Refine terrain and pregeneration

- Add coherent river width variation and shape source and terminal pools.
- Preserve separated hydrology intervals when checking river connectivity.
- Reduce footprint sorting, engine context lookup, and terrain blending work.
- Reuse modded snapshot validation after content and registry checks.
- Explain production pack update staging and restart requirements.
- Retain pregeneration map updates before its desktop window opens.
- Improve pregeneration layout, coordinate hover, keyboard controls, and error details.
- Add the new desktop labels to every supported language catalog.
- Add the buildPsychoLT entry point for verified platform outputs.
- Cover terrain, validation, and desktop behavior with regression tests.

.gitignore

@@ -76,3 +76,8 @@ BUILDS/
 .compatwt/
 
 .worktrees/
+
+/VolmLib/
+/docs/
+/.perf/
+/.codegraph/

adapters/bukkit/nms/v26_3_R1/src/test/java/art/arcane/iris/nativegen/IrisChunkGeneratorHeightCacheTest.java

@@ -14,6 +14,7 @@ import net.minecraft.SharedConstants;
 import net.minecraft.server.Bootstrap;
 import net.minecraft.world.level.LevelHeightAccessor;
 import net.minecraft.world.level.levelgen.Heightmap;
+import org.junit.AfterClass;
 import org.junit.BeforeClass;
 import org.junit.Rule;
 import org.junit.Test;
@@ -45,6 +46,11 @@ public final class IrisChunkGeneratorHeightCacheTest {
         NativeBlockTags.bindHeightmapFixtures();
     }
 
+    @AfterClass
+    public static void restoreBlockTags() {
+        NativeBlockTags.restoreTags();
+    }
+
     @Test
     public void repeatedNativeHeightUsesLiveHeightQueriesAcrossRuntimeChanges() throws Exception {
         Fixture fixture = fixture();

adapters/bukkit/nms/v26_3_R1/src/test/java/art/arcane/iris/nativegen/NativeTransitionColumnTest.java

@@ -20,6 +20,7 @@ import net.minecraft.world.level.block.Blocks;
 import net.minecraft.world.level.block.RotatedPillarBlock;
 import net.minecraft.world.level.block.LiquidBlock;
 import net.minecraft.world.level.levelgen.Heightmap;
+import org.junit.AfterClass;
 import org.junit.BeforeClass;
 import org.junit.Rule;
 import org.junit.Test;
@@ -46,6 +47,11 @@ public final class NativeTransitionColumnTest {
         NativeBlockTags.bindHeightmapFixtures();
     }
 
+    @AfterClass
+    public static void restoreBlockTags() {
+        NativeBlockTags.restoreTags();
+    }
+
     @Test
     public void customKeysUseCarrierForNativeColumnsAndHeightmaps() {
         String key = "itemsadder:rocks/ruby_ore";

adapters/bukkit/nms/v26_3_R1/src/test/java/art/arcane/iris/nativegen/v26_3_R1/NativeBlockTags.java

@@ -1,21 +1,30 @@
 package art.arcane.iris.nativegen.v26_3_R1;
 
 import net.minecraft.core.Holder;
+import net.minecraft.core.HolderSet;
 import net.minecraft.core.registries.BuiltInRegistries;
 import net.minecraft.core.registries.Registries;
 import net.minecraft.tags.BlockTags;
 import net.minecraft.tags.TagLoader;
+import net.minecraft.tags.TagKey;
 import net.minecraft.world.level.block.Block;
 import net.minecraft.world.level.block.Blocks;
 
+import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 
 public final class NativeBlockTags {
+    private static Map<TagKey<Block>, List<Holder<Block>>> originalTags;
+
     private NativeBlockTags() {
     }
 
     public static void bindHeightmapFixtures() {
+        originalTags = new HashMap<>();
+        for (HolderSet.Named<Block> tag : BuiltInRegistries.BLOCK.getTags().toList()) {
+            originalTags.put(tag.key(), tag.stream().toList());
+        }
         List<Holder<Block>> solid = List.of(Blocks.STONE.builtInRegistryHolder(),
                 Blocks.OAK_LOG.builtInRegistryHolder(), Blocks.SPRUCE_LOG.builtInRegistryHolder());
         List<Holder<Block>> canopy = List.of(Blocks.STONE.builtInRegistryHolder(),
@@ -25,4 +34,12 @@ public final class NativeBlockTags {
                 BlockTags.BLOCKS_MOTION_IN_HEIGHTMAP, canopy,
                 BlockTags.BLOCKS_MOTION_IN_HEIGHTMAP_NO_LEAVES, solid))).apply();
     }
+
+    public static void restoreTags() {
+        if (originalTags == null) {
+            return;
+        }
+        BuiltInRegistries.BLOCK.prepareTagReload(new TagLoader.LoadResult<>(Registries.BLOCK, originalTags)).apply();
+        originalTags = null;
+    }
 }

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

@@ -34,6 +34,7 @@ import net.minecraft.world.level.levelgen.structure.pieces.PiecesContainer;
 import net.minecraft.world.level.levelgen.structure.structures.IglooPieces;
 import net.minecraft.world.level.levelgen.structure.structures.SwampHutPiece;
 import net.minecraft.world.level.levelgen.structure.structures.SwampHutStructure;
+import org.junit.AfterClass;
 import org.junit.BeforeClass;
 import org.junit.Test;
 
@@ -68,6 +69,11 @@ public class WorldgenTerrainHeightmapsTest {
         NativeBlockTags.bindHeightmapFixtures();
     }
 
+    @AfterClass
+    public static void restoreBlockTags() {
+        NativeBlockTags.restoreTags();
+    }
+
     @Test
     public void authoringHeightmapsReadPlacedObjectsAndFluidsWithoutTerrainResolvers() {
         ProtoChunk chunk = terrainChunk(new ChunkPos(0, 0));

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

@@ -13,6 +13,7 @@ import com.google.gson.JsonParser;
 import org.bukkit.Bukkit;
 import org.junit.AfterClass;
 import org.junit.BeforeClass;
+import org.junit.ClassRule;
 import org.junit.Test;
 
 import java.io.File;
@@ -26,6 +27,9 @@ import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertThrows;
 
 public final class BareMobSpawnHistoryTest {
+    @ClassRule
+    public static final PaperRegistryIsolation registryIsolation = new PaperRegistryIsolation();
+
     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 =

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

@@ -29,6 +29,7 @@ import net.minecraft.world.level.levelgen.structure.StructureStart;
 import net.minecraft.world.level.levelgen.structure.templatesystem.StructureTemplateManager;
 import net.minecraft.world.level.storage.LevelStorageSource;
 import org.junit.Rule;
+import org.junit.ClassRule;
 import org.junit.Test;
 import org.junit.rules.TemporaryFolder;
 import org.bukkit.craftbukkit.generator.CustomChunkGenerator;
@@ -49,6 +50,9 @@ import static org.mockito.Mockito.spy;
 import static org.mockito.Mockito.verify;
 
 public class HeadlessChunkGeneratorTest {
+    @ClassRule
+    public static final PaperRegistryIsolation registryIsolation = new PaperRegistryIsolation();
+
     @Rule
     public TemporaryFolder temporary = new TemporaryFolder();
 

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

@@ -31,6 +31,7 @@ import net.minecraft.world.level.levelgen.structure.templatesystem.StructureTemp
 import net.minecraft.world.level.storage.LevelStorageSource;
 import org.bukkit.Bukkit;
 import org.junit.Rule;
+import org.junit.ClassRule;
 import org.junit.Test;
 import org.junit.rules.TemporaryFolder;
 
@@ -48,6 +49,9 @@ import static org.junit.Assert.assertThrows;
 import static org.junit.Assert.assertTrue;
 
 public final class HeadlessChunkLightingTest {
+    @ClassRule
+    public static final PaperRegistryIsolation registryIsolation = new PaperRegistryIsolation();
+
     @Rule
     public TemporaryFolder temporary = new TemporaryFolder();
 

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

@@ -38,6 +38,7 @@ import net.minecraft.world.ticks.ScheduledTick;
 import org.bukkit.NamespacedKey;
 import org.bukkit.persistence.PersistentDataType;
 import org.junit.Rule;
+import org.junit.ClassRule;
 import org.junit.Test;
 import org.junit.rules.TemporaryFolder;
 
@@ -54,6 +55,9 @@ import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.when;
 
 public class HeadlessChunkSerializationTest {
+    @ClassRule
+    public static final PaperRegistryIsolation registryIsolation = new PaperRegistryIsolation();
+
     @Rule
     public TemporaryFolder temporary = new TemporaryFolder();
 

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

@@ -9,6 +9,7 @@ import net.minecraft.world.item.Items;
 
 import java.util.Map;
 import net.minecraft.world.level.block.Blocks;
+import org.junit.ClassRule;
 import org.junit.Test;
 import org.bukkit.Bukkit;
 
@@ -18,6 +19,9 @@ import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
 
 public final class HeadlessNativeBootstrapTest {
+    @ClassRule
+    public static final PaperRegistryIsolation registryIsolation = new PaperRegistryIsolation();
+
     @Test
     public void bindsNativeItemComponentsWithoutStartingServer() throws Exception {
         HeadlessNativeBootstrap.bindComponents(HeadlessNativeTestRegistries.get());

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

@@ -7,12 +7,16 @@ import net.minecraft.resources.Identifier;
 import net.minecraft.resources.ResourceKey;
 import net.minecraft.world.level.biome.Biome;
 import net.minecraft.world.level.levelgen.structure.Structure;
+import org.junit.ClassRule;
 import org.junit.Test;
 
 
 import static org.junit.Assert.assertTrue;
 
 public final class HeadlessNativeRegistriesTest {
+    @ClassRule
+    public static final PaperRegistryIsolation registryIsolation = new PaperRegistryIsolation();
+
     @Test
     public void nativeStructureBiomeTagsUseTheLoadedBiomeHolders() throws Exception {
         RegistryAccess registries = HeadlessNativeTestRegistries.get();

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

@@ -4,6 +4,7 @@ import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeRegistryAccess;
 import net.minecraft.core.registries.Registries;
 import org.bukkit.Bukkit;
 import org.junit.BeforeClass;
+import org.junit.ClassRule;
 import org.junit.Test;
 
 import java.util.Map;
@@ -17,6 +18,9 @@ import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertThrows;
 
 public final class HeadlessNativeRegistryTest {
+    @ClassRule
+    public static final PaperRegistryIsolation registryIsolation = new PaperRegistryIsolation();
+
     @BeforeClass
     public static void bootstrap() {
         HeadlessNativeBootstrap.initialize();

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

@@ -11,6 +11,7 @@ import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeTileReader;
 import net.minecraft.nbt.CompoundTag;
 import net.minecraft.data.registries.VanillaRegistries;
 import org.junit.BeforeClass;
+import org.junit.ClassRule;
 import org.junit.Test;
 
 import java.io.ByteArrayInputStream;
@@ -23,6 +24,9 @@ import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertThrows;
 
 public final class HeadlessNativeTileTest {
+    @ClassRule
+    public static final PaperRegistryIsolation registryIsolation = new PaperRegistryIsolation();
+
     @BeforeClass
     public static void bootstrap() {
         HeadlessNativeBootstrap.initialize();

