v

- Restore cave spawning and correct floor placement across platforms.
- Enforce category population limits and clamp ambient spawn batches.
- Honor mob-spawning rules and entity-ticking chunk admission.
- Separate chunk saving from configurable distance-despawn retention.
- Add spawning regressions and Folia gameplay acceptance coverage.

.github/ISSUE_TEMPLATE/bug.yml

@@ -49,9 +49,11 @@ body:
     id: mcversion
     attributes:
       label: Minecraft Version
-      description: What version of Minecraft is the server on? Iris 4.x targets 26.2 only; older versions are not supported.
+      description: What version of Minecraft is the server on? Iris 4.x supports 26.1.2 to 26.3 on Bukkit-family servers and 26.3 on Fabric, Forge and NeoForge; older versions are not supported.
       options:
+        - '26.3'
         - '26.2'
+        - '26.1.2'
         - Other (unsupported)
     validations:
       required: true
@@ -59,7 +61,7 @@ body:
     id: loaderversion
     attributes:
       label: Platform / Loader Version
-      description: Exact server or loader build (see console). For example "Paper 26.2-60", "Fabric Loader 0.19.3", "NeoForge 26.2.0.12-beta".
+      description: Exact server or loader build (see console). For example "Paper 26.3-133", "Fabric Loader 0.19.5", "NeoForge 26.3.0.33-beta".
       placeholder: DO NOT SAY "LATEST"
     validations:
       required: true

README.md

@@ -4,7 +4,7 @@ Iris is a world generation engine for Minecraft servers and mod loaders. It gene
 biomes, caves, structures, objects, and entities from editable JSON packs, with a full in-game
 studio authoring workflow. The same engine runs as a Bukkit-family plugin and as a Fabric, Forge,
 or NeoForge server mod. Cross-platform generation targets deterministic parity for identical
-artifacts, pack bytes, seeds, and test areas. The master branch targets Minecraft 26.2.
+artifacts, pack bytes, seeds, and test areas. The master branch targets Minecraft 26.3.
 
 # [Support](https://discord.gg/3xxPTpT) **|** [Documentation](https://github.com/VolmitSoftware/docs/blob/master/iris/00-overview.md) **|** [Git](https://github.com/IrisDimensions)
 
@@ -20,12 +20,12 @@ Canonical English is defined in the typed Java catalogs under `core/src/main/jav
 
 | Platform | Artifact | Minecraft | Notes |
 |---|---|---|---|
-| Paper / Purpur / Leaf / Canvas | plugin jar | 26.1.2 - 26.2 | Full feature set |
-| Folia | plugin jar | 26.1.2 - 26.2 | Region-safe scheduling throughout |
-| Spigot / CraftBukkit | plugin jar | 26.1.2 - 26.2 | Managed `iris:*` creation and generation; exact vanilla-slot `/iris replace` is unavailable |
-| Fabric | mod jar | 26.2 | Server worldgen + client HUD; requires Fabric Loader 0.19.3+ |
-| Forge | mod jar | 26.2 | Server worldgen + client HUD; current target is Forge 26.2-65.1.1 |
-| NeoForge | mod jar | 26.2 | Server worldgen + client HUD; current target is NeoForge 26.2.0.59 |
+| Paper / Purpur / Leaf / Canvas | plugin jar | 26.1.2 - 26.3 | Full feature set |
+| Folia | plugin jar | 26.1.2 - 26.3 | Region-safe scheduling throughout |
+| Spigot / CraftBukkit | plugin jar | 26.1.2 - 26.3 | Managed `iris:*` creation and generation; exact vanilla-slot `/iris replace` is unavailable |
+| Fabric | mod jar | 26.3 | Server worldgen + client HUD; requires Fabric Loader 0.19.5+ |
+| Forge | mod jar | 26.3 | Server worldgen + client HUD; current target is Forge 26.3-66.0.8 |
+| NeoForge | mod jar | 26.3 | Server worldgen + client HUD; current target is NeoForge 26.3.0.33-beta |
 
 Java 25 is required on every platform.
 
@@ -271,6 +271,12 @@ when it exists, otherwise `build/consumers/` inside the repo. `-Plocation=/path/
 changes only the consumer directory. Both tasks copy all four verified platform jars into
 `../PluginOuts/`.
 
+VolmLib is built from source when a `VolmLib` checkout sits beside the repo or in a parent directory
+(`VOLMLIB_DIR` or `-PlocalVolmLibDirectory=<path>` pick another one). Without one, or with
+`-PuseLocalVolmLib=false`, the build uses VolmLib `master-SNAPSHOT` from JitPack. There is no VolmLib
+version to bump. The build logs which VolmLib it used, and every jar records it in
+`META-INF/volmit/volmlib.properties`.
+
 If you need help compiling as a developer or contributor, ask in the Discord.
 
 ## Adapters / modded development
@@ -298,9 +304,10 @@ properties:
 | `-PirisWorldCheck=<world>` | `iris.worldcheck` | Post-generation world integrity check |
 
 Fabric additionally takes `-PirisClientRunDir=<dir>` to relocate the `runClient` working directory.
-Shared code lives in `adapters/minecraft-common` (all adapters), `adapters/modded-common`
-(loaders + the shared test suite), and `adapters/client-common` (client HUD and world-type
-screens); every adapter adds those source directories, so one edit reaches all three loaders.
+Shared code lives in `adapters/modded-common` (loaders + the shared test suite) and
+`adapters/client-common` (client HUD and world-type screens); every adapter adds those source
+directories, so one edit reaches all three loaders. Shared Minecraft-native code lives in VolmLib
+(`native/minecraft-common`).
 
 For IDE import you can surface the three adapter builds in the root composite with
 `-PincludeModdedAdapters=true`. It is off by default: each adapter includes the root build back to

adapters/bukkit/nms/v26_2_R1/src/test/java/art/arcane/iris/nativegen/IrisChunkGeneratorHeightCacheTest.java

@@ -4,12 +4,12 @@ import art.arcane.volmlib.nativelib.v26_2_R1.terrain.NativeChunkGenerator;
 import art.arcane.volmlib.nativelib.minecraft26_2.terrain.NativeTerrainColumns;
 import art.arcane.iris.platform.bukkit.nms.BukkitTerrainColumnPolicy;
 
-import art.arcane.iris.generation.runtime.IrisComplex;
 import art.arcane.iris.generation.runtime.Engine;
 import art.arcane.iris.generation.runtime.GenerationSessionLease;
 import art.arcane.iris.world.history.BoundaryColumnGeometry;
 import art.arcane.iris.world.history.TerrainBoundarySignature;
 import art.arcane.iris.testsupport.PlatformLeakGuard;
+import art.arcane.volmlib.nativelib.terrain.NativeTerrainColumnPolicy;
 import net.minecraft.SharedConstants;
 import net.minecraft.server.Bootstrap;
 import net.minecraft.world.level.LevelHeightAccessor;
@@ -24,7 +24,7 @@ import java.util.Optional;
 import java.util.OptionalInt;
 
 import static org.junit.Assert.assertEquals;
-import static org.mockito.ArgumentMatchers.anyInt;
+import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.anyString;
 import static org.mockito.Mockito.CALLS_REAL_METHODS;
 import static org.mockito.Mockito.mock;
@@ -32,6 +32,7 @@ import static org.mockito.Mockito.doReturn;
 import static org.mockito.Mockito.times;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
+import static org.mockito.Mockito.never;
 
 public final class IrisChunkGeneratorHeightCacheTest {
     @Rule
@@ -44,68 +45,72 @@ public final class IrisChunkGeneratorHeightCacheTest {
     }
 
     @Test
-    public void repeatedNativeHeightSurvivesResolvedTerrainEvictionAndRuntimeChange() throws Exception {
+    public void repeatedNativeHeightUsesLiveHeightQueriesAcrossRuntimeChanges() throws Exception {
         Fixture fixture = fixture();
         LevelHeightAccessor bounds = LevelHeightAccessor.create(-16, 32);
-        assertEquals(-11, fixture.generator().getBaseHeight(-1, -33, Heightmap.Types.WORLD_SURFACE, bounds, null));
-        when(fixture.complex().resolvedTerrainColumn(-1, -33))
-                .thenThrow(new IllegalStateException("Full terrain was evicted"));
-
+        when(fixture.engine().getHeight(-1, -33, false)).thenReturn(4);
         for (int index = 0; index < 100; index++) {
             assertEquals(-11, fixture.generator().getBaseHeight(
                     -1, -33, Heightmap.Types.WORLD_SURFACE, bounds, null));
         }
-        verify(fixture.complex(), times(1)).resolvedTerrainColumn(-1, -33);
+        verify(fixture.engine(), times(100)).getHeight(-1, -33, false);
 
         when(fixture.engine().getCacheID()).thenReturn(2);
-        doReturn(Optional.of(signature())).when(fixture.complex()).resolvedTerrainColumn(-1, -33);
-        assertEquals(-11, fixture.generator().getBaseHeight(-1, -33, Heightmap.Types.WORLD_SURFACE, bounds, null));
-        verify(fixture.complex(), times(2)).resolvedTerrainColumn(-1, -33);
+        when(fixture.engine().getHeight(-1, -33, false)).thenReturn(7);
+        assertEquals(-8, fixture.generator().getBaseHeight(-1, -33, Heightmap.Types.WORLD_SURFACE, bounds, null));
+        verify(fixture.engine(), never()).getComplex();
+        verify(fixture.engine(), never()).getMode();
     }
 
     @Test
-    public void ordinaryHeightRemainsLiveUntilResolvedTransitionTerrainExists() throws Exception {
+    public void nativeHeightPredicatesSelectFluidOrSolidHeightWithoutGeneratingTerrain() throws Exception {
         Fixture fixture = fixture();
         LevelHeightAccessor bounds = LevelHeightAccessor.create(-16, 32);
-        when(fixture.complex().resolvedTerrainColumn(0, 0))
-                .thenReturn(Optional.empty(), Optional.empty(), Optional.of(signature()));
         when(fixture.engine().getHeight(0, 0, false)).thenReturn(20, 25);
+        when(fixture.engine().getHeight(0, 0, true)).thenReturn(8);
 
         assertEquals(5, fixture.generator().getBaseHeight(0, 0, Heightmap.Types.WORLD_SURFACE, bounds, null));
         assertEquals(10, fixture.generator().getBaseHeight(0, 0, Heightmap.Types.WORLD_SURFACE, bounds, null));
-        assertEquals(-11, fixture.generator().getBaseHeight(0, 0, Heightmap.Types.WORLD_SURFACE, bounds, null));
-        assertEquals(-11, fixture.generator().getBaseHeight(0, 0, Heightmap.Types.WORLD_SURFACE, bounds, null));
+        assertEquals(-7, fixture.generator().getBaseHeight(0, 0, Heightmap.Types.OCEAN_FLOOR, bounds, null));
         verify(fixture.engine(), times(2)).getHeight(0, 0, false);
-        verify(fixture.complex(), times(3)).resolvedTerrainColumn(0, 0);
+        verify(fixture.engine(), times(1)).getHeight(0, 0, true);
+        verify(fixture.engine(), never()).getComplex();
+        verify(fixture.engine(), never()).getMode();
     }
 
     @Test
     public void nativePredicatesAndAccessorBoundsRemainExact() throws Exception {
-        Fixture fixture = fixture();
+        NativeTerrainColumnPolicy policy = mock(NativeTerrainColumnPolicy.class);
+        NativeTerrainColumnPolicy.ColumnSession session = mock(NativeTerrainColumnPolicy.ColumnSession.class);
+        when(policy.openQuery(any())).thenReturn(session);
+        when(policy.placementKey(anyString())).thenAnswer(invocation -> invocation.getArgument(0));
+        doReturn(Optional.of(signature().geometry())).when(session).resolvedColumn();
+        NativeChunkGenerator<?, ?, ?, ?, ?> generator = generator(policy);
         LevelHeightAccessor bounds = LevelHeightAccessor.create(-16, 32);
         for (int repeat = 0; repeat < 2; repeat++) {
-            assertEquals(-11, fixture.generator().getBaseHeight(0, 0, Heightmap.Types.WORLD_SURFACE, bounds, null));
-            assertEquals(-13, fixture.generator().getBaseHeight(0, 0, Heightmap.Types.OCEAN_FLOOR, bounds, null));
-            assertEquals(-13, fixture.generator().getBaseHeight(0, 0, Heightmap.Types.MOTION_BLOCKING, bounds, null));
-            assertEquals(-14, fixture.generator().getBaseHeight(0, 0, Heightmap.Types.MOTION_BLOCKING_NO_LEAVES, bounds, null));
-            assertEquals(-14, fixture.generator().getBaseHeight(0, 0, Heightmap.Types.WORLD_SURFACE,
+            assertEquals(-11, generator.getBaseHeight(0, 0, Heightmap.Types.WORLD_SURFACE, bounds, null));
+            assertEquals(-13, generator.getBaseHeight(0, 0, Heightmap.Types.OCEAN_FLOOR, bounds, null));
+            assertEquals(-13, generator.getBaseHeight(0, 0, Heightmap.Types.MOTION_BLOCKING, bounds, null));
+            assertEquals(-14, generator.getBaseHeight(0, 0, Heightmap.Types.MOTION_BLOCKING_NO_LEAVES, bounds, null));
+            assertEquals(-14, generator.getBaseHeight(0, 0, Heightmap.Types.WORLD_SURFACE,
                     LevelHeightAccessor.create(-16, 2), null));
-            assertEquals(-14, fixture.generator().getBaseHeight(0, 0, Heightmap.Types.MOTION_BLOCKING_NO_LEAVES,
+            assertEquals(-14, generator.getBaseHeight(0, 0, Heightmap.Types.MOTION_BLOCKING_NO_LEAVES,
                     LevelHeightAccessor.create(-14, 3), null));
         }
-        verify(fixture.complex(), times(6)).resolvedTerrainColumn(0, 0);
+        verify(session, times(6)).resolvedColumn();
     }
 
     private static Fixture fixture() throws Exception {
         Engine engine = mock(Engine.class);
-        IrisComplex complex = mock(IrisComplex.class);
-        when(engine.getComplex()).thenReturn(complex);
         when(engine.getCacheID()).thenReturn(1);
         when(engine.acquireGenerationLease(anyString())).thenReturn(GenerationSessionLease.noop());
-        when(complex.resolvedTerrainColumn(anyInt(), anyInt())).thenReturn(Optional.of(signature()));
+        return new Fixture(generator(new BukkitTerrainColumnPolicy(engine, null)), engine);
+    }
+
+    private static NativeChunkGenerator<?, ?, ?, ?, ?> generator(NativeTerrainColumnPolicy policy) throws Exception {
         NativeChunkGenerator<?, ?, ?, ?, ?> generator = mock(NativeChunkGenerator.class, CALLS_REAL_METHODS);
-        set(generator, "terrainColumns", new NativeTerrainColumns(new BukkitTerrainColumnPolicy(engine, null)));
-        return new Fixture(generator, engine, complex);
+        set(generator, "terrainColumns", new NativeTerrainColumns(policy));
+        return generator;
     }
 
     private static void set(NativeChunkGenerator<?, ?, ?, ?, ?> generator, String name, Object value) throws Exception {
@@ -127,6 +132,6 @@ public final class IrisChunkGeneratorHeightCacheTest {
                         new TerrainBoundarySignature.BiomeEncoding(List.of("minecraft:plains"), new short[]{0})), geometry);
     }
 
-    private record Fixture(NativeChunkGenerator<?, ?, ?, ?, ?> generator, Engine engine, IrisComplex complex) {
+    private record Fixture(NativeChunkGenerator<?, ?, ?, ?, ?> generator, Engine engine) {
     }
 }

adapters/bukkit/nms/v26_2_R1/src/test/java/art/arcane/iris/platform/bukkit/nms/v26_2_R1/NmsChunkRetentionTest.java

