals(expected.mixinName() + " client-only flag disagrees with its config section",
+                    "client".equals(section), expected.clientOnly());
+
+            MixinClass mixin = MixinClass.read(config.packageName() + '.' + expected.mixinName());
+            assertTrue(expected.mixinName() + " does not target " + expected.targetClass().className()
+                            + " (targets " + mixin.targets() + ")",
+                    mixin.targets().contains(expected.targetClass().className()));
+            assertTrue(expected.mixinName() + " declares no injector handler named " + expected.handlerMethod()
+                            + " (injectors " + mixin.injectors() + ")",
+                    mixin.injectors().contains(expected.handlerMethod()));
+        }
+    }
+
+    @Test
+    public void everyRegisteredMixinIsAuditedOrDeliberatelyUnaudited() throws IOException {
+        Set<String> registered = registeredConfigs();
+        Assume.assumeFalse("loader metadata on this classpath declares no mixin configs", registered.isEmpty());
+        Set<String> audited = new LinkedHashSet<>();
+        for (ModdedMixinAudit.ExpectedMixin expected : ModdedMixinAudit.EXPECTED) {
+            audited.add(expected.config() + '/' + expected.mixinName());
+        }
+
+        Set<String> listed = new TreeSet<>();
+        for (String configName : registered) {
+            for (String mixinName : MixinConfig.read(configName).sections().keySet()) {
+                listed.add(configName + '/' + mixinName);
+            }
+        }
+
+        Set<String> uncovered = new TreeSet<>(listed);
+        uncovered.removeAll(audited);
+        uncovered.removeAll(UNAUDITED);
+        assertEquals("mixins neither audited nor deliberately unaudited", Set.of(), uncovered);
+
+        Set<String> unregisteredAudits = new TreeSet<>(audited);
+        unregisteredAudits.removeAll(listed);
+        assertEquals("audited mixins missing from the registered configs", Set.of(), unregisteredAudits);
+    }
+
+    private static Set<String> registeredConfigs() throws IOException {
+        Set<String> configs = new LinkedHashSet<>();
+        String fabric = readResource("fabric.mod.json");
+        if (fabric != null) {
+            for (JsonElement entry : JsonParser.parseString(fabric).getAsJsonObject().getAsJsonArray("mixins")) {
+                configs.add(entry.isJsonObject()
+                        ? entry.getAsJsonObject().get("config").getAsString()
+                        : entry.getAsString());
+            }
+        }
+        String neoforge = readResource("META-INF/neoforge.mods.toml");
+        if (neoforge != null) {
+            Matcher matcher = NEOFORGE_MIXIN_CONFIG.matcher(neoforge);
+            while (matcher.find()) {
+                configs.add(matcher.group(1));
+            }
+        }
+        return configs;
+    }
+
+    private static String readResource(String name) throws IOException {
+        try (InputStream input = ModdedMixinAuditTest.class.getClassLoader().getResourceAsStream(name)) {
+            return input == null ? null : new String(input.readAllBytes(), StandardCharsets.UTF_8);
+        }
+    }
+
+    private record MixinConfig(String packageName, Map<String, String> sections) {
+        static MixinConfig read(String name) throws IOException {
+            String json = readResource(name);
+            assertNotNull("Missing mixin config resource " + name, json);
+            JsonObject root = JsonParser.parseString(json).getAsJsonObject();
+            Map<String, String> sections = new LinkedHashMap<>();
+            for (String section : new String[]{"mixins", "client", "server"}) {
+                JsonArray entries = root.getAsJsonArray(section);
+                if (entries == null) {
+                    continue;
+                }
+                for (JsonElement entry : entries) {
+                    sections.put(entry.getAsString(), section);
+                }
+            }
+            return new MixinConfig(root.get("package").getAsString(), sections);
+        }
+    }
+
+    private record MixinClass(Set<String> targets, Set<String> injectors) {
+        static MixinClass read(String className) throws IOException {
+            String resource = className.replace('.', '/') + ".class";
+            byte[] bytes;
+            try (InputStream input = ModdedMixinAuditTest.class.getClassLoader().getResourceAsStream(resource)) {
+                assertNotNull("Missing mixin class " + className, input);
+                bytes = input.readAllBytes();
+            }
+            Set<String> targets = new TreeSet<>();
+            Set<String> injectors = new TreeSet<>();
+            new ClassReader(bytes).accept(new ClassVisitor(Opcodes.ASM9) {
+                @Override
+                public AnnotationVisitor visitAnnotation(String descriptor, boolean visible) {
+                    if (!MIXIN_ANNOTATION.equals(descriptor)) {
+                        return null;
+                    }
+                    return new AnnotationVisitor(Opcodes.ASM9) {
+                        @Override
+                        public AnnotationVisitor visitArray(String name) {
+                            return new AnnotationVisitor(Opcodes.ASM9) {
+                                @Override
+                                public void visit(String ignored, Object value) {
+                                    if (value instanceof Type type) {
+                                        targets.add(type.getClassName());
+                                    } else if (value instanceof String target) {
+                                        targets.add(target.replace('/', '.'));
+                                    }
+                                }
+                            };
+                        }
+                    };
+                }
+
+                @Override
+                public MethodVisitor visitMethod(int access, String name, String descriptor, String signature,
+                                                 String[] exceptions) {
+                    return new MethodVisitor(Opcodes.ASM9) {
+                        @Override
+                        public AnnotationVisitor visitAnnotation(String annotation, boolean visible) {
+                            if (INJECTOR_ANNOTATIONS.contains(annotation)) {
+                                injectors.add(name);
+                            }
+                            return null;
+                        }
+                    };
+                }
+            }, ClassReader.SKIP_CODE | ClassReader.SKIP_DEBUG | ClassReader.SKIP_FRAMES);
+            return new MixinClass(targets, injectors);
+        }
+    }
+}

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

@@ -12,6 +12,7 @@ import net.minecraft.server.level.ServerPlayer;
 import net.minecraft.world.entity.EntitySpawnReason;
 import net.minecraft.world.entity.Mob;
 import net.minecraft.world.level.ServerLevelAccessor;
+import net.minecraft.world.level.biome.Biome;
 import net.minecraft.world.level.block.state.BlockState;
 import org.junit.Rule;
 import org.junit.Test;
@@ -91,6 +92,11 @@ public class ModdedPlatformPathsTest {
             public boolean checkSpawnPosition(Mob mob, ServerLevelAccessor level, EntitySpawnReason reason) {
                 return false;
             }
+
+            @Override
+            public Biome unmodifiedBiome(Biome biome) {
+                return biome;
+            }
         });
     }
 

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

@@ -0,0 +1,256 @@
+package art.arcane.iris.modded;
+
+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.NativeWorldTeleport;
+import art.arcane.volmlib.nativelib.terrain.NativeWorld;
+import org.junit.After;
+import org.junit.Test;
+import org.mockito.MockedStatic;
+import org.mockito.invocation.InvocationOnMock;
+
+import java.util.UUID;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicReference;
+import java.util.function.Consumer;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertSame;
+import static org.junit.Assert.assertTrue;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.anyString;
+import static org.mockito.ArgumentMatchers.argThat;
+import static org.mockito.ArgumentMatchers.contains;
+import static org.mockito.Mockito.doAnswer;
+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;
+
+/**
+ * A configured primary Iris world that did not load used to be skipped silently, leaving every player in the
+ * overworld generating terrain Iris was configured to replace.
+ */
+public class ModdedPrimaryWorldRouterTest {
+    private static final int TICK_INTERVAL = 20;
+    private static final String PRIMARY = "iris:primary";
+
+    @After
+    public void clearRouter() {
+        ModdedPrimaryWorldRouter.clear();
+    }
+
+    @Test
+    public void aPrimaryWorldThisSaveListsButDidNotRestoreRefusesPlayers() {
+        NativeModdedServer server = mock(NativeModdedServer.class);
+        NativeProtocolPlayer online = mock(NativeProtocolPlayer.class);
+        onlinePlayers(server, online);
+        ModdedModConfig routed = config(true, PRIMARY);
+
+        try (MockedStatic<ModdedModConfig> configs = mockStatic(ModdedModConfig.class);
+             MockedStatic<ModdedDimensionManager> manager = mockStatic(ModdedDimensionManager.class);
+             MockedStatic<ModdedDimensionRegistryStore> registry = mockStatic(ModdedDimensionRegistryStore.class);
+             MockedStatic<ModdedStartup> startup = mockStatic(ModdedStartup.class);
+             MockedStatic<ModdedIrisLog> log = mockStatic(ModdedIrisLog.class)) {
+            configs.when(ModdedModConfig::get).thenReturn(routed);
+            manager.when(() -> ModdedDimensionManager.level(server, PRIMARY)).thenReturn(null);
+            registry.when(() -> ModdedDimensionRegistryStore.get(server, PRIMARY)).thenReturn(persisted());
+            startup.when(ModdedStartup::dimensionsRestored).thenReturn(true);
+
+            evaluate(server);
+            evaluate(server);
+
+            verify(online, times(2)).disconnect(contains(PRIMARY));
+            log.verify(() -> ModdedIrisLog.error(argThat((String line) -> line != null && line.startsWith("Cause: ")
+                    && line.contains(PRIMARY))), times(1));
+            NativeProtocolPlayer joining = mock(NativeProtocolPlayer.class);
+            assertTrue(ModdedPrimaryWorldRouter.refuseIfUnavailable(joining));
+            verify(joining).disconnect(contains(PRIMARY));
+        }
+    }
+
+    /**
+     * primaryWorld lives in the instance-wide modded.json, but the dimension it names lives in one save. Another
+     * save, a new world or a reset world folder never had it, so nothing failed there and nothing is refused.
+     */
+    @Test
+    public void aPrimaryWorldThisSaveNeverHadLeavesRoutingIdleWithOneWarning() {
+        NativeModdedServer server = mock(NativeModdedServer.class);
+        NativeProtocolPlayer online = mock(NativeProtocolPlayer.class);
+        onlinePlayers(server, online);
+        ModdedModConfig routed = config(true, PRIMARY);
+
+        try (MockedStatic<ModdedModConfig> configs = mockStatic(ModdedModConfig.class);
+             MockedStatic<ModdedDimensionManager> manager = mockStatic(ModdedDimensionManager.class);
+             MockedStatic<ModdedDimensionRegistryStore> registry = mockStatic(ModdedDimensionRegistryStore.class);
+             MockedStatic<ModdedStartup> startup = mockStatic(ModdedStartup.class);
+             MockedStatic<ModdedIrisLog> log = mockStatic(ModdedIrisLog.class)) {
+            configs.when(ModdedModConfig::get).thenReturn(routed);
+            manager.when(() -> ModdedDimensionManager.level(server, PRIMARY)).thenReturn(null);
+            registry.when(() -> ModdedDimensionRegistryStore.get(server, PRIMARY)).thenReturn(null);
+            startup.when(ModdedStartup::dimensionsRestored).thenReturn(true);
+
+            evaluate(server);
+            evaluate(server);
+
+            verify(online, never()).disconnect(anyString());
+            assertFalse(ModdedPrimaryWorldRouter.refuseIfUnavailable(mock(NativeProtocolPlayer.class)));
+            log.verify(() -> ModdedIrisLog.warn(argThat((String line) -> line != null && line.contains(PRIMARY))), times(1));
+            log.verify(() -> ModdedIrisLog.error(anyString()), never());
+        }
+    }
+
+    /**
+     * Joins are processed before the first Iris tick restores persistent dimensions, so a primary world that is
+     * missing then is still loading, not broken.
+     */
+    @Test
+    public void aPrimaryWorldIsNotJudgedBeforeStartupRestoresDimensions() {
+        NativeModdedServer server = mock(NativeModdedServer.class);
+        NativeProtocolPlayer online = mock(NativeProtocolPlayer.class);
+        onlinePlayers(server, online);
+        ModdedModConfig routed = config(true, PRIMARY);
+
+        try (MockedStatic<ModdedModConfig> configs = mockStatic(ModdedModConfig.class);
+             MockedStatic<ModdedDimensionManager> manager = mockStatic(ModdedDimensionManager.class);
+             MockedStatic<ModdedStartup> startup = mockStatic(ModdedStartup.class);
+             MockedStatic<ModdedIrisLog> log = mockStatic(ModdedIrisLog.class)) {
+            configs.when(ModdedModConfig::get).thenReturn(routed);
+            manager.when(() -> ModdedDimensionManager.level(server, PRIMARY)).thenReturn(null);
+            startup.when(ModdedStartup::dimensionsRestored).thenReturn(false);
+
+            evaluate(server);
+
+            verify(online, never()).disconnect(anyString());
+            assertFalse(ModdedPrimaryWorldRouter.refuseIfUnavailable(mock(NativeProtocolPlayer.class)));
+        }
+    }
+
+    @Test
+    public void refusalLiftsOnceThePrimaryWorldIsLoadedOrUnconfigured() {
+        NativeModdedServer server = mock(NativeModdedServer.class);
+        NativeWorld overworld = mock(NativeWorld.class);
+        when(server.overworld()).thenReturn(overworld);
+        onlinePlayers(server, mock(NativeProtocolPlayer.class));
+        ModdedModConfig routed = config(true, PRIMARY);
+        ModdedModConfig unconfigured = config(true, "");
+
+        try (MockedStatic<ModdedModConfig> configs = mockStatic(ModdedModConfig.class);
+             MockedStatic<ModdedDimensionManager> manager = mockStatic(ModdedDimensionManager.class);
+             MockedStatic<ModdedDimensionRegistryStore> registry = mockStatic(ModdedDimensionRegistryStore.class);
+             MockedStatic<ModdedStartup> startup = mockStatic(ModdedStartup.class);
+             MockedStatic<ModdedIrisLog> log = mockStatic(ModdedIrisLog.class)) {
+            registry.when(() -> ModdedDimensionRegistryStore.get(server, PRIMARY)).thenReturn(persisted());
+            startup.when(ModdedStartup::dimensionsRestored).thenReturn(true);
+            configs.when(ModdedModConfig::get).thenReturn(routed);
+            evaluate(server);
+            assertTrue(ModdedPrimaryWorldRouter.refuseIfUnavailable(mock(NativeProtocolPlayer.class)));
+
+            configs.when(ModdedModConfig::get).thenReturn(unconfigured);
+            evaluate(server);
+            assertFalse(ModdedPrimaryWorldRouter.refuseIfUnavailable(mock(NativeProtocolPlayer.class)));
+
+            configs.when(ModdedModConfig::get).thenReturn(routed);
+            evaluate(server);
+            manager.when(() -> ModdedDimensionManager.level(server, PRIMARY)).thenReturn(overworld);
+            evaluate(server);
+            assertFalse(ModdedPrimaryWorldRouter.refuseIfUnavailable(mock(NativeProtocolPlayer.class)));
+        }
+    }
+
+    /**
+     * A registry that cannot be read cannot prove the primary world was never here, so it counts as expected.
+     */
+    @Test
+    public void anUnreadableRegistryRefusesPlayersRatherThanGuessing() {
+        NativeModdedServer server = mock(NativeModdedServer.class);
+        NativeProtocolPlayer online = mock(NativeProtocolPlayer.class);
+        onlinePlayers(server, online);
+        ModdedModConfig routed = config(true, PRIMARY);
+
+        try (MockedStatic<ModdedModConfig> configs = mockStatic(ModdedModConfig.class);
+             MockedStatic<ModdedDimensionManager> manager = mockStatic(ModdedDimensionManager.class);
+             MockedStatic<ModdedDimensionRegistryStore> registry = mockStatic(ModdedDimensionRegistryStore.class);
+             MockedStatic<ModdedStartup> startup = mockStatic(ModdedStartup.class);
+             MockedStatic<ModdedIrisLog> log = mockStatic(ModdedIrisLog.class)) {
+            configs.when(ModdedModConfig::get).thenReturn(routed);
+            manager.when(() -> ModdedDimensionManager.level(server, PRIMARY)).thenReturn(null);
+            registry.when(() -> ModdedDimensionRegistryStore.get(server, PRIMARY))
+                    .thenThrow(new IllegalStateException("registry could not be read"));
+            startup.when(ModdedStartup::dimensionsRestored).thenReturn(true);
+
+            evaluate(server);
+
+            verify(online).disconnect(contains(PRIMARY));
+            assertTrue(ModdedPrimaryWorldRouter.refuseIfUnavailable(mock(NativeProtocolPlayer.class)));
+        }
+    }
+
+    /**
+     * Routing waits on the primary world's first chunk, which on a cold world also loads the pack and binds the
+     * engine, so it gets the same bounded deadline as /iris tp instead of timing out and retrying every second.
+     */
+    @Test
+    public void routingWaitsForAColdPrimaryWorldWithinTheTeleportDeadline() {
+        NativeModdedServer server = mock(NativeModdedServer.class);
+        NativeWorld overworld = mock(NativeWorld.class);
+        when(overworld.nativeHandle()).thenReturn(new Object());
+        NativeWorld primary = mock(NativeWorld.class);
+        when(primary.nativeHandle()).thenReturn(new Object());
+        when(server.overworld()).thenReturn(overworld);
+        NativeProtocolPlayer player = mock(NativeProtocolPlayer.class);
+        when(player.id()).thenReturn(UUID.randomUUID());
+        when(player.isInWorld(overworld)).thenReturn(true);
+        onlinePlayers(server, player);
+        ModdedModConfig routed = config(true, PRIMARY);
+        AtomicReference<NativeWorldTeleport.Destination> requested = new AtomicReference<>();
+
+        long before = System.nanoTime();
+        try (MockedStatic<ModdedModConfig> configs = mockStatic(ModdedModConfig.class);
+             MockedStatic<ModdedDimensionManager> manager = mockStatic(ModdedDimensionManager.class);
+             MockedStatic<NativeWorldTeleport> teleport = mockStatic(NativeWorldTeleport.class)) {
+            configs.when(ModdedModConfig::get).thenReturn(routed);
+            manager.when(() -> ModdedDimensionManager.level(server, PRIMARY)).thenReturn(primary);
+            teleport.when(() -> NativeWorldTeleport.teleport(any(), any())).thenAnswer((InvocationOnMock invocation) -> {
+                requested.set(invocation.getArgument(1));
+                return new CompletableFuture<Boolean>();
+            });
+
+            evaluate(server);
+        }
+        long after = System.nanoTime();
+
+        assertSame(primary, requested.get().world());
+        long deadline = requested.get().deadlineNanos();
+        assertTrue("deadline must outlast a cold first chunk", deadline - before >= TimeUnit.SECONDS.toNanos(60L));
+        assertTrue("deadline must be bounded", deadline - after <= TimeUnit.SECONDS.toNanos(120L));
+    }
+
+    private static ModdedDimensionRegistryStore.PersistentDimension persisted() {
+        return new ModdedDimensionRegistryStore.PersistentDimension(PRIMARY, "overworld", "overworld", 1337L);
+    }
+
+    private static void evaluate(NativeModdedServer server) {
+        for (int tick = 0; tick < TICK_INTERVAL; tick++) {
+            ModdedPrimaryWorldRouter.tick(server);
+        }
+    }
+
+    @SuppressWarnings("unchecked")
+    private static void onlinePlayers(NativeModdedServer server, NativeProtocolPlayer player) {
+        doAnswer(invocation -> {
+            invocation.getArgument(0, Consumer.class).accept(player);
+            return null;
+        }).when(server).forEachPlayer(any());
+    }
+
+    private static ModdedModConfig config(boolean route, String primary) {
+        ModdedModConfig config = mock(ModdedModConfig.class);
+        when(config.routePlayersToPrimaryWorld()).thenReturn(route);
+        when(config.primaryWorld()).thenReturn(primary);
+        return config;
+    }
+}