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

@@ -17,6 +17,7 @@ import org.bukkit.Bukkit;
 import org.bukkit.NamespacedKey;
 import org.bukkit.persistence.PersistentDataType;
 import org.junit.Rule;
+import org.junit.ClassRule;
 import org.junit.Test;
 import org.junit.rules.TemporaryFolder;
 import org.spigotmc.SpigotWorldConfig;
@@ -36,6 +37,9 @@ import static org.junit.Assert.assertSame;
 import static org.junit.Assert.assertTrue;
 
 public final class HeadlessRegionTerrainTest {
+    @ClassRule
+    public static final PaperRegistryIsolation registryIsolation = new PaperRegistryIsolation();
+
     @Rule
     public TemporaryFolder temporary = new TemporaryFolder();
 

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

@@ -24,6 +24,7 @@ import net.minecraft.world.level.block.state.BlockState;
 import net.minecraft.world.level.chunk.storage.RegionFile;
 import net.minecraft.world.level.chunk.storage.RegionStorageInfo;
 import org.junit.BeforeClass;
+import org.junit.ClassRule;
 import org.junit.Test;
 
 import java.io.DataInputStream;
@@ -38,6 +39,9 @@ import static org.junit.Assert.assertThrows;
 import static org.junit.Assert.assertTrue;
 
 public final class NativeRegionTerrainWriterTest {
+    @ClassRule
+    public static final PaperRegistryIsolation registryIsolation = new PaperRegistryIsolation();
+
     @BeforeClass
     public static void bootstrap() {
         SharedConstants.tryDetectVersion();

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

@@ -26,6 +26,7 @@ import net.minecraft.world.level.material.Fluids;
 import org.bukkit.Bukkit;
 import org.junit.AfterClass;
 import org.junit.BeforeClass;
+import org.junit.ClassRule;
 import org.junit.Test;
 
 import java.util.ArrayList;
@@ -40,6 +41,9 @@ import static org.junit.Assert.assertThrows;
 import static org.junit.Assert.assertTrue;
 
 public final class OfflineNativeFeatureFeasibilityTest {
+    @ClassRule
+    public static final PaperRegistryIsolation registryIsolation = new PaperRegistryIsolation();
+
     private static HeadlessNativeRegistries loaded;
     private static RegistryAccess registries;
     private static DimensionType dimension;

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

@@ -1,6 +1,7 @@
 package art.arcane.iris.probe;
 
 import org.junit.Rule;
+import org.junit.ClassRule;
 import org.junit.Test;
 import org.junit.rules.TemporaryFolder;
 import org.mockito.MockedStatic;
@@ -22,6 +23,9 @@ import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.mockStatic;
 
 public final class OfflineRegionPublicationTest {
+    @ClassRule
+    public static final PaperRegistryIsolation registryIsolation = new PaperRegistryIsolation();
+
     @Rule
     public TemporaryFolder temporary = new TemporaryFolder();
 

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

@@ -0,0 +1,37 @@
+package art.arcane.iris.probe;
+
+import io.papermc.paper.registry.PaperRegistryAccess;
+import org.junit.rules.TestRule;
+import org.junit.runner.Description;
+import org.junit.runners.model.Statement;
+
+import java.lang.reflect.Field;
+import java.util.HashMap;
+import java.util.Map;
+
+public final class PaperRegistryIsolation implements TestRule {
+    @Override
+    public Statement apply(Statement base, Description description) {
+        return new Statement() {
+            @Override
+            public void evaluate() throws Throwable {
+                Map<Object, Object> registries = registries();
+                Map<Object, Object> previous = new HashMap<>(registries);
+                registries.clear();
+                try {
+                    base.evaluate();
+                } finally {
+                    registries.clear();
+                    registries.putAll(previous);
+                }
+            }
+        };
+    }
+
+    @SuppressWarnings("unchecked")
+    private static Map<Object, Object> registries() throws ReflectiveOperationException {
+        Field field = PaperRegistryAccess.class.getDeclaredField("registries");
+        field.setAccessible(true);
+        return (Map<Object, Object>) field.get(PaperRegistryAccess.instance());
+    }
+}

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

@@ -18,6 +18,7 @@
 
 package art.arcane.iris;
 
+import java.util.concurrent.CompletionStage;
 import art.arcane.volmlib.util.diagnostics.BukkitDebugDump;
 import art.arcane.iris.generation.runtime.IrisEngineEffects;
 import art.arcane.iris.generation.runtime.IrisWorldManager;
@@ -1011,20 +1012,21 @@ public class Iris extends VolmitPlugin implements Listener, ReloadAware {
     }
 
     @Override
-    public void onPreUnload(ReloadAware.PreUnloadReason reason) {
+    public CompletionStage<Void> commitReload(ReloadAware.PreUnloadReason reason) {
         teardownPapi();
         if (IrisToolbelt.isServerStopping()) {
             quiesceRuntimeForServerShutdown("pre-unload:" + reason);
             startPostStopFinisher();
             Iris.debug("Pre-unload hook deferred generator teardown until Paper closes its chunk schedulers.");
-            return;
+            return CompletableFuture.completedFuture(null);
         }
         if (alreadyDrained.get()) {
             Iris.debug("Pre-unload hook skipped; Iris already drained.");
-            return;
+            return CompletableFuture.completedFuture(null);
         }
         Iris.debug("BileTools pre-unload hook fired (" + reason + "). Freezing all Iris worlds.");
         drainOnce("pre-unload:" + reason, 45L);
+        return CompletableFuture.completedFuture(null);
     }
 
     /**

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

@@ -25,6 +25,8 @@ import art.arcane.iris.localization.IrisLanguage;
 import art.arcane.iris.pack.datapack.DatapackIngestService;
 import art.arcane.iris.studio.object.ObjectStudioSaveService;
 import art.arcane.iris.generation.runtime.Engine;
+import art.arcane.iris.generation.locator.SubterrainLocator;
+import art.arcane.iris.generation.subterrain.IrisSubterrainFamily;
 import art.arcane.iris.structure.placement.IrisStructureLocator;
 import art.arcane.iris.structure.nativegen.NativeStructureGenerationPolicy;
 import art.arcane.iris.structure.placement.StructureReachability;
@@ -72,7 +74,7 @@ import java.util.Set;
 
 @Director(name = "find", origin = DirectorOrigin.PLAYER, description = "Iris Find commands", descriptionKey = "iris.director.commandfind.director.iris_find_commands", aliases = "goto")
 public class CommandFind implements DirectorExecutor {
-    @Director(description = "Find a biome", descriptionKey = "iris.director.commandfind.director.find_biome")
+    @Director(description = "Find a biome", sync = true, descriptionKey = "iris.director.commandfind.director.find_biome")
     public void biome(
             @Param(description = "The biome to look for", descriptionKey = "iris.director.commandfind.param.biome_look", customHandler = ReachableBiomeHandler.class)
             IrisBiome biome,
@@ -89,6 +91,78 @@ public class CommandFind implements DirectorExecutor {
         EngineBukkitOps.gotoBiome(e, biome, player(), teleport);
     }
 
+    @Director(description = "Find an authored underground feature by id or geometry family", sync = true)
+    public void subterrain(
+            @Param(description = "Feature definition id or family: tectonic_fault, cenote, lava_tube, travertine_terraces")
+            String feature,
+            @Param(description = "Search radius in blocks", defaultValue = "8192")
+            int radius,
+            @Param(description = "Should you be teleported", defaultValue = "true")
+            boolean teleport
+    ) {
+        String key = feature.trim();
+        IrisSubterrainFamily family = null;
+        try {
+            family = IrisSubterrainFamily.valueOf(key.toUpperCase(Locale.ROOT).replace('-', '_'));
+        } catch (IllegalArgumentException ignored) {
+        }
+        locateSubterrain(new SubterrainLocator.Query(family == null ? key : "", family, ""), radius, teleport);
+    }
+
+    @Director(name = "underground-biome", description = "Find a bounded authored underground biome", sync = true)
+    public void undergroundBiome(
+            @Param(description = "The underground biome to look for", customHandler = ReachableBiomeHandler.class)
+            IrisBiome biome,
+            @Param(description = "Search radius in blocks", defaultValue = "8192")
+            int radius,
+            @Param(description = "Should you be teleported", defaultValue = "true")
+            boolean teleport
+    ) {
+        locateSubterrain(new SubterrainLocator.Query("", null, biome.getLoadKey()), radius, teleport);
+    }
+
+    private void locateSubterrain(SubterrainLocator.Query query, int radius, boolean teleport) {
+        Engine activeEngine = engine();
+        VolmitSender commandSender = sender();
+        Player target = player();
+        if (activeEngine == null || commandSender == null || target == null) {
+            if (commandSender != null) {
+                commandSender.sendMessage(C.RED + "Run this command from an Iris world.");
+            }
+            return;
+        }
+        if (radius < 0 || radius > 32768) {
+            commandSender.sendMessage(C.RED + "Search radius must be between 0 and 32768 blocks.");
+            return;
+        }
+        Location origin = target.getLocation();
+        World world = origin.getWorld();
+        commandSender.sendMessage(C.GRAY + "Searching authored underground plans...");
+        J.a(() -> {
+            try {
+                SubterrainLocator.Result found = GenerationSemanticQueries.nearestSubterrain(activeEngine, query,
+                        origin.getBlockX(), origin.getBlockY(), origin.getBlockZ(), radius).orElse(null);
+                if (found == null) {
+                    sendStructureMessage(target, commandSender,
+                            C.YELLOW + "No matching authored underground volume found within " + radius + " blocks.");
+                    return;
+                }
+                String label = found.family().name().toLowerCase(Locale.ROOT) + " " + found.featureId();
+                if (!teleport) {
+                    sendStructureMessage(target, commandSender, C.GREEN + "Found " + label + " at "
+                            + found.x() + ", " + found.y() + ", " + found.z() + ".");
+                    return;
+                }
+                prepareStructureTeleport(target, world, commandSender, label,
+                        new Location(world, found.x(), found.y(), found.z()), true);
+            } catch (Throwable error) {
+                sendStructureMessage(target, commandSender,
+                        C.RED + "Could not locate authored underground volume: " + error.getMessage());
+                Iris.reportError("Could not locate authored underground volume.", error);
+            }
+        });
+    }
+
     @Director(description = "Find a region", descriptionKey = "iris.director.commandfind.director.find_region")
     public void region(
             @Param(description = "The region to look for", descriptionKey = "iris.director.commandfind.param.region_look", customHandler = ReachableRegionHandler.class)

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

@@ -18,6 +18,8 @@
 
 package art.arcane.iris.command;
 