@@ -0,0 +1,84 @@
+package art.arcane.iris.platform.bukkit.nms.v26_2_R1;
+
+import art.arcane.volmlib.nativelib.v26_2_R1.terrain.NativeTerrainAccessImpl;
+import ca.spottedleaf.moonrise.patches.chunk_system.scheduling.ChunkHolderManager;
+import ca.spottedleaf.moonrise.patches.chunk_system.scheduling.ChunkTaskScheduler;
+import net.minecraft.SharedConstants;
+import net.minecraft.server.Bootstrap;
+import net.minecraft.server.level.ChunkLevel;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.server.level.TicketType;
+import net.minecraft.world.level.chunk.status.ChunkStatus;
+import org.bukkit.craftbukkit.CraftWorld;
+import org.junit.BeforeClass;
+import org.junit.Test;
+import org.mockito.ArgumentCaptor;
+
+import java.lang.reflect.Field;
+
+import static org.junit.Assert.assertEquals;
+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.eq;
+import static org.mockito.ArgumentMatchers.isNull;
+import static org.mockito.ArgumentMatchers.same;
+import static org.mockito.Mockito.CALLS_REAL_METHODS;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+public class NmsChunkRetentionTest {
+    @BeforeClass
+    public static void bootstrapMinecraftRegistries() {
+        SharedConstants.tryDetectVersion();
+        Bootstrap.bootStrap();
+    }
+
+    @Test
+    public void retentionRequestsNothingBeyondTheOuterRingOfAFullRequest() {
+        NativeTerrainAccessImpl binding = mock(NativeTerrainAccessImpl.class, CALLS_REAL_METHODS);
+        assertEquals(ChunkLevel.RADIUS_AROUND_FULL_CHUNK, binding.fullChunkDependencyRadius());
+        assertEquals(ChunkLevel.MAX_LEVEL, ChunkHolderManager.MAX_TICKET_LEVEL);
+        assertEquals(ChunkLevel.generationStatus(ChunkLevel.FULL_CHUNK_LEVEL + binding.fullChunkDependencyRadius()),
+                ChunkLevel.generationStatus(ChunkHolderManager.MAX_TICKET_LEVEL));
+        assertEquals(ChunkStatus.STRUCTURE_STARTS, ChunkLevel.generationStatus(ChunkHolderManager.MAX_TICKET_LEVEL));
+    }
+
+    @Test
+    public void retainAndReleaseUseOnePermanentNonPersistentTicketAtTheMaximumLevel() throws Exception {
+        NativeTerrainAccessImpl binding = mock(NativeTerrainAccessImpl.class, CALLS_REAL_METHODS);
+        CraftWorld world = mock(CraftWorld.class);
+        ServerLevel level = mock(ServerLevel.class);
+        ChunkTaskScheduler scheduler = mock(ChunkTaskScheduler.class);
+        ChunkHolderManager manager = mock(ChunkHolderManager.class);
+        Field managerField = ChunkTaskScheduler.class.getField("chunkHolderManager");
+        managerField.setAccessible(true);
+        managerField.set(scheduler, manager);
+        when(world.getHandle()).thenReturn(level);
+        when(level.moonrise$getChunkTaskScheduler()).thenReturn(scheduler);
+        when(manager.addTicketAtLevel(any(TicketType.class), eq(3), eq(-4), eq(ChunkHolderManager.MAX_TICKET_LEVEL), isNull()))
+                .thenReturn(true);
+        when(manager.removeTicketAtLevel(any(TicketType.class), eq(3), eq(-4), eq(ChunkHolderManager.MAX_TICKET_LEVEL), isNull()))
+                .thenReturn(true);
+
+        assertTrue(binding.retainChunk(world, 3, -4));
+        ArgumentCaptor<TicketType> type = ArgumentCaptor.forClass(TicketType.class);
+        verify(manager).addTicketAtLevel(type.capture(), eq(3), eq(-4), eq(ChunkHolderManager.MAX_TICKET_LEVEL), isNull());
+        assertEquals(TicketType.NO_TIMEOUT, type.getValue().timeout());
+        assertTrue(type.getValue().doesLoad());
+        assertFalse(type.getValue().doesSimulate());
+        assertFalse(type.getValue().persist());
+
+        assertTrue(binding.releaseChunk(world, 3, -4));
+        verify(manager).removeTicketAtLevel(same(type.getValue()), eq(3), eq(-4), eq(ChunkHolderManager.MAX_TICKET_LEVEL), isNull());
+
+        binding.retainChunk(world, 3, -4);
+        ArgumentCaptor<TicketType> again = ArgumentCaptor.forClass(TicketType.class);
+        verify(manager, times(2)).addTicketAtLevel(again.capture(), eq(3), eq(-4),
+                eq(ChunkHolderManager.MAX_TICKET_LEVEL), isNull());
+        assertSame(type.getValue(), again.getValue());
+    }
+}

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/nativegen/IrisChunkGeneratorHeightCacheTest.java

@@ -4,12 +4,12 @@ import art.arcane.volmlib.nativelib.v26_3_R1.terrain.NativeChunkGenerator;
 import art.arcane.volmlib.nativelib.v26_3_R1.terrain.NativeTerrainColumns;
 import art.arcane.iris.platform.bukkit.nms.BukkitTerrainColumnPolicy;
 
-import art.arcane.iris.generation.runtime.IrisComplex;
 import art.arcane.iris.generation.runtime.Engine;
 import art.arcane.iris.generation.runtime.GenerationSessionLease;
 import art.arcane.iris.world.history.BoundaryColumnGeometry;
 import art.arcane.iris.world.history.TerrainBoundarySignature;
 import art.arcane.iris.testsupport.PlatformLeakGuard;
+import art.arcane.volmlib.nativelib.terrain.NativeTerrainColumnPolicy;
 import net.minecraft.SharedConstants;
 import net.minecraft.server.Bootstrap;
 import net.minecraft.world.level.LevelHeightAccessor;
@@ -24,7 +24,7 @@ import java.util.Optional;
 import java.util.OptionalInt;
 
 import static org.junit.Assert.assertEquals;
-import static org.mockito.ArgumentMatchers.anyInt;
+import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.anyString;
 import static org.mockito.Mockito.CALLS_REAL_METHODS;
 import static org.mockito.Mockito.mock;
@@ -32,6 +32,7 @@ import static org.mockito.Mockito.doReturn;
 import static org.mockito.Mockito.times;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
+import static org.mockito.Mockito.never;
 
 public final class IrisChunkGeneratorHeightCacheTest {
     @Rule
@@ -45,68 +46,72 @@ public final class IrisChunkGeneratorHeightCacheTest {
     }
 
     @Test
-    public void repeatedNativeHeightSurvivesResolvedTerrainEvictionAndRuntimeChange() throws Exception {
+    public void repeatedNativeHeightUsesLiveHeightQueriesAcrossRuntimeChanges() throws Exception {
         Fixture fixture = fixture();
         LevelHeightAccessor bounds = LevelHeightAccessor.create(-16, 32);
-        assertEquals(-11, fixture.generator().getBaseHeight(-1, -33, Heightmap.Types.WORLD_SURFACE, bounds, null));
-        when(fixture.complex().resolvedTerrainColumn(-1, -33))
-                .thenThrow(new IllegalStateException("Full terrain was evicted"));
-
+        when(fixture.engine().getHeight(-1, -33, false)).thenReturn(4);
         for (int index = 0; index < 100; index++) {
             assertEquals(-11, fixture.generator().getBaseHeight(
                     -1, -33, Heightmap.Types.WORLD_SURFACE, bounds, null));
         }
-        verify(fixture.complex(), times(1)).resolvedTerrainColumn(-1, -33);
+        verify(fixture.engine(), times(100)).getHeight(-1, -33, false);
 
         when(fixture.engine().getCacheID()).thenReturn(2);
-        doReturn(Optional.of(signature())).when(fixture.complex()).resolvedTerrainColumn(-1, -33);
-        assertEquals(-11, fixture.generator().getBaseHeight(-1, -33, Heightmap.Types.WORLD_SURFACE, bounds, null));
-        verify(fixture.complex(), times(2)).resolvedTerrainColumn(-1, -33);
+        when(fixture.engine().getHeight(-1, -33, false)).thenReturn(7);
+        assertEquals(-8, fixture.generator().getBaseHeight(-1, -33, Heightmap.Types.WORLD_SURFACE, bounds, null));
+        verify(fixture.engine(), never()).getComplex();
+        verify(fixture.engine(), never()).getMode();
     }
 
     @Test
-    public void ordinaryHeightRemainsLiveUntilResolvedTransitionTerrainExists() throws Exception {
+    public void nativeHeightPredicatesSelectFluidOrSolidHeightWithoutGeneratingTerrain() throws Exception {
         Fixture fixture = fixture();
         LevelHeightAccessor bounds = LevelHeightAccessor.create(-16, 32);
-        when(fixture.complex().resolvedTerrainColumn(0, 0))
-                .thenReturn(Optional.empty(), Optional.empty(), Optional.of(signature()));
         when(fixture.engine().getHeight(0, 0, false)).thenReturn(20, 25);
+        when(fixture.engine().getHeight(0, 0, true)).thenReturn(8);
 
         assertEquals(5, fixture.generator().getBaseHeight(0, 0, Heightmap.Types.WORLD_SURFACE, bounds, null));
         assertEquals(10, fixture.generator().getBaseHeight(0, 0, Heightmap.Types.WORLD_SURFACE, bounds, null));
-        assertEquals(-11, fixture.generator().getBaseHeight(0, 0, Heightmap.Types.WORLD_SURFACE, bounds, null));
-        assertEquals(-11, fixture.generator().getBaseHeight(0, 0, Heightmap.Types.WORLD_SURFACE, bounds, null));
+        assertEquals(-7, fixture.generator().getBaseHeight(0, 0, Heightmap.Types.OCEAN_FLOOR, bounds, null));
         verify(fixture.engine(), times(2)).getHeight(0, 0, false);
-        verify(fixture.complex(), times(3)).resolvedTerrainColumn(0, 0);
+        verify(fixture.engine(), times(1)).getHeight(0, 0, true);
+        verify(fixture.engine(), never()).getComplex();
+        verify(fixture.engine(), never()).getMode();
     }
 
     @Test
     public void nativePredicatesAndAccessorBoundsRemainExact() throws Exception {
-        Fixture fixture = fixture();
+        NativeTerrainColumnPolicy policy = mock(NativeTerrainColumnPolicy.class);
+        NativeTerrainColumnPolicy.ColumnSession session = mock(NativeTerrainColumnPolicy.ColumnSession.class);
+        when(policy.openQuery(any())).thenReturn(session);
+        when(policy.placementKey(anyString())).thenAnswer(invocation -> invocation.getArgument(0));
+        doReturn(Optional.of(signature().geometry())).when(session).resolvedColumn();
+        NativeChunkGenerator<?, ?, ?, ?, ?> generator = generator(policy);
         LevelHeightAccessor bounds = LevelHeightAccessor.create(-16, 32);
         for (int repeat = 0; repeat < 2; repeat++) {
-            assertEquals(-11, fixture.generator().getBaseHeight(0, 0, Heightmap.Types.WORLD_SURFACE, bounds, null));
-            assertEquals(-13, fixture.generator().getBaseHeight(0, 0, Heightmap.Types.OCEAN_FLOOR, bounds, null));
-            assertEquals(-13, fixture.generator().getBaseHeight(0, 0, Heightmap.Types.MOTION_BLOCKING, bounds, null));
-            assertEquals(-14, fixture.generator().getBaseHeight(0, 0, Heightmap.Types.MOTION_BLOCKING_NO_LEAVES, bounds, null));
-            assertEquals(-14, fixture.generator().getBaseHeight(0, 0, Heightmap.Types.WORLD_SURFACE,
+            assertEquals(-11, generator.getBaseHeight(0, 0, Heightmap.Types.WORLD_SURFACE, bounds, null));
+            assertEquals(-13, generator.getBaseHeight(0, 0, Heightmap.Types.OCEAN_FLOOR, bounds, null));
+            assertEquals(-13, generator.getBaseHeight(0, 0, Heightmap.Types.MOTION_BLOCKING, bounds, null));
+            assertEquals(-14, generator.getBaseHeight(0, 0, Heightmap.Types.MOTION_BLOCKING_NO_LEAVES, bounds, null));
+            assertEquals(-14, generator.getBaseHeight(0, 0, Heightmap.Types.WORLD_SURFACE,
                     LevelHeightAccessor.create(-16, 2), null));
-            assertEquals(-14, fixture.generator().getBaseHeight(0, 0, Heightmap.Types.MOTION_BLOCKING_NO_LEAVES,
+            assertEquals(-14, generator.getBaseHeight(0, 0, Heightmap.Types.MOTION_BLOCKING_NO_LEAVES,
                     LevelHeightAccessor.create(-14, 3), null));
         }
-        verify(fixture.complex(), times(6)).resolvedTerrainColumn(0, 0);
+        verify(session, times(6)).resolvedColumn();
     }
 
     private static Fixture fixture() throws Exception {
         Engine engine = mock(Engine.class);
-        IrisComplex complex = mock(IrisComplex.class);
-        when(engine.getComplex()).thenReturn(complex);
         when(engine.getCacheID()).thenReturn(1);
         when(engine.acquireGenerationLease(anyString())).thenReturn(GenerationSessionLease.noop());
-        when(complex.resolvedTerrainColumn(anyInt(), anyInt())).thenReturn(Optional.of(signature()));
+        return new Fixture(generator(new BukkitTerrainColumnPolicy(engine, null)), engine);
+    }
+
+    private static NativeChunkGenerator<?, ?, ?, ?, ?> generator(NativeTerrainColumnPolicy policy) throws Exception {
         NativeChunkGenerator<?, ?, ?, ?, ?> generator = mock(NativeChunkGenerator.class, CALLS_REAL_METHODS);
-        set(generator, "terrainColumns", new NativeTerrainColumns(new BukkitTerrainColumnPolicy(engine, null)));
-        return new Fixture(generator, engine, complex);
+        set(generator, "terrainColumns", new NativeTerrainColumns(policy));
+        return generator;
     }
 
     private static void set(NativeChunkGenerator<?, ?, ?, ?, ?> generator, String name, Object value) throws Exception {
@@ -128,6 +133,6 @@ public final class IrisChunkGeneratorHeightCacheTest {
                         new TerrainBoundarySignature.BiomeEncoding(List.of("minecraft:plains"), new short[]{0})), geometry);
     }
 
-    private record Fixture(NativeChunkGenerator<?, ?, ?, ?, ?> generator, Engine engine, IrisComplex complex) {
+    private record Fixture(NativeChunkGenerator<?, ?, ?, ?, ?> generator, Engine engine) {
     }
 }

adapters/bukkit/nms/v26_3_R1/src/test/java/art/arcane/iris/platform/bukkit/nms/v26_3_R1/CustomBiomeCodecTest.java

@@ -13,6 +13,7 @@ import net.minecraft.data.registries.VanillaRegistries;
 import net.minecraft.resources.RegistryOps;
 import net.minecraft.server.Bootstrap;
 import net.minecraft.world.attribute.EnvironmentAttributes;
+import net.minecraft.world.attribute.modifier.MobSpawnSettingsModifier;
 import net.minecraft.world.entity.MobCategory;
 import net.minecraft.world.level.biome.Biome;
 import net.minecraft.world.level.biome.MobSpawnSettings;
@@ -53,5 +54,7 @@ public class CustomBiomeCodecTest {
         assertEquals(2, decoded.count().minInclusive());
         assertEquals(4, decoded.count().maxInclusive());
         assertEquals(0x102030, biome.getWaterColor() & 0xFFFFFF);
+        assertEquals(MobSpawnSettingsModifier.overlay(),
+                biome.getAttributes().get(EnvironmentAttributes.NATURAL_MOB_SPAWNS).modifier());
     }
 }

adapters/bukkit/nms/v26_3_R1/src/test/java/art/arcane/iris/platform/bukkit/nms/v26_3_R1/NmsChunkRetentionTest.java

@@ -0,0 +1,84 @@
+package art.arcane.iris.platform.bukkit.nms.v26_3_R1;
+
+import art.arcane.volmlib.nativelib.v26_3_R1.terrain.NativeTerrainAccessImpl;
+import ca.spottedleaf.moonrise.patches.chunk_system.scheduling.ChunkHolderManager;
+import ca.spottedleaf.moonrise.patches.chunk_system.scheduling.ChunkTaskScheduler;
+import net.minecraft.SharedConstants;
+import net.minecraft.server.Bootstrap;
+import net.minecraft.server.level.ChunkLevel;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.server.level.TicketType;
+import net.minecraft.world.level.chunk.status.ChunkStatus;
+import org.bukkit.craftbukkit.CraftWorld;
+import org.junit.BeforeClass;
+import org.junit.Test;
+import org.mockito.ArgumentCaptor;
+
+import java.lang.reflect.Field;
+
+import static org.junit.Assert.assertEquals;
+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.eq;
+import static org.mockito.ArgumentMatchers.isNull;
+import static org.mockito.ArgumentMatchers.same;
+import static org.mockito.Mockito.CALLS_REAL_METHODS;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+public class NmsChunkRetentionTest {
+    @BeforeClass
+    public static void bootstrapMinecraftRegistries() {
+        SharedConstants.tryDetectVersion();
+        Bootstrap.bootStrap();
+    }
+
+    @Test
+    public void retentionRequestsNothingBeyondTheOuterRingOfAFullRequest() {
+        NativeTerrainAccessImpl binding = mock(NativeTerrainAccessImpl.class, CALLS_REAL_METHODS);
+        assertEquals(ChunkLevel.RADIUS_AROUND_FULL_CHUNK, binding.fullChunkDependencyRadius());
+        assertEquals(ChunkLevel.MAX_LEVEL, ChunkHolderManager.MAX_TICKET_LEVEL);
+        assertEquals(ChunkLevel.generationStatus(ChunkLevel.FULL_CHUNK_LEVEL + binding.fullChunkDependencyRadius()),
+                ChunkLevel.generationStatus(ChunkHolderManager.MAX_TICKET_LEVEL));
+        assertEquals(ChunkStatus.STRUCTURE_STARTS, ChunkLevel.generationStatus(ChunkHolderManager.MAX_TICKET_LEVEL));
+    }
+
+    @Test
+    public void retainAndReleaseUseOnePermanentNonPersistentTicketAtTheMaximumLevel() throws Exception {
+        NativeTerrainAccessImpl binding = mock(NativeTerrainAccessImpl.class, CALLS_REAL_METHODS);
+        CraftWorld world = mock(CraftWorld.class);
+        ServerLevel level = mock(ServerLevel.class);
+        ChunkTaskScheduler scheduler = mock(ChunkTaskScheduler.class);
+        ChunkHolderManager manager = mock(ChunkHolderManager.class);
+        Field managerField = ChunkTaskScheduler.class.getField("chunkHolderManager");
+        managerField.setAccessible(true);
+        managerField.set(scheduler, manager);
+        when(world.getHandle()).thenReturn(level);
+        when(level.moonrise$getChunkTaskScheduler()).thenReturn(scheduler);
+        when(manager.addTicketAtLevel(any(TicketType.class), eq(3), eq(-4), eq(ChunkHolderManager.MAX_TICKET_LEVEL), isNull()))
+                .thenReturn(true);
+        when(manager.removeTicketAtLevel(any(TicketType.class), eq(3), eq(-4), eq(ChunkHolderManager.MAX_TICKET_LEVEL), isNull()))
+                .thenReturn(true);
+
+        assertTrue(binding.retainChunk(world, 3, -4));
+        ArgumentCaptor<TicketType> type = ArgumentCaptor.forClass(TicketType.class);
+        verify(manager).addTicketAtLevel(type.capture(), eq(3), eq(-4), eq(ChunkHolderManager.MAX_TICKET_LEVEL), isNull());
+        assertEquals(TicketType.NO_TIMEOUT, type.getValue().timeout());
+        assertTrue(type.getValue().doesLoad());
+        assertFalse(type.getValue().doesSimulate());
+        assertFalse(type.getValue().persist());
+
+        assertTrue(binding.releaseChunk(world, 3, -4));
+        verify(manager).removeTicketAtLevel(same(type.getValue()), eq(3), eq(-4), eq(ChunkHolderManager.MAX_TICKET_LEVEL), isNull());
+
+        binding.retainChunk(world, 3, -4);
+        ArgumentCaptor<TicketType> again = ArgumentCaptor.forClass(TicketType.class);
+        verify(manager, times(2)).addTicketAtLevel(again.capture(), eq(3), eq(-4),
+                eq(ChunkHolderManager.MAX_TICKET_LEVEL), isNull());
+        assertSame(type.getValue(), again.getValue());
+    }
+}