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

@@ -0,0 +1,71 @@
+package art.arcane.iris.modded;
+
+import art.arcane.iris.pack.PackValidationRegistry;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeModdedServer;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeProtocolPlayer;
+import org.junit.After;
+import org.junit.Test;
+import org.mockito.MockedStatic;
+
+import java.util.List;
+
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.anyString;
+import static org.mockito.ArgumentMatchers.argThat;
+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;
+
+/**
+ * A persistent dimension that cannot be re-injected is skipped, which already writes no chunks. The skip used to be
+ * one console line; it has to be a banner and has to reach the operators who can fix it.
+ */
+public class ModdedStartupReinjectFailureTest {
+    @After
+    public void resetStartup() {
+        ModdedStartup.reset();
+        PackValidationRegistry.clear();
+    }
+
+    @Test
+    public void aDimensionThatFailsToReinjectIsBanneredAndReportedToOperatorsOnJoin() {
+        NativeModdedServer server = mock(NativeModdedServer.class);
+        ModdedDimensionRegistryStore.PersistentDimension moon =
+                new ModdedDimensionRegistryStore.PersistentDimension("iris:moon", "overworld", "overworld", 1337L);
+        IllegalStateException failure = new IllegalStateException("Iris generation history is unusable for 'iris:moon'");
+
+        try (MockedStatic<ModdedDimensionRegistryStore> store = mockStatic(ModdedDimensionRegistryStore.class);
+             MockedStatic<ModdedDimensionManager> manager = mockStatic(ModdedDimensionManager.class);
+             MockedStatic<ModdedIrisLog> log = mockStatic(ModdedIrisLog.class)) {
+            store.when(() -> ModdedDimensionRegistryStore.loadForStartup(server)).thenReturn(List.of(moon));
+            manager.when(() -> ModdedDimensionManager.restorePersistent(server, "iris:moon", "overworld", "overworld", 1337L))
+                    .thenThrow(failure);
+
+            ModdedStartup.reinjectPersistentDimensions(server);
+
+            log.verify(() -> ModdedIrisLog.error(argThat((String line) -> line != null && line.contains("iris:moon")
+                    && line.startsWith("Iris refused"))), times(1));
+            log.verify(() -> ModdedIrisLog.error(argThat((String line) -> line != null && line.startsWith("Cause: ")
+                    && line.contains("generation history is unusable"))), times(1));
+        }
+
+        NativeProtocolPlayer operator = mock(NativeProtocolPlayer.class);
+        when(operator.isGameMaster()).thenReturn(true);
+        NativeProtocolPlayer player = mock(NativeProtocolPlayer.class);
+        ModdedStartup.warnStartupFailuresTo(operator);
+        ModdedStartup.warnStartupFailuresTo(player);
+
+        verify(operator).sendMessage(argThat((String message) -> message.contains("iris:moon")
+                && message.contains("generation history is unusable")));
+        verify(player, never()).sendMessage(anyString());
+
+        ModdedStartup.reset();
+        NativeProtocolPlayer laterOperator = mock(NativeProtocolPlayer.class);
+        when(laterOperator.isGameMaster()).thenReturn(true);
+        ModdedStartup.warnStartupFailuresTo(laterOperator);
+        verify(laterOperator, never()).sendMessage(any());
+    }
+}

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

@@ -0,0 +1,145 @@
+package art.arcane.iris.modded.command;
+
+import art.arcane.iris.localization.IrisLanguage;
+import art.arcane.iris.modded.IrisModdedChunkGenerator;
+import art.arcane.iris.modded.ModdedDimensionManager;
+import art.arcane.iris.modded.localization.ModdedCommandMessages;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeCommandSource;
+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.NativeWorldGenerators;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeWorldTeleport;
+import art.arcane.volmlib.nativelib.terrain.NativeWorld;
+import art.arcane.volmlib.util.localization.MessageArgument;
+import net.minecraft.SharedConstants;
+import net.minecraft.core.registries.Registries;
+import net.minecraft.resources.Identifier;
+import net.minecraft.resources.ResourceKey;
+import net.minecraft.server.Bootstrap;
+import net.minecraft.server.MinecraftServer;
+import net.minecraft.server.level.ServerChunkCache;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.level.Level;
+import org.junit.BeforeClass;
+import org.junit.Test;
+import org.mockito.MockedStatic;
+import org.mockito.invocation.InvocationOnMock;
+
+import java.util.UUID;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CompletionException;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
+import java.util.concurrent.atomic.AtomicReference;
+
+import static org.junit.Assert.assertEquals;
+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.Mockito.mock;
+import static org.mockito.Mockito.mockStatic;
+import static org.mockito.Mockito.when;
+
+public class IrisModdedCommandsTeleportTest {
+    private static final String DIMENSION = "irisworldgen:1";
+
+    @BeforeClass
+    public static void bootstrap() {
+        SharedConstants.tryDetectVersion();
+        Bootstrap.bootStrap();
+    }
+
+    @Test
+    public void teleportWaitsForAColdDestinationWithinABoundedDeadline() {
+        NativeModdedServer server = mock(NativeModdedServer.class);
+        NativeCommandSource source = mock(NativeCommandSource.class);
+        when(source.server()).thenReturn(server);
+        NativeWorld level = mock(NativeWorld.class);
+        when(level.name()).thenReturn(DIMENSION);
+        NativeProtocolPlayer player = mock(NativeProtocolPlayer.class);
+        when(player.name()).thenReturn("Tester");
+        AtomicReference<NativeWorldTeleport.Destination> requested = new AtomicReference<>();
+
+        long before = System.nanoTime();
+        try (MockedStatic<NativeWorldGenerators> generators = mockStatic(NativeWorldGenerators.class);
+             MockedStatic<ModdedDimensionManager> dimensions = mockStatic(ModdedDimensionManager.class);
+             MockedStatic<NativeWorldTeleport> teleport = mockStatic(NativeWorldTeleport.class)) {
+            generators.when(() -> NativeWorldGenerators.find(level, IrisModdedChunkGenerator.class))
+                    .thenReturn(mock(IrisModdedChunkGenerator.class));
+            dimensions.when(() -> ModdedDimensionManager.level(server, DIMENSION)).thenReturn(level);
+            teleport.when(() -> NativeWorldTeleport.teleport(any(), any())).thenAnswer((InvocationOnMock invocation) -> {
+                requested.set(invocation.getArgument(1));
+                return new CompletableFuture<Boolean>();
+            });
+
+            assertEquals(1, IrisModdedCommands.tp(source, level, player));
+        }
+        long after = System.nanoTime();
+
+        long deadline = requested.get().deadlineNanos();
+        assertTrue("deadline must outlast a cold first chunk", deadline - before >= TimeUnit.SECONDS.toNanos(60L));
+        assertTrue("deadline must be bounded", deadline - after <= TimeUnit.SECONDS.toNanos(120L));
+    }
+
+    @Test(timeout = 15_000L)
+    public void expiredTeleportReportsTheCallersDeadline() throws Exception {
+        MinecraftServer server = mock(MinecraftServer.class);
+        when(server.isSameThread()).thenReturn(true);
+        ResourceKey<Level> dimension = ResourceKey.create(Registries.DIMENSION, Identifier.parse(DIMENSION));
+        ServerChunkCache chunks = mock(ServerChunkCache.class);
+        when(chunks.addTicketAndLoadWithRadius(any(), any(), anyInt())).thenReturn(new CompletableFuture<>());
+        ServerLevel serverLevel = mock(ServerLevel.class);
+        when(serverLevel.getServer()).thenReturn(server);
+        when(serverLevel.dimension()).thenReturn(dimension);
+        when(serverLevel.getChunkSource()).thenReturn(chunks);
+        when(server.getLevel(dimension)).thenReturn(serverLevel);
+        ServerPlayer serverPlayer = mock(ServerPlayer.class);
+        when(serverPlayer.getUUID()).thenReturn(UUID.randomUUID());
+        NativeWorld level = mock(NativeWorld.class);
+        when(level.nativeHandle()).thenReturn(serverLevel);
+
+        CompletableFuture<Boolean> teleport = NativeWorldTeleport.teleport(NativeProtocolPlayer.fromHandle(serverPlayer),
+                new NativeWorldTeleport.Destination(NativeModdedServer.fromHandle(server), level, 8.5D,
+                        Double.MIN_VALUE, 8.5D, System.nanoTime() + TimeUnit.SECONDS.toNanos(2L)));
+
+        ExecutionException failure = assertThrows(ExecutionException.class, () -> teleport.get(10L, TimeUnit.SECONDS));
+        assertTrue(failure.getCause() instanceof TimeoutException);
+        assertTrue(failure.getCause().getMessage(), failure.getCause().getMessage().contains("within 2 seconds"));
+    }
+
+    @Test
+    public void failureReportsItsRootCauseInsteadOfAnUnloadedDimension() {
+        String message = IrisModdedCommands.teleportFailure(DIMENSION, "Tester",
+                new CompletionException(new IllegalStateException("Exception generating new chunk")), true, true);
+
+        assertEquals(IrisLanguage.plain(ModdedCommandMessages.IRIS_MODDED_COMMANDS_TELEPORT_FAILED_REASON,
+                MessageArgument.untrusted("dimensionId", DIMENSION),
+                MessageArgument.untrusted("reason", "Exception generating new chunk")), message);
+    }
+
+    @Test
+    public void failureWithoutMessageNamesTheFailureType() {
+        String message = IrisModdedCommands.teleportFailure(DIMENSION, "Tester", new TimeoutException(), true, true);
+
+        assertEquals(IrisLanguage.plain(ModdedCommandMessages.IRIS_MODDED_COMMANDS_TELEPORT_FAILED_REASON,
+                MessageArgument.untrusted("dimensionId", DIMENSION),
+                MessageArgument.untrusted("reason", "TimeoutException")), message);
+    }
+
+    @Test
+    public void unloadedDimensionIsReportedOnlyWhenItIsGone() {
+        assertEquals(IrisLanguage.plain(ModdedCommandMessages.IRIS_MODDED_COMMANDS_TELEPORT_FAILED_DIMENSION_IS_NOT_LOADED,
+                        MessageArgument.untrusted("dimensionId", DIMENSION)),
+                IrisModdedCommands.teleportFailure(DIMENSION, "Tester", null, false, true));
+        assertEquals(IrisLanguage.plain(ModdedCommandMessages.IRIS_MODDED_COMMANDS_TELEPORT_CANCELLED_PLAYER_OFFLINE,
+                        MessageArgument.untrusted("dimensionId", DIMENSION),
+                        MessageArgument.untrusted("value", "Tester")),
+                IrisModdedCommands.teleportFailure(DIMENSION, "Tester", null, true, false));
+        assertEquals(IrisLanguage.plain(ModdedCommandMessages.IRIS_MODDED_COMMANDS_TELEPORT_REFUSED,
+                        MessageArgument.untrusted("dimensionId", DIMENSION)),
+                IrisModdedCommands.teleportFailure(DIMENSION, "Tester", null, true, true));
+    }
+}

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

@@ -0,0 +1,56 @@
+package art.arcane.iris.modded.command;
+
+import art.arcane.iris.generation.runtime.Engine;
+import art.arcane.volmlib.nativelib.view.WorldView;
+import org.junit.Test;
+import org.mockito.invocation.InvocationOnMock;
+
+import java.util.Optional;
+import java.util.UUID;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicReference;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.anyInt;
+import static org.mockito.ArgumentMatchers.eq;
+import static org.mockito.Mockito.doAnswer;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+public class ModdedVisionOverlayTest {
+    /**
+     * A Vision click can land anywhere in the world, so the destination chunk is usually cold and gets the same
+     * bounded deadline as /iris tp.
+     */
+    @Test
+    public void teleportWaitsForAColdDestinationWithinTheTeleportDeadline() {
+        WorldView world = mock(WorldView.class);
+        doAnswer((InvocationOnMock invocation) -> {
+            invocation.getArgument(0, Runnable.class).run();
+            return null;
+        }).when(world).execute(any());
+        UUID opener = UUID.randomUUID();
+        AtomicReference<WorldView.Destination> requested = new AtomicReference<>();
+        when(world.teleport(eq(opener), any())).thenAnswer((InvocationOnMock invocation) -> {
+            requested.set(invocation.getArgument(1));
+            return Optional.empty();
+        });
+        Engine engine = mock(Engine.class);
+        when(engine.getMinHeight()).thenReturn(-64);
+        when(engine.getHeight(anyInt(), anyInt(), eq(false))).thenReturn(130);
+
+        long before = System.nanoTime();
+        new ModdedVisionOverlay(new ModdedVisionOverlay.Context(world, engine, opener)).teleport(-3.5D, 17.25D);
+        long after = System.nanoTime();
+
+        WorldView.Destination destination = requested.get();
+        assertEquals(-3.5D, destination.x(), 0D);
+        assertEquals(68D, destination.y(), 0D);
+        assertEquals(17.5D, destination.z(), 0D);
+        assertTrue("deadline must outlast a cold first chunk",
+                destination.deadlineNanos() - before >= TimeUnit.SECONDS.toNanos(60L));
+        assertTrue("deadline must be bounded", destination.deadlineNanos() - after <= TimeUnit.SECONDS.toNanos(120L));
+    }
+}

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

@@ -2,15 +2,30 @@ package art.arcane.iris.modded.service;
 
 import art.arcane.volmlib.nativelib.minecraft26_2.modded.ModdedPlatformWorld;
 