+import art.arcane.iris.pack.PackFingerprints;
+
 import art.arcane.iris.Iris;
 import art.arcane.iris.pack.validation.PackCompatReport;
 import art.arcane.iris.pack.PackDirectoryResolver;
@@ -174,7 +176,6 @@ public class CommandPack implements DirectorExecutor {
                 s.sendMessage(IrisLanguage.text(BukkitRuntimeMessages.COMMAND_PACK_NO_CLEANUP_CANDIDATES_FOUND_PACK, MessageArgument.untrusted("pack", String.valueOf(pack))));
                 return;
             }
-            PackValidationRegistry.remove(packFolder.getName());
             s.sendMessage(IrisLanguage.text(BukkitRuntimeMessages.COMMAND_PACK_QUARANTINED_CLEANUP_CANDIDATE_S_UNDER, MessageArgument.untrusted("size", String.valueOf(result.quarantinedPaths().size())), MessageArgument.untrusted("quarantinePath", String.valueOf(result.quarantinePath()))));
             reportPaths(s, result.quarantinedPaths(), BukkitRuntimeMessages.COMMAND_PACK_PATH_QUARANTINED);
             return;
@@ -230,7 +231,6 @@ public class CommandPack implements DirectorExecutor {
                 s.sendMessage(IrisLanguage.text(BukkitRuntimeMessages.COMMAND_PACK_NOTHING_RESTORE_PACK, MessageArgument.untrusted("pack", String.valueOf(pack))));
                 return;
             }
-            PackValidationRegistry.remove(packFolder.getName());
             s.sendMessage(IrisLanguage.text(BukkitRuntimeMessages.COMMAND_PACK_RESTORED_FILE_S_FROM, MessageArgument.untrusted("size", String.valueOf(result.restoredPaths().size())), MessageArgument.untrusted("dumpPath", String.valueOf(result.dumpPath()))));
             reportPaths(s, result.restoredPaths(), BukkitRuntimeMessages.COMMAND_PACK_PATH_RESTORED);
             return;
@@ -363,47 +363,79 @@ public class CommandPack implements DirectorExecutor {
         return persisted == null || persisted.isBlank() ? "unknown" : persisted;
     }
 
-    private PackValidationResult runValidate(VolmitSender s, File packFolder) {
+    PackValidationResult runValidate(VolmitSender s, File packFolder) {
+        PackValidationRegistry.ValidationTicket ticket =
+                PackValidationRegistry.tryBeginValidation(packFolder.toPath());
+        PackValidationResult result;
+        String contentFingerprint = "";
+        String contextFingerprint = "";
         try {
-            PackValidationResult result = PackValidator.validate(packFolder);
+            if (ticket == null) {
-            PackValidationRegistry.publish(result);
+                throw new IllegalStateException("Pack content is currently being changed.");
-            reportResult(s, result);
+            }
-            return result;
+            contentFingerprint = PackFingerprints.computePackTreeFingerprint(packFolder);
+            contextFingerprint = PackValidationCache.contextFingerprint();
+            result = PackValidator.validate(packFolder);
+            if (!contentFingerprint.equals(PackFingerprints.computePackTreeFingerprint(packFolder))
+                    || !contextFingerprint.equals(PackValidationCache.contextFingerprint())) {
+                throw new IllegalStateException("Pack content or validation context changed during validation.");
+            }
         } catch (Throwable e) {
             Iris.reportError("Pack validation failed for '" + packFolder.getName() + "'", e);
             String detail = e.getMessage() == null || e.getMessage().isBlank()
                     ? e.getClass().getSimpleName()
                     : e.getMessage();
-            PackValidationResult result = new PackValidationResult(
+            result = new PackValidationResult(
                     packFolder.getName(),
                     List.of("Pack validation failed with " + e.getClass().getSimpleName() + ": " + detail),
                     List.of(),
                     System.currentTimeMillis());
+            contentFingerprint = "";
+            contextFingerprint = "";
+        }
+        if (PackValidationRegistry.publishIfCurrent(ticket, result, contentFingerprint, contextFingerprint)) {
             PackValidationRegistry.publish(result);
+        } else {
+            result = new PackValidationResult(packFolder.getName(),
+                    List.of("Pack content changed during validation."), List.of(), System.currentTimeMillis());
+        }
         reportResult(s, result);
         return result;
     }
-    }
 
     private void persistValidationCache(File packsRoot) {
+        try {
+            String contextFingerprint = PackValidationCache.contextFingerprint();
+            PackFingerprints.PackContentSnapshot snapshot = PackFingerprints.computePackContentSnapshot(packsRoot);
             List<File> packDirectories = PackDirectoryResolver.listVisiblePackDirectories(packsRoot);
             List<PackValidationResult> results = new ArrayList<>(packDirectories.size());
             for (File packDirectory : packDirectories) {
-            PackValidationResult result = PackValidationRegistry.get(packDirectory.getName());
+                PackValidationResult result = PackValidationRegistry.getMatching(
+                        packDirectory.toPath(), snapshot.packContents().get(packDirectory.getName()));
                 if (result == null) {
-                // The boot cache only loads when it covers every pack, so a partial write is
-                // pointless - but say so instead of silently skipping the persist forever.
                     Iris.warn("Pack validation cache not written: \"" + packDirectory.getName()
-                        + "\" has no registered result. Run /iris pack validate all to repopulate it.");
+                            + "\" has no validation matching its current content. Run /iris pack validate to refresh it.");
                     return;
                 }
                 results.add(result);
             }
-        try {
+            if (!snapshot.content().equals(PackFingerprints.computePackContentSnapshot(packsRoot).content())
+                    || !contextFingerprint.equals(PackValidationCache.contextFingerprint())) {
+                Iris.warn("Pack validation cache not written because pack content or validation context changed.");
+                return;
+            }
+            for (int index = 0; index < packDirectories.size(); index++) {
+                File packDirectory = packDirectories.get(index);
+                if (PackValidationRegistry.getMatching(packDirectory.toPath(),
+                        snapshot.packContents().get(packDirectory.getName())) != results.get(index)) {
+                    Iris.warn("Pack validation cache not written because validation changed during persistence.");
+                    return;
+                }
+            }
             PackValidationCache.save(
                     Iris.instance.getDataFile("cache", "pack-validation.json").toPath(),
-                    PackValidationCache.contentFingerprint(packsRoot),
+                    snapshot.content(),
-                    PackValidationCache.contextFingerprint(),
+                    contextFingerprint,
                     results);
         } catch (IOException | RuntimeException e) {
             Iris.reportError("Could not persist refreshed pack-validation results", 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);
+                double chunksPerSecond = registered.generationRate.sampleChunksPerSecond(engine.getGenerated(), now);
-                worldSnapshots.add(EngineTelemetrySnapshot.capture(engine, chunksPerSecond, 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 final GenerationRateWindow generationRate = new GenerationRateWindow();
-        private int lastGeneratedCount;
 
         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/IrisWorldGeneratorResolver.java

@@ -18,8 +18,9 @@
 
 package art.arcane.iris.world;
 
+import art.arcane.iris.pack.PackFingerprints;
+
 import art.arcane.iris.configuration.IrisSettings;
-import art.arcane.iris.pack.datapack.ServerConfigurator;
 
 import art.arcane.iris.Iris;
 import art.arcane.iris.world.lifecycle.WorldLifecycleStaging;
@@ -184,12 +185,12 @@ public final class IrisWorldGeneratorResolver {
         }
         List<String> packNames = packDirs.stream().map(File::getName).sorted().toList();
         Path cacheFile = IrisPlatforms.get().dataFile("cache", "pack-validation.json").toPath();
-        ServerConfigurator.PackContentSnapshot contentSnapshot =
+        PackFingerprints.PackContentSnapshot contentSnapshot =
-                new ServerConfigurator.PackContentSnapshot("", Map.of());
+                new PackFingerprints.PackContentSnapshot("", Map.of());
         String contextFingerprint = "";
         Optional<List<PackValidationResult>> cached = Optional.empty();
         try {
-            contentSnapshot = ServerConfigurator.computePackContentSnapshot(packsRoot);
+            contentSnapshot = PackFingerprints.computePackContentSnapshot(packsRoot);
             contextFingerprint = PackValidationCache.contextFingerprint();
             if (!externalContentChanged) {
                 cached = PackValidationCache.load(
@@ -274,19 +275,19 @@ public final class IrisWorldGeneratorResolver {
     private static FreshValidation validateStablePacks(
             File packsRoot,
             List<File> initialPackDirs,
-            ServerConfigurator.PackContentSnapshot initialSnapshot
+            PackFingerprints.PackContentSnapshot initialSnapshot
     ) {
         List<File> packDirs = initialPackDirs;
-        ServerConfigurator.PackContentSnapshot before = initialSnapshot;
+        PackFingerprints.PackContentSnapshot before = initialSnapshot;
         for (int attempt = 0; attempt < VALIDATION_STABILITY_ATTEMPTS; attempt++) {
             List<String> packNames = packDirs.stream().map(File::getName).sorted().toList();
             List<PackValidationResult> results = validatePacks(packDirs);
-            ServerConfigurator.PackContentSnapshot after;
+            PackFingerprints.PackContentSnapshot after;
             try {
-                after = ServerConfigurator.computePackContentSnapshot(packsRoot);
+                after = PackFingerprints.computePackContentSnapshot(packsRoot);
             } catch (RuntimeException exception) {
                 Iris.reportError("Could not verify Iris pack bytes after validation", exception);
-                after = new ServerConfigurator.PackContentSnapshot("", Map.of());
+                after = new PackFingerprints.PackContentSnapshot("", Map.of());
             }
             List<File> afterPackDirs = PackDirectoryResolver.listVisiblePackDirectories(packsRoot);
             List<String> afterPackNames = afterPackDirs.stream().map(File::getName).sorted().toList();
@@ -923,7 +924,7 @@ public final class IrisWorldGeneratorResolver {
 
     private record FreshValidation(
             List<File> packDirs,
-            ServerConfigurator.PackContentSnapshot contentSnapshot,
+            PackFingerprints.PackContentSnapshot contentSnapshot,
             List<PackValidationResult> results,
             boolean stable
     ) {

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

@@ -0,0 +1,47 @@
+{
+  "name": "Flat",
+  "derivative": "minecraft:plains",
+  "vanillaDerivative": "minecraft:plains",
+  "layers": [
+    {
+      "minHeight": 1,
+      "maxHeight": 1,
+      "palette": [
+        {
+          "block": "minecraft:lime_wool"
+        }
+      ]
+    },
+    {
+      "minHeight": 384,
+      "maxHeight": 384,
+      "palette": [
+        {
+          "block": "minecraft:green_concrete"
+        }
+      ]
+    }
+  ],
+  "generators": [
+    {
+      "generator": "flat",
+      "min": 96,
+      "max": 96
+    }
+  ],
+  "decorators": [
+    {
+      "palette": [
+        {
+          "block": "minecraft:oak_stairs",
+          "data": {
+            "half": "bottom",
+            "facing": "north"
+          }
+        }
+      ],
+      "chance": 1,
+      "forcePlace": true
+    }
+  ]
+}