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/build.gradle

@@ -2,15 +2,11 @@ String apiVersion = providers.gradleProperty('apiVersion').get()
 def mainClass = 'art.arcane.iris.Iris'
 def bootstrapperClass = 'art.arcane.iris.IrisBootstrap'
 
-String volmLibCoordinate = providers.gradleProperty('volmLibCoordinate')
-    .orElse('com.github.VolmitSoftware:VolmLib:master-SNAPSHOT')
-    .get()
-
 dependencies {
     compileOnly(project(':core'))
     compileOnly(libs.lombok)
     annotationProcessor(libs.lombok)
-    compileOnly(volmLibCoordinate) {
+    compileOnly('com.github.VolmitSoftware.VolmLib:volmlib-shared:master-SNAPSHOT') {
         transitive = false
     }
     compileOnly(libs.paper.api)
@@ -23,7 +19,7 @@ dependencies {
     testImplementation(libs.bstats)
     testImplementation(project(':core'))
     testImplementation(testFixtures(project(':core')))
-    testImplementation(volmLibCoordinate) {
+    testImplementation('com.github.VolmitSoftware.VolmLib:volmlib-shared:master-SNAPSHOT') {
         transitive = false
     }
     compileOnly(libs.placeholderApi)

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/api/tree/TreeFellerRunHooks.java

@@ -1,6 +1,10 @@
 package art.arcane.iris.api.tree;
 
 public interface TreeFellerRunHooks {
+    default boolean requiresSneaking() {
+        return true;
+    }
+
     TreeFellerRunHooks NONE = new TreeFellerRunHooks() {
         @Override
         public void onActivationAccepted() {

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/generation/runtime/GenerationRateWindow.java

@@ -0,0 +1,35 @@
+package art.arcane.iris.generation.runtime;
+
+final class GenerationRateWindow {
+    static final long TIMING_IDLE_MILLIS = 10_000L;
+
+    private long lastSampleAtMs;
+    private int lastGeneratedCount;
+    private long lastGenerationAtMs;
+
+    double sampleChunksPerSecond(int generatedCount, long sampledAtMs) {
+        int safeGeneratedCount = Math.max(0, generatedCount);
+        long previousAt = lastSampleAtMs;
+        int previousCount = lastGeneratedCount;
+        lastSampleAtMs = sampledAtMs;
+        lastGeneratedCount = safeGeneratedCount;
+        if (previousAt <= 0L) {
+            if (safeGeneratedCount > 0) {
+                lastGenerationAtMs = sampledAtMs;
+            }
+            return 0D;
+        }
+        if (sampledAtMs <= previousAt) {
+            return 0D;
+        }
+        int generatedDelta = Math.max(0, safeGeneratedCount - previousCount);
+        if (generatedDelta > 0) {
+            lastGenerationAtMs = sampledAtMs;
+        }
+        return generatedDelta * 1000D / (sampledAtMs - previousAt);
+    }
+
+    boolean generationTimingsFresh(long sampledAtMs) {
+        return lastGenerationAtMs > 0L && sampledAtMs - lastGenerationAtMs <= TIMING_IDLE_MILLIS;
+    }
+}

adapters/bukkit/plugin/src/main/java/art/arcane/iris/generation/runtime/IrisEngineSVC.java

@@ -460,8 +460,12 @@ public final class IrisEngineSVC implements IrisService {
                     continue;
                 }
 
-                double chunksPerSecond = registered.sampleChunksPerSecond(engine.getGenerated(), now);
-                worldSnapshots.add(EngineTelemetrySnapshot.capture(engine, chunksPerSecond, now));
+                double chunksPerSecond = registered.generationRate.sampleChunksPerSecond(engine.getGenerated(), now);
+                worldSnapshots.add(EngineTelemetrySnapshot.capture(
+                        engine,
+                        chunksPerSecond,
+                        registered.generationRate.generationTimingsFresh(now),
+                        now));
                 registered.clearMetricsFailure();
             } catch (Throwable exception) {
                 if (EngineMaintenance.isMantleClosed(exception)) {
@@ -552,6 +556,7 @@ public final class IrisEngineSVC implements IrisService {
                 progress.generated(),
                 progress.totalChunks(),
                 progress.chunksRemaining(),
+                progress.chunksInFlight(),
                 progress.chunksPerSecond(),
                 progress.eta(),
                 progress.elapsed(),
@@ -612,8 +617,7 @@ public final class IrisEngineSVC implements IrisService {
         private final AtomicReference<CompletableFuture<Void>> activeMaintenance = new AtomicReference<>();
         private volatile ScheduledFuture<?> maintenance;
         private volatile boolean closed;
-        private long lastGeneratedSampleAtMs;
-        private int lastGeneratedCount;
+        private final GenerationRateWindow generationRate = new GenerationRateWindow();
 
         private Registered(Registration registration, ScheduledThreadPoolExecutor executor) {
             name = registration.name();
@@ -696,19 +700,6 @@ public final class IrisEngineSVC implements IrisService {
             return activeMaintenance.get() != null;
         }
 
-        private double sampleChunksPerSecond(int generatedCount, long sampledAtMs) {
-            int safeGeneratedCount = Math.max(0, generatedCount);
-            long previousAt = lastGeneratedSampleAtMs;
-            int previousCount = lastGeneratedCount;
-            lastGeneratedSampleAtMs = sampledAtMs;
-            lastGeneratedCount = safeGeneratedCount;
-            if (previousAt <= 0L || sampledAtMs <= previousAt) {
-                return 0D;
-            }
-            int generatedDelta = Math.max(0, safeGeneratedCount - previousCount);
-            return generatedDelta * 1000D / (sampledAtMs - previousAt);
-        }
-
         private void close() {
             if (closed) {
                 return;

adapters/bukkit/plugin/src/main/java/art/arcane/iris/generation/runtime/IrisTelemetrySnapshot.java

@@ -101,6 +101,7 @@ public record IrisTelemetrySnapshot(
             long generated,
             long total,
             long remaining,
+            long inFlight,
             double chunksPerSecond,
             long etaMs,
             long elapsedMs,
@@ -115,6 +116,7 @@ public record IrisTelemetrySnapshot(
                 0L,
                 0L,
                 0L,
+                0L,
                 0D,
                 0L,
                 0L,
@@ -130,6 +132,7 @@ public record IrisTelemetrySnapshot(
             generated = Math.max(0L, generated);
             total = Math.max(0L, total);
             remaining = Math.max(0L, remaining);
+            inFlight = Math.max(0L, inFlight);
             chunksPerSecond = Double.isFinite(chunksPerSecond) ? Math.max(0D, chunksPerSecond) : 0D;
             etaMs = Math.max(0L, etaMs);
             elapsedMs = Math.max(0L, elapsedMs);

adapters/bukkit/plugin/src/main/java/art/arcane/iris/integration/IrisIntegrationService.java

@@ -319,6 +319,7 @@ public class IrisIntegrationService implements IrisService, IntegrationServiceCo
                     IntegrationMetricSchema.IRIS_PREGEN_GENERATED,
                     IntegrationMetricSchema.IRIS_PREGEN_TOTAL,
                     IntegrationMetricSchema.IRIS_PREGEN_QUEUE,
+                    IntegrationMetricSchema.IRIS_PREGEN_REMAINING,
                     IntegrationMetricSchema.IRIS_PREGEN_THROUGHPUT,
                     IntegrationMetricSchema.IRIS_PREGEN_ETA_MS,
                     IntegrationMetricSchema.IRIS_PREGEN_ELAPSED_MS,
@@ -332,7 +333,8 @@ public class IrisIntegrationService implements IrisService, IntegrationServiceCo
         put(samples, IntegrationMetricSchema.IRIS_PREGEN_PROGRESS, pregenerator.progressPercent(), sampledAtMs);
         put(samples, IntegrationMetricSchema.IRIS_PREGEN_GENERATED, pregenerator.generated(), sampledAtMs);
         put(samples, IntegrationMetricSchema.IRIS_PREGEN_TOTAL, pregenerator.total(), sampledAtMs);
-        put(samples, IntegrationMetricSchema.IRIS_PREGEN_QUEUE, pregenerator.remaining(), sampledAtMs);
+        put(samples, IntegrationMetricSchema.IRIS_PREGEN_QUEUE, pregenerator.inFlight(), sampledAtMs);
+        put(samples, IntegrationMetricSchema.IRIS_PREGEN_REMAINING, pregenerator.remaining(), sampledAtMs);
         put(samples, IntegrationMetricSchema.IRIS_PREGEN_THROUGHPUT, pregenerator.chunksPerSecond(), sampledAtMs);
         put(samples, IntegrationMetricSchema.IRIS_PREGEN_ETA_MS, pregenerator.etaMs(), sampledAtMs);
         put(samples, IntegrationMetricSchema.IRIS_PREGEN_ELAPSED_MS, pregenerator.elapsedMs(), sampledAtMs);

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/main/java/art/arcane/iris/world/tree/TreeFellerSVC.java

@@ -219,7 +219,7 @@ public class TreeFellerSVC implements IrisService, IrisTreeFellerService {
     @EventHandler(priority = EventPriority.MONITOR, ignoreCancelled = true)
     public void haltWhenSneakingStops(PlayerToggleSneakEvent event) {
         if (!event.isSneaking()) {
-            runner.finishRuns(event.getPlayer().getUniqueId());
+            runner.finishSneakRuns(event.getPlayer().getUniqueId());
         }
     }
 

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

@@ -523,10 +523,15 @@ final class TreeFellingRunner {
     }
 
     private boolean isRunControlActive(FellingRun run, Player player) {
-        return player.isOnline()
-                && player.getGameMode() == GameMode.SURVIVAL
-                && player.isSneaking()
-                && player.getWorld().equals(run.candidate.world());
+        try {
+            return player.isOnline()
+                    && player.getGameMode() == GameMode.SURVIVAL
+                    && (!run.runHooks.requiresSneaking() || player.isSneaking())
+                    && player.getWorld().equals(run.candidate.world());
+        } catch (RuntimeException error) {
+            IrisLogging.reportError("An Iris tree-feller integration control check failed.", error);
+            return false;
+        }
     }
 
     private boolean reserveLogCost(FellingRun run) {
@@ -622,6 +627,24 @@ final class TreeFellingRunner {
         }
     }
 
+    void finishSneakRuns(UUID playerId) {
+        Set<FellingRun> runs = service.activeRuns.get(playerId);
+        if (runs == null) {
+            return;
+        }
+        for (FellingRun run : List.copyOf(runs)) {
+            try {
+                if (!run.runHooks.requiresSneaking()) {
+                    continue;
+                }
+            } catch (RuntimeException error) {
+                IrisLogging.reportError("An Iris tree-feller integration control check failed.", error);
+            }
+            run.abortReason = "halted";
+            finish(run);
+        }
+    }
+
     private Map<ChunkPosition, List<TreeMarkerTraversal.Position>> groupByChunk(
             List<TreeMarkerTraversal.Position> positions
     ) {

adapters/bukkit/plugin/src/test/gameplay/natural-spawning-fixture/build.gradle

@@ -0,0 +1,35 @@
+plugins {
+    id 'java'
+}
+
+version = '1.0.0'
+
+repositories {
+    mavenCentral()
+    maven { url = 'https://repo.papermc.io/repository/maven-public/' }
+}
+
+dependencies {
+    compileOnly files(providers.gradleProperty('irisJar').get())
+    compileOnly files(providers.gradleProperty('irisGsonJar').get())
+    compileOnly 'io.papermc.paper:paper-api:26.1.2.build.74-stable'
+}
+
+java {
+    toolchain.languageVersion = JavaLanguageVersion.of(25)
+}
+
+sourceSets {
+    main {
+        java.srcDirs = ['src']
+        resources.srcDirs = ['resources']
+    }
+}
+
+tasks.withType(JavaCompile).configureEach {
+    options.compilerArgs += '-parameters'
+}
+
+tasks.named('jar') {
+    archiveBaseName = 'IrisNaturalSpawningFixture'
+}

adapters/bukkit/plugin/src/test/gameplay/natural-spawning-fixture/resources/plugin.yml

@@ -0,0 +1,12 @@
+name: IrisNaturalSpawningFixture
+version: 1.0.0
+main: art.arcane.iris.fixture.NaturalSpawningFixture
+api-version: '26.1.2'
+folia-supported: true
+depend: [Iris]
+commands:
+  irisspawnqa:
+    permission: irisspawnqa.run
+permissions:
+  irisspawnqa.run:
+    default: op

adapters/bukkit/plugin/src/test/gameplay/natural-spawning-fixture/settings.gradle

@@ -0,0 +1 @@
+rootProject.name = 'iris-natural-spawning-fixture'

adapters/bukkit/plugin/src/test/gameplay/natural-spawning-fixture/src/art/arcane/iris/fixture/NaturalSpawningFixture.java