+import art.arcane.iris.configuration.IrisSettings;
+import art.arcane.iris.generation.mantle.EngineMantle;
 import art.arcane.iris.generation.runtime.Engine;
 import art.arcane.iris.generation.runtime.EngineMetrics;
+import art.arcane.iris.modded.IrisModdedChunkGenerator;
+import art.arcane.iris.modded.ModdedLootApplier;
+import art.arcane.iris.spi.IrisLogging;
 import art.arcane.iris.world.IrisWorld;
+import art.arcane.iris.world.history.SavedBiomeUnavailableException;
 import art.arcane.iris.world.storage.matter.TileWrapper;
+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.NativeWorldMaintenance;
+import art.arcane.volmlib.nativelib.terrain.NativeBlockPoint;
+import art.arcane.volmlib.nativelib.terrain.NativeBlockState;
+import art.arcane.volmlib.nativelib.terrain.NativeWorld;
 import art.arcane.volmlib.util.function.Consumer4;
+import art.arcane.volmlib.util.mantle.flag.MantleFlag;
+import art.arcane.volmlib.util.mantle.runtime.Mantle;
 import art.arcane.volmlib.util.mantle.runtime.MantleChunk;
 import art.arcane.volmlib.util.mantle.runtime.MantleDataAdapter;
 import art.arcane.volmlib.util.mantle.runtime.MantleHooks;
 import art.arcane.volmlib.util.matter.Matter;
+import art.arcane.volmlib.util.matter.MatterSlice;
 import art.arcane.volmlib.util.matter.MatterUpdate;
 import art.arcane.volmlib.util.matter.slices.UpdateMatter;
 import net.minecraft.SharedConstants;
@@ -24,19 +39,33 @@ import net.minecraft.world.level.block.state.BlockState;
 import net.minecraft.world.level.material.FlowingFluid;
 import org.junit.Test;
 import org.mockito.InOrder;
+import org.mockito.MockedConstruction;
+import org.mockito.MockedStatic;
+import org.mockito.invocation.InvocationOnMock;
 
 import java.lang.reflect.Proxy;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.function.LongConsumer;
 
 import static org.junit.Assert.assertEquals;
 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.ArgumentMatchers.contains;
 import static org.mockito.ArgumentMatchers.eq;
+import static org.mockito.Mockito.doAnswer;
 import static org.mockito.Mockito.inOrder;
 import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.mockConstruction;
+import static org.mockito.Mockito.mockStatic;
+import static org.mockito.Mockito.never;
+import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
 public class ModdedChunkUpdateServiceTest {
@@ -70,6 +99,148 @@ public class ModdedChunkUpdateServiceTest {
         assertTrue(chunk.deleted());
     }
 
+    @Test
+    public void loadingSavedBiomeDefersThePassAndForgetsOnlyCompletedLoot() {
+        SharedConstants.tryDetectVersion();
+        Bootstrap.bootStrap();
+        IrisWorld world = mock(IrisWorld.class);
+        when(world.minHeight()).thenReturn(-64);
+        Engine engine = mock(Engine.class);
+        when(engine.getWorld()).thenReturn(world);
+        when(engine.getMetrics()).thenReturn(new EngineMetrics(8));
+        ServerLevel level = mock(ServerLevel.class);
+        when(level.getMinY()).thenReturn(-64);
+        when(level.getMaxY()).thenReturn(319);
+        when(level.getHeight()).thenReturn(384);
+        when(level.getBlockState(any(BlockPos.class))).thenReturn(Blocks.CHEST.defaultBlockState());
+        ChestUpdateMantleChunk chunk = new ChestUpdateMantleChunk();
+        SavedBiomeUnavailableException loading = new SavedBiomeUnavailableException(
+                "Saved biome information is loading at chunk 0,0. Try again shortly.", true);
+
+        try (MockedStatic<ModdedLootApplier> loot = mockStatic(ModdedLootApplier.class)) {
+            loot.when(() -> ModdedLootApplier.apply(any(), any(), any(), any(), any())).thenAnswer((InvocationOnMock invocation) -> {
+                NativeBlockPoint position = invocation.getArgument(2);
+                if (position.x() == 2) {
+                    throw loading;
+                }
+                return null;
+            });
+
+            SavedBiomeUnavailableException thrown = assertThrows(SavedBiomeUnavailableException.class,
+                    () -> new ModdedChunkUpdateService().runUpdatePass(
+                            engine, new ModdedPlatformWorld(level), 0, 0, chunk));
+
+            assertSame(loading, thrown);
+        }
+        assertFalse(chunk.deleted());
+        verify(chunk.slice).set(1, 5, 1, null);
+        verify(chunk.slice, never()).set(2, 5, 2, null);
+    }
+
+    @Test
+    public void loadingSavedBiomeLeavesTheChunkUnetchedWithoutAnErrorAndRetriesOnTheNextPass() {
+        ChestUpdateMantleChunk chunk = new ChestUpdateMantleChunk();
+        Engine engine = updateEngine(chunk);
+        NativeWorld level = chestLevel();
+        AtomicInteger loadingAttempts = new AtomicInteger();
+        ModdedChunkUpdateService service = new ModdedChunkUpdateService();
+
+        try (MockedStatic<ModdedLootApplier> loot = mockStatic(ModdedLootApplier.class);
+             MockedStatic<IrisLogging> logging = mockStatic(IrisLogging.class)) {
+            loot.when(() -> ModdedLootApplier.apply(any(), any(), any(), any(), any())).thenAnswer((InvocationOnMock invocation) -> {
+                NativeBlockPoint position = invocation.getArgument(2);
+                if (position.x() == 2 && loadingAttempts.getAndIncrement() == 0) {
+                    throw new SavedBiomeUnavailableException("Saved biome information is loading at chunk 0,0.", true);
+                }
+                return null;
+            });
+
+            service.updateRegeneratedChunk(engine, level, 0, 0);
+
+            assertFalse(chunk.isFlagged(MantleFlag.ETCHED));
+            assertFalse(chunk.isFlagged(MantleFlag.UPDATE));
+            assertFalse(chunk.deleted());
+            logging.verify(() -> IrisLogging.reportError(any(Throwable.class)), never());
+            logging.verify(() -> IrisLogging.reportError(anyString(), any(Throwable.class)), never());
+
+            service.updateRegeneratedChunk(engine, level, 0, 0);
+
+            assertTrue(chunk.isFlagged(MantleFlag.ETCHED));
+            assertTrue(chunk.deleted());
+        }
+    }
+
+    @Test
+    public void permanentSavedBiomeUnavailabilityCompletesThePassWithAWarning() {
+        ChestUpdateMantleChunk chunk = new ChestUpdateMantleChunk();
+        Engine engine = updateEngine(chunk);
+        NativeWorld level = chestLevel();
+        String reason = "This chunk has no exact saved Iris biome assignment for generation 3.";
+
+        try (MockedStatic<ModdedLootApplier> loot = mockStatic(ModdedLootApplier.class);
+             MockedStatic<IrisLogging> logging = mockStatic(IrisLogging.class)) {
+            loot.when(() -> ModdedLootApplier.apply(any(), any(), any(), any(), any())).thenAnswer((InvocationOnMock invocation) -> {
+                NativeBlockPoint position = invocation.getArgument(2);
+                if (position.x() == 2) {
+                    throw new SavedBiomeUnavailableException(reason, false);
+                }
+                return null;
+            });
+
+            new ModdedChunkUpdateService().updateRegeneratedChunk(engine, level, 0, 0);
+
+            assertTrue(chunk.isFlagged(MantleFlag.ETCHED));
+            assertTrue(chunk.deleted());
+            logging.verify(() -> IrisLogging.warnOnce(anyString(), contains(reason)));
+            logging.verify(() -> IrisLogging.reportError(any(Throwable.class)), never());
+            logging.verify(() -> IrisLogging.reportError(anyString(), any(Throwable.class)), never());
+        }
+    }
+
+    @Test
+    public void failedChunkDoesNotStopTheLevelPassForItsOtherChunks() {
+        IrisSettings previousSettings = IrisSettings.settings;
+        IrisSettings.settings = new IrisSettings();
+        FailingMantleChunk failing = new FailingMantleChunk();
+        ChestUpdateMantleChunk healthy = new ChestUpdateMantleChunk();
+        @SuppressWarnings("unchecked")
+        Mantle<Matter> mantle = mock(Mantle.class);
+        when(mantle.isChunkLoaded(anyInt(), anyInt())).thenReturn(true);
+        when(mantle.useChunk(0, 0)).thenAnswer((InvocationOnMock invocation) -> failing.use());
+        when(mantle.useChunk(4, 0)).thenAnswer((InvocationOnMock invocation) -> healthy.use());
+        Engine engine = engineWith(mantle);
+        NativeWorld level = chestLevel();
+        NativeModdedServer server = mock(NativeModdedServer.class);
+        when(server.worlds()).thenReturn(List.of(level));
+        IrisModdedChunkGenerator generator = mock(IrisModdedChunkGenerator.class);
+        when(generator.engineIfBound()).thenReturn(engine);
+
+        try (MockedStatic<NativeWorldGenerators> generators = mockStatic(NativeWorldGenerators.class);
+             MockedStatic<ModdedLootApplier> loot = mockStatic(ModdedLootApplier.class);
+             MockedStatic<IrisLogging> logging = mockStatic(IrisLogging.class);
+             MockedConstruction<NativeWorldMaintenance> maintenance = mockConstruction(NativeWorldMaintenance.class,
+                     (NativeWorldMaintenance mocked, MockedConstruction.Context context) -> {
+                         when(mocked.hasForcedChunks()).thenReturn(true);
+                         doAnswer((InvocationOnMock invocation) -> {
+                             LongConsumer action = invocation.getArgument(0);
+                             action.accept(0L);
+                             action.accept(4L);
+                             return null;
+                         }).when(mocked).forEachForcedChunk(any(LongConsumer.class));
+                     })) {
+            generators.when(() -> NativeWorldGenerators.find(level, IrisModdedChunkGenerator.class)).thenReturn(generator);
+
+            new ModdedChunkUpdateService().onServerTick(server);
+
+            assertFalse(failing.isFlagged(MantleFlag.ETCHED));
+            assertTrue(healthy.isFlagged(MantleFlag.ETCHED));
+            assertTrue(healthy.deleted());
+            logging.verify(() -> IrisLogging.errorOnce(anyString(), anyString()));
+        } finally {
+            IrisSettings.settings = previousSettings;
+        }
+    }
+
     @Test
     public void scansWhenPlayersArePresent() {
         assertTrue(ModdedChunkUpdateService.hasUpdateTargets(true, false));
@@ -166,6 +337,94 @@ public class ModdedChunkUpdateServiceTest {
         }
     }
 
+    private static final class ChestUpdateMantleChunk extends MantleChunk<Matter> {
+        @SuppressWarnings("unchecked")
+        private final MatterSlice<MatterUpdate> slice = mock(MatterSlice.class);
+        private final Matter section = mock(Matter.class);
+        private boolean deleted;
+
+        private ChestUpdateMantleChunk() {
+            super(1, 0, 0, emptyAdapter(), MantleHooks.NONE);
+            when(section.hasSlice(MatterUpdate.class)).thenReturn(true);
+            when(section.getSlice(MatterUpdate.class)).thenReturn(slice);
+        }
+
+        @Override
+        public Matter get(int index) {
+            return section;
+        }
+
+        @Override
+        public <T> void iterate(
+                Class<T> type,
+                Consumer4<Integer, Integer, Integer, T> iterator
+        ) {
+            if (type == MatterUpdate.class) {
+                iterator.accept(1, 5, 1, type.cast(UpdateMatter.ON));
+                iterator.accept(2, 5, 2, type.cast(UpdateMatter.ON));
+            }
+        }
+
+        @Override
+        public void deleteSlices(Class<?> type) {
+            if (type == MatterUpdate.class) {
+                deleted = true;
+            }
+        }
+
+        private boolean deleted() {
+            return deleted;
+        }
+    }
+
+    private static Engine updateEngine(ChestUpdateMantleChunk chunk) {
+        @SuppressWarnings("unchecked")
+        Mantle<Matter> mantle = mock(Mantle.class);
+        when(mantle.isChunkLoaded(0, 0)).thenReturn(true);
+        when(mantle.hasFlag(0, 0, MantleFlag.ETCHED)).thenAnswer((InvocationOnMock invocation) -> chunk.isFlagged(MantleFlag.ETCHED));
+        when(mantle.useChunk(0, 0)).thenAnswer((InvocationOnMock invocation) -> chunk.use());
+        return engineWith(mantle);
+    }
+
+    private static Engine engineWith(Mantle<Matter> mantle) {
+        IrisWorld world = mock(IrisWorld.class);
+        when(world.minHeight()).thenReturn(-64);
+        EngineMantle engineMantle = mock(EngineMantle.class);
+        when(engineMantle.getMantle()).thenReturn(mantle);
+        Engine engine = mock(Engine.class);
+        when(engine.getWorld()).thenReturn(world);
+        when(engine.getMetrics()).thenReturn(new EngineMetrics(8));
+        when(engine.getMantle()).thenReturn(engineMantle);
+        return engine;
+    }
+
+    private static NativeWorld chestLevel() {
+        NativeBlockState chest = mock(NativeBlockState.class);
+        when(chest.isStorage()).thenReturn(true);
+        when(chest.isStorageChest()).thenReturn(true);
+        NativeWorld level = mock(NativeWorld.class);
+        when(level.name()).thenReturn("example:updates");
+        when(level.minHeight()).thenReturn(-64);
+        when(level.maxHeight()).thenReturn(320);
+        when(level.isChunkLoaded(anyInt(), anyInt())).thenReturn(true);
+        when(level.getBlock(anyInt(), anyInt(), anyInt())).thenReturn(chest);
+        return level;
+    }
+
+    private static final class FailingMantleChunk extends MantleChunk<Matter> {
+        private FailingMantleChunk() {
+            super(1, 0, 0, emptyAdapter(), MantleHooks.NONE);
+        }
+
+        @Override
+        public <T> void iterate(
+                Class<T> type,
+                Consumer4<Integer, Integer, Integer, T> iterator
+        ) {
+            throw new IllegalStateException("corrupt " + type.getSimpleName() + " slice");
+        }
+    }
+
     @SuppressWarnings("unchecked")
     private static MantleDataAdapter<Matter> emptyAdapter() {
         return (MantleDataAdapter<Matter>) Proxy.newProxyInstance(

core/src/main/java/art/arcane/iris/generation/biome/IrisBiomeLayerGenerator.java

@@ -24,6 +24,7 @@ import art.arcane.iris.structure.object.IrisObject;
 import art.arcane.iris.structure.object.IrisObjectPlacement;
 
 import art.arcane.iris.pack.loading.IrisData;
+import art.arcane.iris.generation.runtime.GenerationFailures;
 import art.arcane.iris.generation.runtime.IrisComplex;
 import art.arcane.iris.generation.runtime.Engine;
 import art.arcane.iris.spi.IrisLogging;
@@ -233,6 +234,7 @@ final class IrisBiomeLayerGenerator {
                 data.add(layer.get(random, layerIndex + offset,
                         (wx + offset) / zoom, offset, (wz - offset) / zoom, rdata));
             } catch (Throwable error) {
+                GenerationFailures.rethrowEngineFailure(error);
                 IrisLogging.reportError(error);
             }
         }
@@ -330,6 +332,7 @@ final class IrisBiomeLayerGenerator {
                 blocks.add(layer.get(random, layerIndex + offset,
                         (x + offset) / zoom, offset, (z - offset) / zoom, data));
             } catch (Throwable error) {
+                GenerationFailures.rethrowEngineFailure(error);
                 IrisLogging.reportError(error);
             }
         }

core/src/main/java/art/arcane/iris/generation/decoration/DecoratorCore.java

@@ -18,6 +18,7 @@
 
 package art.arcane.iris.generation.decoration;
 
+import art.arcane.iris.generation.runtime.GenerationFailures;
 import art.arcane.iris.pack.loading.IrisData;
 import art.arcane.iris.generation.mantle.EngineMantle;
 import art.arcane.iris.generation.biome.IrisBiome;
@@ -89,6 +90,7 @@ final class DecoratorCore {
                     }
                 }
             } catch (Throwable e) {
+                GenerationFailures.rethrowEngineFailure(e);
                 IrisLogging.reportError(e);
             }
         }
@@ -163,6 +165,7 @@ final class DecoratorCore {
                 data.set(x, lowerY, z, lower);
                 data.set(x, upperY, z, upper);
             } catch (Throwable e) {
+                GenerationFailures.rethrowEngineFailure(e);
                 IrisLogging.reportError(e);
             }
             return;
@@ -356,6 +359,7 @@ final class DecoratorCore {
                 data.set(xf, lowerY, zf, lower);
                 data.set(xf, upperY, zf, upper);
             } catch (Throwable e) {
+                GenerationFailures.rethrowEngineFailure(e);
                 IrisLogging.reportError(e);
             }
             return;

core/src/main/java/art/arcane/iris/generation/hydrology/HydrologyTileCache.java

@@ -1,5 +1,6 @@
 package art.arcane.iris.generation.hydrology;
 