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

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

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

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

adapters/bukkit/plugin/src/test/gameplay/decorators.mjs

@@ -0,0 +1,40 @@
+import { readFile } from 'node:fs/promises'
+import path from 'node:path'
+
+export default {
+  name: 'iris-decorators',
+  description: 'Verify authored stair decorations occupy one block and retain their half state.',
+  async run(context) {
+    const source = await readFile(path.join(context.server.directory, '.server-source'), 'utf8')
+    context.expect(/^isolated=true\s*$/m.test(source), 'Decorator generation requires an isolated instance')
+    await context.step('create a world with authored stair decorations', async () => {
+      const response = await context.command('/iris create name=decorator_probe type=decorator-fixture seed=78264193',
+        /Successfully created your world|Failed to create/, 180000)
+      context.expect(response.includes('Successfully created your world'), response)
+    })
+    await context.step('client sees single bottom-half stair decorations', async () => {
+      let checked = 0
+      await context.waitUntil(() => {
+        checked = 0
+        const center = context.bot.entity.position.floored()
+        for (let x = -6; x <= 6; x++) {
+          for (let z = -6; z <= 6; z++) {
+            for (let y = -4; y <= 1; y++) {
+              const position = center.offset(x, y, z)
+              if (context.bot.blockAt(position)?.name !== 'lime_wool') continue
+              const decoration = context.bot.blockAt(position.offset(0, 1, 0))
+              const above = context.bot.blockAt(position.offset(0, 2, 0))
+              if (!decoration || !above) return false
+              if (decoration.name !== 'oak_stairs' || decoration.getProperties().half !== 'bottom'
+                || above.name !== 'air') return false
+              checked++
+            }
+          }
+        }
+        return checked >= 100
+      }, { label: 'At least 100 authored stair columns with empty space above', timeoutMs: 60000, intervalMs: 250 })
+      context.expect(checked >= 100, 'Client verified generated decorator columns', { checked })
+      context.report.decoratorColumns = checked
+    })
+  }
+}

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

@@ -4,6 +4,13 @@ import art.arcane.volmlib.nativelib.NativeAdapters;
 import art.arcane.iris.world.runtime.RuntimeInjection;
 import art.arcane.iris.world.IrisCreator;
 import art.arcane.iris.world.IrisToolbelt;
+import art.arcane.iris.world.IrisWorldStorage;
+import art.arcane.iris.world.WorldCreatorCompat;
+import art.arcane.iris.world.lifecycle.LifecycleOperationCoordinator;
+import art.arcane.iris.platform.bootstrap.ServerProperties;
+import org.bukkit.Location;
+import org.bukkit.entity.Player;
+import org.bukkit.configuration.file.YamlConfiguration;
 import org.bukkit.Material;
 import org.bukkit.block.Biome;
 import art.arcane.volmlib.nativelib.terrain.NativeTerrainAccess;
@@ -19,6 +26,10 @@ import org.bukkit.command.CommandSender;
 import org.bukkit.generator.ChunkGenerator;
 import org.bukkit.plugin.java.JavaPlugin;
 
+import java.io.File;
+import java.nio.file.Files;
+import java.nio.file.LinkOption;
+import java.nio.file.Path;
 import java.util.concurrent.CompletableFuture;
 import java.util.List;
 import java.util.logging.Level;
@@ -26,6 +37,7 @@ import java.util.logging.Level;
 public final class NativeLifecycleFixture extends JavaPlugin implements WorldRuntimeExecution {
     private static final NamespacedKey WORLD_KEY = NamespacedKey.minecraft("native_lifecycle_probe");
     private static final NamespacedKey TERRAIN_KEY = new NamespacedKey("iris", "native_terrain_probe");
+    private static final NamespacedKey COMMAND_KEY = new NamespacedKey("iris", "lifecycle_probe");
     private static final long WORLD_SEED = 78264193L;
     private NativeWorldRuntime runtime;
 
@@ -45,7 +57,7 @@ public final class NativeLifecycleFixture extends JavaPlugin implements WorldRun
     @Override
     public boolean onCommand(CommandSender sender, Command command, String label, String[] arguments) {
         if (arguments.length != 1) {
-            sender.sendMessage("Use /irislifecycle create|unload|status|structures|terrain-create|terrain-check|terrain-unload");
+            sender.sendMessage("Use /irislifecycle create|unload|status|structures|terrain-create|terrain-check|terrain-unload|lifecycle-status|lifecycle-entry");
             return true;
         }
         try {
@@ -56,6 +68,8 @@ public final class NativeLifecycleFixture extends JavaPlugin implements WorldRun
                 case "terrain-create" -> createTerrain(sender);
                 case "terrain-check" -> checkTerrain(sender);
                 case "terrain-unload" -> unloadTerrain(sender);
+                case "lifecycle-status" -> lifecycleStatus(sender);
+                case "lifecycle-entry" -> lifecycleEntry(sender);
                 case "status" -> sender.sendMessage("NATIVE_STATUS available=" + runtime.available()
                         + " loaded=" + (Bukkit.getWorld(WORLD_KEY) != null));
                 default -> throw new IllegalArgumentException("Unknown lifecycle operation");
@@ -66,6 +80,61 @@ public final class NativeLifecycleFixture extends JavaPlugin implements WorldRun
         return true;
     }
 
+    private void lifecycleStatus(CommandSender sender) throws Exception {
+        World world = Bukkit.getWorld(COMMAND_KEY);
+        Path storage = WorldCreatorCompat.persistentLevelRoot(COMMAND_KEY).toPath();
+        Path levelRoot = IrisWorldStorage.levelRoot().toPath();
+        Path registry = levelRoot.resolve("iris/worlds.json");
+        boolean registered = Files.exists(registry)
+                && Files.readString(registry).contains("\"" + COMMAND_KEY + "\"");
+        String startupName = IrisWorldStorage.configuredWorldName(COMMAND_KEY, levelRoot.getFileName().toString());
+        YamlConfiguration configuration = YamlConfiguration.loadConfiguration(ServerProperties.BUKKIT_YML);
+        boolean configured = configuration.getConfigurationSection("worlds") != null
+                && configuration.getConfigurationSection("worlds").contains(startupName);
+        File quarantineRoot = levelRoot.resolve("dimensions/iris").toFile();
+        File[] quarantines = quarantineRoot.listFiles((directory, name) -> name.startsWith(".iris-delete-"));
+        int quarantineCount = quarantines == null ? 0 : quarantines.length;
+        Path queueFile = Bukkit.getPluginManager().getPlugin("Iris").getDataFolder().toPath()
+                .resolve("pending-world-deletes.txt");
+        List<String> queue = Files.exists(queueFile) ? Files.readAllLines(queueFile) : List.of();
+        boolean queued = quarantineCount > 0;
+        if (quarantines != null) {
+            for (File quarantine : quarantines) {
+                queued &= queue.contains(quarantine.getName());
+            }
+        }
+        boolean disk = Files.exists(storage, LinkOption.NOFOLLOW_LINKS);
+        String cleanup = disk ? "present" : quarantineCount == 0 ? "deleted" : queued ? "queued" : "unsafe";
+        boolean idle = true;
+        LifecycleOperationCoordinator coordinator = LifecycleOperationCoordinator.get();
+        for (LifecycleOperationCoordinator.Domain domain : LifecycleOperationCoordinator.Domain.values()) {
+            idle &= coordinator.active(domain).isEmpty();
+        }
+        sender.sendMessage("IRIS_LIFECYCLE loaded=" + (world != null) + " registered=" + registered
+                + " configured=" + configured + " disk=" + disk + " quarantines=" + quarantineCount
+                + " cleanup=" + cleanup + " idle=" + idle);
+    }
+
+    private void lifecycleEntry(CommandSender sender) {
+        if (!(sender instanceof Player player)) {
+            throw new IllegalArgumentException("Lifecycle entry requires a player");
+        }
+        World world = Bukkit.getWorld(COMMAND_KEY);
+        if (world == null || player.getWorld() != world || world.getSeed() != WORLD_SEED
+                || !IrisToolbelt.isIrisWorld(world)) {
+            throw new IllegalStateException("Player did not enter the requested seeded Iris world");
+        }
+        Location feet = player.getLocation();
+        Material floor = world.getBlockAt(feet.getBlockX(), feet.getBlockY() - 1, feet.getBlockZ()).getType();
+        if (floor != Material.LIME_WOOL || !floor.isSolid()
+                || !world.getBlockAt(feet.getBlockX(), feet.getBlockY(), feet.getBlockZ()).isPassable()
+                || !world.getBlockAt(feet.getBlockX(), feet.getBlockY() + 1, feet.getBlockZ()).isPassable()) {
+            throw new IllegalStateException("Lifecycle player entry lacks a safe fixture floor");
+        }
+        sender.sendMessage("IRIS_LIFECYCLE_ENTRY world=" + COMMAND_KEY + " seed=" + world.getSeed()
+                + " floor=lime_wool safe=true");
+    }
+
     private void create(CommandSender sender) throws ReflectiveOperationException {
         if (!runtime.available() || Bukkit.getWorld(WORLD_KEY) != null) {
             throw new IllegalStateException("Native runtime unavailable or probe world already loaded");
@@ -124,6 +193,7 @@ public final class NativeLifecycleFixture extends JavaPlugin implements WorldRun
                         int y = world.getHighestBlockYAt(x, z);
                         if (y < 90 || y > 100 || world.getBlockAt(x, y, z).getType() != Material.LIME_WOOL
                                 || world.getBlockAt(x, y - 3, z).getType() != Material.GREEN_CONCRETE
+                                || world.getBlockAt(x, world.getMinHeight(), z).getType() != Material.GREEN_CONCRETE
                                 || world.getBiome(x, y, z) != Biome.PLAINS) {
                             throw new IllegalStateException("Terrain column differs at " + x + "," + y + "," + z
                                     + ": " + world.getBlockAt(x, y, z).getType());

adapters/bukkit/plugin/src/test/gameplay/native-terrain-pack/biomes/flat.json

@@ -11,6 +11,15 @@
           "block": "minecraft:lime_wool"
         }
       ]
+    },
+    {
+      "minHeight": 384,
+      "maxHeight": 384,
+      "palette": [
+        {
+          "block": "minecraft:green_concrete"
+        }
+      ]
     }
   ],
   "generators": [

adapters/bukkit/plugin/src/test/gameplay/native-terrain-pack/dimensions/native-terrain.json

@@ -21,7 +21,7 @@
   "rockPalette": {
     "palette": [
       {
-        "block": "minecraft:green_concrete"
+        "block": "minecraft:red_concrete"
       }
     ]
   }