@@ -0,0 +1,472 @@
+package art.arcane.iris.fixture;
+
+import art.arcane.iris.configuration.IrisSettings;
+import art.arcane.iris.generation.biome.IrisBiome;
+import art.arcane.iris.generation.runtime.BiomeEnvironment;
+import art.arcane.iris.generation.runtime.Engine;
+import art.arcane.iris.world.IrisCreator;
+import art.arcane.iris.world.entity.IrisSpawner;
+import art.arcane.iris.world.entity.IrisEntitySpawn;
+import art.arcane.iris.world.entity.IrisEntity;
+import art.arcane.iris.platform.bukkit.BukkitPlatform;
+import art.arcane.iris.platform.bukkit.BukkitEntityType;
+import art.arcane.iris.world.IrisToolbelt;
+import art.arcane.iris.world.history.SavedBiomeUnavailableException;
+import org.bukkit.Bukkit;
+import org.bukkit.Chunk;
+import org.bukkit.Difficulty;
+import org.bukkit.GameMode;
+import org.bukkit.HeightMap;
+import org.bukkit.GameRules;
+import org.bukkit.Location;
+import org.bukkit.Material;
+import org.bukkit.NamespacedKey;
+import org.bukkit.World;
+import org.bukkit.command.Command;
+import org.bukkit.command.CommandSender;
+import org.bukkit.entity.Entity;
+import org.bukkit.entity.EntityType;
+import org.bukkit.entity.LivingEntity;
+import org.bukkit.entity.Player;
+import org.bukkit.event.EventHandler;
+import org.bukkit.event.EventPriority;
+import org.bukkit.event.Listener;
+import org.bukkit.event.entity.CreatureSpawnEvent;
+import org.bukkit.plugin.java.JavaPlugin;
+
+import java.lang.reflect.Field;
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.TreeMap;
+import java.util.concurrent.CompletableFuture;
+import java.util.logging.Level;
+
+public final class NaturalSpawningFixture extends JavaPlugin implements Listener {
+    private static final NamespacedKey WORLD_KEY = new NamespacedKey("iris", "spawn_qa");
+    private static final long WORLD_SEED = 78264193L;
+    private static final int FROG_CAPACITY = 16;
+    private static final int ZOMBIE_CAPACITY = 2;
+    private static final int BIOME_READY_ATTEMPTS = 60;
+    private static final long BIOME_RETRY_TICKS = 10L;
+
+    private boolean previousAmbient;
+    private boolean previousMarkers;
+    private boolean previousForcedPersistence;
+    private volatile boolean ready;
+    private int firstZombieBatch;
+    private int ambientEvents;
+    private int cancelledAmbientEvents;
+    private final ThreadLocal<Boolean> ambientInvocation = ThreadLocal.withInitial(() -> false);
+
+    @Override
+    public void onEnable() {
+        Bukkit.getPluginManager().registerEvents(this, this);
+        previousAmbient = IrisSettings.get().getWorld().isAmbientEntitySpawningSystem();
+        previousMarkers = IrisSettings.get().getWorld().isMarkerEntitySpawningSystem();
+        previousForcedPersistence = IrisSettings.get().getWorld().isForcePersistEntities();
+        IrisSettings.get().getWorld().setAmbientEntitySpawningSystem(false);
+        IrisSettings.get().getWorld().setMarkerEntitySpawningSystem(false);
+        IrisSettings.get().getWorld().setForcePersistEntities(false);
+        getLogger().info("Natural spawning fixture ready; commands use the Iris ambient path on the owning region.");
+    }
+
+    @Override
+    public void onDisable() {
+        IrisSettings.get().getWorld().setAmbientEntitySpawningSystem(previousAmbient);
+        IrisSettings.get().getWorld().setMarkerEntitySpawningSystem(previousMarkers);
+        IrisSettings.get().getWorld().setForcePersistEntities(previousForcedPersistence);
+    }
+
+    @Override
+    public boolean onCommand(CommandSender sender, Command command, String label, String[] arguments) {
+        if (arguments.length != 1) {
+            notifySender(sender, "Use /irisspawnqa setup|frogs|zombies|stress|check|surface|cave");
+            return true;
+        }
+        try {
+            switch (arguments[0]) {
+                case "setup" -> setup(sender);
+                case "frogs" -> runRegion(sender, () -> spawnFrogs(sender));
+                case "zombies" -> runRegion(sender, () -> spawnZombies(sender));
+                case "stress" -> runRegion(sender, () -> stress(sender));
+                case "check" -> runRegion(sender, () -> check(sender));
+                case "surface" -> view(sender, 67D);
+                case "cave" -> view(sender, -46D);
+                default -> throw new IllegalArgumentException("Unknown spawning operation");
+            }
+        } catch (Throwable failure) {
+            fail(sender, failure);
+        }
+        return true;
+    }
+
+    @EventHandler(priority = EventPriority.HIGHEST)
+    public void isolateSpawns(CreatureSpawnEvent event) {
+        if (!WORLD_KEY.equals(event.getLocation().getWorld().getKey())) {
+            return;
+        }
+        if (!ambientInvocation.get()) {
+            event.setCancelled(true);
+            return;
+        }
+        ambientEvents++;
+        if (event.isCancelled()) {
+            cancelledAmbientEvents++;
+        }
+    }
+
+    private void setup(CommandSender sender) {
+        if (!(sender instanceof Player)) {
+            throw new IllegalArgumentException("Setup requires a player");
+        }
+        World world = Bukkit.getWorld(WORLD_KEY);
+        if (world != null) {
+            require(IrisToolbelt.isIrisWorld(world) && world.getSeed() == WORLD_SEED,
+                    "Existing fixture key is not the owned Iris world with the expected seed");
+            ready = false;
+            Bukkit.getGlobalRegionScheduler().execute(this, () -> configureWorld(sender, world));
+            return;
+        }
+        ready = false;
+        Bukkit.getAsyncScheduler().runNow(this, task -> createWorld(sender));
+    }
+
+    private void createWorld(CommandSender sender) {
+        try {
+            World world = new IrisCreator().name(WORLD_KEY.toString()).dimension("spawn-qa")
+                    .seed(WORLD_SEED).create();
+            Bukkit.getGlobalRegionScheduler().execute(this, () -> configureWorld(sender, world));
+        } catch (Throwable failure) {
+            fail(sender, failure);
+        }
+    }
+
+    private void configureWorld(CommandSender sender, World world) {
+        try {
+            world.setDifficulty(Difficulty.NORMAL);
+            world.setGameRule(GameRules.SPAWN_MOBS, true);
+            List<CompletableFuture<Void>> chunks = new ArrayList<>();
+            for (int chunkX = -1; chunkX <= 1; chunkX++) {
+                for (int chunkZ = -1; chunkZ <= 1; chunkZ++) {
+                    chunks.add(retainChunk(world, chunkX, chunkZ));
+                }
+            }
+            CompletableFuture.allOf(chunks.toArray(CompletableFuture[]::new)).whenComplete((ignored, failure) -> {
+                if (failure != null) {
+                    fail(sender, failure);
+                } else {
+                    Bukkit.getRegionScheduler().execute(this, world, 0, 0, () -> prepareChunk(sender, world));
+                }
+            });
+        } catch (Throwable failure) {
+            fail(sender, failure);
+        }
+    }
+
+    private CompletableFuture<Void> retainChunk(World world, int chunkX, int chunkZ) {
+        CompletableFuture<Void> retained = new CompletableFuture<>();
+        world.getChunkAtAsync(chunkX, chunkZ, true).whenComplete((chunk, failure) -> {
+            if (failure != null) {
+                retained.completeExceptionally(failure);
+                return;
+            }
+            Bukkit.getRegionScheduler().execute(this, world, chunkX, chunkZ, () -> {
+                try {
+                    chunk.addPluginChunkTicket(this);
+                    retained.complete(null);
+                } catch (Throwable error) {
+                    retained.completeExceptionally(error);
+                }
+            });
+        });
+        return retained;
+    }
+
+    private void prepareChunk(CommandSender sender, World world) {
+        try {
+            require(WORLD_KEY.equals(world.getKey()) && IrisToolbelt.isIrisWorld(world)
+                    && world.getSeed() == WORLD_SEED, "Fixture world ownership changed");
+            Chunk chunk = world.getChunkAt(0, 0);
+            int removed = 0;
+            for (Entity entity : chunk.getEntities()) {
+                if (entity instanceof LivingEntity && !(entity instanceof Player)) {
+                    entity.remove();
+                    removed++;
+                }
+            }
+            for (Entity entity : chunk.getEntities()) {
+                require(!(entity instanceof LivingEntity) || entity instanceof Player || !entity.isValid(),
+                        "Fixture target chunk retained a living mob after cleanup: " + entity.getType());
+            }
+            getLogger().info("SPAWN_QA_CLEANUP removed=" + removed + " chunk=0,0");
+            firstZombieBatch = 0;
+            ambientEvents = 0;
+            cancelledAmbientEvents = 0;
+            for (int x = 0; x < 16; x++) {
+                for (int z = 0; z < 16; z++) {
+                    chunk.getBlock(x, 64, z).setType(Material.GRASS_BLOCK, false);
+                    for (int y = 65; y <= 68; y++) {
+                        chunk.getBlock(x, y, z).setType(Material.AIR, false);
+                    }
+                    for (int y = -48; y <= -42; y++) {
+                        boolean shell = y == -48 || y == -42 || x == 0 || x == 15 || z == 0 || z == 15;
+                        chunk.getBlock(x, y, z).setType(shell ? Material.STONE : Material.CAVE_AIR, false);
+                    }
+                }
+            }
+            if (!IrisToolbelt.isIrisWorld(world) || world.getSeed() != WORLD_SEED) {
+                throw new IllegalStateException("Fixture is not the requested Iris world");
+            }
+            awaitBiomeEnvironment(sender, world, 0);
+        } catch (Throwable failure) {
+            fail(sender, failure);
+        }
+    }
+
+    private void awaitBiomeEnvironment(CommandSender sender, World world, int attempt) {
+        try {
+            Engine engine = IrisToolbelt.access(world).getEngine();
+            engine.getSurfaceBiomeEnvironment(8, 8);
+            ready = true;
+            teleport(sender, world, 67D, "SPAWN_QA_SETUP world=" + WORLD_KEY + " seed=" + WORLD_SEED);
+        } catch (SavedBiomeUnavailableException unavailable) {
+            if (!unavailable.isLoading() || attempt >= BIOME_READY_ATTEMPTS) {
+                fail(sender, unavailable);
+                return;
+            }
+            Bukkit.getRegionScheduler().runDelayed(this, world, 0, 0,
+                    task -> awaitBiomeEnvironment(sender, world, attempt + 1), BIOME_RETRY_TICKS);
+        } catch (Throwable failure) {
+            fail(sender, failure);
+        }
+    }
+
+    private void spawnFrogs(CommandSender sender) {
+        Chunk chunk = requireWorld().getChunkAt(0, 0);
+        RuntimeSpawn spawn = runtimeSpawn(chunk, "frogs");
+        getLogger().info(spawnDiagnostics(spawn, chunk));
+        for (int attempt = 0; attempt < 12; attempt++) {
+            invokeAmbient(spawn, chunk);
+            require(count(chunk, EntityType.FROG) <= FROG_CAPACITY, "Frog batch exceeded its category capacity");
+        }
+        require(count(chunk, EntityType.FROG) == FROG_CAPACITY,
+                "Frog ambient category did not fill: " + spawnDiagnostics(spawn, chunk));
+        require(count(chunk, EntityType.ZOMBIE) == 0, "Unexpected zombie before cave phase");
+        verifyPersistence(chunk);
+        evidence(sender, "SPAWN_QA_FROGS frogs=" + count(chunk, EntityType.FROG)
+                + " persistent=true removable=true ambient=true");
+    }
+
+    private void spawnZombies(CommandSender sender) {
+        Chunk chunk = requireWorld().getChunkAt(0, 0);
+        require(count(chunk, EntityType.FROG) == FROG_CAPACITY, "Frogs must fill their category before cave spawning");
+        require(count(chunk, EntityType.ZOMBIE) == 0, "Cave phase already ran");
+        RuntimeSpawn spawn = runtimeSpawn(chunk, "cave-zombies");
+        getLogger().info(spawnDiagnostics(spawn, chunk));
+        invokeAmbient(spawn, chunk);
+        firstZombieBatch = count(chunk, EntityType.ZOMBIE);
+        require(firstZombieBatch == ZOMBIE_CAPACITY,
+                "Authored seven-zombie batch was not clamped to capacity two: " + spawnDiagnostics(spawn, chunk));
+        require(count(chunk, EntityType.FROG) == FROG_CAPACITY, "Cave spawning changed the passive population");
+        verifyPersistence(chunk);
+        evidence(sender, "SPAWN_QA_ZOMBIES frogs=" + count(chunk, EntityType.FROG)
+                + " zombies=" + firstZombieBatch + " firstBatch=" + firstZombieBatch + " ambient=true");
+    }
+
+    private void stress(CommandSender sender) {
+        Chunk chunk = requireWorld().getChunkAt(0, 0);
+        RuntimeSpawn spawn = runtimeSpawn(chunk, "cave-zombies");
+        for (int attempt = 0; attempt < 50; attempt++) {
+            invokeAmbient(spawn, chunk);
+            require(count(chunk, EntityType.ZOMBIE) == ZOMBIE_CAPACITY, "Saturated zombie category exceeded capacity");
+        }
+        evidence(sender, "SPAWN_QA_STRESS attempts=50 zombies=" + count(chunk, EntityType.ZOMBIE));
+    }
+
+    private void check(CommandSender sender) {
+        Chunk chunk = requireWorld().getChunkAt(0, 0);
+        require(count(chunk, EntityType.FROG) == FROG_CAPACITY, "Passive population differs");
+        require(count(chunk, EntityType.ZOMBIE) == ZOMBIE_CAPACITY, "Hostile population differs");
+        require(firstZombieBatch == ZOMBIE_CAPACITY, "First hostile batch was not pinned");
+        require(chunk.getBlock(8, -47, 8).getType() == Material.CAVE_AIR, "Cave is not real CAVE_AIR");
+        require(chunk.getBlock(8, -47, 8).getLightLevel() == 0, "Cave is not dark");
+        for (Entity entity : chunk.getEntities()) {
+            if (entity.getType() == EntityType.ZOMBIE) {
+                require(entity.getLocation().getY() < -42, "Hostile spawned outside the cave");
+            }
+        }
+        verifyPersistence(chunk);
+        evidence(sender, "SPAWN_QA_RESULT frogs=16 zombies=2 firstBatch=2 persistent=true removable=true caveAir=true light=0");
+    }
+
+    private RuntimeSpawn runtimeSpawn(Chunk chunk, String biomeKey) {
+        try {
+            Engine engine = IrisToolbelt.access(chunk.getWorld()).getEngine();
+            BiomeEnvironment surface = engine.getSurfaceBiomeEnvironment(8, 8);
+            IrisBiome biome = surface.data().getBiomeLoader().load(biomeKey);
+            require(biome != null, "Synthetic biome was not loaded");
+            BiomeEnvironment selected = new BiomeEnvironment(surface.activationId(), biome, surface.region(),
+                    surface.dimension(), surface.data());
+            Object manager = engine.getWorldManager();
+            Field field = manager.getClass().getDeclaredField("entitySpawner");
+            field.setAccessible(true);
+            Object spawner = field.get(manager);
+            Method method = spawner.getClass().getDeclaredMethod("spawnAmbient", Chunk.class, boolean.class, BiomeEnvironment.class);
+            method.setAccessible(true);
+            return new RuntimeSpawn(engine, spawner, method, selected);
+        } catch (ReflectiveOperationException failure) {
+            throw new IllegalStateException("Could not access Iris ambient spawning", failure);
+        }
+    }
+
+    private String spawnDiagnostics(RuntimeSpawn spawn, Chunk chunk) {
+        World world = chunk.getWorld();
+        int floor = world.getHighestBlockYAt(8, 8, HeightMap.OCEAN_FLOOR);
+        int top = world.getHighestBlockYAt(8, 8, HeightMap.WORLD_SURFACE);
+        Map<String, Integer> categories = new TreeMap<>();
+        Map<String, Integer> types = new TreeMap<>();
+        for (Entity entity : chunk.getEntities()) {
+            if (entity instanceof LivingEntity && !(entity instanceof Player)) {
+                categories.merge(BukkitEntityType.of(entity.getType()).spawnCategory(), 1, Integer::sum);
+                types.merge(entity.getType().name(), 1, Integer::sum);
+            }
+        }
+        StringBuilder diagnostics = new StringBuilder("SPAWN_QA_DIAGNOSTICS frogs=")
+                .append(count(chunk, EntityType.FROG)).append(" zombies=").append(count(chunk, EntityType.ZOMBIE))
+                .append(" categories=").append(categories).append(" types=").append(types)
+                .append(" loadLevel=").append(chunk.getLoadLevel())
+                .append(" spawnMobs=").append(world.getGameRuleValue(GameRules.SPAWN_MOBS))
+                .append(" animals=").append(world.getAllowAnimals()).append(" monsters=").append(world.getAllowMonsters())
+                .append(" floor=").append(floor).append(" top=").append(top)
+                .append(" support=").append(world.getBlockAt(8, top, 8).getType())
+                .append(" above=").append(world.getBlockAt(8, top + 1, 8).getType())
+                .append(" light=").append(world.getBlockAt(8, top + 1, 8).getLightLevel())
+                .append(" events=").append(ambientEvents).append(" cancelled=").append(cancelledAmbientEvents);
+        for (String key : spawn.environment().biome().getEntitySpawners()) {
+            IrisSpawner spawner = spawn.environment().data().getSpawnerLoader().load(key);
+            if (spawner == null) {
+                diagnostics.append(" spawner=").append(key).append(":missing");
+                continue;
+            }
+            diagnostics.append(" spawner=").append(key).append(" canSpawn=")
+                    .append(spawner.canSpawn(spawn.engine(), chunk.getX(), chunk.getZ()))
+                    .append(" excluded=").append(spawner.isCompatExcluded())
+                    .append(" group=").append(spawner.getGroup()).append(" capacity=").append(spawner.getMaxEntitiesPerChunk());
+            for (IrisEntitySpawn entry : spawner.getSpawns()) {
+                IrisEntity entity = entry.getRealEntity(spawn.engine());
+                diagnostics.append(" entity=").append(entry.getEntity());
+                if (entity == null) {
+                    diagnostics.append(":missing");
+                    continue;
+                }
+                diagnostics.append(" type=").append(entity.getBukkitType()).append(" category=").append(entity.spawnCategory())
+                        .append(" surface=").append(entity.getSurface())
+                        .append(" supportMatches=").append(entity.getSurface().matches(world.getBlockAt(8, top, 8)))
+                        .append(" bounds=").append(BukkitPlatform.entityBoundingBox(entity.getBukkitType()));
+            }
+        }
+        return diagnostics.toString();
+    }
+
+    private void invokeAmbient(RuntimeSpawn spawn, Chunk chunk) {
+        ambientInvocation.set(true);
+        try (BiomeEnvironment.Scope ignored = spawn.engine().openBiomeEnvironmentScope(spawn.environment())) {
+            spawn.method().invoke(spawn.spawner(), chunk, false, spawn.environment());
+        } catch (InvocationTargetException failure) {
+            throw new IllegalStateException("Iris ambient spawning failed", failure.getCause());
+        } catch (ReflectiveOperationException failure) {
+            throw new IllegalStateException("Could not invoke Iris ambient spawning", failure);
+        } finally {
+            ambientInvocation.remove();
+        }
+    }
+
+    private int count(Chunk chunk, EntityType type) {
+        int count = 0;
+        for (Entity entity : chunk.getEntities()) {
+            if (entity.getType() == type) {
+                count++;
+            }
+        }
+        return count;
+    }
+
+    private void verifyPersistence(Chunk chunk) {
+        for (Entity entity : chunk.getEntities()) {
+            if (entity.getType() == EntityType.FROG || entity.getType() == EntityType.ZOMBIE) {
+                require(entity.isPersistent(), "Ambient entity stopped participating in chunk saves");
+                require(entity instanceof LivingEntity living && living.getRemoveWhenFarAway(),
+                        "Ambient entity has distance despawning disabled");
+            }
+        }
+    }
+
+    private void view(CommandSender sender, double y) {
+        teleport(sender, requireWorld(), y, "SPAWN_QA_VIEW y=" + (int) y);
+    }
+
+    private void teleport(CommandSender sender, World world, double y, String message) {
+        if (!(sender instanceof Player player)) {
+            throw new IllegalArgumentException("Viewing requires a player");
+        }
+        player.getScheduler().run(this, task -> {
+            player.setGameMode(GameMode.CREATIVE);
+            player.setAllowFlight(true);
+            player.setFlying(true);
+            player.teleportAsync(new Location(world, 40.5D, y, 8.5D)).whenComplete((success, failure) -> {
+                if (failure != null || !Boolean.TRUE.equals(success)) {
+                    fail(sender, failure == null ? new IllegalStateException("Fixture teleport failed") : failure);
+                } else {
+                    notifySender(sender, message);
+                }
+            });
+        }, null);
+    }
+
+    private World requireWorld() {
+        World world = Bukkit.getWorld(WORLD_KEY);
+        require(ready && world != null, "Run setup before a spawning phase");
+        return world;
+    }
+
+    private void runRegion(CommandSender sender, Runnable operation) {
+        World world = requireWorld();
+        Bukkit.getRegionScheduler().execute(this, world, 0, 0, () -> {
+            try {
+                operation.run();
+            } catch (Throwable failure) {
+                fail(sender, failure);
+            }
+        });
+    }
+
+    private void evidence(CommandSender sender, String message) {
+        getLogger().info(message);
+        notifySender(sender, message);
+    }
+
+    private void notifySender(CommandSender sender, String message) {
+        if (sender instanceof Player player) {
+            player.getScheduler().run(this, task -> player.sendMessage(message), null);
+        } else {
+            sender.sendMessage(message);
+        }
+    }
+
+    private void fail(CommandSender sender, Throwable failure) {
+        getLogger().log(Level.SEVERE, "Spawning acceptance failed", failure);
+        notifySender(sender, "SPAWN_QA_FAILED " + failure.getMessage());
+    }
+
+    private static void require(boolean condition, String message) {
+        if (!condition) {
+            throw new IllegalStateException(message);
+        }
+    }
+
+    private record RuntimeSpawn(Engine engine, Object spawner, Method method, BiomeEnvironment environment) {
+    }
+}

adapters/bukkit/plugin/src/test/gameplay/natural-spawning-pack/biomes/cave-zombies.json