+import art.arcane.iris.generation.runtime.GenerationClosedException;
 import art.arcane.iris.spi.IrisLogging;
 import art.arcane.iris.generation.concurrent.MultiBurst;
 import art.arcane.iris.generation.stream.ProvisionalSampling;
@@ -713,7 +714,7 @@ public final class HydrologyTileCache implements AutoCloseable {
 
     public void enableSharedCache(SharedCacheScope scope, Path persistentRoot) {
         if (closed.get()) {
-            throw new IllegalStateException("Hydrology tile cache is closed.");
+            throw new GenerationClosedException("Hydrology tile cache is closed.");
         }
         sharedCacheScope = Objects.requireNonNull(scope, "scope");
         persistentStore = persistentRoot == null

core/src/main/java/art/arcane/iris/generation/mantle/MantleFloatingObjectComponent.java

@@ -20,6 +20,7 @@ package art.arcane.iris.generation.mantle;
 
 import java.io.UncheckedIOException;
 import art.arcane.iris.pack.loading.IrisData;
+import art.arcane.iris.generation.runtime.GenerationFailures;
 import art.arcane.iris.generation.runtime.IrisComplex;
 import art.arcane.iris.generation.cache.Cache;
 import art.arcane.iris.generation.biome.FloatingIslandSample;
@@ -231,6 +232,7 @@ public class MantleFloatingObjectComponent extends IrisMantleComponent {
                 throw failure;
             } catch (Throwable e) {
                 transaction.discard();
+                GenerationFailures.rethrowEngineFailure(e);
                 IrisLogging.reportError(e);
             }
         }
@@ -326,6 +328,7 @@ public class MantleFloatingObjectComponent extends IrisMantleComponent {
                 throw failure;
             } catch (Throwable e) {
                 transaction.discard();
+                GenerationFailures.rethrowEngineFailure(e);
                 IrisLogging.reportError(e);
             }
         }
@@ -438,6 +441,7 @@ public class MantleFloatingObjectComponent extends IrisMantleComponent {
                 throw failure;
             } catch (Throwable e) {
                 transaction.discard();
+                GenerationFailures.rethrowEngineFailure(e);
                 IrisLogging.reportError(e);
             }
         }
@@ -611,11 +615,13 @@ public class MantleFloatingObjectComponent extends IrisMantleComponent {
                             maxObjectExtent = Math.max(maxObjectExtent, computePlacementRadius(entry.resolveBottomObjects(target), data, sizeCache, warnedLargeObjects));
                         }
                     } catch (Throwable e) {
+                        GenerationFailures.rethrowEngineFailure(e);
                         IrisLogging.reportError(e);
                     }
                 }
             }
         } catch (Throwable e) {
+            GenerationFailures.rethrowEngineFailure(e);
             IrisLogging.reportError(e);
         }
         return maxObjectExtent;
@@ -649,6 +655,7 @@ public class MantleFloatingObjectComponent extends IrisMantleComponent {
                     }
                     radius = Math.max(radius, reach);
                 } catch (Throwable e) {
+                    GenerationFailures.rethrowEngineFailure(e);
                     IrisLogging.reportError(e);
                 }
             }

core/src/main/java/art/arcane/iris/generation/mantle/MantleObjectComponent.java

@@ -22,6 +22,7 @@ package art.arcane.iris.generation.mantle;
 import art.arcane.iris.configuration.IrisSettings;
 import art.arcane.iris.generation.block.B;
 import art.arcane.iris.generation.cache.Cache;
+import art.arcane.iris.generation.runtime.GenerationFailures;
 import art.arcane.iris.generation.runtime.IrisComplex;
 import art.arcane.iris.generation.runtime.UpperDimensionContext;
 import art.arcane.iris.generation.runtime.Engine;
@@ -475,6 +476,7 @@ public class MantleObjectComponent extends IrisMantleComponent {
                     nullObjects += result.nullObjects();
                     errors += result.errors();
                 } catch (Throwable e) {
+                    GenerationFailures.rethrowEngineFailure(e);
                     errors++;
                     IrisLogging.reportError(e);
                     IrisLogging.error("Failed to place objects in the following biome: " + surfaceBiome.getName());
@@ -508,6 +510,7 @@ public class MantleObjectComponent extends IrisMantleComponent {
                     nullObjects += result.nullObjects();
                     errors += result.errors();
                 } catch (Throwable e) {
+                    GenerationFailures.rethrowEngineFailure(e);
                     errors++;
                     IrisLogging.reportError(e);
                     IrisLogging.error("Failed to place cave objects in the following biome: " + caveBiome.getName());
@@ -538,6 +541,7 @@ public class MantleObjectComponent extends IrisMantleComponent {
                     nullObjects += result.nullObjects();
                     errors += result.errors();
                 } catch (Throwable e) {
+                    GenerationFailures.rethrowEngineFailure(e);
                     errors++;
                     IrisLogging.reportError(e);
                     IrisLogging.error("Failed to place objects in the following region: " + region.getName());
@@ -571,6 +575,7 @@ public class MantleObjectComponent extends IrisMantleComponent {
                     nullObjects += result.nullObjects();
                     errors += result.errors();
                 } catch (Throwable e) {
+                    GenerationFailures.rethrowEngineFailure(e);
                     errors++;
                     IrisLogging.reportError(e);
                     IrisLogging.error("Failed to place cave objects in the following region: " + region.getName());
@@ -760,6 +765,7 @@ public class MantleObjectComponent extends IrisMantleComponent {
                                 + " commit=" + commitResult);
                     }
                 } catch (Throwable e) {
+                    GenerationFailures.rethrowEngineFailure(e);
                     IrisLogging.reportError(e);
                     IrisLogging.error("Failed to place procedural object '" + p.getName() + "' in " + scope);
                 }
@@ -988,6 +994,7 @@ public class MantleObjectComponent extends IrisMantleComponent {
                             + " density=" + density);
                 }
             } catch (Throwable e) {
+                GenerationFailures.rethrowEngineFailure(e);
                 errors++;
                 IrisLogging.reportError(e);
                 IrisLogging.error("Regen object placement exception: chunk=" + chunkX + "," + chunkZ
@@ -1192,6 +1199,7 @@ public class MantleObjectComponent extends IrisMantleComponent {
                             + " density=" + density);
                 }
             } catch (Throwable e) {
+                GenerationFailures.rethrowEngineFailure(e);
                 errors++;
                 IrisLogging.reportError(e);
                 IrisLogging.error("Regen cave object placement exception: chunk=" + metricChunkX + "," + metricChunkZ
@@ -1251,6 +1259,7 @@ public class MantleObjectComponent extends IrisMantleComponent {
                 try {
                     placeUpperObject(writer, rng, chunkX, chunkZ, i, upperCtx, complex, forcePlace, traceRegen, "upper-biome-surface");
                 } catch (Throwable e) {
+                    GenerationFailures.rethrowEngineFailure(e);
                     IrisLogging.reportError(e);
                     IrisLogging.error("Failed to place upper-dimension objects in biome " + upperBiome.getName()
                             + ": " + i.getPlace().toString(", ") + " (" + e.getClass().getSimpleName() + ")");
@@ -1266,6 +1275,7 @@ public class MantleObjectComponent extends IrisMantleComponent {
                 try {
                     placeUpperObject(writer, rng, chunkX, chunkZ, i, upperCtx, complex, forcePlace, traceRegen, "upper-region-surface");
                 } catch (Throwable e) {
+                    GenerationFailures.rethrowEngineFailure(e);
                     IrisLogging.reportError(e);
                     IrisLogging.error("Failed to place upper-dimension objects in region " + upperRegion.getName()
                             + ": " + i.getPlace().toString(", ") + " (" + e.getClass().getSimpleName() + ")");
@@ -1790,6 +1800,7 @@ public class MantleObjectComponent extends IrisMantleComponent {
                     }
                     radius = Math.max(radius, reach);
                 } catch (Throwable e) {
+                    GenerationFailures.rethrowEngineFailure(e);
                     IrisLogging.reportError(e);
                 }
             }

core/src/main/java/art/arcane/iris/generation/mantle/MantleWriter.java

@@ -29,6 +29,7 @@ import art.arcane.iris.integration.Identifier;
 import art.arcane.iris.world.WorldMaintenance;
 import art.arcane.iris.pack.loading.IrisData;
 import art.arcane.iris.generation.runtime.Engine;
+import art.arcane.iris.generation.runtime.GenerationFailures;
 import art.arcane.iris.generation.runtime.IrisComplex;
 import art.arcane.iris.generation.terrain.Terrain3DColumn;
 import art.arcane.iris.world.history.TransitionGenerationPlan;
@@ -1495,6 +1496,7 @@ public class MantleWriter implements ObjectPassPlacer, AutoCloseable {
         try {
             setData(pos.getX(), pos.getY(), pos.getZ(), data);
         } catch (Throwable e) {
+            GenerationFailures.rethrowEngineFailure(e);
             // Reached per position while an object writes past the edge of the writer window, which is
             // how a large object is clipped. Nothing here is actionable from outside the engine.
             IrisLogging.debug("No set? " + data.toString() + " for " + pos.toString());

core/src/main/java/art/arcane/iris/generation/mode/ModeOverworld.java

@@ -23,7 +23,6 @@ import art.arcane.iris.generation.stage.IrisDecorantActuator;
 import art.arcane.iris.generation.stage.IrisTerrainNormalActuator;
 import art.arcane.iris.generation.runtime.Engine;
 import art.arcane.iris.generation.runtime.EngineMode;
-import art.arcane.iris.generation.runtime.EnginePlatformHooks;
 import art.arcane.iris.generation.runtime.EngineStage;
 import art.arcane.iris.generation.runtime.IrisEngineMode;
 import art.arcane.iris.generation.stage.IrisCarveModifier;
@@ -32,17 +31,10 @@ import art.arcane.iris.generation.stage.IrisDepositModifier;
 import art.arcane.iris.generation.stage.IrisFloatingChildBiomeModifier;
 import art.arcane.iris.generation.stage.IrisPerfectionModifier;
 import art.arcane.iris.generation.stage.IrisPostModifier;
-import art.arcane.iris.spi.IrisLogging;
-
-import java.util.concurrent.atomic.AtomicLong;
 
 public class ModeOverworld extends IrisEngineMode implements EngineMode {
-    private static final AtomicLong lastMaintenanceBypassLog = new AtomicLong(0L);
-    private final EnginePlatformHooks platformHooks;
-
     public ModeOverworld(Engine engine) {
         super(engine);
-        platformHooks = engine.getPlatformHooks();
         IrisTerrainNormalActuator terrain = new IrisTerrainNormalActuator(getEngine());
         IrisBiomeActuator biome = new IrisBiomeActuator(getEngine());
         IrisDecorantActuator decorant = new IrisDecorantActuator(getEngine());
@@ -53,51 +45,17 @@ public class ModeOverworld extends IrisEngineMode implements EngineMode {
         IrisCustomModifier custom = new IrisCustomModifier(getEngine());
         IrisFloatingChildBiomeModifier floatingChildBiomes = new IrisFloatingChildBiomeModifier(getEngine());
         EngineStage sBiome = (x, z, k, p, m, c) -> biome.actuate(x, z, p, m, c);
-        EngineStage sGenMatter = (x, z, k, p, m, c) -> {
-            if (shouldBypassMantleStages()) {
-                return;
-            }
-            generateTerrainMatter(
-                    x >> 4,
-                    z >> 4,
-                    m || getEngine().isStudio(),
-                    c);
-        };
+        EngineStage sGenMatter = (x, z, k, p, m, c) -> generateTerrainMatter(x >> 4, z >> 4, m || getEngine().isStudio(), c);
         EngineStage sTerrain = (x, z, k, p, m, c) -> terrain.actuate(x, z, k, m, c);
         EngineStage sDecorant = (x, z, k, p, m, c) -> decorant.actuate(x, z, k, m, c);
-        EngineStage sCave = (x, z, k, p, m, c) -> {
-            if (shouldBypassMantleStages()) {
-                return;
-            }
-            cave.modify(x >> 4, z >> 4, k, m, c);
-        };
-        EngineStage sDeposit = (x, z, k, p, m, c) -> {
-            if (shouldBypassMantleStages()) {
-                return;
-            }
-            deposit.modify(x, z, k, m, c);
-        };
-        EngineStage sPost = (x, z, k, p, m, c) -> {
-            if (shouldBypassMantleStages()) {
-                return;
-            }
-            post.modify(x, z, k, m, c);
-        };
-        EngineStage sInsertMatter = (x, z, K, p, m, c) -> {
-            if (shouldBypassMantleStages()) {
-                return;
-            }
-            getMantle().insertMatter(x >> 4, z >> 4, K, m, c);
-        };
+        EngineStage sCave = (x, z, k, p, m, c) -> cave.modify(x >> 4, z >> 4, k, m, c);
+        EngineStage sDeposit = (x, z, k, p, m, c) -> deposit.modify(x, z, k, m, c);
+        EngineStage sPost = (x, z, k, p, m, c) -> post.modify(x, z, k, m, c);
+        EngineStage sInsertMatter = (x, z, K, p, m, c) -> getMantle().insertMatter(x >> 4, z >> 4, K, m, c);
         EngineStage sFloatingTerrainSolid = (x, z, k, p, m, c) -> floatingChildBiomes.modify(x, z, k, m, c);
         EngineStage sFloatingDecorate = (x, z, k, p, m, c) -> floatingChildBiomes.decorateColumns(x, z, k, m, c);
         EngineStage sPerfection = (x, z, k, p, m, c) -> perfection.modify(x, z, k, m, c);
-        EngineStage sCustom = (x, z, k, p, m, c) -> {
-            if (shouldBypassMantleStages()) {
-                return;
-            }
-            custom.modify(x, z, k, m, c);
-        };
+        EngineStage sCustom = (x, z, k, p, m, c) -> custom.modify(x, z, k, m, c);
 
         // Matter runs on the calling thread so its window fans out across the burst pool (a pool
         // thread would run every chunk of the window inline) while biome and terrain run alongside.
@@ -114,11 +72,7 @@ public class ModeOverworld extends IrisEngineMode implements EngineMode {
         // the surface sInsertMatter writes), so parallel order is scheduler-dependent. The
         // production path already runs them inline in this order; sequential registration
         // makes studio (the only multicore path) match production and the goldenhash baseline.
-        registerStage((x, z, k, p, m, c) -> {
-            if (!shouldBypassMantleStages()) {
-                generateContentMatter(x >> 4, z >> 4, m || getEngine().isStudio(), c);
-            }
-        });
+        registerStage((x, z, k, p, m, c) -> generateContentMatter(x >> 4, z >> 4, m || getEngine().isStudio(), c));
         registerStage(sDeposit);
         registerStage(sInsertMatter);
         registerStage(sDecorant);
@@ -128,17 +82,4 @@ public class ModeOverworld extends IrisEngineMode implements EngineMode {
             registerStage(sCustom);
         }
     }
-
-    private boolean shouldBypassMantleStages() {
-        boolean active = platformHooks.shouldBypassMantleStages(getEngine());
-        if (active) {
-            long now = System.currentTimeMillis();
-            long last = lastMaintenanceBypassLog.get();
-            if (now - last >= 5000L && lastMaintenanceBypassLog.compareAndSet(last, now)) {
-                IrisLogging.info("Maintenance regen bypass: skipping mantle-backed overworld stages for Folia safety.");
-            }
-        }
-        return active;
-    }
-
 }

core/src/main/java/art/arcane/iris/generation/runtime/DimensionTerrainContext.java

@@ -335,6 +335,7 @@ public final class DimensionTerrainContext implements DataProvider {
                         }
                         return new NoiseBounds(minimum, maximum);
                     } catch (Throwable e) {
+                        GenerationFailures.rethrowEngineFailure(e);
                         IrisLogging.reportError(e);
                         return ZERO_NOISE_BOUNDS;
                     }

core/src/main/java/art/arcane/iris/generation/runtime/EnginePlatformHooks.java

@@ -94,7 +94,11 @@ public interface EnginePlatformHooks {
         return false;
     }
 
-    default boolean shouldBypassMantleStages(Engine engine) {
+    /**
+     * True while world maintenance forbids the mantle-backed stages. Generating without them would persist a
+     * chunk with no objects, caves or deposits, so the engine refuses the chunk instead.
+     */
+    default boolean shouldRefuseGeneration(Engine engine) {
         return false;
     }
 

core/src/main/java/art/arcane/iris/generation/runtime/GenerationClosedException.java