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 +1,701 @@
+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.IrisMarker;
+import art.arcane.iris.world.entity.EntitySpawnSeed;
+import art.arcane.volmlib.util.mantle.flag.MantleFlag;
+import art.arcane.iris.pack.value.IrisPosition;
+import art.arcane.volmlib.util.math.RNG;
+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.inventory.ItemStack;
+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.Collections;
+import java.util.HexFormat;
+import java.util.List;
+import java.util.Map;
+import java.util.TreeMap;
+import java.util.Set;
+import java.util.concurrent.atomic.AtomicInteger;
+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|seeded|completion|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 "seeded" -> seeded(sender);
+                case "completion" -> completion(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.setTime(6000L);
+            world.setStorm(false);
+            world.setThundering(false);
+            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);
+                    for (Entity entity : chunk.getEntities()) {
+                        if (entity instanceof LivingEntity && !(entity instanceof Player)) {
+                            entity.remove();
+                        }
+                    }
+                    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 completion(CommandSender sender) {
+        World world = requireWorld();
+        Bukkit.getGlobalRegionScheduler().execute(this, () -> {
+            world.setGameRule(GameRules.SPAWN_MOBS, false);
+            runRegion(sender, () -> beginCompletion(sender, world));
+        });
+    }
+
+    private void beginCompletion(CommandSender sender, World world) {
+        try {
+            Engine engine = IrisToolbelt.access(world).getEngine();
+            Object manager = engine.getWorldManager();
+            Field field = manager.getClass().getDeclaredField("chunkMaintenance");
+            field.setAccessible(true);
+            Object maintenance = field.get(manager);
+            Method run = maintenance.getClass().getDeclaredMethod("runInitialSpawn", World.class, int.class, int.class, Runnable.class);
+            run.setAccessible(true);
+            Field pending = maintenance.getClass().getDeclaredField("markerFlagQueue");
+            pending.setAccessible(true);
+            AtomicInteger callbacks = new AtomicInteger();
+            Runnable callback = () -> {
+                require(Bukkit.isOwnedByCurrentRegion(world, 0, 0), "Initial callback ran outside its owning region");
+                callbacks.incrementAndGet();
+                Chunk chunk = world.getChunkAt(0, 0);
+                invokeAmbient(runtimeSpawn(chunk, "seeded"), chunk, true);
+            };
+            run.invoke(maintenance, world, 0, 0, callback);
+            awaitSkippedInitial(sender, world, new CompletionRun(engine, maintenance, run, pending, callback, callbacks), 0);
+        } catch (ReflectiveOperationException failure) {
+            throw new IllegalStateException("Could not start initial completion test", failure);
+        }
+    }
+
+    private void awaitSkippedInitial(CommandSender sender, World world, CompletionRun state, int attempt) {
+        Bukkit.getRegionScheduler().runDelayed(this, world, 0, 0, task -> {
+            try {
+                require(state.callbacks().get() == 0, "Disabled mob spawning consumed the initial pass");
+                if (!((Set<?>) state.pending().get(state.maintenance())).isEmpty()) {
+                    require(attempt < 100, "Skipped initial pass did not release its pending state");
+                    awaitSkippedInitial(sender, world, state, attempt + 1);
+                    return;
+                }
+                Bukkit.getGlobalRegionScheduler().execute(this, () -> {
+                    world.setGameRule(GameRules.SPAWN_MOBS, true);
+                    runRegion(sender, () -> retryInitialCompletion(sender, world, state));
+                });
+            } catch (Throwable failure) {
+                fail(sender, failure);
+            }
+        }, 2L);
+    }
+
+    private void retryInitialCompletion(CommandSender sender, World world, CompletionRun state) {
+        try {
+            state.run().invoke(state.maintenance(), world, 0, 0, state.callback());
+            state.run().invoke(state.maintenance(), world, 0, 0, state.callback());
+            awaitInitialCompletion(sender, world, state, 0);
+        } catch (ReflectiveOperationException failure) {
+            throw new IllegalStateException("Could not retry initial spawning", failure);
+        }
+    }
+
+    private void awaitInitialCompletion(CommandSender sender, World world, CompletionRun state, int attempt) {
+        Bukkit.getRegionScheduler().runDelayed(this, world, 0, 0, task -> {
+            try {
+                if (state.callbacks().get() == 0 || !((Set<?>) state.pending().get(state.maintenance())).isEmpty()) {
+                    require(attempt < 100, "Initial spawning did not complete after retry");
+                    awaitInitialCompletion(sender, world, state, attempt + 1);
+                    return;
+                }
+                require(state.callbacks().get() == 1, "Concurrent initial requests spawned duplicate populations");
+                state.run().invoke(state.maintenance(), world, 0, 0, state.callback());
+                Bukkit.getAsyncScheduler().runNow(this, ignored -> {
+                    try {
+                        require(state.engine().getMantle().getMantle().hasFlag(0, 0, MantleFlag.INITIAL_SPAWNED_MARKER), "Initial completion was not persisted");
+                        require(state.callbacks().get() == 1, "Completed initial pass ran again");
+                        evidence(sender, "SPAWN_QA_COMPLETION retry=true callbacks=1 persisted=true owned=true");
+                    } catch (Throwable failure) {
+                        fail(sender, failure);
+                    }
+                });
+            } catch (Throwable failure) {
+                fail(sender, failure);
+            }
+        }, 2L);
+    }
+
+    private void seeded(CommandSender sender) {
+        requireWorld();
+        List<List<String>> baseline = new ArrayList<>();
+        sampleInitial(0, false).thenCompose(first -> {
+            baseline.add(first);
+            return sampleInitial(1, false);
+        }).thenCompose(second -> {
+            baseline.add(second);
+            return sampleInitial(1, false);
+        }).thenCompose(repeated -> {
+            require(baseline.get(1).equals(repeated), "Second chunk changed after reversed generation order");
+            return sampleInitial(0, false);
+        }).thenCompose(repeated -> {
+            require(baseline.get(0).equals(repeated), "First chunk changed after reversed generation order");
+            return sampleInitial(0, true);
+        }).thenCompose(marker -> {
+            baseline.add(marker);
+            return sampleInitial(1, true);
+        }).thenCompose(marker -> {
+            baseline.add(marker);
+            return sampleInitial(1, true);
+        }).thenCompose(repeated -> {
+            require(baseline.get(3).equals(repeated), "Second marker changed after reversed generation order");
+            return sampleInitial(0, true);
+        }).whenComplete((repeated, failure) -> {
+            if (failure != null) {
+                fail(sender, failure);
+                return;
+            }
+            try {
+                require(baseline.get(2).equals(repeated), "First marker changed after reversed generation order");
+                evidence(sender, "SPAWN_QA_SEEDED chunks=2 markers=2 repeats=2 equipment=true attributes=true");
+            } catch (Throwable error) {
+                fail(sender, error);
+            }
+        });
+    }
+
+    private CompletableFuture<List<String>> sampleInitial(int chunkX, boolean marker) {
+        CompletableFuture<List<String>> result = new CompletableFuture<>();
+        World world = requireWorld();
+        Bukkit.getRegionScheduler().execute(this, world, chunkX, 0, () -> {
+            try {
+                Chunk chunk = world.getChunkAt(chunkX, 0);
+                for (Entity entity : chunk.getEntities()) {
+                    if (entity instanceof LivingEntity && !(entity instanceof Player)) {
+                        entity.remove();
+                    }
+                }
+                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);
+                        }
+                    }
+                }
+                RuntimeSpawn spawn = runtimeSpawn(chunk, "seeded");
+                IrisSpawner definition = spawn.environment().data().getSpawnerLoader().load("qa/seeded");
+                require(!definition.canSpawn(spawn.engine(), chunkX, 0), "Ongoing weather/time gate unexpectedly allowed spawning");
+                for (int i = 0; i < 100 + chunkX; i++) {
+                    RNG.r.nextLong();
+                }
+                ambientInvocation.set(true);
+                try {
+                    for (int i = 0; i < 5; i++) {
+                        LivingEntity witness = (LivingEntity) world.spawnEntity(new Location(world, (chunkX << 4) + 8.5, 65, 8.5), EntityType.ZOMBIE);
+                        witness.setCustomName("Population witness");
+                        witness.setAI(false);
+                        witness.setGravity(false);
+                    }
+                } finally {
+                    ambientInvocation.remove();
+                }
+                if (marker) {
+                    invokeInitialMarker(spawn, definition, new IrisPosition((chunkX << 4) + 5, 64, 5));
+                } else {
+                    invokeAmbient(spawn, chunk, true);
+                }
+                List<String> snapshot = new ArrayList<>();
+                for (Entity entity : chunk.getEntities()) {
+                    String name = entity.getCustomName();
+                    if (!(entity instanceof LivingEntity living) || name == null || !name.startsWith("Seeded ")) {
+                        continue;
+                    }
+                    ItemStack hand = living.getEquipment().getItemInMainHand();
+                    ItemStack helmet = living.getEquipment().getHelmet();
+                    require(hand.hasItemMeta() && hand.getItemMeta().hasAttributeModifiers(), "Spawned gear has no authored attributes");
+                    require(helmet != null && helmet.getType() == Material.IRON_HELMET, "Spawned helmet was not authored equipment");
+                    Location at = entity.getLocation();
+                    snapshot.add(entity.getType() + ":" + at.getX() + ":" + at.getY() + ":" + at.getZ()
+                            + ":" + HexFormat.of().formatHex(hand.serializeAsBytes())
+                            + ":" + HexFormat.of().formatHex(helmet.serializeAsBytes()));
+                }
+                require(snapshot.size() >= 2 && snapshot.size() <= 4, "Initial population was blocked by runtime gates or cap: " + snapshot.size());
+                Collections.sort(snapshot);
+                result.complete(List.copyOf(snapshot));
+            } catch (Throwable failure) {
+                result.completeExceptionally(failure);
+            }
+        });
+        return result;
+    }
+
+    private void invokeInitialMarker(RuntimeSpawn spawn, IrisSpawner definition, IrisPosition position) {
+        ambientInvocation.set(true);
+        try (BiomeEnvironment.Scope ignored = spawn.engine().openBiomeEnvironmentScope(spawn.environment())) {
+            Method method = spawn.spawner().getClass().getDeclaredMethod("spawnMarker", IrisPosition.class, IrisSpawner.class, IrisMarker.class, RNG.class, boolean.class);
+            method.setAccessible(true);
+            method.invoke(spawn.spawner(), position, definition, null, EntitySpawnSeed.marker(spawn.engine().getSeedManager().getEntity(), position.getX(), position.getY(), position.getZ()), true);
+        } catch (InvocationTargetException failure) {
+            throw new IllegalStateException("Initial marker spawning failed", failure.getCause());
+        } catch (ReflectiveOperationException failure) {
+            throw new IllegalStateException("Could not invoke initial marker spawning", failure);
+        } finally {
+            ambientInvocation.remove();
+        }
+    }
+
+    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, false);
+            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, false);
+        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, false);
+            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, boolean initial) {
+        ambientInvocation.set(true);
+        try (BiomeEnvironment.Scope ignored = spawn.engine().openBiomeEnvironmentScope(spawn.environment())) {
+            spawn.method().invoke(spawn.spawner(), chunk, initial, 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 CompletionRun(Engine engine, Object maintenance, Method run, Field pending, Runnable callback, AtomicInteger callbacks) {
+    }
+
+    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/biomes/seeded.json

@@ -0,0 +1,26 @@
+{
+  "name": "Seeded population",
+  "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/seeded"
+  ]
+}