@@ -0,0 +1,26 @@
+{
+  "name": "Cave Zombies",
+  "derivative": "minecraft:plains",
+  "vanillaDerivative": "minecraft:plains",
+  "layers": [
+    {
+      "minHeight": 1,
+      "maxHeight": 1,
+      "palette": [
+        {
+          "block": "minecraft:grass_block"
+        }
+      ]
+    }
+  ],
+  "generators": [
+    {
+      "generator": "flat",
+      "min": 64,
+      "max": 64
+    }
+  ],
+  "entitySpawners": [
+    "qa/cave-zombies"
+  ]
+}

adapters/bukkit/plugin/src/test/gameplay/natural-spawning-pack/biomes/frogs.json

@@ -0,0 +1,26 @@
+{
+  "name": "Frogs",
+  "derivative": "minecraft:plains",
+  "vanillaDerivative": "minecraft:plains",
+  "layers": [
+    {
+      "minHeight": 1,
+      "maxHeight": 1,
+      "palette": [
+        {
+          "block": "minecraft:grass_block"
+        }
+      ]
+    }
+  ],
+  "generators": [
+    {
+      "generator": "flat",
+      "min": 64,
+      "max": 64
+    }
+  ],
+  "entitySpawners": [
+    "qa/frogs"
+  ]
+}

adapters/bukkit/plugin/src/test/gameplay/natural-spawning-pack/dimensions/spawn-qa.json

@@ -0,0 +1,28 @@
+{
+  "name": "Spawn QA",
+  "version": 1,
+  "mode": {
+    "type": "OVERWORLD"
+  },
+  "regions": [
+    "flat"
+  ],
+  "focusRegion": "flat",
+  "focus": "frogs",
+  "landChance": 1,
+  "environment": "NORMAL",
+  "dimensionHeight": {
+    "min": -64,
+    "max": 320
+  },
+  "logicalHeight": 384,
+  "fluidHeight": 0,
+  "bedrock": false,
+  "rockPalette": {
+    "palette": [
+      {
+        "block": "minecraft:stone"
+      }
+    ]
+  }
+}

adapters/bukkit/plugin/src/test/gameplay/natural-spawning-pack/entities/qa/frog.json

@@ -0,0 +1,8 @@
+{
+  "type": "minecraft:frog",
+  "reason": "NATURAL",
+  "surface": "LAND",
+  "ai": false,
+  "aware": false,
+  "gravity": false
+}

adapters/bukkit/plugin/src/test/gameplay/natural-spawning-pack/entities/qa/zombie.json

@@ -0,0 +1,8 @@
+{
+  "type": "minecraft:zombie",
+  "reason": "NATURAL",
+  "surface": "LAND",
+  "ai": false,
+  "aware": false,
+  "gravity": false
+}

adapters/bukkit/plugin/src/test/gameplay/natural-spawning-pack/generators/flat.json

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

adapters/bukkit/plugin/src/test/gameplay/natural-spawning-pack/regions/flat.json

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

adapters/bukkit/plugin/src/test/gameplay/natural-spawning-pack/spawners/qa/cave-zombies.json

@@ -0,0 +1,16 @@
+{
+  "group": "CAVE",
+  "maxEntitiesPerChunk": 2,
+  "allowedLightLevels": {
+    "min": 0,
+    "max": 0
+  },
+  "spawns": [
+    {
+      "entity": "qa/zombie",
+      "rarity": 1,
+      "minSpawns": 7,
+      "maxSpawns": 7
+    }
+  ]
+}

adapters/bukkit/plugin/src/test/gameplay/natural-spawning-pack/spawners/qa/frogs.json

@@ -0,0 +1,12 @@
+{
+  "group": "NORMAL",
+  "maxEntitiesPerChunk": 16,
+  "spawns": [
+    {
+      "entity": "qa/frog",
+      "rarity": 1,
+      "minSpawns": 7,
+      "maxSpawns": 7
+    }
+  ]
+}

adapters/bukkit/plugin/src/test/gameplay/natural-spawning.mjs

@@ -0,0 +1,41 @@
+export default {
+  name: 'iris-natural-spawning',
+  description: 'Observe category-limited Iris ambient frogs and cave zombies on Folia.',
+  async run(context) {
+    const wait = (predicate, label, timeoutMs = 30000) => context.waitUntil(predicate, { label, timeoutMs, intervalMs: 100 })
+    const command = async (operation, expected, timeoutMs = 30000) => {
+      const response = await context.command(`/irisspawnqa ${operation}`, /SPAWN_QA_[A-Z]+(?:\s|$)/, timeoutMs)
+      context.expect(response.includes(expected) && !response.includes('SPAWN_QA_FAILED'), response)
+      return response
+    }
+    const entities = name => Object.values(context.bot.entities).filter(entity => entity.name === name)
+    await context.step('prepare the synthetic Iris world and dark cave', async () => {
+      await command('setup', 'SPAWN_QA_SETUP world=iris:spawn_qa seed=78264193', 180000)
+      await wait(() => Math.abs(context.bot.entity.position.y - 67) < 1, 'Fixture world teleport')
+    })
+    await context.step('fill the passive category through real Iris ambient spawning', async () => {
+      await command('frogs', 'SPAWN_QA_FROGS frogs=16 persistent=true removable=true ambient=true', 60000)
+      await wait(() => entities('frog').length === 16, 'All sixteen ambient frogs became visible')
+      context.report.irisNaturalSpawning = { visibleFrogs: entities('frog').length }
+    })
+    await context.step('spawn an authored seven-zombie batch with capacity two despite existing frogs', async () => {
+      await command('zombies', 'SPAWN_QA_ZOMBIES frogs=16 zombies=2 firstBatch=2 ambient=true', 60000)
+      await command('cave', 'SPAWN_QA_VIEW y=-46')
+      await wait(() => Math.abs(context.bot.entity.position.y + 46) < 1, 'Underground fixture teleport')
+      await wait(() => context.bot.blockAt(context.bot.entity.position.clone().set(8, -47, 8))?.name === 'cave_air', 'Live cave_air block reached the client')
+      await wait(() => entities('zombie').length === 2, 'Both ambient cave zombies became visible')
+      context.expect(entities('zombie').every(entity => entity.position.y < -42), 'Zombies were not inside the underground chamber')
+      context.report.irisNaturalSpawning.visibleZombies = entities('zombie').length
+      context.report.irisNaturalSpawning.caveAir = true
+    })
+    await context.step('repeat fifty ambient attempts without exceeding the hostile capacity', async () => {
+      await command('stress', 'SPAWN_QA_STRESS attempts=50 zombies=2', 60000)
+      await command('check', 'SPAWN_QA_RESULT frogs=16 zombies=2 firstBatch=2 persistent=true removable=true caveAir=true light=0', 30000)
+      context.expect(entities('zombie').length === 2, 'Client observed a hostile capacity overflow')
+      context.report.irisNaturalSpawning.saturatedAttempts = 50
+      context.report.irisNaturalSpawning.firstHostileBatch = 2
+      context.report.irisNaturalSpawning.removeWhenFarAwayAllowed = true
+      context.report.irisNaturalSpawning.chunkSaving = true
+    })
+  }
+}

adapters/bukkit/plugin/src/test/gameplay/seed-cohesion.mjs

@@ -0,0 +1,102 @@
+import { createHash } from 'node:crypto'
+import { readFile, writeFile } from 'node:fs/promises'
+import path from 'node:path'
+
+const chunks = [[-64, -64], [64, -64], [-64, 64], [64, 64]]
+
+export default {
+  name: 'iris-seed-cohesion',
+  description: 'Compare client-visible decorated chunks in two same-seed worlds explored in opposite orders.',
+  async run(context) {
+    const source = await readFile(path.join(context.server.directory, '.server-source'), 'utf8')
+    context.expect(/^isolated=true\s*$/m.test(source), 'Seed cohesion requires an isolated instance')
+    const wait = (predicate, label) => context.waitUntil(predicate, { label, timeoutMs: 60000, intervalMs: 100 })
+    const currentWorld = async () => {
+      const observation = await context.observe()
+      const player = observation.players.find(entry => entry.username === context.bot.username)
+      return observation.worlds.find(entry => entry.id === player?.world)
+    }
+    const enter = async name => {
+      await context.command(`/iris tp ${name}`)
+      await wait(async () => (await currentWorld())?.key === `iris:${name}`
+        || (await currentWorld())?.name.endsWith(name), `Enter ${name}`)
+      await context.command('/minecraft:gamemode spectator @s')
+      await wait(() => context.bot.game.gameMode === 'spectator', 'Spectator mode')
+      await context.command('/minecraft:seed', /Seed:.*1337/)
+    }
+    const capture = async coordinates => {
+      const hashes = {}
+      const decorators = {}
+      let decorationCount = 0
+      for (const [cx, cz] of coordinates) {
+        const x = cx * 16
+        const z = cz * 16
+        await context.command(`/minecraft:tp @s ${x + 8.5} 48 ${z + 8.5}`, /Teleported/i, 30000)
+        await wait(() => Math.abs(context.bot.entity.position.x - x - 8.5) < 1
+          && Math.abs(context.bot.entity.position.z - z - 8.5) < 1, 'Chunk sample teleport')
+        const position = context.bot.entity.position.clone()
+        await wait(() => context.bot.blockAt(position.clone().set(x, 1, z))
+          && context.bot.blockAt(position.clone().set(x + 15, 63, z + 15)), 'Complete sample chunk')
+        const digest = createHash('sha256')
+        let decoration = 0
+        let terrain = 0
+        for (let dx = 0; dx < 16; dx++) {
+          for (let dz = 0; dz < 16; dz++) {
+            for (let y = 0; y < 64; y++) {
+              const block = context.bot.blockAt(position.set(x + dx, y, z + dz))
+              context.expect(block !== null, 'Missing sampled block', { x: x + dx, y, z: z + dz })
+              digest.update(`${block.stateId},`)
+              if (block.name === 'granite' || block.name === 'andesite') decoration++
+              if (block.name === 'stone') terrain++
+            }
+          }
+        }
+        context.expect(terrain > 1000, 'Fixture terrain was not generated', { cx, cz, terrain })
+        decorationCount += decoration
+        decorators[`${cx},${cz}`] = decoration
+        hashes[`${cx},${cz}`] = digest.digest('hex')
+      }
+      context.expect(decorationCount > 0, 'Fixture decorators were not generated in sampled chunks', { decorators })
+      context.report.decoratorCoverage ??= []
+      context.report.decoratorCoverage.push(decorators)
+      return hashes
+    }
+    const baseline = 'seed-cohesion-forward'
+    const reverse = 'seed-cohesion-reverse'
+    const stateFile = path.join(context.server.directory, '.seed-cohesion.json')
+    const jarHash = createHash('sha256').update(await readFile(path.join(context.server.directory, 'plugins', 'Iris.jar'))).digest('hex')
+    const restart = context.options.command === 'restart-check'
+    const saved = restart ? JSON.parse(await readFile(stateFile, 'utf8')) : undefined
+    if (restart) {
+      context.expect(jarHash === saved.jarHash, 'Restart-check requires the same Iris jar', { before: saved.jarHash, after: jarHash })
+      context.expect((await context.observe()).processId !== saved.processId, 'Restart-check requires a cold server restart')
+    }
+    const outputs = []
+    for (const [name, coordinates] of [[baseline, chunks], [reverse, [...chunks].reverse()]]) {
+      await context.step(`${restart ? 'Reload' : 'Create'} and sample ${name}`, async () => {
+        if (!restart) {
+          await context.command(`/iris create name=${name} type=cohesion seed=1337`, /Successfully created your world/i, 180000)
+        }
+        await enter(name)
+        const output = await capture(coordinates)
+        if (restart) {
+          for (const [coordinate, hash] of Object.entries(output)) {
+            context.expect(saved.hashes[coordinate] === hash, 'Persisted chunk changed after restart', { name, coordinate, before: saved.hashes[coordinate], after: hash })
+          }
+          Object.assign(output, await capture(coordinates.map(([cx, cz]) => [cx * 3, cz * 3])))
+        }
+        outputs.push(output)
+      })
+    }
+    await context.step('Compare all sampled blocks', async () => {
+      for (const [coordinate, hash] of Object.entries(outputs[0])) {
+        context.expect(outputs[1][coordinate] === hash, 'Same-seed worlds differ',
+          { coordinate, forward: hash, reverse: outputs[1][coordinate] })
+      }
+      context.report.seedCohesion = { seed: 1337, jarHash, blocksPerChunk: 16384, restart, hashes: outputs[0] }
+      if (!restart) {
+        await writeFile(stateFile, JSON.stringify({ processId: (await context.observe()).processId, jarHash, hashes: outputs[0] }))
+      }
+    })
+  }
+}

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/generation/runtime/GenerationRateWindowTest.java

@@ -0,0 +1,46 @@
+package art.arcane.iris.generation.runtime;
+
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+public class GenerationRateWindowTest {
+    @Test
+    public void generationTimingsGoStaleOnceChunksStopGenerating() {
+        GenerationRateWindow window = new GenerationRateWindow();
+
+        window.sampleChunksPerSecond(0, 1_000L);
+        assertEquals(20D, window.sampleChunksPerSecond(20, 2_000L), 0D);
+        assertTrue(window.generationTimingsFresh(2_000L));
+
+        assertEquals(0D, window.sampleChunksPerSecond(20, 7_000L), 0D);
+        assertTrue(window.generationTimingsFresh(7_000L));
+        assertEquals(0D, window.sampleChunksPerSecond(20, 12_001L), 0D);
+        assertFalse(window.generationTimingsFresh(12_001L));
+
+        window.sampleChunksPerSecond(21, 13_001L);
+        assertTrue(window.generationTimingsFresh(13_001L));
+    }
+
+    @Test
+    public void anIdleWorldNeverPublishesTimings() {
+        GenerationRateWindow window = new GenerationRateWindow();
+
+        window.sampleChunksPerSecond(0, 1_000L);
+        window.sampleChunksPerSecond(0, 2_000L);
+
+        assertFalse(window.generationTimingsFresh(2_000L));
+    }
+
+    @Test
+    public void chunksGeneratedBeforeTheFirstSampleCountAsRecentGeneration() {
+        GenerationRateWindow window = new GenerationRateWindow();
+
+        assertEquals(0D, window.sampleChunksPerSecond(400, 5_000L), 0D);
+
+        assertTrue(window.generationTimingsFresh(5_000L));
+        assertFalse(window.generationTimingsFresh(5_000L + GenerationRateWindow.TIMING_IDLE_MILLIS + 1L));
+    }
+}

adapters/bukkit/plugin/src/test/java/art/arcane/iris/integration/IrisIntegrationServiceTest.java

@@ -49,6 +49,7 @@ public class IrisIntegrationServiceTest {
                         100L,
                         200L,
                         100L,
+                        48L,
                         8D,
                         2_000L,
                         5_000L,
@@ -64,6 +65,8 @@ public class IrisIntegrationServiceTest {
                 IntegrationMetricSchema.IRIS_LOADED_CHUNKS,
                 IntegrationMetricSchema.IRIS_CHUNKS_GENERATED_TOTAL,
                 IntegrationMetricSchema.IRIS_PREGEN_THROUGHPUT,
+                IntegrationMetricSchema.IRIS_PREGEN_QUEUE,
+                IntegrationMetricSchema.IRIS_PREGEN_REMAINING,
                 IntegrationMetricSchema.IRIS_GENERATION_TOTAL_MS,
                 "iris.unsupported"
         ));
@@ -73,6 +76,8 @@ public class IrisIntegrationServiceTest {
         assertEquals(20D, value(samples, IntegrationMetricSchema.IRIS_LOADED_CHUNKS), 0D);
         assertEquals(50D, value(samples, IntegrationMetricSchema.IRIS_CHUNKS_GENERATED_TOTAL), 0D);
         assertEquals(8D, value(samples, IntegrationMetricSchema.IRIS_PREGEN_THROUGHPUT), 0D);
+        assertEquals(48D, value(samples, IntegrationMetricSchema.IRIS_PREGEN_QUEUE), 0D);
+        assertEquals(100D, value(samples, IntegrationMetricSchema.IRIS_PREGEN_REMAINING), 0D);
         assertEquals(4D, value(samples, IntegrationMetricSchema.IRIS_GENERATION_TOTAL_MS), 0D);
         assertFalse(samples.get("iris.unsupported").available());
         assertEquals("unsupported-key", samples.get("iris.unsupported").message());
@@ -84,9 +89,12 @@ public class IrisIntegrationServiceTest {
         assertEquals("minecraft:overworld", overworld.scopeId());
         assertEquals(1D, value(overworld.samples(), IntegrationMetricSchema.IRIS_PREGEN_ACTIVE), 0D);
         assertEquals(8D, value(overworld.samples(), IntegrationMetricSchema.IRIS_PREGEN_THROUGHPUT), 0D);
+        assertEquals(48D, value(overworld.samples(), IntegrationMetricSchema.IRIS_PREGEN_QUEUE), 0D);
+        assertEquals(100D, value(overworld.samples(), IntegrationMetricSchema.IRIS_PREGEN_REMAINING), 0D);
         assertEquals("minecraft:the_nether", nether.scopeId());
         assertEquals(0D, value(nether.samples(), IntegrationMetricSchema.IRIS_PREGEN_ACTIVE), 0D);
         assertFalse(nether.samples().get(IntegrationMetricSchema.IRIS_PREGEN_QUEUE).available());
+        assertFalse(nether.samples().get(IntegrationMetricSchema.IRIS_PREGEN_REMAINING).available());
     }
 
     @Test

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/build.gradle

@@ -32,11 +32,7 @@ buildscript {
         maven { url = uri('https://jitpack.io') }
     }
     dependencies {
-        Properties libraryProperties = new Properties()
-        file('../../gradle.properties').withInputStream { InputStream stream -> libraryProperties.load(stream) }
-        String libraryCoordinate = providers.gradleProperty('volmLibCoordinate')
-            .getOrElse(libraryProperties.getProperty('volmLibCoordinate'))
-        classpath("com.github.VolmitSoftware.VolmLib:packaging:${libraryCoordinate.tokenize(':').last()}")
+        classpath('com.github.VolmitSoftware.VolmLib:packaging:master-SNAPSHOT')
     }
 }
 