@@ -0,0 +1,7 @@
+package art.arcane.iris.generation.runtime;
+
+public final class GenerationClosedException extends IllegalStateException {
+    public GenerationClosedException(String message) {
+        super(message);
+    }
+}

core/src/main/java/art/arcane/iris/generation/runtime/GenerationFailures.java

@@ -0,0 +1,73 @@
+package art.arcane.iris.generation.runtime;
+
+import art.arcane.iris.world.history.SavedBiomeUnavailableException;
+import art.arcane.volmlib.util.mantle.MantleClosedException;
+
+import java.io.InterruptedIOException;
+import java.nio.channels.ClosedChannelException;
+import java.util.concurrent.CancellationException;
+import java.util.concurrent.RejectedExecutionException;
+import java.util.concurrent.TimeoutException;
+import java.util.function.Predicate;
+
+/**
+ * Separates failures of the engine, its mantle, generation history, executors or the JVM from failures of one
+ * piece of content. Content loops (objects, decorators, layers) may skip a failed item because every rebuild
+ * skips it the same way. An engine failure is transient, so skipping would cache and persist terrain that a
+ * healthy engine never produces: it must fail the whole chunk instead.
+ */
+public final class GenerationFailures {
+    private static final int MAXIMUM_CAUSE_DEPTH = 32;
+
+    private GenerationFailures() {
+    }
+
+    public static boolean isEngineFailure(Throwable failure) {
+        return isShutdownFailure(failure) || hasCause(failure, (Throwable cause) -> cause instanceof Error
+                || cause instanceof WrongEngineBroException
+                || cause instanceof SavedBiomeUnavailableException unavailable && unavailable.isLoading()
+                || cause instanceof TimeoutException);
+    }
+
+    /**
+     * The engine failures that only mean a runtime, pool or thread is stopping. They say nothing about the world, so
+     * nothing may remember them against it once the next runtime is up.
+     */
+    public static boolean isShutdownFailure(Throwable failure) {
+        return Thread.currentThread().isInterrupted() || hasCause(failure, (Throwable cause) ->
+                cause instanceof GenerationClosedException
+                        || cause instanceof MantleClosedException
+                        || cause instanceof GenerationSessionException session && session.isExpectedTeardown()
+                        || cause instanceof InterruptedException
+                        || cause instanceof InterruptedIOException
+                        || cause instanceof ClosedChannelException
+                        || cause instanceof RejectedExecutionException
+                        || cause instanceof CancellationException);
+    }
+
+    private static boolean hasCause(Throwable failure, Predicate<Throwable> match) {
+        Throwable current = failure;
+        for (int depth = 0; current != null && depth < MAXIMUM_CAUSE_DEPTH; depth++, current = current.getCause()) {
+            if (match.test(current)) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    public static void rethrowEngineFailure(Throwable failure) {
+        if (!isEngineFailure(failure)) {
+            return;
+        }
+        if (failure instanceof RuntimeException runtimeFailure) {
+            throw runtimeFailure;
+        }
+        if (failure instanceof Error error) {
+            throw error;
+        }
+        if (failure instanceof InterruptedException) {
+            Thread.currentThread().interrupt();
+        }
+        throw new IllegalStateException("Iris generation stopped: " + failure, failure);
+    }
+}

core/src/main/java/art/arcane/iris/generation/runtime/IrisComplex.java

@@ -2044,6 +2044,7 @@ public class IrisComplex implements DataProvider {
                 GeneratorBounds bounds = complex.resolveGeneratorBounds(engine, generators, bx, cachedBounds, localBounds);
                 return bounds.noiseBounds;
             } catch (Throwable e) {
+                GenerationFailures.rethrowEngineFailure(e);
                 long now = System.currentTimeMillis();
                 long last = lastBoundsFailureLog.get();
                 // The five second gate keeps this off the hot path; the once key keeps it out of a log

core/src/main/java/art/arcane/iris/generation/runtime/IrisEngine.java

@@ -86,6 +86,8 @@ import java.util.function.Supplier;
 @Data
 public class IrisEngine implements Engine {
     static final long SESSION_DRAIN_TIMEOUT_MILLIS = 15000L;
+    private static final long MAINTENANCE_REFUSAL_WARNING_MILLIS = 5000L;
+    private static final AtomicLong lastMaintenanceRefusalWarning = new AtomicLong();
 
     private final AtomicInteger bud;
     private final AtomicInteger buds;
@@ -1083,10 +1085,10 @@ public class IrisEngine implements Engine {
                 throw new IllegalArgumentException("Generation runtime binding belongs to a different Iris engine.");
             }
             if (retiringGenerationRuntimes.contains(required.runtime)) {
-                throw new IllegalStateException("Iris generation runtime binding is retiring.");
+                throw new GenerationClosedException("Iris generation runtime binding is retiring.");
             }
             if (!isGenerationRuntimeBindingLive(required)) {
-                throw new IllegalStateException("Iris generation runtime binding is closed or no longer owned.");
+                throw new GenerationClosedException("Iris generation runtime binding is closed or no longer owned.");
             }
             return threadState.open(required);
         }
@@ -1485,6 +1487,9 @@ public class IrisEngine implements Engine {
     @Override
     public void generate(int x, int z, Hunk<NativeBlockState> vblocks, Hunk<NativeBiome> vbiomes, boolean multicore) throws WrongEngineBroException {
         awaitGenerationCacheWarm();
+        if (platformHooks.shouldRefuseGeneration(this)) {
+            refuseMaintenanceGeneration(x >> 4, z >> 4);
+        }
         try (GenerationHistoryRuntimeRouter.CoordinateScope historyScope =
                      openGenerationHistoryCoordinateScope(x, z);
              GenerationSessionLease lease = acquireGenerationLease("chunk_generate");
@@ -1505,20 +1510,17 @@ public class IrisEngine implements Engine {
                 activeMode.generate(x, z, blocks, vbiomes, multicore, lease.sessionId());
             }
 
-            boolean skipRealFlag = platformHooks.shouldBypassMantleStages(this);
-            if (!skipRealFlag) {
-                MantleChunk<Matter> chunk = getMantle().getMantle().useChunk(x >> 4, z >> 4);
-                try {
-                    synchronized (chunk) {
-                        Matter section = chunk.get(0);
-                        if (section != null) {
-                            section.deleteSlice(ObjectContinuationBundle.class);
-                        }
-                        chunk.flag(MantleFlag.REAL, true);
+            MantleChunk<Matter> chunk = getMantle().getMantle().useChunk(x >> 4, z >> 4);
+            try {
+                synchronized (chunk) {
+                    Matter section = chunk.get(0);
+                    if (section != null) {
+                        section.deleteSlice(ObjectContinuationBundle.class);
                     }
-                } finally {
-                    chunk.release();
+                    chunk.flag(MantleFlag.REAL, true);
                 }
+            } finally {
+                chunk.release();
             }
             getMetrics().getTotal().put(p.getMilliseconds());
             generated.incrementAndGet();
@@ -1538,6 +1540,17 @@ public class IrisEngine implements Engine {
         }
     }
 
+    private void refuseMaintenanceGeneration(int chunkX, int chunkZ) throws GenerationSessionException {
+        long now = System.currentTimeMillis();
+        long last = lastMaintenanceRefusalWarning.get();
+        if (now - last >= MAINTENANCE_REFUSAL_WARNING_MILLIS && lastMaintenanceRefusalWarning.compareAndSet(last, now)) {
+            IrisLogging.warn("Iris refused chunk " + chunkX + "," + chunkZ + " in " + getWorld().name()
+                    + ": world maintenance forbids mantle generation, the chunk stays ungenerated");
+        }
+        throw new GenerationSessionException("Iris refused chunk " + chunkX + "," + chunkZ + " in "
+                + getWorld().name() + " during world maintenance.", true);
+    }
+
     @Override
     public GenerationSessionManager getGenerationSessions() {
         return generationSessions;
@@ -1682,7 +1695,7 @@ public class IrisEngine implements Engine {
 
     void requireRunning(String operation) {
         if (closed || closing.get() || lifecycleState != LifecycleState.RUNNING || runtime == null) {
-            throw new IllegalStateException("Cannot " + operation + " while Iris engine " + getWorld().name()
+            throw new GenerationClosedException("Cannot " + operation + " while Iris engine " + getWorld().name()
                     + " is " + lifecycleState.name().toLowerCase() + ".");
         }
     }

core/src/main/java/art/arcane/iris/generation/stage/IrisFloatingChildBiomeModifier.java

@@ -21,6 +21,7 @@ package art.arcane.iris.generation.stage;
 
 import art.arcane.iris.pack.loading.IrisData;
 import art.arcane.iris.generation.runtime.DimensionStackLayout;
+import art.arcane.iris.generation.runtime.GenerationFailures;
 import art.arcane.iris.generation.runtime.IrisComplex;
 import art.arcane.iris.generation.decoration.FloatingDecorator;
 import art.arcane.iris.generation.decoration.IrisSeaSurfaceDecorator;
@@ -100,6 +101,7 @@ public class IrisFloatingChildBiomeModifier extends EngineAssignedModifier<Nativ
                 try {
                     generated.add(layer.get(random.nextParallelRNG(i + j), (wx + j) / layer.getZoom(), j, (wz - j) / layer.getZoom(), data));
                 } catch (Throwable e) {
+                    GenerationFailures.rethrowEngineFailure(e);
                     IrisLogging.reportError(e);
                 }
             }
@@ -345,6 +347,7 @@ public class IrisFloatingChildBiomeModifier extends EngineAssignedModifier<Nativ
                             RNG colRng = rng.nextParallelRNG((int) FloatingIslandSample.columnSeed(baseSeed, wx, wz));
                             FloatingDecorator.decorateColumn(getEngine(), target, IrisDecorationPart.NONE, xf, zf, wx, wz, topY, max, output, colRng, NOOP_DECORATION_MISS);
                         } catch (Throwable e) {
+                            GenerationFailures.rethrowEngineFailure(e);
                             IrisLogging.reportError(e);
                         }
                     }
@@ -377,6 +380,7 @@ public class IrisFloatingChildBiomeModifier extends EngineAssignedModifier<Nativ
                         try {
                             seaSurfaceDecorator.decorate(xf, zf, wx, wx + 1, wx - 1, wz, wz + 1, wz - 1, output, target, fluidTopY, chunkHeight);
                         } catch (Throwable e) {
+                            GenerationFailures.rethrowEngineFailure(e);
                             IrisLogging.reportError(e);
                         }
                     }
@@ -432,6 +436,7 @@ public class IrisFloatingChildBiomeModifier extends EngineAssignedModifier<Nativ
                 context.floatingBiomes(chunkHeight).record(wx & 15, y, wz & 15, matter.identity());
             }
         } catch (Throwable e) {
+            GenerationFailures.rethrowEngineFailure(e);
             IrisLogging.reportError(e);
         }
     }

core/src/main/java/art/arcane/iris/platform/bukkit/nms/BukkitBinding.java

@@ -55,7 +55,7 @@ public final class BukkitBinding implements INMSBinding {
 
     @Override
     public PlatformGenerationRegistry generationRegistry() {
-        return new BukkitGenerationRegistry(registry, "bukkit-generation-registry-v1", generation.generationRendererIdentity());
+        return new BukkitGenerationRegistry(registry, "bukkit-generation-registry-v1");
     }
 
     @Override

core/src/main/java/art/arcane/iris/platform/bukkit/nms/BukkitGenerationRegistry.java

@@ -9,13 +9,11 @@ import java.util.Objects;
 
 public record BukkitGenerationRegistry(
         NativeGenerationRegistry registry,
-        String runtimeIdentity,
-        String generatedDefinitionRendererIdentity
+        String runtimeIdentity
 ) implements PlatformGenerationRegistry {
     public BukkitGenerationRegistry {
         registry = Objects.requireNonNull(registry, "registry");
         runtimeIdentity = requireText(runtimeIdentity, "runtimeIdentity");
-        generatedDefinitionRendererIdentity = requireText(generatedDefinitionRendererIdentity, "rendererIdentity");
     }
 
     @Override

core/src/main/java/art/arcane/iris/structure/nativegen/NativeStructureOwnershipStore.java

@@ -1,6 +1,7 @@
 package art.arcane.iris.structure.nativegen;
 
 import art.arcane.iris.generation.runtime.Engine;
+import art.arcane.iris.generation.runtime.GenerationClosedException;
 
 import art.arcane.iris.generation.runtime.IrisEngine;
 import art.arcane.iris.world.history.GenerationHistoryRuntimeRouter;
@@ -165,7 +166,7 @@ public final class NativeStructureOwnershipStore {
             lifecycleLock.writeLock().lock();
             try {
                 if (closed) {
-                    throw new IllegalStateException("Native structure ownership store is closed");
+                    throw new GenerationClosedException("Native structure ownership store is closed");
                 }
                 flushDirty();
             } finally {
@@ -214,7 +215,7 @@ public final class NativeStructureOwnershipStore {
         private void requireOpen() {
             engine();
             if (closed) {
-                throw new IllegalStateException("Native structure ownership store is closed");
+                throw new GenerationClosedException("Native structure ownership store is closed");
             }
         }
 

core/src/main/java/art/arcane/iris/structure/object/IrisObjectPlacementRunner.java

@@ -29,6 +29,7 @@ import art.arcane.iris.generation.decoration.IrisVacuumSettings;
 import art.arcane.iris.world.entity.IrisMarker;
 
 import art.arcane.iris.pack.loading.IrisData;
+import art.arcane.iris.generation.runtime.GenerationFailures;
 import art.arcane.iris.generation.runtime.IrisComplex;
 import art.arcane.iris.generation.runtime.Engine;
 import art.arcane.volmlib.nativelib.terrain.structure.NativeStructureVolume;
@@ -519,6 +520,7 @@ final class IrisObjectPlacementRunner {
                         tile = states.get(g);
                     }
                 } catch (Throwable e) {
+                    GenerationFailures.rethrowEngineFailure(e);
                     IrisLogging.reportError(e);
                     IrisLogging.warn("Failed to read block node " + g.getBlockX() + "," + g.getBlockY() + "," + g.getBlockZ() + " in object " + self.getLoadKey() + " (cme)");
                     d = IrisObject.States.air();
@@ -713,6 +715,7 @@ final class IrisObjectPlacementRunner {
                     try {
                         sourceData = stiltCursor.value();
                     } catch (Throwable e) {
+                        GenerationFailures.rethrowEngineFailure(e);
                         IrisLogging.reportError(e);
                         IrisLogging.warn("Failed to read block node " + g.getBlockX() + "," + g.getBlockY() + "," + g.getBlockZ() + " in object " + self.getLoadKey() + " (stilt cme)");
                         sourceData = IrisObject.States.air();

core/src/main/java/art/arcane/iris/structure/object/IrisObjectRotation.java

@@ -18,6 +18,7 @@
 
 package art.arcane.iris.structure.object;
 
+import art.arcane.iris.generation.runtime.GenerationFailures;
 import art.arcane.iris.pack.value.IrisDirection;
 import art.arcane.iris.pack.value.IrisPosition;
 
@@ -450,6 +451,7 @@ public class IrisObjectRotation {
                 }
             }
         } catch (Throwable e) {
+            GenerationFailures.rethrowEngineFailure(e);
             IrisLogging.reportError(e);
 
         }

core/src/main/java/art/arcane/iris/studio/StudioSVC.java

@@ -1098,12 +1098,14 @@ public class StudioSVC implements IrisService {
     }
 
     private void destroyStudioWorld(World world, PlatformChunkGenerator generator) {
-        IrisToolbelt.beginWorldMaintenance(world, "studio-disable", true);
         try {
             IrisToolbelt.evacuate(world);
         } catch (Throwable e) {
             IrisLogging.reportError("Failed to evacuate studio world \"" + world.getName() + "\" during shutdown cleanup.", e);
         }
+        // Entered after the evacuation: maintenance that forbids mantle stages refuses every chunk, and Folia
+        // treats a refused chunk as a chunk system failure.
+        IrisToolbelt.beginWorldMaintenance(world, "studio-disable", true);
         try {
             WorldLifecycleService.get().unloadAsync(world, false)
                     .thenCompose(unloaded -> {

core/src/main/java/art/arcane/iris/studio/object/StudioOpenCoordinator.java

@@ -459,12 +459,14 @@ public final class StudioOpenCoordinator {
     ) {
         AtomicBoolean unloadConfirmed = new AtomicBoolean(false);
         AtomicBoolean folderDeleted = new AtomicBoolean(!deleteFolder);
-        if (world != null) {
-            IrisToolbelt.beginWorldMaintenance(world, "studio-close", true);
-        }
 
         CompletableFuture<Void> sequence = sequenceStudioClose(
                 () -> evacuateWorldFamily(worldName, world),
+                () -> {
+                    if (world != null) {
+                        IrisToolbelt.beginWorldMaintenance(world, "studio-close", true);
+                    }
+                },
                 () -> unloadWorldFamily(worldName, world).thenRun(() -> unloadConfirmed.set(true)),
                 () -> provider == null ? CompletableFuture.completedFuture(null) : provider.closeAsync(),
                 () -> deleteFolder
@@ -491,14 +493,22 @@ public final class StudioOpenCoordinator {
                 });
     }
 