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/seeded-husk.json

@@ -0,0 +1,29 @@
+{
+  "type": "minecraft:husk",
+  "reason": "NATURAL",
+  "surface": "LAND",
+  "ai": false,
+  "aware": false,
+  "gravity": false,
+  "customName": "Seeded husk",
+  "invulnerable": true,
+  "helmet": {
+    "type": "IRON_HELMET",
+    "minDurability": 0.1,
+    "maxDurability": 0.9
+  },
+  "mainHand": {
+    "type": "IRON_SWORD",
+    "minDurability": 0.1,
+    "maxDurability": 0.9,
+    "attributes": [
+      {
+        "name": "seeded_damage",
+        "attribute": "minecraft:attack_damage",
+        "minAmount": 1.25,
+        "maxAmount": 6.75,
+        "chance": 1
+      }
+    ]
+  }
+}

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

@@ -0,0 +1,29 @@
+{
+  "type": "minecraft:zombie",
+  "reason": "NATURAL",
+  "surface": "LAND",
+  "ai": false,
+  "aware": false,
+  "gravity": false,
+  "customName": "Seeded zombie",
+  "invulnerable": true,
+  "helmet": {
+    "type": "IRON_HELMET",
+    "minDurability": 0.1,
+    "maxDurability": 0.9
+  },
+  "mainHand": {
+    "type": "IRON_SWORD",
+    "minDurability": 0.1,
+    "maxDurability": 0.9,
+    "attributes": [
+      {
+        "name": "seeded_damage",
+        "attribute": "minecraft:attack_damage",
+        "minAmount": 1.25,
+        "maxAmount": 6.75,
+        "chance": 1
+      }
+    ]
+  }
+}

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-pack/spawners/qa/seeded.json

@@ -0,0 +1,33 @@
+{
+  "group": "NORMAL",
+  "maxEntitiesPerChunk": 4,
+  "allowedLightLevels": {
+    "min": 0,
+    "max": 0
+  },
+  "weather": "DOWNFALL",
+  "timeBlock": {
+    "startHour": 20,
+    "endHour": 3
+  },
+  "maximumRate": {
+    "amount": 1,
+    "per": {
+      "days": 1
+    }
+  },
+  "initialSpawns": [
+    {
+      "entity": "qa/seeded-zombie",
+      "rarity": 1,
+      "minSpawns": 2,
+      "maxSpawns": 4
+    },
+    {
+      "entity": "qa/seeded-husk",
+      "rarity": 2,
+      "minSpawns": 2,
+      "maxSpawns": 4
+    }
+  ]
+}

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

@@ -0,0 +1,42 @@
+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
+      && entity.position.x >= 0 && entity.position.x < 16 && entity.position.z >= 0 && entity.position.z < 16)
+    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/noise-pack/biomes/flat.json

@@ -0,0 +1,32 @@
+{
+  "name": "Flat",
+  "derivative": "minecraft:plains",
+  "vanillaDerivative": "minecraft:plains",
+  "layers": [
+    {
+      "minHeight": 1,
+      "maxHeight": 1,
+      "palette": [
+        {
+          "block": "minecraft:lime_wool"
+        }
+      ]
+    },
+    {
+      "minHeight": 384,
+      "maxHeight": 384,
+      "palette": [
+        {
+          "block": "minecraft:green_concrete"
+        }
+      ]
+    }
+  ],
+  "generators": [
+    {
+      "generator": "flat",
+      "min": 64,
+      "max": 96
+    }
+  ]
+}

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

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

adapters/bukkit/plugin/src/test/gameplay/noise-pack/expressions/terrain.json

@@ -0,0 +1,3 @@
+{
+  "expression": "0.5 + sin(x * 0.15) * 0.25 + cos(y * 0.13) * 0.25"
+}

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

@@ -0,0 +1,22 @@
+{
+  "interpolator": {
+    "function": "NONE",
+    "horizontalScale": 1
+  },
+  "seed": 310,
+  "composite": [
+    {
+      "seed": 310,
+      "style": {
+        "expression": "terrain"
+      }
+    },
+    {
+      "seed": 311,
+      "style": {
+        "style": "CLOVER_HERMITE",
+        "zoom": 0.1
+      }
+    }
+  ]
+}

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

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

adapters/bukkit/plugin/src/test/gameplay/noise.mjs

@@ -0,0 +1,48 @@
+import { readFile } from 'node:fs/promises'
+import path from 'node:path'
+
+export default {
+  name: 'iris-noise',
+  description: 'Verify expression and interpolated noise produce varied, bounded terrain visible to a player.',
+  async run(context) {
+    const source = await readFile(path.join(context.server.directory, '.server-source'), 'utf8')
+    context.expect(/^isolated=true\s*$/m.test(source), 'Noise generation requires an isolated instance')
+    await context.step('create a world with expression and Clover noise', async () => {
+      const response = await context.command('/iris create name=noise_probe type=noise-fixture seed=78264193',
+        /Successfully created your world|Failed to create/, 180000)
+      context.expect(response.includes('Successfully created your world'), response)
+    })
+    await context.step('client observes bounded terrain with varying heights', async () => {
+      let columns = 0
+      let minimum = Infinity
+      let maximum = -Infinity
+      await context.waitUntil(() => {
+        columns = 0
+        minimum = Infinity
+        maximum = -Infinity
+        const center = context.bot.entity.position.floored()
+        for (let x = -8; x <= 8; x++) {
+          for (let z = -8; z <= 8; z++) {
+            let surface = null
+            for (let y = 60; y <= 100; y++) {
+              const position = center.offset(x, y - center.y, z)
+              const block = context.bot.blockAt(position)
+              if (!block) return false
+              if (block.name === 'lime_wool') {
+                if (surface !== null || context.bot.blockAt(position.offset(0, 1, 0))?.name !== 'air') return false
+                surface = y
+              }
+            }
+            if (surface === null || surface < 64 || surface > 96) return false
+            columns++
+            minimum = Math.min(minimum, surface)
+            maximum = Math.max(maximum, surface)
+          }
+        }
+        return columns === 289 && maximum - minimum >= 3
+      }, { label: '289 noise columns with bounded, varied surfaces', timeoutMs: 60000, intervalMs: 250 })
+      context.expect(columns === 289 && maximum - minimum >= 3, 'Client verified noise terrain', { columns, minimum, maximum })
+      context.report.noiseTerrain = { columns, minimum, maximum }
+    })
+  }
+}

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/gameplay/seeded-entities.mjs

@@ -0,0 +1,24 @@
+export default {
+  name: 'iris-seeded-entities',
+  description: 'Replay initial chunk and marker populations in reversed order, comparing positions and complete equipment data.',
+  async run(context) {
+    const command = async (operation, expected, timeoutMs) => {
+      const response = await context.command(`/irisspawnqa ${operation}`, /SPAWN_QA_[A-Z]+(?:\s|$)/, timeoutMs)
+      context.expect(response.includes(expected) && !response.includes('SPAWN_QA_FAILED'), response)
+    }
+    await context.step('prepare a controlled Iris world', async () => {
+      await command('setup', 'SPAWN_QA_SETUP', 180000)
+    })
+    await context.step('replay initial mobs despite unrelated randomness and live spawn restrictions', async () => {
+      await command('seeded', 'SPAWN_QA_SEEDED chunks=2 markers=2 repeats=2 equipment=true attributes=true', 60000)
+      await context.waitUntil(() => Object.values(context.bot.entities).some(entity => entity.name === 'zombie' || entity.name === 'husk'), {
+        label: 'Generated mobs reached the client', timeoutMs: 10000, intervalMs: 100
+      })
+      context.report.seededEntities = { chunks: 2, markers: 2, repeats: 2, positions: true, equipmentBytes: true, attributeIds: true }
+    })
+    await context.step('retry a skipped initial pass and persist completion once', async () => {
+      await command('completion', 'SPAWN_QA_COMPLETION retry=true callbacks=1 persisted=true owned=true', 30000)
+      context.report.seededEntities.completionRetry = true
+    })
+  }
+}

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

@@ -0,0 +1,45 @@
+{
+  "name": "Flat",
+  "derivative": "minecraft:plains",
+  "vanillaDerivative": "minecraft:plains",
+  "layers": [
+    {
+      "minHeight": 1,
+      "maxHeight": 1,
+      "palette": [
+        {
+          "block": "minecraft:lime_wool"
+        }
+      ]
+    },
+    {
+      "minHeight": 384,
+      "maxHeight": 384,
+      "palette": [
+        {
+          "block": "minecraft:stone"
+        }
+      ]
+    }
+  ],
+  "generators": [
+    {
+      "generator": "flat",
+      "min": 64,
+      "max": 64
+    }
+  ],
+  "objects": [
+    {
+      "place": [
+        "object"
+      ],
+      "chance": 1,
+      "density": 4,
+      "mode": "CENTER_HEIGHT",
+      "rotation": {
+        "enabled": false
+      }
+    }
+  ]
+}

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

@@ -0,0 +1,66 @@
+{
+  "name": "Structure Fixture",
+  "version": 1,
+  "mode": {
+    "type": "OVERWORLD"
+  },
+  "regions": [
+    "flat"
+  ],
+  "focusRegion": "flat",
+  "focus": "flat",
+  "landChance": 1,
+  "environment": "NORMAL",
+  "dimensionHeight": {
+    "min": -64,
+    "max": 320
+  },
+  "logicalHeight": 384,
+  "fluidHeight": 0,
+  "bedrock": false,
+  "rockPalette": {
+    "palette": [
+      {
+        "block": "minecraft:stone"
+      }
+    ]
+  },
+  "structures": [
+    {
+      "structures": [
+        "surface"
+      ],
+      "placementId": "surface",
+      "distribution": "DENSITY",
+      "density": 1,
+      "anchor": "SURFACE",
+      "terrain": {
+        "mode": "PRESERVE"
+      },
+      "stilt": {
+        "maxDepth": 16,
+        "palette": {
+          "palette": [
+            {
+              "block": "minecraft:diamond_block"
+            }
+          ]
+        }
+      }
+    },
+    {
+      "structures": [
+        "buried"
+      ],
+      "placementId": "buried",
+      "distribution": "DENSITY",
+      "density": 1,
+      "anchor": "HEIGHT_BAND",
+      "minHeight": 24,
+      "maxHeight": 24,
+      "terrain": {
+        "mode": "BORE"
+      }
+    }
+  ]
+}

adapters/bukkit/plugin/src/test/gameplay/structure-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/structure-pack/jigsaw-pieces/buried.json

@@ -0,0 +1,8 @@
+{
+  "object": "buried",
+  "connectors": [],
+  "rotatable": false,
+  "rules": {
+    "terminal": true
+  }
+}

adapters/bukkit/plugin/src/test/gameplay/structure-pack/jigsaw-pieces/surface.json

@@ -0,0 +1,8 @@
+{
+  "object": "surface",
+  "connectors": [],
+  "rotatable": false,
+  "rules": {
+    "terminal": true
+  }
+}

adapters/bukkit/plugin/src/test/gameplay/structure-pack/jigsaw-pools/buried.json

@@ -0,0 +1,8 @@
+{
+  "pieces": [
+    {
+      "piece": "buried",
+      "weight": 1
+    }
+  ]
+}

adapters/bukkit/plugin/src/test/gameplay/structure-pack/jigsaw-pools/surface.json