@@ -56,13 +52,13 @@ interface IrisFileOperations {
 IrisFileOperations irisFileOperations = objects.newInstance(IrisFileOperations)
 
 apply from: file('../../gradle/modded-generation-build-revision.gradle')
+apply from: file('../../gradle/volmlib-stamp.gradle')
 
 Properties rootProperties = new Properties()
 file('../../gradle.properties').withInputStream { InputStream stream -> rootProperties.load(stream) }
-String irisVersion = providers.gradleProperty('irisVersion').getOrElse(rootProperties.getProperty('irisVersion', '4.1.2-26.2'))
-String minecraftVersion = providers.gradleProperty('minecraftVersion').getOrElse(rootProperties.getProperty('minecraftVersion', '26.2'))
-String fabricLoaderVersion = providers.gradleProperty('fabricLoaderVersion').getOrElse(rootProperties.getProperty('fabricLoaderVersion', '0.19.3'))
-String volmLibCoordinate = providers.gradleProperty('volmLibCoordinate').getOrElse(rootProperties.getProperty('volmLibCoordinate', 'com.github.VolmitSoftware:VolmLib:master-SNAPSHOT'))
+String irisVersion = providers.gradleProperty('irisVersion').getOrElse(rootProperties.getProperty('irisVersion', '4.3.0-26.2'))
+String minecraftVersion = providers.gradleProperty('minecraftVersion').getOrElse(rootProperties.getProperty('minecraftVersion', '26.3'))
+String fabricLoaderVersion = providers.gradleProperty('fabricLoaderVersion').getOrElse(rootProperties.getProperty('fabricLoaderVersion', '0.19.5'))
 Closure<String> irisArtifactName = { String platform, String targetVersion ->
     return "Iris v${project.version} [${platform}] ${targetVersion}.jar"
 }
@@ -83,7 +79,6 @@ sourceSets {
     main {
         java {
             srcDir '../modded-common/src/main/java'
-            srcDir '../minecraft-common/src/main/java'
             srcDir '../client-common/src/main/java'
         }
         resources {
@@ -181,10 +176,10 @@ dependencies {
     compileOnly(libs.spigot) {
         transitive = false
     }
-    add('bundle', volmLibCoordinate) {
+    add('bundle', 'com.github.VolmitSoftware.VolmLib:volmlib-shared:master-SNAPSHOT') {
         transitive = false
     }
-    add('devBundle', volmLibCoordinate) {
+    add('devBundle', 'com.github.VolmitSoftware.VolmLib:volmlib-shared:master-SNAPSHOT') {
         transitive = false
     }
     add('bundle', libs.zip) {
@@ -201,6 +196,7 @@ dependencies {
         libs.asm,
         libs.lru,
         libs.caffeine,
+        'com.fulcrumgenomics:jlibdeflate:0.2.0',
         libs.dom4j,
         libs.jaxen
     ]
@@ -286,6 +282,9 @@ tasks.named('shadowJar', ShadowJar).configure {
             spec.delete(staleLoaderJars, legacyLoaderJar)
         }
     }
+    from(tasks.named('generateVolmLibStamp')) {
+        into('META-INF/volmit')
+    }
     archiveFileName.set(irisArtifactName('Fabric', "${minecraftVersion}+${fabricLoaderVersion}"))
     configurations = [project.configurations.named('bundle').get()]
     mergeServiceFiles()

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/main/resources/fabric.mod.json

@@ -70,7 +70,7 @@
     }
   ],
   "depends": {
-    "fabricloader": ">=0.19.3",
+    "fabricloader": ">=0.19.5",
     "minecraft": "~${minecraftVersion}",
     "java": ">=25"
   }

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/fabric/src/test/java/art/arcane/volmlib/nativelib/minecraft26_2/fabric/NativeFabricSpawnPositionTest.java

@@ -0,0 +1,43 @@
+package art.arcane.volmlib.nativelib.minecraft26_2.fabric;
+
+import art.arcane.volmlib.nativelib.modded.NativeLoaderOptions;
+import net.minecraft.SharedConstants;
+import net.minecraft.server.Bootstrap;
+import net.minecraft.world.entity.EntitySpawnReason;
+import net.minecraft.world.entity.Mob;
+import net.minecraft.world.level.ServerLevelAccessor;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import java.util.function.BooleanSupplier;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+public class NativeFabricSpawnPositionTest {
+    @BeforeClass
+    public static void bootstrap() {
+        SharedConstants.tryDetectVersion();
+        Bootstrap.bootStrap();
+    }
+
+    @Test
+    public void chunkGenerationSpawnsUseTheVanillaRulesAndObstructionChecks() {
+        NativeFabricLoader loader = new NativeFabricLoader(
+                new NativeLoaderOptions("irisworldgen", "treefeller", BooleanSupplier::getAsBoolean));
+        ServerLevelAccessor level = mock(ServerLevelAccessor.class);
+        Mob mob = mock(Mob.class);
+        when(mob.checkSpawnRules(level, EntitySpawnReason.CHUNK_GENERATION)).thenReturn(true);
+        when(mob.checkSpawnObstruction(level)).thenReturn(true);
+        assertTrue(loader.checkSpawnPosition(mob, level, EntitySpawnReason.CHUNK_GENERATION));
+
+        when(mob.checkSpawnObstruction(level)).thenReturn(false);
+        assertFalse(loader.checkSpawnPosition(mob, level, EntitySpawnReason.CHUNK_GENERATION));
+
+        when(mob.checkSpawnObstruction(level)).thenReturn(true);
+        when(mob.checkSpawnRules(level, EntitySpawnReason.CHUNK_GENERATION)).thenReturn(false);
+        assertFalse(loader.checkSpawnPosition(mob, level, EntitySpawnReason.CHUNK_GENERATION));
+    }
+}

adapters/forge/build.gradle

@@ -32,17 +32,13 @@ buildscript {
         maven { url = uri('https://jitpack.io') }
     }
     dependencies {
-        Properties libraryProperties = new Properties()
-        file('../../gradle.properties').withInputStream { InputStream stream -> libraryProperties.load(stream) }
-        String libraryCoordinate = providers.gradleProperty('volmLibCoordinate')
-            .getOrElse(libraryProperties.getProperty('volmLibCoordinate'))
-        classpath("com.github.VolmitSoftware.VolmLib:packaging:${libraryCoordinate.tokenize(':').last()}")
+        classpath('com.github.VolmitSoftware.VolmLib:packaging:master-SNAPSHOT')
     }
 }
 
 plugins {
     id 'java'
-    id 'net.minecraftforge.gradle' version '7.0.31'
+    id 'net.minecraftforge.gradle' version '7.0.40'
     alias(libs.plugins.shadow)
 }
 
@@ -56,13 +52,13 @@ interface IrisFileOperations {
 IrisFileOperations irisFileOperations = objects.newInstance(IrisFileOperations)
 
 apply from: file('../../gradle/modded-generation-build-revision.gradle')
+apply from: file('../../gradle/volmlib-stamp.gradle')
 
 Properties rootProperties = new Properties()
 file('../../gradle.properties').withInputStream { InputStream stream -> rootProperties.load(stream) }
-String irisVersion = providers.gradleProperty('irisVersion').getOrElse(rootProperties.getProperty('irisVersion', '4.1.2-26.2'))
-String minecraftVersion = providers.gradleProperty('minecraftVersion').getOrElse(rootProperties.getProperty('minecraftVersion', '26.2'))
-String forgeVersion = providers.gradleProperty('forgeVersion').getOrElse(rootProperties.getProperty('forgeVersion', '26.2-65.1.1'))
-String volmLibCoordinate = providers.gradleProperty('volmLibCoordinate').getOrElse(rootProperties.getProperty('volmLibCoordinate', 'com.github.VolmitSoftware:VolmLib:master-SNAPSHOT'))
+String irisVersion = providers.gradleProperty('irisVersion').getOrElse(rootProperties.getProperty('irisVersion', '4.3.0-26.2'))
+String minecraftVersion = providers.gradleProperty('minecraftVersion').getOrElse(rootProperties.getProperty('minecraftVersion', '26.3'))
+String forgeVersion = providers.gradleProperty('forgeVersion').getOrElse(rootProperties.getProperty('forgeVersion', '26.3-66.0.8'))
 Closure<String> loaderDisplayVersion = { String loaderVersion ->
     String coordinatePrefix = "${minecraftVersion}-"
     if (loaderVersion.startsWith(coordinatePrefix)) {
@@ -91,7 +87,6 @@ sourceSets {
     main {
         java {
             srcDir '../modded-common/src/main/java'
-            srcDir '../minecraft-common/src/main/java'
             srcDir '../client-common/src/main/java'
         }
         resources {
@@ -174,13 +169,13 @@ dependencies {
     compileOnly(libs.spigot) {
         transitive = false
     }
-    add('bundle', volmLibCoordinate) {
+    add('bundle', 'com.github.VolmitSoftware.VolmLib:volmlib-shared:master-SNAPSHOT') {
         transitive = false
     }
-    add('devBundle', volmLibCoordinate) {
+    add('devBundle', 'com.github.VolmitSoftware.VolmLib:volmlib-shared:master-SNAPSHOT') {
         transitive = false
     }
-    add('runBundle', volmLibCoordinate) {
+    add('runBundle', 'com.github.VolmitSoftware.VolmLib:volmlib-shared:master-SNAPSHOT') {
         transitive = false
     }
     add('bundle', libs.zip) {
@@ -200,6 +195,7 @@ dependencies {
         libs.asm,
         libs.lru,
         libs.caffeine,
+        'com.fulcrumgenomics:jlibdeflate:0.2.0',
         libs.dom4j,
         libs.jaxen
     ]
@@ -271,8 +267,11 @@ tasks.named('shadowJar', ShadowJar).configure {
             spec.delete(staleLoaderJars, legacyLoaderJar)
         }
     }
+    from(tasks.named('generateVolmLibStamp')) {
+        into('META-INF/volmit')
+    }
     manifest {
-        // FML 26.2 has no TOML mixin handling at all (ModFileParser reads neither [[mixins]] nor
+        // FML 26.3 has no TOML mixin handling at all (ModFileParser reads neither [[mixins]] nor
         // accessTransformers on Forge). This manifest attribute is the only registration mechanism;
         // do not move it into mods.toml.
         attributes('MixinConfigs': 'volmlib.entity.mixins.json,volmlib.client.mixins.json')

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

@@ -1,5 +1,5 @@
 modLoader = "javafml"
-loaderVersion = "[65,66)"
+loaderVersion = "[66,67)"
 license = "GPL-3.0"
 issueTrackerURL = "https://github.com/VolmitSoftware/Iris/issues"
 
@@ -16,7 +16,7 @@ logoFile = "assets/irisworldgen/icon.png"
 [[dependencies.irisworldgen]]
 modId = "forge"
 mandatory = true
-versionRange = "[65,66)"
+versionRange = "[66,67)"
 ordering = "NONE"
 side = "BOTH"
 

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

@@ -0,0 +1,52 @@
+package art.arcane.volmlib.nativelib.minecraft26_2.forge;
+
+import art.arcane.volmlib.nativelib.modded.NativeLoaderOptions;
+import net.minecraft.SharedConstants;
+import net.minecraft.server.Bootstrap;
+import net.minecraft.world.entity.EntitySpawnReason;
+import net.minecraft.world.entity.Mob;
+import net.minecraft.world.level.ServerLevelAccessor;
+import net.minecraftforge.common.util.Result;
+import net.minecraftforge.event.entity.living.MobSpawnEvent;
+import net.minecraftforge.eventbus.api.listener.EventListener;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import java.util.concurrent.atomic.AtomicReference;
+import java.util.function.BooleanSupplier;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+public class NativeForgeSpawnPositionTest {
+    @BeforeClass
+    public static void bootstrap() {
+        SharedConstants.tryDetectVersion();
+        Bootstrap.bootStrap();
+    }
+
+    @Test
+    public void chunkGenerationSpawnsFireThePositionCheckEventAndHonorItsDenial() {
+        NativeForgeLoader loader = new NativeForgeLoader(
+                new NativeLoaderOptions("irisworldgen", "treefeller", BooleanSupplier::getAsBoolean));
+        ServerLevelAccessor level = mock(ServerLevelAccessor.class);
+        Mob mob = mock(Mob.class);
+        when(mob.checkSpawnRules(level, EntitySpawnReason.CHUNK_GENERATION)).thenReturn(true);
+        when(mob.checkSpawnObstruction(level)).thenReturn(true);
+        AtomicReference<EntitySpawnReason> observed = new AtomicReference<>();
+        EventListener listener = MobSpawnEvent.PositionCheck.BUS.addListener((MobSpawnEvent.PositionCheck event) -> {
+            observed.set(event.getSpawnReason());
+            event.setResult(Result.DENY);
+        });
+        try {
+            assertFalse(loader.checkSpawnPosition(mob, level, EntitySpawnReason.CHUNK_GENERATION));
+        } finally {
+            MobSpawnEvent.PositionCheck.BUS.removeListener(listener);
+        }
+        assertEquals(EntitySpawnReason.CHUNK_GENERATION, observed.get());
+        assertTrue(loader.checkSpawnPosition(mob, level, EntitySpawnReason.CHUNK_GENERATION));
+    }
+}

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

@@ -44,6 +44,7 @@ import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeFeatureBiomeSourc
 import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeDimensionRuntime;
 
 import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeModdedServer;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeModdedLoader;
 
 import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeGeneratorOwner;
 import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeGeneratorHandle;
@@ -58,6 +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;
@@ -66,12 +68,12 @@ import art.arcane.iris.world.history.TerrainNativeBlockKeys;
 
 import art.arcane.volmlib.nativelib.terrain.NativeChunkWritePolicy;
 
-import art.arcane.iris.world.history.TerrainBoundarySignature;
 import art.arcane.iris.world.history.NativeBiomeSpawnSelection;
 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;
@@ -240,6 +242,7 @@ public final class IrisModdedChunkGenerator implements NativeGeneratorOwner, Nat
         this.announced.set(false);
         resetRuntimeCaches();
         this.engineBinding.complete(replacement);
+        this.nativeGenerator.initializeStructureState(level);
         // Bind time: a feature-order cycle in the new pack is reported here, once, and degrades to features-off.
         // Never waits on a build owned by another thread: this method owns the generator monitor and the build
         // path can need it.
@@ -440,12 +443,14 @@ public final class IrisModdedChunkGenerator implements NativeGeneratorOwner, Nat
         }
         Engine current = engineIfBound();
         if (NativeDimensionRuntime.sameWorld(boundLevel, level) && current != null && current.getComplex() != null) {
+            nativeGenerator.initializeStructureState(level);
             return;
         }
         requireCompletedShutdown(engine);
         unloading = false;
         Engine bound = bindEngine(level);
         nativeGenerator.installVolumeIndex(level, bound);
+        nativeGenerator.initializeStructureState(level);
         // Bind time: a feature-order cycle is reported here, once, and degrades to features-off. Non-waiting for
         // the same reason as repointAndBind: this method owns the generator monitor.
         importedFeatures.prepareWithoutWaiting(bound);
@@ -454,11 +459,14 @@ 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 +508,7 @@ 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 +520,31 @@ 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 +598,11 @@ 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 +1007,7 @@ 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;
@@ -1012,6 +1035,11 @@ public final class IrisModdedChunkGenerator implements NativeGeneratorOwner, Nat
         return ModdedEngineBootstrap.currentServer();
     }
 
+    @Override
+    public NativeModdedLoader loader() {
+        return ModdedEngineBootstrap.loader();
+    }
+
     @Override
     public Engine current() {
         return engine();
@@ -1072,6 +1100,12 @@ public final class IrisModdedChunkGenerator implements NativeGeneratorOwner, Nat
         return current.getDimensionStackContext() != null;
     }
 
+    @Override
+    public boolean terrainTransformed() {
+        Engine current = engine;
+        return current != null && current.getComplex().getTerrainTransform() != null;
+    }
+
     @Override
     public int runtimeId(Engine current) {
         return current.getCacheID();
@@ -1086,7 +1120,7 @@ public final class IrisModdedChunkGenerator implements NativeGeneratorOwner, Nat
 
     @Override
     public NativeBlockColumn resolvedColumn(Engine current, int x, int z) {
-        return current.getComplex().resolvedTerrainColumn(x, z).map(TerrainBoundarySignature::geometry).orElse(null);
+        return null;
     }
 
     @Override

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

@@ -29,6 +29,7 @@ import java.util.function.LongSupplier;
 
 
 import art.arcane.iris.pack.loading.IrisData;
+import art.arcane.iris.generation.stream.ProvisionalSampling;
 import art.arcane.iris.generation.runtime.DimensionStackContext;
 import art.arcane.iris.generation.runtime.DimensionStackLayout;
 import art.arcane.iris.generation.runtime.DimensionTerrainContext;
@@ -71,6 +72,7 @@ final class ModdedBiomePolicy<H, S> implements NativeModdedBiomePolicy<H, S> {
     private volatile BiomeHolderTable<H> visibleBiomeCache = new BiomeHolderTable<>();
     private volatile BiomeHolderTable<H> structureBiomeCache = new BiomeHolderTable<>();
     private volatile BiomeHolderTable<H> surfaceStructureBiomeCache = new BiomeHolderTable<>();
+    private volatile BiomeHolderTable<H> naturalStructureBiomeCache = new BiomeHolderTable<>();
     private volatile RuntimeCallbacks runtime;
     private volatile Set<String> possibleStructureBiomeKeys;
     private volatile BiomeKeySets biomeKeySets;
@@ -93,6 +95,7 @@ final class ModdedBiomePolicy<H, S> implements NativeModdedBiomePolicy<H, S> {
         visibleBiomeCache = new BiomeHolderTable<>();
         structureBiomeCache = new BiomeHolderTable<>();
         surfaceStructureBiomeCache = new BiomeHolderTable<>();
+        naturalStructureBiomeCache = new BiomeHolderTable<>();
         warnedUnresolvedBiomeKeys.clear();
         possibleStructureBiomeKeys = null;
         biomeKeySets = null;
@@ -103,6 +106,7 @@ final class ModdedBiomePolicy<H, S> implements NativeModdedBiomePolicy<H, S> {
         visibleBiomeCache.evictRuntime(runtimeIdentity);
         structureBiomeCache.evictRuntime(runtimeIdentity);
         surfaceStructureBiomeCache.evictRuntime(runtimeIdentity);
+        naturalStructureBiomeCache.evictRuntime(runtimeIdentity);
     }
 