+    /**
+     * Maintenance that forbids mantle stages refuses every chunk, and Folia treats a refused chunk as a chunk
+     * system failure, so it is entered only once no player is left to request one.
+     */
     static CompletableFuture<Void> sequenceStudioClose(
             Supplier<CompletableFuture<Void>> evacuate,
+            Runnable enterMaintenance,
             Supplier<CompletableFuture<Void>> unload,
             Supplier<CompletableFuture<Void>> closeGenerator,
             Supplier<CompletableFuture<Void>> deleteFolders
     ) {
         return invokePhase(evacuate)
-                .thenCompose(ignored -> invokePhase(unload))
+                .thenCompose(ignored -> {
+                    enterMaintenance.run();
+                    return invokePhase(unload);
+                })
                 .thenCompose(ignored -> invokePhase(closeGenerator))
                 .thenCompose(ignored -> invokePhase(deleteFolders));
     }

core/src/main/java/art/arcane/iris/world/IrisCreator.java

@@ -756,12 +756,17 @@ public class IrisCreator {
             }
         }
         if (activeWorld != null) {
-            IrisToolbelt.beginWorldMaintenance(activeWorld, "world-create-rollback", true);
+            boolean maintenanceEntered = false;
             try {
                 PlatformChunkGenerator generator = IrisToolbelt.access(activeWorld);
                 boolean evacuated = Boolean.TRUE.equals(IrisToolbelt.evacuateAsync(activeWorld)
                         .get(ROLLBACK_PHASE_TIMEOUT_SECONDS, TimeUnit.SECONDS));
-                if (!evacuated) {
+                if (evacuated) {
+                    // Maintenance that forbids mantle stages refuses every chunk, and Folia treats a refused chunk
+                    // as a chunk system failure, so it starts only once no player is left to request one.
+                    IrisToolbelt.beginWorldMaintenance(activeWorld, "world-create-rollback", true);
+                    maintenanceEntered = true;
+                } else {
                     safeToDelete = false;
                     failure.addSuppressed(new IllegalStateException(
                             "Rollback could not evacuate world \"" + name + "\"."));
@@ -789,7 +794,9 @@ public class IrisCreator {
                     ServerConfigurator.restart("World creation rollback timed out for \"" + name + "\".");
                 }
             } finally {
-                IrisToolbelt.endWorldMaintenance(activeWorld, "world-create-rollback", true);
+                if (maintenanceEntered) {
+                    IrisToolbelt.endWorldMaintenance(activeWorld, "world-create-rollback", true);
+                }
             }
         }
 

core/src/main/java/art/arcane/iris/world/IrisWorldStorage.java

@@ -18,11 +18,14 @@ import java.util.Locale;
 import java.util.Objects;
 import java.util.Optional;
 import java.util.Properties;
+import java.util.Set;
 import java.util.stream.Stream;
 
 public final class IrisWorldStorage {
     private static final String IRIS_NAMESPACE = "iris";
     private static final String DEFAULT_LEVEL_NAME = "world";
+    private static final Set<String> OS_METADATA_FILES = Set.of(".DS_Store", "Thumbs.db", "desktop.ini");
+    private static final String APPLE_DOUBLE_PREFIX = "._";
 
     /**
      * Server#getLevelDirectory is Paper-API-only. Once a call throws NoSuchMethodError (plain
@@ -327,6 +330,46 @@ public final class IrisWorldStorage {
         return target.toFile();
     }
 
+    /**
+     * True when the world folder's {@code iris/} entry holds anything of Iris' own, which makes the folder an Iris
+     * world whatever its dimension namespace.
+     * <p>
+     * The desktop file managers recreate a directory to hold their own metadata while a delete is still in
+     * flight - on macOS a world folder can come back holding nothing but {@code iris/.DS_Store} - and a folder
+     * that holds only that is exactly as worthless as one with no {@code iris/} entry at all. Only files are
+     * ever treated as metadata: a directory, a symbolic link, an unreadable entry and anything that is not on
+     * the list all count as content.
+     */
+    public static boolean holdsIrisContent(Path dimensionRoot) {
+        Path irisRoot = Objects.requireNonNull(dimensionRoot, "dimensionRoot").resolve(IRIS_NAMESPACE);
+        if (Files.isSymbolicLink(irisRoot)) {
+            return true;
+        }
+        if (!Files.exists(irisRoot, LinkOption.NOFOLLOW_LINKS)) {
+            return false;
+        }
+        if (!Files.isDirectory(irisRoot, LinkOption.NOFOLLOW_LINKS)) {
+            return true;
+        }
+        try (Stream<Path> entries = Files.list(irisRoot)) {
+            return entries.anyMatch(entry -> !isOperatingSystemMetadata(entry));
+        } catch (IOException unreadable) {
+            return true;
+        }
+    }
+
+    private static boolean isOperatingSystemMetadata(Path entry) {
+        if (!Files.isRegularFile(entry, LinkOption.NOFOLLOW_LINKS)) {
+            return false;
+        }
+        Path name = entry.getFileName();
+        if (name == null) {
+            return false;
+        }
+        String fileName = name.toString();
+        return OS_METADATA_FILES.contains(fileName) || fileName.startsWith(APPLE_DOUBLE_PREFIX);
+    }
+
     /**
      * True when the level root holds at least one Iris-managed world directory. Used by the failure paths
      * that have to decide whether letting the server continue would put vanilla terrain into Iris storage.

core/src/main/java/art/arcane/iris/world/history/GenerationAdmission.java

@@ -1,5 +1,7 @@
 package art.arcane.iris.world.history;
 
+import art.arcane.iris.generation.runtime.GenerationClosedException;
+
 import java.nio.file.Path;
 import java.util.Objects;
 import java.util.concurrent.ConcurrentHashMap;
@@ -137,7 +139,7 @@ public final class GenerationAdmission {
 
         private void requireOpen() {
             if (closed) {
-                throw new IllegalStateException("Generation admission belongs to a closed runtime.");
+                throw new GenerationClosedException("Generation admission belongs to a closed runtime.");
             }
         }
 

core/src/main/java/art/arcane/iris/world/history/GenerationHistory.java

@@ -1,5 +1,6 @@
 package art.arcane.iris.world.history;
 
+import art.arcane.iris.generation.runtime.GenerationClosedException;
 import art.arcane.iris.pack.AtomicDirectoryPublisher;
 import art.arcane.iris.world.storage.Durability;
 import it.unimi.dsi.fastutil.longs.Long2ObjectOpenHashMap;
@@ -1386,7 +1387,7 @@ public final class GenerationHistory {
                 throw new IllegalArgumentException("Generation stage belongs to a different history.");
             }
             if (closed) {
-                throw new IllegalStateException("Generation stage is closed.");
+                throw new GenerationClosedException("Generation stage is closed.");
             }
         }
     }

core/src/main/java/art/arcane/iris/world/history/GenerationHistoryRuntimeRouter.java

@@ -9,6 +9,7 @@ import art.arcane.iris.pack.loading.IrisData;
 import art.arcane.iris.generation.runtime.IrisEngine;
 import art.arcane.iris.generation.runtime.IrisEngineMantle;
 import art.arcane.iris.generation.runtime.EngineTarget;
+import art.arcane.iris.generation.runtime.GenerationClosedException;
 import art.arcane.iris.generation.runtime.GenerationTransitionGate;
 import art.arcane.iris.generation.mantle.ObjectContinuationBundle;
 import art.arcane.iris.world.storage.matter.IrisMatterContext;
@@ -749,7 +750,7 @@ public final class GenerationHistoryRuntimeRouter implements AutoCloseable {
             throw propagate(entry.failure, "Saved mantle for activation " + entry.activationId + " is unavailable.");
         }
         if (closed) {
-            throw new IllegalStateException("Generation-history runtime router is closed.");
+            throw new GenerationClosedException("Generation-history runtime router is closed.");
         }
         try {
             inactive.await();
@@ -800,7 +801,7 @@ public final class GenerationHistoryRuntimeRouter implements AutoCloseable {
     private void awaitRetirementLocked(long activationId) throws IOException {
         while (true) {
             if (closed) {
-                throw new IllegalStateException("Generation-history runtime router is closed.");
+                throw new GenerationClosedException("Generation-history runtime router is closed.");
             }
             RuntimeRetirement retirement = retiringBindings.get(activationId);
             if (retirement == null) {
@@ -1032,7 +1033,7 @@ public final class GenerationHistoryRuntimeRouter implements AutoCloseable {
         stateLock.lock();
         try {
             if (closed) {
-                throw new IllegalStateException("Generation-history runtime router is closed.");
+                throw new GenerationClosedException("Generation-history runtime router is closed.");
             }
             activeOperations++;
             operationDepth.set(operationDepth.get() + 1);
@@ -1045,7 +1046,7 @@ public final class GenerationHistoryRuntimeRouter implements AutoCloseable {
         stateLock.lock();
         try {
             if (closed) {
-                throw new IllegalStateException("Generation-history runtime router is closed.");
+                throw new GenerationClosedException("Generation-history runtime router is closed.");
             }
             activeOperations++;
         } finally {
@@ -1202,7 +1203,7 @@ public final class GenerationHistoryRuntimeRouter implements AutoCloseable {
         public Scope openScope() {
             synchronized (this) {
                 if (closed) {
-                    throw new IllegalStateException("Saved chunk mantle is closed.");
+                    throw new GenerationClosedException("Saved chunk mantle is closed.");
                 }
                 activeScopes++;
             }
@@ -1535,7 +1536,7 @@ public final class GenerationHistoryRuntimeRouter implements AutoCloseable {
         public RuntimeScope openRuntimeScope() {
             synchronized (this) {
                 if (closed) {
-                    throw new IllegalStateException("Generation-history runtime route is closed.");
+                    throw new GenerationClosedException("Generation-history runtime route is closed.");
                 }
                 activeScopes++;
             }

core/src/main/java/art/arcane/iris/world/history/GenerationRegistryContractFactory.java

@@ -552,15 +552,14 @@ public final class GenerationRegistryContractFactory {
             for (Map.Entry<GenerationRegistryContract.PhysicalResourceKey, GenerationRegistryContract.GeneratedSource>
                     entry
                     : requiredContract.generatedSources().entrySet()) {
-                GenerationRegistryContract.GeneratedSource previous = generatedSources.get(entry.getKey());
+                GenerationRegistryContract.GeneratedSource previous = generatedSources.putIfAbsent(
+                        entry.getKey(),
+                        entry.getValue()
+                );
                 if (previous != null && !sameGeneratedSemantic(previous, entry.getValue())) {
                     throw new IOException("Retained generation epochs require conflicting generated sources for "
                             + entry.getKey().registryKey() + " / " + entry.getKey().resourceKey() + ".");
                 }
-                generatedSources.put(
-                        entry.getKey(),
-                        preferredGeneratedSource(previous, entry.getValue(), registry)
-                );
             }
         }
         Map<GenerationRegistryContract.PhysicalResourceKey, String> captured = new TreeMap<>();
@@ -596,18 +595,6 @@ public final class GenerationRegistryContractFactory {
         return GenerationRegistryContract.fromDefinitions(captured);
     }
 
-    public static String requireGeneratedSource(
-            GenerationRegistryContract contract,
-            GenerationRegistryContract.PhysicalResourceKey key
-    ) throws IOException {
-        return requireGeneratedSource(
-                contract,
-                key,
-                DataVersion.getRuntime().get(),
-                IrisPlatforms.get().registries().generationRegistry()
-        );
-    }
-
     public static String renderGeneratedSource(
             GenerationRegistryContract contract,
             GenerationRegistryContract.PhysicalResourceKey key,
@@ -622,68 +609,9 @@ public final class GenerationRegistryContractFactory {
                     + requiredKey.registryKey() + " / " + requiredKey.resourceKey() + ".");
         }
         requireGeneratedSemanticFingerprint(requiredKey, source, requiredContract.definitions().get(requiredKey));
-        String sourceFingerprint = fingerprintDefinition(requiredKey,
-                PlatformGenerationRegistry.Definition.exactJson(source.sourceJson()), "generated");
-        if (!source.renderedDefinitionSha256().equals(sourceFingerprint)) {
-            throw new IOException("Historical generated registry source changed for "
-                    + requiredKey.registryKey() + " / " + requiredKey.resourceKey() + ".");
-        }
         return renderGeneratedSemantic(requiredKey, source, requiredFixer);
     }
 
-    public static String requireGeneratedSource(
-            GenerationRegistryContract contract,
-            GenerationRegistryContract.PhysicalResourceKey key,
-            IDataFixer fixer
-    ) throws IOException {
-        return requireGeneratedSource(
-                contract,
-                key,
-                fixer,
-                IrisPlatforms.get().registries().generationRegistry()
-        );
-    }
-
-    public static String requireGeneratedSource(
-            GenerationRegistryContract contract,
-            GenerationRegistryContract.PhysicalResourceKey key,
-            PlatformGenerationRegistry generationRegistry
-    ) throws IOException {
-        return requireGeneratedSource(
-                contract,
-                key,
-                DataVersion.getRuntime().get(),
-                generationRegistry
-        );
-    }
-
-    public static String requireGeneratedSource(
-            GenerationRegistryContract contract,
-            GenerationRegistryContract.PhysicalResourceKey key,
-            IDataFixer fixer,
-            PlatformGenerationRegistry generationRegistry
-    ) throws IOException {
-        GenerationRegistryContract requiredContract = Objects.requireNonNull(contract, "contract");
-        GenerationRegistryContract.PhysicalResourceKey requiredKey = Objects.requireNonNull(key, "key");
-        IDataFixer requiredFixer = Objects.requireNonNull(fixer, "fixer");
-        PlatformGenerationRegistry registry = Objects.requireNonNull(
-                generationRegistry,
-                "generationRegistry"
-        );
-        GenerationRegistryContract.GeneratedSource source = requiredContract.generatedSources().get(requiredKey);
-        if (source == null) {
-            throw new IOException("Historical generated registry source is missing for "
-                    + requiredKey.registryKey() + " / " + requiredKey.resourceKey() + ".");
-        }
-        String expectedFingerprint = requiredContract.definitions().get(requiredKey);
-        if (expectedFingerprint == null) {
-            throw new IOException("Historical generated registry definition is missing for "
-                    + requiredKey.registryKey() + " / " + requiredKey.resourceKey() + ".");
-        }
-        requireGeneratedSemanticFingerprint(requiredKey, source, expectedFingerprint);
-        return canonicalGeneratedDefinition(requiredKey, source, requiredFixer, registry).value();
-    }
-
     public static String fingerprintDefinition(
             GenerationRegistryContract.PhysicalResourceKey key,
             PlatformGenerationRegistry.Definition definition,
@@ -783,7 +711,7 @@ public final class GenerationRegistryContractFactory {
                 DIMENSION_TYPE_EFFECTIVE_SOURCE_SCHEMA,
                 GenerationEpochContractFactory.fingerprintDimensionType(dimension.getDimensionType()),
                 GenerationEpochContractFactory.dimensionTypeSemanticJson(dimension.getDimensionType()),
-                registry.generatedDefinitionRendererIdentity(),
+                rendererIdentity(fixer),
                 canonicalDefinition
         );
     }
@@ -833,7 +761,7 @@ public final class GenerationRegistryContractFactory {
                         CUSTOM_BIOME_EFFECTIVE_SOURCE_SCHEMA,
                         generated.semanticFingerprint(),
                         generated.semanticJson(),
-                        registry.generatedDefinitionRendererIdentity(),
+                        rendererIdentity(fixer),
                         generated.definition()
                 );
                 Set<String> tags = biomeTags.computeIfAbsent(generated.physicalKey().resourceKey(), ignored -> new TreeSet<>());
@@ -882,7 +810,7 @@ public final class GenerationRegistryContractFactory {
                     CUSTOM_BIOME_EFFECTIVE_SOURCE_SCHEMA,
                     generated.semanticFingerprint(),
                     generated.semanticJson(),
-                    registry.generatedDefinitionRendererIdentity(),
+                    rendererIdentity(fixer),
                     generated.definition()
             );
         }
@@ -1087,32 +1015,9 @@ public final class GenerationRegistryContractFactory {
         }
     }
 