@@ -0,0 +1,8 @@
+{
+  "pieces": [
+    {
+      "piece": "surface",
+      "weight": 1
+    }
+  ]
+}

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

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

adapters/bukkit/plugin/src/test/gameplay/structure-pack/structures/buried.json

@@ -0,0 +1,6 @@
+{
+  "startPool": "buried",
+  "maxDepth": 1,
+  "maxSizeChunks": 1,
+  "placeMode": "STRUCTURE_PIECE"
+}

adapters/bukkit/plugin/src/test/gameplay/structure-pack/structures/surface.json

@@ -0,0 +1,6 @@
+{
+  "startPool": "surface",
+  "maxDepth": 1,
+  "maxSizeChunks": 1,
+  "placeMode": "STRUCTURE_PIECE"
+}

adapters/bukkit/plugin/src/test/gameplay/structures.mjs

@@ -0,0 +1,52 @@
+import { readFile } from 'node:fs/promises'
+import { createHash } from 'node:crypto'
+import path from 'node:path'
+
+export default {
+  name: 'iris-structures',
+  description: 'Verify surface foundations, buried rooms, and waterlogged object blocks in generated chunks.',
+  async run(context) {
+    const source = await readFile(path.join(context.server.directory, '.server-source'), 'utf8')
+    context.expect(/^isolated=true\s*$/m.test(source), 'Structure generation requires an isolated instance')
+    const world = context.options.command ?? 'structure_probe'
+    context.expect(/^[a-z0-9_]+$/.test(world), 'Fixture world name must be a simple identifier')
+    await context.step('create the structure fixture world', async () => {
+      const response = await context.command(`/iris create name=${world} type=structure-fixture seed=78264193`,
+        /World ready|Failed to create/, 180000)
+      context.expect(response.includes('World ready'), response)
+    })
+    await context.step('observe structures and objects above and below terrain', async () => {
+      await context.waitUntil(() => {
+        if (Math.abs(context.bot.entity.position.x) > 32 || Math.abs(context.bot.entity.position.z) > 32) return false
+        for (let x = -16; x < 32; x += 16) {
+          for (let z = -16; z < 32; z += 16) {
+            for (let y = 16; y <= 80; y += 16) {
+              if (!context.bot.blockAt(context.bot.entity.position.clone().set(x, y, z))) return false
+            }
+          }
+        }
+        return true
+      }, { label: 'Complete structure fixture chunks', timeoutMs: 60000, intervalMs: 100 })
+      const digest = createHash('sha256')
+      const counts = { emerald_block: 0, diamond_block: 0, blue_concrete: 0, gold_block: 0, oak_slab: 0 }
+      for (let x = -16; x < 32; x++) {
+        for (let z = -16; z < 32; z++) {
+          for (let y = 16; y <= 80; y++) {
+            const block = context.bot.blockAt(context.bot.entity.position.clone().set(x, y, z))
+            context.expect(block !== null, 'Every sampled structure block must be loaded')
+            digest.update(`${block.stateId}\n`)
+            if (Object.hasOwn(counts, block.name)) counts[block.name]++
+            if (block.name === 'emerald_block') context.expect(y > 64, 'Surface platform must be above terrain')
+            if (block.name === 'blue_concrete') context.expect(y < 40, 'Buried room must remain underground')
+            if (block.name === 'oak_slab') context.expect(block.getProperties().waterlogged === false,
+              'Object slabs placed on dry ground must clear waterlogging')
+          }
+        }
+      }
+      for (const [block, count] of Object.entries(counts)) {
+        context.expect(count > 0, `Generated fixture must contain ${block}`, { count })
+      }
+      context.report.structures = { counts, hash: digest.digest('hex') }
+    })
+  }
+}

adapters/bukkit/plugin/src/test/gameplay/studio-open.mjs

@@ -0,0 +1,74 @@
+import { readFile, stat } from 'node:fs/promises'
+import { createHash } from 'node:crypto'
+import path from 'node:path'
+
+export default {
+  name: 'iris-studio-open',
+  description: 'Measure repeated Studio entry and verify visible terrain, spectator mode, and world cleanup.',
+  async run(context) {
+    const source = await readFile(path.join(context.server.directory, '.server-source'), 'utf8')
+    context.expect(/^isolated=true\s*$/m.test(source), 'Studio entry requires an isolated instance')
+    const match = /^([a-z0-9_-]+):([1-4])$/.exec(context.options.command ?? 'overworld:2')
+    context.expect(match, 'Expected pack:cycles with one to four cycles')
+    context.report.studioOpen = []
+    for (let cycle = 0; cycle < Number(match[2]); cycle++) {
+      await context.step(`open and close Studio ${cycle + 1}`, async () => {
+        const before = new Set((await context.observe()).worlds.map(world => world.id))
+        const start = Date.now()
+        let world
+        let center
+        await context.command(`/iris studio open ${match[1]} seed=1337`)
+        await context.waitUntil(async () => {
+          const observation = await context.observe()
+          const player = observation.players.find(entry => entry.username === context.bot.username)
+          world = observation.worlds.find(entry => entry.id === player?.world)
+          if (!world || before.has(world.id) || !/iris-[0-9a-f-]{36}$/.test(world.name)) return false
+          center = context.bot.entity.position.floored()
+          return world.loadedChunks > 0 && context.bot.blockAt(center) !== null && context.bot.game.gameMode === 'spectator'
+        }, { label: 'Studio arrival with terrain and spectator mode', timeoutMs: 180000, intervalMs: 100 })
+        const arrivalMs = Date.now() - start
+        context.expect(Number.isInteger(context.bot.game.minY) && Number.isInteger(context.bot.game.height),
+          'Studio dimension must report its vertical range')
+        await context.waitUntil(() => {
+          for (let x = -1; x <= 1; x++) {
+            for (let z = -1; z <= 1; z++) {
+              for (let y = context.bot.game.minY; y < context.bot.game.minY + context.bot.game.height; y += 16) {
+                if (context.bot.blockAt(center.offset(x, y - center.y, z)) === null) return false
+              }
+            }
+          }
+          return true
+        }, { label: 'Complete neighboring Studio columns', timeoutMs: 60000, intervalMs: 100 })
+        const digest = createHash('sha256')
+        let solid = 0
+        for (let x = -1; x <= 1; x++) {
+          for (let z = -1; z <= 1; z++) {
+            for (let y = context.bot.game.minY; y < context.bot.game.minY + context.bot.game.height; y++) {
+              const block = context.bot.blockAt(center.offset(x, y - center.y, z))
+              context.expect(block !== null, 'Studio entry column must be available')
+              digest.update(`${block.name}\n`)
+              if (!['air', 'cave_air', 'void_air', 'water', 'lava'].includes(block.name)) solid++
+            }
+          }
+        }
+        context.expect(solid > 0, 'Studio entry must contain solid terrain')
+        context.report.studioOpen.push({ cycle, arrivalMs, world: world.name, x: center.x, z: center.z,
+          terrainHash: digest.digest('hex'), solid })
+        const closed = await context.command('/iris studio close', /^Studio closed\.$|Studio close failed:/, 180000)
+        context.expect(closed === 'Studio closed.', closed)
+        await context.waitUntil(async () => !(await context.observe()).worlds.some(entry => entry.id === world.id),
+          { label: 'Studio world unload', timeoutMs: 90000, intervalMs: 100 })
+        const transientName = /iris-[0-9a-f-]{36}$/.exec(world.name)[0]
+        const properties = await readFile(path.join(context.server.directory, 'server.properties'), 'utf8')
+        const level = /^level-name=(.+)$/m.exec(properties)?.[1].trim() ?? 'world'
+        const directory = path.join(context.server.directory, level, 'dimensions', 'iris', transientName)
+        await context.waitUntil(async () => {
+          try { await stat(directory); return false } catch (error) {
+            if (error.code === 'ENOENT') return true
+            throw error
+          }
+        }, { label: 'Studio directory cleanup', timeoutMs: 90000, intervalMs: 100 })
+      })
+    }
+  }
+}

adapters/bukkit/plugin/src/test/gameplay/world-lifecycle.mjs

@@ -0,0 +1,98 @@
+import { readFile } from 'node:fs/promises'
+import path from 'node:path'
+
+const worldName = 'lifecycle_probe'
+const worldKey = `iris:${worldName}`
+const storageName = `world_iris_${worldName}`
+
+export default {
+  name: 'iris-world-lifecycle',
+  description: 'Create, enter, evacuate, reload, and remove an Iris world through the player commands.',
+  async run(context) {
+    const source = await readFile(path.join(context.server.directory, '.server-source'), 'utf8')
+    context.expect(/^isolated=true\s*$/m.test(source), 'World lifecycle requires an isolated instance')
+    const wait = (predicate, label, timeoutMs = 180000) => context.waitUntil(predicate, {
+      label, timeoutMs, intervalMs: 250
+    })
+    const playerWorld = 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)?.name
+    }
+    const status = async () => {
+      const response = await context.command('/irislifecycle lifecycle-status', /IRIS_LIFECYCLE |NATIVE_FAILED/, 10000)
+      context.expect(!response.includes('NATIVE_FAILED'), response)
+      return response
+    }
+    const settledStatus = async expected => {
+      const response = await status()
+      return response.includes(expected) && response.includes('idle=true')
+    }
+    const assertEvacuated = async label => {
+      let destination
+      await wait(async () => {
+        destination = await playerWorld()
+        return Boolean(destination && destination !== storageName)
+      }, label, 30000)
+      context.expect(destination && destination !== storageName, label, { destination })
+    }
+    const assertSafeEntry = async () => {
+      await wait(async () => (await playerWorld()) === storageName, 'Player entered the lifecycle world')
+      await wait(() => {
+        const feet = context.bot.entity.position.floored()
+        const floor = context.bot.blockAt(feet.offset(0, -1, 0))
+        const body = context.bot.blockAt(feet)
+        const head = context.bot.blockAt(feet.offset(0, 1, 0))
+        return context.bot.entity.onGround && floor?.name === 'lime_wool'
+          && body?.boundingBox === 'empty' && head?.boundingBox === 'empty'
+      }, 'Client sees solid terrain below unobstructed player entry', 30000)
+      const response = await context.command('/irislifecycle lifecycle-entry', /IRIS_LIFECYCLE_ENTRY|NATIVE_FAILED/, 10000)
+      context.expect(response.includes(`IRIS_LIFECYCLE_ENTRY world=${worldKey} seed=78264193 floor=lime_wool safe=true`), response)
+    }
+    await context.step('confirm disposable world is absent', async () => {
+      const response = await status()
+      context.expect(response.includes('loaded=false registered=false configured=false disk=false quarantines=0 cleanup=deleted idle=true'), response)
+      await context.command('/minecraft:gamemode survival @s')
+      await wait(() => context.bot.game.gameMode === 'survival', 'Survival mode', 10000)
+    })
+    await context.step('create through Iris and automatically enter safe terrain', async () => {
+      await context.command(`/iris create name=${worldName} type=native-terrain seed=78264193`)
+      await wait(async () => await settledStatus('loaded=true registered=true configured=true disk=true'), 'Created world registration and storage')
+      await assertSafeEntry()
+    })
+    await context.step('unload while the player is inside and verify evacuation', async () => {
+      context.expect((await playerWorld()) === storageName, 'Player must be inside the world before unload')
+      await context.command(`/iris unloadWorld ${worldKey}`)
+      await wait(async () => await settledStatus('loaded=false registered=true configured=true disk=true'), 'World unloaded with storage preserved')
+      await assertEvacuated('Unload evacuated the player to a loaded world')
+    })
+    await context.step('reload the saved world and enter it again', async () => {
+      await context.command(`/iris loadWorld ${worldName}`)
+      await wait(async () => await settledStatus('loaded=true registered=true configured=true disk=true'), 'World reloaded')
+      await context.command(`/iris tp ${worldKey}`)
+      await assertSafeEntry()
+    })
+    await context.step('remove the occupied world and verify disk cleanup', async () => {
+      await context.command(`/iris remove world=${worldName} delete=true`)
+      let finalStatus
+      await wait(async () => {
+        finalStatus = await status()
+        return finalStatus.includes('loaded=false registered=false configured=false disk=false')
+          && /cleanup=(deleted|queued)\b/.test(finalStatus) && finalStatus.includes('idle=true')
+      }, 'Removal detached registrations and deleted or queued quarantine')
+      await assertEvacuated('Removal evacuated the player to a loaded world')
+      context.report.worldLifecycle = { world: worldKey, cleanup: /cleanup=(deleted|queued)\b/.exec(finalStatus)[1] }
+    })
+    if (process.env.IRIS_QA_PACK_URL) {
+      await context.step('download and overwrite the fixture pack through Iris', async () => {
+        const response = await context.command(
+          `/iris download link=${process.env.IRIS_QA_PACK_URL} overwrite=true`,
+          /Iris pack 'native-terrain' installed|Iris pack download failed\./,
+          120000
+        )
+        context.expect(response.includes("Iris pack 'native-terrain' installed"), response)
+      })
+    }
+
+  }
+}