     /**
@@ -262,7 +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);
         }
@@ -284,7 +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();
         }
@@ -338,7 +342,12 @@ final class ModdedBiomePolicy<H, S> implements NativeModdedBiomePolicy<H, S> {
                 return cached;
             }
         }
-        H resolved = resolveStructureBiome(engine, quartX, quartY, quartZ, sampler);
+        H resolved;
+        try {
+            resolved = ProvisionalSampling.memoizable(() -> resolveStructureBiome(engine, quartX, quartY, quartZ, sampler));
+        } catch (ProvisionalSampling.Unmemoizable provisional) {
+            return provisional.value();
+        }
         if (cacheable) {
             cache.put(runtimeIdentity, key, resolved);
         }
@@ -346,7 +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);
         }
@@ -388,8 +397,13 @@ final class ModdedBiomePolicy<H, S> implements NativeModdedBiomePolicy<H, S> {
                 return cached;
             }
         }
-        H resolved = resolveVisibleBiome(
-                engine, quartX, quartY, quartZ, sampler, null);
+        H resolved;
+        try {
+            resolved = ProvisionalSampling.memoizable(() -> resolveVisibleBiome(
+                    engine, quartX, quartY, quartZ, sampler, null));
+        } catch (ProvisionalSampling.Unmemoizable provisional) {
+            return provisional.value();
+        }
         if (cacheable) {
             cache.put(runtimeIdentity, key, resolved);
         }
@@ -397,7 +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;
         }
@@ -406,15 +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);
@@ -449,7 +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());
         }
@@ -480,7 +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();
         }
@@ -531,7 +545,12 @@ final class ModdedBiomePolicy<H, S> implements NativeModdedBiomePolicy<H, S> {
         if (cached != null) {
             return cached;
         }
-        H resolved = resolveSurfaceStructureBiome(engine, quartX, quartZ, sampler);
+        H resolved;
+        try {
+            resolved = ProvisionalSampling.memoizable(() -> resolveSurfaceStructureBiome(engine, quartX, quartZ, sampler));
+        } catch (ProvisionalSampling.Unmemoizable provisional) {
+            return provisional.value();
+        }
         cache.put(runtimeIdentity, key, resolved);
         return resolved;
     }
@@ -775,11 +794,40 @@ final class ModdedBiomePolicy<H, S> implements NativeModdedBiomePolicy<H, S> {
                 if (!isReady(engine)) {
                     throw new IllegalStateException("Iris structure biome lookup has no active engine runtime");
                 }
-                return getNoiseBiome(engine, quartX, quartY, quartZ, sampler);
+                return getNaturalStructureBiome(engine, quartX, quartZ);
             }
         }
     }
 
+    // The structure state only samples biomes for the concentric-ring search, which reaches ~24k blocks out for
+    // strongholds. The natural surface answers there without planning hydrology tiles, the same as the Bukkit ring search.
+    private H getNaturalStructureBiome(Engine engine, int quartX, int quartZ) {
+        long key = packColumnKey(quartX, quartZ);
+        int runtimeIdentity = engine.getCacheID();
+        BiomeHolderTable<H> cache = naturalStructureBiomeCache;
+        H cached = cache.get(runtimeIdentity, key);
+        if (cached != null) {
+            return cached;
+        }
+        NativeBiomeSourceAccess.RegistryView<H> registry = biomeRegistry();
+        if (registry == null) {
+            throw new IllegalStateException("Iris structure biome lookup has no biome registry");
+        }
+        int blockX = quartX << 2;
+        int blockZ = quartZ << 2;
+        IrisBiome irisBiome = engine.getComplex().getNaturalTrueBiomeStream().get(blockX, blockZ);
+        if (irisBiome == null) {
+            throw new IllegalStateException("Iris returned no natural structure biome at block " + blockX + "," + blockZ);
+        }
+        H resolved = resolveHolder(registry, irisBiome.getStructureDerivativeKey());
+        if (resolved == null) {
+            throw new IllegalStateException("Iris natural structure biome derivative '"
+                    + irisBiome.getStructureDerivativeKey() + "' is not registered at block " + blockX + "," + blockZ);
+        }
+        cache.put(runtimeIdentity, key, resolved);
+        return resolved;
+    }
+
     static long biomeResolutionSeed(long worldSeed, int blockX, int blockY, int blockZ) {
         return worldSeed
                 ^ ((long) blockX * 341873128712L)
@@ -826,7 +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);
         }
     }
 
@@ -391,10 +457,7 @@ public final class ModdedEngineBootstrap {
                 BlockDataMergeSupport.StateMerger previousMerger = BlockDataMergeSupport.bindPlatformMerger(new NativeStateMerger(ModdedBlockResolution.BLOCKS)::merge);
                 rollback.add(() -> BlockDataMergeSupport.restorePlatformMerger(previousMerger));
 
-                NativeTileReader nativeTileReader = new NativeTileReader(() -> {
-                    NativeModdedServer server = boundLoader.currentServer();
-                    return server == null ? null : server.registryAccess();
-                });
+                NativeTileReader nativeTileReader = NativeModdedServer.tileReader(boundLoader::currentServer);
                 TileData.TileReader previousTileReader = TileData.bindPlatformReader(in -> ModdedTileData.wrap(nativeTileReader.read(in)));
                 rollback.add(() -> TileData.restorePlatformReader(previousTileReader));
 

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

@@ -61,11 +61,12 @@ public final class ModdedEntitySpawner {
         }
 
         double x = blockX + 0.5;
-        double y = blockY + 0.5;
+        double verticalOffset = irisEntity.getSurface().isFluid() ? 0.5 : 0;
+        double y = blockY + verticalOffset;
         double z = blockZ + 0.5;
         boolean riseEffectActive = irisEntity.isSpawnEffectRiseOutOfGround() && level.hasPlayersNearby(new NativeEntityRuntime.Position(x, y, z), PLAYER_EFFECT_RADIUS);
         int spawnBlockY = riseEffectActive ? blockY - 5 : blockY;
-        double spawnY = spawnBlockY + 0.5;
+        double spawnY = spawnBlockY + verticalOffset;
 
         NativeSpawnedEntity created = create(irisEntity, level, x, spawnY, z);
         if (created == null) {
@@ -98,8 +99,7 @@ public final class ModdedEntitySpawner {
         String customName = irisEntity.getCustomName();
         entity.applyBase(irisEntity, customName == null ? null : colorize(customName));
 
-        boolean persistent = irisEntity.isKeepEntity() || forcePersist();
-        applyPersistence(entity, persistent);
+        applyPersistence(irisEntity, entity, forcePersist());
 
         applyPassengers(engine, irisEntity, entity, level, blockX, blockY, blockZ, rng);
 
@@ -273,8 +273,8 @@ public final class ModdedEntitySpawner {
         return IrisSettings.get().getWorld().isForcePersistEntities();
     }
 
-    private static void applyPersistence(NativeSpawnedEntity entity, boolean persistent) {
-        if (!entity.persistence(persistent)) {
+    static void applyPersistence(IrisEntity options, NativeSpawnedEntity entity, boolean forcePersistence) {
+        if (!entity.persistence(options.isKeepEntity() || forcePersistence)) {
             String type = entity.typeKey();
             if (WARNED_PERSISTENCE_TYPES.add(type)) {
                 IrisLogging.warn("Iris entity: vanilla cannot persist non-serializable entity type '" + type + "'");

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_2.getPackFormat() + '\n').getBytes(StandardCharsets.UTF_8));
+                + '|' + dataVersion.getPackFormat() + '\n').getBytes(StandardCharsets.UTF_8));
         String inputFingerprint = IrisDatapackCompiler.computeInputFingerprint(
                 compilationPackRoots(),
                 List.of(),
-                DataVersion.V26_2.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_2.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_2.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/ModdedNativeStructurePolicy.java

@@ -102,7 +102,8 @@ final class ModdedNativeStructurePolicy implements NativeModdedStructureStage.Po
 
     @Override
     public NativeBlockPositionPredicate protectedPositions(Engine context) {
-        return GenerationWritePolicy.protectedPositions(context.getDimension().getStaticObjectLayer(context.getData()),
+        return GenerationWritePolicy.protectedPositions(context.getDimension().getStaticObjectLayer(context.getData())
+                        .forTransition(context),
                 context.getDimensionStackContext(), context.getMinHeight());
     }
 

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

@@ -20,7 +20,6 @@ package art.arcane.iris.modded;
 
 import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeModdedServer;
 
-import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeRegistryAccess;
 import art.arcane.volmlib.nativelib.minecraft26_2.terrain.NativeRegistryDefinitions;
 import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeEntitySpawns;
 import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeModdedLoader;
@@ -38,8 +37,6 @@ import art.arcane.iris.spi.PlatformScheduler;
 import art.arcane.iris.spi.PlatformStructureHooks;
 import art.arcane.volmlib.nativelib.terrain.NativeWorld;
 
-import net.minecraft.core.HolderLookup;
-
 import java.io.File;
 import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
@@ -63,25 +60,13 @@ public final class ModdedPlatform implements IrisPlatform {
     public ModdedPlatform(NativeModdedLoader loader) {
         this.loader = loader;
         this.registries = new ModdedRegistries(
-                new NativeRegistryAccess(new NativeRegistryAccess.Configuration(
-                        ModdedPlatform::nativeRegistries, ModdedPlatform::reloadableRegistries,
-                        ModdedRegistries::warnNotReady)),
-                ModdedPlatform::generationRegistry);
+                NativeModdedServer.registryAccess(ModdedEngineBootstrap::currentServer, ModdedRegistries::warnNotReady),
+                () -> generationRegistry(loader));
         this.scheduler = new ModdedScheduler();
         this.structureHooks = new ModdedStructureHooks(ModdedEngineBootstrap::currentServer);
         this.biomeWriter = new ModdedBiomeWriter(new NativeBiomeRegistry(ModdedEngineBootstrap::currentServer, "minecraft:plains"));
     }
 
-    private static HolderLookup.Provider nativeRegistries() {
-        NativeModdedServer server = ModdedEngineBootstrap.currentServer();
-        return server == null ? null : server.registryAccess();
-    }
-
-    private static HolderLookup.Provider reloadableRegistries() {
-        NativeModdedServer server = ModdedEngineBootstrap.currentServer();
-        return server == null ? null : server.reloadableRegistries();
-    }
-
     public static void errorSink(Consumer<Throwable> sink) {
         ERROR_SINK = sink;
     }
@@ -367,13 +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/ModdedWorldManager.java

@@ -55,6 +55,7 @@ import art.arcane.volmlib.util.matter.Matter;
 import art.arcane.volmlib.util.matter.MatterMarker;
 import art.arcane.volmlib.util.matter.slices.MarkerMatter;
 
+import java.util.Map;
 import java.util.HashSet;
 import java.util.List;
 import java.util.ArrayList;
@@ -245,7 +246,7 @@ public final class ModdedWorldManager implements EngineWorldManager {
             return true;
         }
 
-        MantleChunk<Matter> chunk = mantle.getChunk(chunkX, chunkZ).use();
+        MantleChunk<Matter> chunk = mantle.useChunk(chunkX, chunkZ);
         try {
             List<PreparedMarkerSpawn> markers = markerSystemEnabled()
                     ? prepareMarkerSpawns(level, chunkX, chunkZ, chunk) : List.of();
@@ -380,7 +381,7 @@ public final class ModdedWorldManager implements EngineWorldManager {
             return;
         }
 
-        MantleChunk<Matter> chunk = mantle.getChunk(chunkX, chunkZ).use();
+        MantleChunk<Matter> chunk = mantle.useChunk(chunkX, chunkZ);
         try {
             if (markerSystemEnabled()) {
                 spawnPreparedMarkers(level, prepareMarkerSpawns(level, chunkX, chunkZ, chunk), false);
@@ -511,13 +512,16 @@ public final class ModdedWorldManager implements EngineWorldManager {
     }
 
     private void spawnAmbient(NativeWorld level, int chunkX, int chunkZ, boolean initial, BiomeEnvironment environment) {
+        if (!NativeSpawnQueries.ambientAllowed(level, chunkX, chunkZ, initial)) {
+            return;
+        }
         IrisComplex complex = engine.getComplex();
         if (complex == null) {
             return;
         }
 
         IrisBiome biome = environment.biome();
-        int chunkMobs = countChunkLivingEntities(level, chunkX, chunkZ);
+        Map<String, Integer> chunkMobs = NativeSpawnQueries.livingEntityCategories(level, chunkX, chunkZ);
 
         KList<IrisEntitySpawn> pool = new KList<>();
         collectSpawns(pool, environment.data().getSpawnerLoader().loadAll(environment.dimension().getEntitySpawners()), biome, chunkX, chunkZ, chunkMobs, initial);
@@ -535,20 +539,18 @@ public final class ModdedWorldManager implements EngineWorldManager {
         if (!canSpawn(spawner, chunkX, chunkZ)) {
             return;
         }
-        int spawned = spawnEntry(level, chosen, spawner, chunkX, chunkZ);
+        int spawned = spawnEntry(level, chosen, spawner, chunkX, chunkZ,
+                remainingCapacity(chosen, spawner, chunkMobs));
         if (spawned > 0) {
             spawner.spawn(engine, chunkX, chunkZ);
         }
     }
 
-    private void collectSpawns(KList<IrisEntitySpawn> pool, KList<IrisSpawner> spawners, IrisBiome biomeFilter, int chunkX, int chunkZ, int chunkMobs, boolean initial) {
+    private void collectSpawns(KList<IrisEntitySpawn> pool, KList<IrisSpawner> spawners, IrisBiome biomeFilter, int chunkX, int chunkZ, Map<String, Integer> chunkMobs, boolean initial) {
         for (IrisSpawner spawner : spawners) {
             if (spawner == null) {
                 continue;
             }
-            if (spawner.getMaxEntitiesPerChunk() <= chunkMobs) {
-                continue;
-            }
             if (biomeFilter != null && !spawner.isValid(biomeFilter)) {
                 continue;
             }
@@ -559,12 +561,19 @@ public final class ModdedWorldManager implements EngineWorldManager {
             for (IrisEntitySpawn entry : spawns) {
                 entry.setReferenceSpawner(spawner);
                 entry.setReferenceMarker(spawner.getReferenceMarker());
-                pool.add(entry);
+                if (remainingCapacity(entry, spawner, chunkMobs) > 0) {
+                    pool.add(entry);
+                }
             }
         }
     }
 
-    private int spawnEntry(NativeWorld level, IrisEntitySpawn entry, IrisSpawner spawner, int chunkX, int chunkZ) {
+    private int remainingCapacity(IrisEntitySpawn entry, IrisSpawner spawner, Map<String, Integer> counts) {
+        IrisEntity entity = entry.getRealEntity(engine);
+        return spawner.remainingCapacity(entity, counts);
+    }
+
+    private int spawnEntry(NativeWorld level, IrisEntitySpawn entry, IrisSpawner spawner, int chunkX, int chunkZ, int remainingCapacity) {
         IrisEntity irisEntity = entry.getRealEntity(engine);
         if (irisEntity == null) {
             return 0;
@@ -572,7 +581,7 @@ public final class ModdedWorldManager implements EngineWorldManager {
 
         int min = entry.getMinSpawns();
         int max = entry.getMaxSpawns();
-        int count = LootResolver.inclusive(RNG.r, min, max);
+        int count = Math.min(Math.max(0, remainingCapacity), LootResolver.inclusive(RNG.r, min, max));
         if (count <= 0) {
             return 0;
         }
@@ -593,7 +602,7 @@ public final class ModdedWorldManager implements EngineWorldManager {
                 }
                 IrisPosition caveFloor = caveFloors.getRandom(RNG.r);
                 worldX = caveFloor.getX();
-                worldY = caveFloor.getY() + 1;
+                worldY = caveFloor.getY();
                 worldZ = caveFloor.getZ();
             } else {
                 worldX = (chunkX << 4) + RNG.r.i(16);
@@ -708,10 +717,6 @@ public final class ModdedWorldManager implements EngineWorldManager {
                 || NativeSpawnQueries.solid(level.getBlock(worldX, worldY + 2, worldZ));
     }
 
-    private int countChunkLivingEntities(NativeWorld level, int chunkX, int chunkZ) {
-        return NativeSpawnQueries.livingEntities(level, chunkX, chunkZ);
-    }
-
     /**
      * ServerChunkCache.tickChunks rebuilds NaturalSpawner.SpawnState every tick from every entity in the
      * level, so read that instead of walking all entities again on an Iris timer. The count is the natural

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_2.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_2.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_2.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/ModdedPregenMethod.java

@@ -116,6 +116,11 @@ public final class ModdedPregenMethod implements PregeneratorMethod {
             }
             ModdedIrisLog.info("Iris modded pregen done: dim={} completed={} peakInFlight={} finalLimit={}",
                     runtime.worldIdentity(), completed.get(), inFlightPeak.get(), adaptiveLimit.get());
+            try {
+                engine.syncGenerationHistory();
+            } catch (RuntimeException e) {
+                ModdedIrisLog.error("Iris modded pregen could not force generation history to stable storage", e);
+            }
             if (deferFinalSaveIfRequested()) {
                 return;
             }
@@ -498,7 +503,7 @@ public final class ModdedPregenMethod implements PregeneratorMethod {
     /**
      * A dedicated server with {@code pause-when-empty-seconds > 0} returns from
      * {@code MinecraftServer#tickServer} before {@code tickChildren} once it has been empty for that
-     * long (26.2 only keeps {@code tickConnection} plus the task/chunk-poll window alive). That
+     * long (26.3 only keeps {@code tickConnection} plus the task/chunk-poll window alive). That
      * freezes every per-tick Iris service - world manager, scheduler, protocol sync, pregen HUD - and
      * the loader's own generation hooks for the whole job, and console pregen on a default
      * server.properties is always empty. The guard zeroes the setting for the duration of the job