-    private static GenerationRegistryContract.GeneratedSource preferredGeneratedSource(
-            GenerationRegistryContract.GeneratedSource previous,
-            GenerationRegistryContract.GeneratedSource candidate,
-            PlatformGenerationRegistry registry
-    ) {
-        if (previous == null) {
-            return candidate;
-        }
-        String currentRenderer = requireText(
-                registry.generatedDefinitionRendererIdentity(),
-                "Generated registry renderer identity"
-        );
-        boolean previousMatches = previous.rendererIdentity().equals(currentRenderer);
-        boolean candidateMatches = candidate.rendererIdentity().equals(currentRenderer);
-        if (previousMatches != candidateMatches) {
-            return candidateMatches ? candidate : previous;
-        }
-        return generatedSourceOrder(candidate).compareTo(generatedSourceOrder(previous)) < 0
-                ? candidate
-                : previous;
-    }
-
-    private static String generatedSourceOrder(GenerationRegistryContract.GeneratedSource source) {
-        return source.rendererIdentity() + '\u0000'
-                + source.renderedDefinitionSha256() + '\u0000'
-                + source.sourceJson();
+    // Recorded for diagnostics only. Validation always re-renders the semantics with the current fixer.
+    private static String rendererIdentity(IDataFixer fixer) {
+        return fixer.getClass().getName();
     }
 
     private static boolean sameGeneratedSemantic(
@@ -1130,36 +1035,19 @@ public final class GenerationRegistryContractFactory {
             IDataFixer fixer,
             PlatformGenerationRegistry registry
     ) throws IOException {
-        String currentRenderer = requireText(
-                registry.generatedDefinitionRendererIdentity(),
-                "Generated registry renderer identity"
-        );
-        String renderedSource;
-        if (source.rendererIdentity().equals(currentRenderer)) {
-            renderedSource = source.sourceJson();
-        } else {
-            renderedSource = renderGeneratedSemantic(key, source, fixer);
-        }
-        PlatformGenerationRegistry.Definition definition;
+        String renderedSource = renderGeneratedSemantic(key, source, fixer);
         try {
-            definition = registry.canonicalDefinition(
+            PlatformGenerationRegistry.Definition definition = registry.canonicalDefinition(
                     key.registryKey(),
                     key.resourceKey(),
                     renderedSource
             );
             requireGeneratedDefinition(definition, "historical generated registry definition");
+            return definition;
         } catch (RuntimeException failure) {
             throw new IOException("Historical generated registry source is incompatible for "
                     + key.registryKey() + " / " + key.resourceKey() + ".", failure);
         }
-        if (source.rendererIdentity().equals(currentRenderer)) {
-            String renderedFingerprint = fingerprintDefinition(key, definition, "generated");
-            if (!source.renderedDefinitionSha256().equals(renderedFingerprint)) {
-                throw new IOException("Historical generated registry source changed for "
-                        + key.registryKey() + " / " + key.resourceKey() + ".");
-            }
-        }
-        return definition;
     }
 
     private static String renderGeneratedSemantic(

core/src/main/java/art/arcane/iris/world/history/SavedBiomeRuntime.java

@@ -1,5 +1,6 @@
 package art.arcane.iris.world.history;
 
+import art.arcane.iris.generation.runtime.GenerationClosedException;
 import art.arcane.iris.pack.loading.IrisData;
 import art.arcane.iris.generation.runtime.IrisEngine;
 import art.arcane.iris.generation.runtime.BiomeEnvironment;
@@ -365,7 +366,7 @@ public final class SavedBiomeRuntime implements AutoCloseable {
             }
             if (!refresh) {
                 if (closed || prepared == null) {
-                    loading.result.completeExceptionally(new IllegalStateException("Saved biome runtime is closed."));
+                    loading.result.completeExceptionally(new GenerationClosedException("Saved biome runtime is closed."));
                 } else {
                     loading.result.complete(prepared);
                 }
@@ -480,7 +481,7 @@ public final class SavedBiomeRuntime implements AutoCloseable {
 
     private void requireOpen() {
         if (closed) {
-            throw new IllegalStateException("Saved biome runtime is closed.");
+            throw new GenerationClosedException("Saved biome runtime is closed.");
         }
     }
 

core/src/main/java/art/arcane/iris/world/lifecycle/BukkitWorldConfiguration.java

@@ -4,6 +4,7 @@ import art.arcane.iris.world.IrisWorldStorage;
 import art.arcane.iris.world.WorldSlotKey;
 import art.arcane.iris.generation.runtime.IrisEngineMantle;
 import art.arcane.iris.world.history.GenerationHistoryPaths;
+import art.arcane.iris.world.safeguard.GenerationRefusalNotice;
 import org.bukkit.NamespacedKey;
 import org.bukkit.configuration.ConfigurationSection;
 import org.bukkit.configuration.InvalidConfigurationException;
@@ -26,11 +27,16 @@ import java.util.List;
 import java.util.Map;
 import java.util.Objects;
 import java.util.function.Predicate;
+import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
 public final class BukkitWorldConfiguration {
     private static final String DEFAULT_WORLD_CONTAINER = ".";
     private static final Object MUTATION_LOCK = new Object();
+    private static final List<NamespacedKey> VANILLA_SLOTS = List.of(
+            NamespacedKey.minecraft("overworld"),
+            NamespacedKey.minecraft("the_nether"),
+            NamespacedKey.minecraft("the_end"));
 
     private BukkitWorldConfiguration() {
     }
@@ -160,7 +166,8 @@ public final class BukkitWorldConfiguration {
     }
 
     /**
-     * Classifies the world storage behind every Iris entry in bukkit.yml.
+     * Classifies the world storage behind every Iris entry in bukkit.yml, and behind every vanilla slot of the level
+     * that holds an Iris world, bound or not.
      * <p>
      * {@link #readIrisGeneratorBindings} answers "which worlds can Iris bind", which deliberately drops
      * anything without storage. Startup needs the opposite view: a world whose folder is on disk but whose
@@ -178,22 +185,34 @@ public final class BukkitWorldConfiguration {
         Path requiredLevelRoot = Objects.requireNonNull(levelRoot, "levelRoot")
                 .toAbsolutePath()
                 .normalize();
-        Path configurationPath = requiredConfigurationFile.toPath();
-        if (!Files.exists(configurationPath, LinkOption.NOFOLLOW_LINKS)) {
-            return List.of();
-        }
         Path worldContainer = requiredLevelRoot.getParent();
         if (worldContainer == null) {
             throw new IOException("Selected level root has no world container: " + requiredLevelRoot);
         }
         synchronized (MUTATION_LOCK) {
+            YamlConfiguration configuration = Files.exists(requiredConfigurationFile.toPath(), LinkOption.NOFOLLOW_LINKS)
+                    ? load(requiredConfigurationFile)
+                    : new YamlConfiguration();
             List<IrisWorldStorageEntry> entries = new ArrayList<>();
-            for (IrisWorldCandidate candidate : readIrisWorldCandidates(
-                    load(requiredConfigurationFile),
-                    requiredLevelName
-            )) {
+            for (IrisWorldCandidate candidate : readIrisWorldCandidates(configuration, requiredLevelName)) {
                 entries.add(classifyStorage(worldContainer, requiredLevelRoot, candidate));
             }
+            for (NamespacedKey vanillaSlot : VANILLA_SLOTS) {
+                Path dimensionRoot = expectedDimensionRoot(requiredLevelRoot, vanillaSlot);
+                if (!IrisWorldStorage.holdsIrisContent(dimensionRoot)) {
+                    continue;
+                }
+                String configuredName = IrisWorldStorage.configuredWorldName(vanillaSlot, requiredLevelName);
+                if (configuration.get("worlds." + configuredName + ".generator") instanceof String generator
+                        && isIrisGenerator(generator.trim())) {
+                    entries.add(classifyStorage(worldContainer, requiredLevelRoot,
+                            new IrisWorldCandidate(configuredName, vanillaSlot, generator.trim())));
+                } else {
+                    entries.add(new IrisWorldStorageEntry(configuredName,
+                            new WorldSlotKey(vanillaSlot.getNamespace(), vanillaSlot.getKey()), dimensionRoot,
+                            IrisWorldStorageState.UNBOUND, "bukkit.yml does not name Iris as its generator"));
+                }
+            }
             return List.copyOf(entries);
         }
     }
@@ -249,12 +268,21 @@ public final class BukkitWorldConfiguration {
                     hasWorldData(resolvedRoot)
                             ? IrisWorldStorageState.UNUSABLE
                             : IrisWorldStorageState.EMPTY,
-                    unusablePack.getMessage());
+                    describe(unusablePack));
         }
         return new IrisWorldStorageEntry(configuredName, slotKey, resolvedRoot,
                 IrisWorldStorageState.PRESENT, null);
     }
 
+    /**
+     * The cause chain on one line: why a history cannot be read sits below the failure that names the world.
+     */
+    private static String describe(Throwable failure) {
+        return GenerationRefusalNotice.causes(failure).stream()
+                .map((String cause) -> cause.lines().findFirst().orElse(cause))
+                .collect(Collectors.joining("; "));
+    }
+
     /**
      * True when the world folder holds something a vanilla generator could overwrite: an {@code iris/}
      * directory marking it as an Iris world whose pack snapshot broke, or stored chunk data.
@@ -372,8 +400,7 @@ public final class BukkitWorldConfiguration {
                         + "\" is not a string.");
             }
             String configuredGenerator = generator.trim();
-            if (!configuredGenerator.equalsIgnoreCase("Iris")
-                    && !configuredGenerator.regionMatches(true, 0, "Iris:", 0, 5)) {
+            if (!isIrisGenerator(configuredGenerator)) {
                 continue;
             }
 
@@ -395,6 +422,59 @@ public final class BukkitWorldConfiguration {
         return candidates;
     }
 
+    /**
+     * True when a bukkit.yml world the server loads names Iris as its generator: the level's overworld, nether or
+     * end, or a world whose dimension folder exists. CraftServer asks a plugin for a generator only for worlds it
+     * creates, so these are the ones a disabled Iris would hand to vanilla; an entry for a world that is never
+     * created is not.
+     */
+    public static boolean configuresLoadingIrisWorld(File configurationFile, Path levelRoot) throws IOException {
+        Path configurationPath = Objects.requireNonNull(configurationFile, "configurationFile").toPath();
+        Path root = Objects.requireNonNull(levelRoot, "levelRoot").toAbsolutePath().normalize();
+        Path levelName = root.getFileName();
+        Path worldContainer = root.getParent();
+        if (levelName == null || worldContainer == null) {
+            throw new IOException("Selected level root has no world container: " + root);
+        }
+        if (!Files.exists(configurationPath, LinkOption.NOFOLLOW_LINKS)) {
+            return false;
+        }
+        synchronized (MUTATION_LOCK) {
+            ConfigurationSection worlds = load(configurationFile).getConfigurationSection("worlds");
+            if (worlds == null) {
+                return false;
+            }
+            for (String worldName : worlds.getKeys(false)) {
+                if (worlds.get(worldName + ".generator") instanceof String generator
+                        && isIrisGenerator(generator.trim())
+                        && loadsAtStartup(worldContainer, root, levelName.toString(), worldName)) {
+                    return true;
+                }
+            }
+            return false;
+        }
+    }
+
+    private static boolean loadsAtStartup(Path worldContainer, Path levelRoot, String levelName, String worldName) {
+        if (worldName.equals(levelName)
+                || worldName.equals(levelName + "_nether")
+                || worldName.equals(levelName + "_the_end")) {
+            return true;
+        }
+        NamespacedKey worldKey;
+        try {
+            worldKey = IrisWorldStorage.keyFromConfiguredWorldName(worldName, levelName);
+        } catch (IllegalArgumentException unmappable) {
+            return false;
+        }
+        return hasDimensionDirectory(worldContainer, levelRoot, worldName, worldKey);
+    }
+
+    private static boolean isIrisGenerator(String configuredGenerator) {
+        return configuredGenerator.equalsIgnoreCase("Iris")
+                || configuredGenerator.regionMatches(true, 0, "Iris:", 0, 5);
+    }
+
     public static GeneratorReplacement replaceIfMatching(
             File configurationFile,
             String worldName,
@@ -738,7 +818,12 @@ public final class BukkitWorldConfiguration {
          * A world directory the server will load, whose frozen pack snapshot cannot be used. Iris cannot
          * generate it and nothing else may.
          */
-        UNUSABLE
+        UNUSABLE,
+        /**
+         * An Iris world in a vanilla slot whose bukkit.yml entry does not name Iris, so the server would build
+         * it with the vanilla generator.
+         */
+        UNBOUND
     }
 
     public record IrisWorldStorageEntry(

core/src/main/java/art/arcane/iris/world/lifecycle/HuskWorldQuarantine.java

@@ -16,7 +16,6 @@ import java.time.format.DateTimeFormatter;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Objects;
-import java.util.Set;
 import java.util.function.Consumer;
 import java.util.regex.Pattern;
 import java.util.stream.Stream;
@@ -41,8 +40,6 @@ public final class HuskWorldQuarantine {
     private static final String[] CHUNK_DATA_DIRECTORIES = {
             "region", "entities", "poi", IrisEngineMantle.STORAGE_FOLDER_NAME
     };
-    private static final Set<String> OS_METADATA_FILES = Set.of(".DS_Store", "Thumbs.db", "desktop.ini");
-    private static final String APPLE_DOUBLE_PREFIX = "._";
     private static final DateTimeFormatter STAMP = DateTimeFormatter
             .ofPattern("yyyyMMdd'T'HHmmss")
             .withZone(ZoneOffset.UTC);
@@ -117,7 +114,7 @@ public final class HuskWorldQuarantine {
         if (!isReadableDirectory(dimensionRoot)) {
             return false;
         }
-        if (holdsIrisContent(dimensionRoot.resolve("iris"))) {
+        if (IrisWorldStorage.holdsIrisContent(dimensionRoot)) {
             return false;
         }
         for (String directory : CHUNK_DATA_DIRECTORIES) {
@@ -128,44 +125,6 @@ public final class HuskWorldQuarantine {
         return true;
     }
 
-    /**
-     * True when the {@code iris/} entry holds anything of Iris' own.
-     * <p>
-     * The desktop file managers recreate a directory to hold their own metadata while a delete is still in
-     * flight - on macOS a world folder can come back holding nothing but {@code iris/.DS_Store} - and a folder
-     * that holds only that is exactly as worthless as one with no {@code iris/} entry at all. Only files are
-     * ever treated as metadata: a directory, a symbolic link, an unreadable entry and anything that is not on
-     * the list all count as content.
-     */
-    private static boolean holdsIrisContent(Path irisRoot) {
-        if (Files.isSymbolicLink(irisRoot)) {
-            return true;
-        }
-        if (!Files.exists(irisRoot, LinkOption.NOFOLLOW_LINKS)) {
-            return false;
-        }
-        if (!Files.isDirectory(irisRoot, LinkOption.NOFOLLOW_LINKS)) {
-            return true;
-        }
-        try (Stream<Path> entries = Files.list(irisRoot)) {
-            return entries.anyMatch(entry -> !isOperatingSystemMetadata(entry));
-        } catch (IOException unreadable) {
-            return true;
-        }
-    }
-
-    private static boolean isOperatingSystemMetadata(Path entry) {
-        if (!Files.isRegularFile(entry, LinkOption.NOFOLLOW_LINKS)) {
-            return false;
-        }
-        Path name = entry.getFileName();
-        if (name == null) {
-            return false;
-        }
-        String fileName = name.toString();
-        return OS_METADATA_FILES.contains(fileName) || fileName.startsWith(APPLE_DOUBLE_PREFIX);
-    }
-
     /**
      * True when the path is a real directory that can actually be listed. The permission bits alone are not
      * the answer: what matters is whether Iris can see everything in it before deciding it holds nothing.

core/src/main/java/art/arcane/iris/world/lifecycle/IrisWorldRemovalService.java

@@ -152,15 +152,21 @@ public final class IrisWorldRemovalService {
             boolean deleteFiles,
             AtomicBoolean terminal
     ) {
+        // Maintenance that forbids mantle stages refuses every chunk, and Folia treats a refused chunk as a chunk
+        // system failure, so it starts only once no player is left to request one.
+        AtomicBoolean maintenanceEntered = new AtomicBoolean(false);
         CompletableFuture<RemovalResult> operation = phase(
-                RemovalStatus.RESOLUTION_FAILED,
-                () -> backend.beginMaintenance(resolved).thenApply(ignored -> resolved),
+                RemovalStatus.TELEPORT_FAILED,
+                () -> backend.evacuatePlayers(resolved).thenApply(ignored -> resolved),
                 terminal
         )
                 .thenCompose(activeWorld -> phase(
-                        RemovalStatus.TELEPORT_FAILED,
-                        () -> backend.evacuatePlayers(activeWorld)
-                                .thenApply(ignored -> activeWorld),
+                        RemovalStatus.RESOLUTION_FAILED,
+                        () -> {
+                            CompletableFuture<Void> begun = backend.beginMaintenance(activeWorld);
+                            maintenanceEntered.set(true);
+                            return begun.thenApply(ignored -> activeWorld);
+                        },
                         terminal
                 ))
                 .thenCompose(activeWorld -> phase(
@@ -198,7 +204,7 @@ public final class IrisWorldRemovalService {
                     );
                 }));
 
-        return operation.handle((result, throwable) -> backend.endMaintenance(resolved)
+        return operation.handle((result, throwable) -> endMaintenance(resolved, maintenanceEntered.get())
                 .handle((ignored, cleanupFailure) -> {
                     if (cleanupFailure != null) {
                         Throwable unwrappedCleanup = unwrap(cleanupFailure);
@@ -216,6 +222,10 @@ public final class IrisWorldRemovalService {
                 })).thenCompose(result -> result);
     }
 