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) {
@@ -188,13 +205,18 @@ public final class ModdedChunkUpdateService implements ModdedTickableService {
             return;
         }
 
-        MantleChunk<Matter> chunk = mantle.getChunk(chunkX, chunkZ).use();
+        MantleChunk<Matter> chunk = mantle.useChunk(chunkX, chunkZ);
         try {
             chunk.raiseFlagUnchecked(MantleFlag.ETCHED, () -> {
                 chunk.raiseFlagUnchecked(MantleFlag.TILE, () -> runTilePass(engine, level, chunkX, chunkZ, chunk));
                 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/main/resources/pack.mcmeta

@@ -0,0 +1,7 @@
+{
+  "pack": {
+    "description": "Iris client resources and mod data",
+    "min_format": [97, 1],
+    "max_format": [121, 0]
+  }
+}

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

@@ -72,10 +72,10 @@ public class IrisModLanguageAssetsTest {
     }
 
     private Set<String> resourceFiles() throws Exception {
-        URL resource = IrisModLanguageAssetsTest.class.getClassLoader().getResource(ROOT);
-        assertNotNull("Missing mod language resource directory: " + ROOT, resource);
+        URL resource = IrisModLanguageAssetsTest.class.getClassLoader().getResource(ROOT + "en_us.json");
+        assertNotNull("Missing English mod language resource", resource);
         assertEquals("Mod language resources must resolve to a directory on disk", "file", resource.getProtocol());
-        Path directory = Path.of(resource.toURI());
+        Path directory = Path.of(resource.toURI()).getParent();
         try (Stream<Path> paths = Files.list(directory)) {
             return paths
                     .filter(Files::isRegularFile)

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

@@ -6,6 +6,7 @@ import net.minecraft.SharedConstants;
 import net.minecraft.server.Bootstrap;
 import net.minecraft.util.random.Weighted;
 import net.minecraft.util.random.WeightedList;
+import net.minecraft.util.valueproviders.UniformInt;
 import net.minecraft.world.entity.EntityTypes;
 import net.minecraft.world.level.biome.MobSpawnSettings;
 import org.junit.Test;
@@ -24,10 +25,10 @@ public class IrisModdedChunkGeneratorSpawnTest {
 
     @Test
     public void explicitSpawnsReplaceMatchingVanillaTypesAndPreserveOthers() {
-        MobSpawnSettings.SpawnerData zombie = new MobSpawnSettings.SpawnerData(EntityTypes.ZOMBIE, 1, 4);
-        MobSpawnSettings.SpawnerData vanillaSlime = new MobSpawnSettings.SpawnerData(EntityTypes.SLIME, 1, 1);
-        MobSpawnSettings.SpawnerData explicitSlime = new MobSpawnSettings.SpawnerData(EntityTypes.SLIME, 2, 5);
-        MobSpawnSettings.SpawnerData explicitCow = new MobSpawnSettings.SpawnerData(EntityTypes.COW, 2, 4);
+        MobSpawnSettings.SpawnerData zombie = new MobSpawnSettings.SpawnerData(EntityTypes.ZOMBIE, UniformInt.of(1, 4));
+        MobSpawnSettings.SpawnerData vanillaSlime = new MobSpawnSettings.SpawnerData(EntityTypes.SLIME, UniformInt.of(1, 1));
+        MobSpawnSettings.SpawnerData explicitSlime = new MobSpawnSettings.SpawnerData(EntityTypes.SLIME, UniformInt.of(2, 5));
+        MobSpawnSettings.SpawnerData explicitCow = new MobSpawnSettings.SpawnerData(EntityTypes.COW, UniformInt.of(2, 4));
         WeightedList<MobSpawnSettings.SpawnerData> vanilla = WeightedList.of(List.of(
                 new Weighted<>(zombie, 100),
                 new Weighted<>(vanillaSlime, 1)));

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

@@ -1,6 +1,13 @@
 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;
+import art.arcane.volmlib.util.stream.ProceduralStream;
+import art.arcane.volmlib.util.stream.interpolation.Interpolated;
 import org.junit.Test;
 
 import java.util.ArrayList;
@@ -13,6 +20,9 @@ import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertSame;
 import static org.junit.Assert.assertThrows;
 import static org.junit.Assert.assertTrue;
+import static org.mockito.ArgumentMatchers.anyString;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
 
 public class ModdedBiomePolicyTest {
     @Test
@@ -52,6 +62,52 @@ public class ModdedBiomePolicyTest {
         assertTrue(failure.getMessage().contains("example:missing"));
     }
 
+    @Test
+    public void structureRingBiomesResolveFromTheNaturalSurfaceWithoutPlanningHydrology() throws Exception {
+        BiomeToken forest = new BiomeToken("minecraft:forest");
+        IrisBiome natural = mock(IrisBiome.class);
+        when(natural.getStructureDerivativeKey()).thenReturn(forest.key());
+        IrisComplex complex = mock(IrisComplex.class);
+        when(complex.getNaturalTrueBiomeStream()).thenReturn(
+                ProceduralStream.of((x, z) -> natural, Interpolated.of(value -> 0D, value -> null)));
+        when(complex.getTrueBiomeStream()).thenThrow(
+                new AssertionError("Stronghold ring lookups must not plan hydrology"));
+        Engine engine = mock(Engine.class);
+        when(engine.getComplex()).thenReturn(complex);
+        when(engine.getMinHeight()).thenReturn(-64);
+        when(engine.acquireGenerationLease(anyString())).thenReturn(GenerationSessionLease.noop());
+        ModdedBiomePolicy<BiomeToken, Object> policy = new ModdedBiomePolicy<>(
+                new Access(new ArrayList<>(List.of(forest))));
+        policy.bind(new ModdedBiomePolicy.RuntimeCallbacks(() -> engine, () -> engine, bound -> true,
+                () -> Set.of(forest.key()), bound -> Set.of(), () -> 0L));
+
+        assertSame(forest, policy.requiredStructureBiome(6000, 0, -6000, null));
+        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/ModdedClientPackageIsolationTest.java

@@ -17,7 +17,7 @@ import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertTrue;
 
 /**
- * Dist gate. The loader source sets fold modded-common, minecraft-common and client-common into one output, so
+ * Dist gate. The loader source sets fold modded-common and client-common into one output, so
  * nothing at compile time stops a server-side class from touching a client-only type. On a dedicated server
  * that is a NoClassDefFoundError at the first call, usually deep inside worldgen.
  *

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

@@ -79,7 +79,7 @@ public class ModdedDimensionTypeParityTest {
         IrisDimension end = dimension("the_end", IrisEnvironment.THE_END, 0, 256, 256, new IrisDimensionTypeOptions());
         IrisDimension custom = dimension("custom_contract", IrisEnvironment.CUSTOM, -128, 384, 384, customOptions);
         List<IrisDimension> dimensions = List.of(overworld, nether, end, custom);
-        IDataFixer fixer = DataVersion.V26_2.get();
+        IDataFixer fixer = DataVersion.V26_3.get();
         Path packDirectory = Files.createTempDirectory("iris-dimension-contracts");
         KList<File> roots = new KList<>();
         roots.add(packDirectory.toFile());

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/ModdedEntityPersistenceTest.java

@@ -2,6 +2,13 @@ package art.arcane.iris.modded;
 
 import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeEntityBehavior;
 
+import art.arcane.iris.world.entity.IrisEntity;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeSpawnedEntity;
+import net.minecraft.SharedConstants;
+import net.minecraft.server.Bootstrap;
+import net.minecraft.world.entity.EntityType;
+import org.junit.BeforeClass;
+import net.minecraft.world.entity.Mob;
 import org.junit.Test;
 import org.junit.Before;
 import art.arcane.volmlib.nativelib.modded.EntityBehaviorTags;
@@ -11,18 +18,31 @@ import java.util.Set;
 
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
+import static org.mockito.ArgumentMatchers.anyString;
+import static org.mockito.Mockito.atLeastOnce;
+import static org.mockito.Mockito.doReturn;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.never;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
 
 public class ModdedEntityPersistenceTest {
+    @BeforeClass
+    public static void bootstrapMinecraftRegistries() {
+        SharedConstants.tryDetectVersion();
+        Bootstrap.bootStrap();
+    }
+
     @Before
     public void configureEntityTags() {
         NativeEntityBehavior.bind(new EntityBehaviorTags("iris_non_persistent", "iris_unaware"));
     }
 
     @Test
-    public void generatedNonPersistentEntityIsExcludedFromVanillaSaves() {
+    public void explicitlyExcludedEntityIsExcludedFromVanillaSaves() {
         Set<String> tags = new HashSet<>();
 
-        NativeEntityBehavior.configurePersistenceTags(tags, false);
+        NativeEntityBehavior.configureSavingTags(tags, false);
 
         assertFalse(NativeEntityBehavior.shouldSave(tags, true));
     }
@@ -30,9 +50,9 @@ public class ModdedEntityPersistenceTest {
     @Test
     public void positivePersistenceRemovesTheSaveExclusion() {
         Set<String> tags = new HashSet<>();
-        NativeEntityBehavior.configurePersistenceTags(tags, false);
+        NativeEntityBehavior.configureSavingTags(tags, false);
 
-        NativeEntityBehavior.configurePersistenceTags(tags, true);
+        NativeEntityBehavior.configureSavingTags(tags, true);
 
         assertTrue(NativeEntityBehavior.shouldSave(tags, true));
     }
@@ -41,8 +61,57 @@ public class ModdedEntityPersistenceTest {
     public void interceptionNeverOverridesVanillaSaveRejection() {
         Set<String> tags = new HashSet<>();
 
-        NativeEntityBehavior.configurePersistenceTags(tags, true);
+        NativeEntityBehavior.configureSavingTags(tags, true);
 
         assertFalse(NativeEntityBehavior.shouldSave(tags, false));
     }
+
+    @Test
+    public void defaultAmbientMobSavesWithoutBecomingPermanent() {
+        Mob mob = mob();
+        NativeSpawnedEntity entity = new NativeSpawnedEntity(mob);
+        IrisEntity options = new IrisEntity();
+
+        ModdedEntitySpawner.applyPersistence(options, entity, false);
+        entity.configureMob(options);
+
+        assertTrue(NativeEntityBehavior.shouldSave(mob, true));
+        verify(mob, never()).setPersistenceRequired();
+    }
+
+    @Test
+    public void explicitKeepForceAndRemovalFlagsControlNativeDespawn() {
+        for (boolean keep : new boolean[]{false, true}) {
+            for (boolean force : new boolean[]{false, true}) {
+                for (boolean removable : new boolean[]{false, true}) {
+                    Mob mob = mob();
+                    NativeSpawnedEntity entity = new NativeSpawnedEntity(mob);
+                    IrisEntity options = new IrisEntity().setKeepEntity(keep).setRemovable(removable);
+
+                    ModdedEntitySpawner.applyPersistence(options, entity, force);
+                    entity.configureMob(options);
+
+                    assertTrue(NativeEntityBehavior.shouldSave(mob, true));
+                    if (keep || force || !removable) {
+                        verify(mob, atLeastOnce()).setPersistenceRequired();
+                    } else {
+                        verify(mob, never()).setPersistenceRequired();
+                    }
+                }
+            }
+        }
+    }
+
+    private static Mob mob() {
+        Mob mob = mock(Mob.class);
+        EntityType<?> type = mock(EntityType.class);
+        Set<String> tags = new HashSet<>();
+        when(type.canSerialize()).thenReturn(true);
+        doReturn(type).when(mob).getType();
+        when(mob.entityTags()).thenReturn(tags);
+        when(mob.shouldBeSaved()).thenReturn(true);
+        when(mob.removeTag(anyString())).thenAnswer(invocation -> tags.remove(invocation.getArgument(0)));
+        when(mob.addTag(anyString())).thenAnswer(invocation -> tags.add(invocation.getArgument(0)));
+        return mob;
+    }
 }

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

@@ -21,7 +21,7 @@ import static org.junit.Assert.assertTrue;
 
 public class ModdedEntitySpawnerParityTest {
     @Test
-    public void collisionCheckUsesPaperInclusiveIntegerDimensions() {
+    public void landBodyFitsTwoBlockCaveAndRejectsSecondBlockCeiling() {
         Set<BlockPos> checked = new HashSet<>();
 
         boolean clear = NativeEntityRuntime.isAreaClearForSpawn(
@@ -32,6 +32,36 @@ public class ModdedEntitySpawnerParityTest {
 
         assertTrue(clear);
         assertEquals(Set.of(new BlockPos(10, 64, 20), new BlockPos(10, 65, 20)), checked);
+        assertTrue(NativeEntityRuntime.isAreaClearForSpawn(10, 64, 20, 0.6F, 1.95F,
+                (x, y, z) -> y >= 64 && y < 66));
+        assertFalse(NativeEntityRuntime.isAreaClearForSpawn(10, 64, 20, 0.6F, 1.95F,
+                (x, y, z) -> y == 64));
+    }
+
+    @Test
+    public void fractionalWideLandBodiesIncludeAdjacentObstructions() {
+        Set<BlockPos> checked = new HashSet<>();
+        assertTrue(NativeEntityRuntime.isAreaClearForSpawn(-1, -49, -1, 1.3F, 1.95F,
+                (x, y, z) -> {
+                    checked.add(new BlockPos(x, y, z));
+                    return true;
+                }));
+        assertEquals(18, checked.size());
+        assertTrue(checked.contains(new BlockPos(-2, -48, -2)));
+        assertTrue(checked.contains(new BlockPos(0, -49, 0)));
+        assertFalse(NativeEntityRuntime.isAreaClearForSpawn(-1, -49, -1, 1.3F, 1.95F,
+                (x, y, z) -> !new BlockPos(x, y, z).equals(new BlockPos(0, -48, -1))));
+    }
+
+    @Test
+    public void exactLandBodyBoundariesExcludeUntouchedBlocks() {
+        Set<BlockPos> checked = new HashSet<>();
+        assertTrue(NativeEntityRuntime.isAreaClearForSpawn(0, -49, 0, 1F, 2F,
+                (x, y, z) -> {
+                    checked.add(new BlockPos(x, y, z));
+                    return true;
+                }));
+        assertEquals(Set.of(new BlockPos(0, -49, 0), new BlockPos(0, -48, 0)), checked);
     }
 
     @Test

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;
@@ -48,23 +51,48 @@ 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
-    public void metadataRetains262FormatWhenBukkitAlsoSupports263() throws IOException {
+    public void metadataUses263DataFormat() throws IOException {
         Path packDirectory = Files.createTempDirectory("iris-modded-pack-format");
         try {
             ModdedForcedDatapack.writePackMeta(packDirectory);
             JSONObject pack = new JSONObject(Files.readString(packDirectory.resolve("pack.mcmeta")))
                     .getJSONObject("pack");
-            assertEquals(107, pack.getInt("pack_format"));
-            assertEquals(107, pack.getInt("min_format"));
-            assertEquals(107, pack.getInt("max_format"));
+            assertEquals(121, pack.getInt("pack_format"));
+            assertEquals(121, pack.getInt("min_format"));
+            assertEquals(121, pack.getInt("max_format"));
         } finally {
             deleteTree(packDirectory);
         }
     }
 
+    @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 +1,195 @@
+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/ServerLevelStructureBootstrapMixin",
+            "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/ModdedPackMetadataTest.java

@@ -0,0 +1,45 @@
+package art.arcane.iris.modded;
+
+import com.google.gson.JsonObject;
+import com.google.gson.JsonParser;
+import com.mojang.serialization.JsonOps;
+import net.minecraft.SharedConstants;
+import net.minecraft.server.Bootstrap;
+import net.minecraft.server.packs.PackType;
+import net.minecraft.server.packs.metadata.pack.PackMetadataSection;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.nio.charset.StandardCharsets;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertTrue;
+
+public class ModdedPackMetadataTest {
+    @BeforeClass
+    public static void bootstrapMinecraftRegistries() {
+        SharedConstants.tryDetectVersion();
+        Bootstrap.bootStrap();
+    }
+
+    @Test
+    public void metadataLoadsClientResourcesAndServerDataForCurrentMinecraft() throws IOException {
+        try (InputStream resource = ModdedPackMetadataTest.class.getResourceAsStream("/pack.mcmeta")) {
+            assertNotNull(resource);
+            try (InputStreamReader reader = new InputStreamReader(resource, StandardCharsets.UTF_8)) {
+                JsonObject metadata = JsonParser.parseReader(reader).getAsJsonObject();
+                for (PackType type : PackType.values()) {
+                    PackMetadataSection section = PackMetadataSection.forPackType(type).codec()
+                            .parse(JsonOps.INSTANCE, metadata.get("pack")).getOrThrow();
+                    assertEquals("Iris client resources and mod data", section.description().getString());
+                    assertTrue(type.toString(), section.supportedFormats().isValueInRange(
+                            SharedConstants.getCurrentVersion().packVersion(type)));
+                }
+            }
+        }
+    }
+}

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

@@ -9,6 +9,10 @@ import art.arcane.volmlib.nativelib.minecraft26_2.modded.ModdedServerAccess;
 import art.arcane.volmlib.nativelib.minecraft26_2.modded.ModdedServerLevels;
 import net.minecraft.server.level.ServerLevel;
 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;
@@ -33,7 +37,7 @@ public class ModdedPlatformPathsTest {
 
             @Override
             public String minecraftVersion() {
-                return "26.2";
+                return "26.3";
             }
 
             @Override
@@ -83,6 +87,16 @@ public class ModdedPlatformPathsTest {
             public boolean canBreakBlock(ServerLevel level, ServerPlayer player, BlockPos position, BlockState state) {
                 return false;
             }
+
+            @Override
+            public boolean checkSpawnPosition(Mob mob, ServerLevelAccessor level, EntitySpawnReason reason) {
+                return false;
+            }
+
+            @Override
+            public Biome unmodifiedBiome(Biome biome) {
+                return biome;
+            }
         });
     }