+    private CompletableFuture<Void> endMaintenance(ResolvedWorld resolved, boolean entered) {
+        return entered ? backend.endMaintenance(resolved) : CompletableFuture.completedFuture(null);
+    }
+
     private CompletableFuture<ResolvedWorld> validateResolvedWorld(ResolvedWorld resolvedWorld) {
         if (!resolvedWorld.managed()) {
             return CompletableFuture.failedFuture(new RemovalFailure(

core/src/main/java/art/arcane/iris/world/lifecycle/MissingWorldStorageLog.java

@@ -61,7 +61,7 @@ public final class MissingWorldStorageLog {
         }
         emit(new String[]{
                 IrisLogging.format("Iris world %s has an empty world folder at %s: no pack snapshot, no region"
-                        + " data; it will generate as vanilla terrain.", worldName, worldStorage),
+                        + " data; Iris refuses to generate it and no other generator gets it.", worldName, worldStorage),
                 IrisLogging.format("Delete that folder, or drop the world with /iris remove world=%s delete=true.",
                         worldName)
         });

core/src/main/java/art/arcane/iris/world/safeguard/GenerationRefusalNotice.java

@@ -0,0 +1,64 @@
+package art.arcane.iris.world.safeguard;
+
+import java.nio.file.FileSystemException;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.IdentityHashMap;
+import java.util.List;
+import java.util.Objects;
+import java.util.Set;
+
+/**
+ * The framed console block Iris prints when it refuses to generate a world. Every platform prints the same shape
+ * so a refusal is found the same way in any server log.
+ */
+public final class GenerationRefusalNotice {
+    private static final String RULE = "=".repeat(78);
+
+    private GenerationRefusalNotice() {
+    }
+
+    public static List<String> compose(String headline, List<String> causes, List<String> consequences) {
+        List<String> lines = new ArrayList<>(causes.size() + consequences.size() + 3);
+        lines.add(RULE);
+        lines.add(Objects.requireNonNull(headline, "headline"));
+        for (int index = 0; index < causes.size(); index++) {
+            lines.add((index == 0 ? "Cause: " : "Caused by: ") + causes.get(index));
+        }
+        lines.addAll(consequences);
+        lines.add(RULE);
+        return List.copyOf(lines);
+    }
+
+    /**
+     * Every distinct message in the cause chain, outermost first. A wrapper whose message only repeats its cause
+     * (CompletionException, a rethrow with the same text) adds nothing and is skipped. A file system failure carries
+     * only a path, so its type is named with it.
+     */
+    public static List<String> causes(Throwable failure) {
+        List<String> causes = new ArrayList<>();
+        Set<Throwable> seen = Collections.newSetFromMap(new IdentityHashMap<>());
+        Throwable current = failure;
+        while (current != null && seen.add(current)) {
+            Throwable cause = current.getCause();
+            String message = current.getMessage();
+            boolean repeatsCause = cause != null && cause.toString().equals(message);
+            if (!repeatsCause) {
+                String text = message == null || message.isBlank()
+                        ? current.getClass().getSimpleName()
+                        : current instanceof FileSystemException
+                        ? current.getClass().getSimpleName() + ": " + message.trim()
+                        : message.trim();
+                if (causes.isEmpty() || !causes.getLast().equals(text)) {
+                    causes.add(text);
+                }
+            }
+            current = cause;
+        }
+        return List.copyOf(causes);
+    }
+
+    public static String summary(Throwable failure) {
+        return String.join("; ", causes(failure));
+    }
+}

core/src/main/resources/languages/de_DE.toml

@@ -769,6 +769,9 @@ opening_your_editor = "Öffne {value} {value2} in deinem Editor."
 console_must_name_player_iris_tp_dimension_player = "Die Konsole muss einen Spieler benennen: /iris tp <dimension> <player>"
 is_not_generated_by_iris = "{value} wird nicht von Iris generiert."
 teleport_failed_dimension_is_not_loaded = "Teleportation fehlgeschlagen: Dimension {dimensionId} ist nicht geladen."
+teleport_failed_reason = "Teleport nach {dimensionId} fehlgeschlagen: {reason}"
+teleport_cancelled_player_offline = "Teleport nach {dimensionId} abgebrochen: {value} ist nicht mehr online."
+teleport_refused = "Teleport nach {dimensionId} wurde vom Server abgelehnt."
 teleporting = "Teleportiere {value} nach {dimensionId}..."
 is_not_generated_by_iris_2 = "{value} wird nicht von Iris generiert."
 cannot_evacuate_primary_world_there_is_nowhere_send_players = "Die primäre Welt kann nicht evakuiert werden, da es kein Ziel für die Spieler gibt."

core/src/main/resources/languages/es_ES.toml

@@ -769,6 +769,9 @@ opening_your_editor = "Abriendo {value} {value2} en tu editor."
 console_must_name_player_iris_tp_dimension_player = "La consola debe indicar un jugador: /iris tp <dimension> <player>"
 is_not_generated_by_iris = "{value} no se genera por Iris."
 teleport_failed_dimension_is_not_loaded = "El teletransporte falló: la dimensión {dimensionId} no está cargada."
+teleport_failed_reason = "El teletransporte a {dimensionId} falló: {reason}"
+teleport_cancelled_player_offline = "Teletransporte a {dimensionId} cancelado: {value} ya no está conectado."
+teleport_refused = "El servidor rechazó el teletransporte a {dimensionId}."
 teleporting = "Teletransportando a {value} a {dimensionId}..."
 is_not_generated_by_iris_2 = "{value} no se genera por Iris."
 cannot_evacuate_primary_world_there_is_nowhere_send_players = "No se puede evacuar el mundo principal porque no hay adónde enviar a los jugadores."

core/src/main/resources/languages/fi_FI.toml

@@ -774,6 +774,9 @@ opening_your_editor = "Avaaminen {value}  {value2} Päätoimittajassasi."
 console_must_name_player_iris_tp_dimension_player = "Konsolin on nimettävä pelaaja: /iris tp <dimension> <player>"
 is_not_generated_by_iris = "{value} ei ole tuotettu Iris."
 teleport_failed_dimension_is_not_loaded = "Teleportti epäonnistui: ulottuvuus {dimensionId} ei ole ladattu."
+teleport_failed_reason = "Teleporttaus ulottuvuuteen {dimensionId} epäonnistui: {reason}"
+teleport_cancelled_player_offline = "Teleporttaus ulottuvuuteen {dimensionId} peruttiin: {value} ei ole enää paikalla."
+teleport_refused = "Palvelin hylkäsi teleporttauksen ulottuvuuteen {dimensionId}."
 teleporting = "Telesiirtäminen {value} - {dimensionId}..."
 is_not_generated_by_iris_2 = "{value} ei ole tuotettu Iris."
 cannot_evacuate_primary_world_there_is_nowhere_send_players = "Ensisijaista maailmaa ei voida evakuoida; pelaajia ei voi lähettää minnekään."

core/src/main/resources/languages/fr_FR.toml

@@ -769,6 +769,9 @@ opening_your_editor = "Ouverture de {value} {value2} dans votre éditeur."
 console_must_name_player_iris_tp_dimension_player = "La console doit indiquer un joueur : /iris tp <dimension> <player>"
 is_not_generated_by_iris = "{value} n'est pas généré par Iris."
 teleport_failed_dimension_is_not_loaded = "Échec de la téléportation : la dimension {dimensionId} n'est pas chargée."
+teleport_failed_reason = "Échec de la téléportation vers {dimensionId} : {reason}"
+teleport_cancelled_player_offline = "Téléportation vers {dimensionId} annulée : {value} n'est plus connecté."
+teleport_refused = "Le serveur a refusé la téléportation vers {dimensionId}."
 teleporting = "Téléportation de {value} vers {dimensionId}..."
 is_not_generated_by_iris_2 = "{value} n'est pas généré par Iris."
 cannot_evacuate_primary_world_there_is_nowhere_send_players = "Impossible d'évacuer le monde principal, car aucun autre monde ne peut accueillir les joueurs."

core/src/main/resources/languages/he_IL.toml

@@ -774,6 +774,9 @@ opening_your_editor = "פתיחה {value}  {value2} בעורך שלך."
 console_must_name_player_iris_tp_dimension_player = "הקונסולה חייבת לקרוא לשחקן: /iris tp <dimension> <player>"
 is_not_generated_by_iris = "{value} לא נוצר על ידי Iris."
 teleport_failed_dimension_is_not_loaded = "טלפורט נכשל: ממד {dimensionId} לא טעון."
+teleport_failed_reason = "השיגור אל {dimensionId} נכשל: {reason}"
+teleport_cancelled_player_offline = "השיגור אל {dimensionId} בוטל: {value} כבר לא מחובר."
+teleport_refused = "השרת דחה את השיגור אל {dimensionId}."
 teleporting = "תקשורת {value} כדי {dimensionId}..."
 is_not_generated_by_iris_2 = "{value} לא נוצר על ידי Iris."
 cannot_evacuate_primary_world_there_is_nowhere_send_players = "לא ניתן לפנות לעולם הראשי, אין מקום לשלוח שחקנים."

core/src/main/resources/languages/it_IT.toml

@@ -769,6 +769,9 @@ opening_your_editor = "Apertura di {value} {value2} nel tuo editor."
 console_must_name_player_iris_tp_dimension_player = "La console deve specificare un giocatore: /iris tp <dimension> <player>"
 is_not_generated_by_iris = "{value} non è generato da Iris."
 teleport_failed_dimension_is_not_loaded = "Teletrasporto non riuscito: la dimensione {dimensionId} non è caricata."
+teleport_failed_reason = "Teletrasporto verso {dimensionId} non riuscito: {reason}"
+teleport_cancelled_player_offline = "Teletrasporto verso {dimensionId} annullato: {value} non è più online."
+teleport_refused = "Il server ha rifiutato il teletrasporto verso {dimensionId}."
 teleporting = "Teletrasporto di {value} verso {dimensionId}..."
 is_not_generated_by_iris_2 = "{value} non è generato da Iris."
 cannot_evacuate_primary_world_there_is_nowhere_send_players = "Impossibile evacuare il mondo principale: non esiste una destinazione per i giocatori."

core/src/main/resources/languages/ja-JP.toml

@@ -772,6 +772,9 @@ opening_your_editor = "エディターで {value} {value2} を開いています
 console_must_name_player_iris_tp_dimension_player = "コンソールではプレイヤーを指定してください: /iris tp <dimension> <player>"
 is_not_generated_by_iris = "{value} は Iris によって生成されていません。"
 teleport_failed_dimension_is_not_loaded = "テレポートに失敗しました: ディメンション {dimensionId} は読み込まれていません。"
+teleport_failed_reason = "{dimensionId} へのテレポートに失敗しました: {reason}"
+teleport_cancelled_player_offline = "{dimensionId} へのテレポートを中止しました: {value} はオフラインです。"
+teleport_refused = "サーバーが {dimensionId} へのテレポートを拒否しました。"
 teleporting = "{value} を {dimensionId} にテレポートしています..."
 is_not_generated_by_iris_2 = "{value} は Iris によって生成されていません。"
 cannot_evacuate_primary_world_there_is_nowhere_send_players = "プライマリーワールドからは退避できません。プレイヤーの移動先がありません。"

core/src/main/resources/languages/ko_KR.toml

@@ -772,6 +772,9 @@ opening_your_editor = "편집기에서 {value} {value2} 여는 중입니다."
 console_must_name_player_iris_tp_dimension_player = "콘솔은 플레이어를 지정해야 합니다: /iris tp <dimension> <player>"
 is_not_generated_by_iris = "{value} 에 의해 생성되지 않음 Iris."
 teleport_failed_dimension_is_not_loaded = "Teleport 실패: 차원 {dimensionId} 로드 되지 않습니다."
+teleport_failed_reason = "{dimensionId}(으)로 순간이동 실패: {reason}"
+teleport_cancelled_player_offline = "{dimensionId}(으)로 순간이동 취소됨: {value} 님이 더 이상 접속해 있지 않습니다."
+teleport_refused = "서버가 {dimensionId}(으)로의 순간이동을 거부했습니다."
 teleporting = "팟캐스트 {value} 으로 {dimensionId}..."
 is_not_generated_by_iris_2 = "{value} 에 의해 생성되지 않음 Iris."
 cannot_evacuate_primary_world_there_is_nowhere_send_players = "1 차 세계를 피할 수 없습니다. 플레이어에게 보내는 곳이 없습니다."

core/src/main/resources/languages/lt_LT.toml

@@ -774,6 +774,9 @@ opening_your_editor = "Atidaryti {value}  {value2} redaktoriuje."
 console_must_name_player_iris_tp_dimension_player = "Konsolė turi pavadinti žaidėją: /iris tp <dimension> <player>"
 is_not_generated_by_iris = "{value} generuoja ne Iris."
 teleport_failed_dimension_is_not_loaded = "Teleportas nepavyko: dimensija {dimensionId} neįkrauta."
+teleport_failed_reason = "Teleportavimas į {dimensionId} nepavyko: {reason}"
+teleport_cancelled_player_offline = "Teleportavimas į {dimensionId} atšauktas: {value} nebėra prisijungęs."
+teleport_refused = "Serveris atmetė teleportavimą į {dimensionId}."
 teleporting = "Teleportavimas {value} iki {dimensionId}..."
 is_not_generated_by_iris_2 = "{value} generuoja ne Iris."
 cannot_evacuate_primary_world_there_is_nowhere_send_players = "Negalima evakuoti pirminio pasaulio; nėra kur siųsti žaidėjų."

core/src/main/resources/languages/nl_NL.toml

@@ -769,6 +769,9 @@ opening_your_editor = "Openen {value}  {value2} in uw redacteur."
 console_must_name_player_iris_tp_dimension_player = "Console moet een speler een naam geven: /iris tp <dimension> <player>"
 is_not_generated_by_iris = "{value} wordt niet gegenereerd door Iris."
 teleport_failed_dimension_is_not_loaded = "Teleporteren mislukt: dimensie {dimensionId} is niet geladen."
+teleport_failed_reason = "Teleporteren naar {dimensionId} mislukt: {reason}"
+teleport_cancelled_player_offline = "Teleporteren naar {dimensionId} geannuleerd: {value} is niet meer online."
+teleport_refused = "De server heeft het teleporteren naar {dimensionId} geweigerd."
 teleporting = "Teleporteren {value} tot {dimensionId}..."
 is_not_generated_by_iris_2 = "{value} wordt niet gegenereerd door Iris."
 cannot_evacuate_primary_world_there_is_nowhere_send_players = "Kan de primaire wereld niet evacueren; er is geen plek om spelers te sturen."

core/src/main/resources/languages/pl_PL.toml

@@ -774,6 +774,9 @@ opening_your_editor = "Otwarcie {value}  {value2} w twoim wydawcy."
 console_must_name_player_iris_tp_dimension_player = "Konsola musi nazwać gracza: /iris tp <dimension> <player>"
 is_not_generated_by_iris = "{value} nie jest generowany przez Iris."
 teleport_failed_dimension_is_not_loaded = "Teleport nie powiódł się: wymiar {dimensionId} nie jest załadowany."
+teleport_failed_reason = "Teleportacja do {dimensionId} nie powiodła się: {reason}"
+teleport_cancelled_player_offline = "Teleportacja do {dimensionId} anulowana: {value} nie jest już online."
+teleport_refused = "Serwer odrzucił teleportację do {dimensionId}."
 teleporting = "Teleportowanie {value} do {dimensionId}..."
 is_not_generated_by_iris_2 = "{value} nie jest generowany przez Iris."
 cannot_evacuate_primary_world_there_is_nowhere_send_players = "Nie można ewakuować głównego świata; nie ma gdzie wysłać graczy."

core/src/main/resources/languages/pt_PT.toml

@@ -769,6 +769,9 @@ opening_your_editor = "Abertura {value}  {value2} no seu editor."
 console_must_name_player_iris_tp_dimension_player = "A consola deve nomear um jogador: /iris tp <dimension> <player>"
 is_not_generated_by_iris = "{value} não é gerado por Iris."
 teleport_failed_dimension_is_not_loaded = "Falha no teletransporte: dimensão {dimensionId} não está carregada."
+teleport_failed_reason = "Falha no teletransporte para {dimensionId}: {reason}"
+teleport_cancelled_player_offline = "Teletransporte para {dimensionId} cancelado: {value} já não está online."
+teleport_refused = "O servidor recusou o teletransporte para {dimensionId}."
 teleporting = "Teletransportando {value} para {dimensionId}..."
 is_not_generated_by_iris_2 = "{value} não é gerado por Iris."
 cannot_evacuate_primary_world_there_is_nowhere_send_players = "Não é possível evacuar o mundo primário; não há nenhum lugar para enviar jogadores."