adapters/bukkit/plugin/src/test/java/art/arcane/iris/command/CommandPackValidationPublicationTest.java

@@ -0,0 +1,126 @@
+package art.arcane.iris.command;
+
+import art.arcane.iris.pack.PackFingerprints;
+
+import art.arcane.iris.Iris;
+import art.arcane.iris.pack.PackValidationRegistry;
+import art.arcane.iris.pack.PackValidationCache;
+import art.arcane.iris.pack.PackValidationResult;
+import art.arcane.iris.pack.PackValidator;
+import art.arcane.iris.platform.bukkit.plugin.VolmitSender;
+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.nio.file.Files;
+import java.util.List;
+import java.lang.reflect.Method;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertSame;
+import static org.junit.Assert.assertTrue;
+import static org.mockito.Mockito.CALLS_REAL_METHODS;
+import static org.mockito.Mockito.when;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.mockStatic;
+
+public class CommandPackValidationPublicationTest {
+    @Rule
+    public TemporaryFolder temporaryFolder = new TemporaryFolder();
+
+    @After
+    public void clearValidation() {
+        PackValidationRegistry.clear();
+    }
+
+    @Test
+    public void changedCachedPackCannotBePersistedAsFreshValidation() throws Exception {
+        File packs = temporaryFolder.newFolder("packs");
+        File root = new File(packs, "terrain");
+        Files.createDirectories(root.toPath());
+        File content = new File(root, "dimension.json");
+        Files.writeString(content.toPath(), "original");
+        File cacheFile = new File(temporaryFolder.getRoot(), "validation-cache.json");
+        Iris previousPlugin = Iris.instance;
+        Iris plugin = mock(Iris.class);
+        Iris.instance = plugin;
+        when(plugin.getDataFile("cache", "pack-validation.json")).thenReturn(cacheFile);
+        try (MockedStatic<Iris> iris = mockStatic(Iris.class);
+             MockedStatic<PackValidationCache> cache = mockStatic(PackValidationCache.class, CALLS_REAL_METHODS)) {
+            cache.when(PackValidationCache::contextFingerprint).thenReturn("context");
+            PackValidationResult valid = new PackValidationResult(root.getName(), List.of(), List.of(), 1L);
+            PackValidationRegistry.publish(valid);
+            PackValidationRegistry.publish(root.toPath(), valid,
+                    PackFingerprints.computePackTreeFingerprint(root), "context");
+            Files.writeString(content.toPath(), "changed");
+            Method persist = CommandPack.class.getDeclaredMethod("persistValidationCache", File.class);
+            persist.setAccessible(true);
+
+            persist.invoke(new CommandPack(), packs);
+
+            assertFalse(cacheFile.exists());
+            Files.writeString(content.toPath(), "original");
+
+            persist.invoke(new CommandPack(), packs);
+
+            assertTrue(cacheFile.exists());
+            assertTrue(PackValidationCache.load(cacheFile.toPath(),
+                    PackFingerprints.computePackContentSnapshot(packs).content(), "context",
+                    List.of(root.getName())).orElseThrow().getFirst().isLoadable());
+        } finally {
+            Iris.instance = previousPlugin;
+        }
+    }
+
+    @Test
+    public void commandPublishesCanonicalRootValidation() throws Exception {
+        File root = temporaryFolder.newFolder("terrain");
+        PackValidationResult valid = new PackValidationResult(root.getName(), List.of(), List.of(), 1L);
+        try (MockedStatic<PackValidator> validator = mockStatic(PackValidator.class)) {
+            validator.when(() -> PackValidator.validate(root)).thenReturn(valid);
+
+            assertSame(valid, new CommandPack().runValidate(mock(VolmitSender.class), root));
+
+            assertSame(valid, PackValidationRegistry.get(root.toPath()));
+            assertSame(valid, PackValidationRegistry.get(root.getName()));
+        }
+    }
+
+    @Test
+    public void mutationDuringValidationCannotRepublishStaleResult() throws Exception {
+        File root = temporaryFolder.newFolder("terrain");
+        try (MockedStatic<PackValidator> validator = mockStatic(PackValidator.class);
+             MockedStatic<Iris> iris = mockStatic(Iris.class)) {
+            validator.when(() -> PackValidator.validate(root)).thenAnswer(invocation -> {
+                try (PackValidationRegistry.RootMutation mutation = PackValidationRegistry.beginRootMutation(root.toPath())) {
+                    return new PackValidationResult(root.getName(), List.of(), List.of(), 1L);
+                }
+            });
+
+            assertFalse(new CommandPack().runValidate(mock(VolmitSender.class), root).isLoadable());
+            assertNull(PackValidationRegistry.get(root.toPath()));
+            assertNull(PackValidationRegistry.get(root.getName()));
+        }
+    }
+
+    @Test
+    public void externalEditDuringValidationPublishesBlockedResult() throws Exception {
+        File root = temporaryFolder.newFolder("terrain");
+        File content = new File(root, "dimension.json");
+        Files.writeString(content.toPath(), "original");
+        try (MockedStatic<PackValidator> validator = mockStatic(PackValidator.class);
+             MockedStatic<Iris> iris = mockStatic(Iris.class)) {
+            validator.when(() -> PackValidator.validate(root)).thenAnswer(invocation -> {
+                Files.writeString(content.toPath(), "changed");
+                return new PackValidationResult(root.getName(), List.of(), List.of(), 1L);
+            });
+
+            assertFalse(new CommandPack().runValidate(mock(VolmitSender.class), root).isLoadable());
+            assertFalse(PackValidationRegistry.get(root.toPath()).isLoadable());
+        }
+    }
+}

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/fabric/build.gradle

@@ -56,7 +56,7 @@ 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 irisVersion = providers.gradleProperty('irisVersion').getOrElse(rootProperties.getProperty('irisVersion', '4.3.1-26.2'))
 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 ->

adapters/forge/build.gradle

@@ -56,7 +56,7 @@ 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 irisVersion = providers.gradleProperty('irisVersion').getOrElse(rootProperties.getProperty('irisVersion', '4.3.1-26.2'))
 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 ->

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

@@ -195,8 +195,6 @@ public final class IrisModdedChunkGenerator implements NativeGeneratorOwner, Nat
         if (!nativeGenerator.represents(level)) {
             throw new IllegalArgumentException("NativeWorld does not use Iris generator '" + dimensionKey + "'");
         }
-        requireGlobalStructureGeneration(
-                NativeModdedServer.forWorld(level).generateStructures(), dimensionKey);
         Engine activeEngine = engineIfBound();
         Engine replacement = ModdedWorldEngines.prepareReplacement(
                 level,
@@ -242,6 +240,7 @@ 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.
@@ -442,12 +441,14 @@ 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);
@@ -459,13 +460,6 @@ public final class IrisModdedChunkGenerator implements NativeGeneratorOwner, Nat
         // 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) {
-            recordBindFailure(level, error);
-            throw error;
-        }
         // Cache the owning level so hot paths never scan the level map to find themselves.
         boundLevel = level;
         Engine cached = engine;
@@ -572,29 +566,6 @@ public final class IrisModdedChunkGenerator implements NativeGeneratorOwner, Nat
         }
     }
 
-    static void requireGlobalStructureGeneration(boolean enabled, String dimensionKey) {
-        if (enabled) {
-            return;
-        }
-        String remedy = integratedEnvironment()
-                ? "enable 'Generate Structures' for this world; Iris requires it, then deny families through "
-                        + "importedStructures.disabled or complete keys through importedStructures.disabledExact"
-                : "set generate-structures=true in server.properties, restart the server, "
-                        + "then deny families through importedStructures.disabled or complete keys through "
-                        + "importedStructures.disabledExact";
-        throw new IllegalStateException("Iris generator '" + dimensionKey
-                + "' cannot bind while generate-structures=false; " + remedy);
-    }
-
-    private static boolean integratedEnvironment() {
-        try {
-            return ModdedEngineBootstrap.loader().clientEnvironment();
-        } catch (Throwable e) {
-            // No loader bound (unit tests, very early boot): assume dedicated wording.
-            return false;
-        }
-    }
-
     /**
      * 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.
@@ -1097,6 +1068,12 @@ 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();

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

@@ -325,7 +325,7 @@ final class ModdedBiomePolicy<H, S> implements NativeModdedBiomePolicy<H, S> {
 
     private H getNoiseBiome(Engine engine, int quartX, int quartY, int quartZ,
                                         S sampler) {
-        if (isGuaranteedSurfaceBiome(quartY, engine.getMinHeight())) {
+        if (isGuaranteedSurfaceBiome(engine, quartY)) {
             return getSurfaceStructureBiome(engine, quartX, quartZ, sampler);
         }
         boolean cacheable = isBiomeCacheable(
@@ -512,7 +512,7 @@ final class ModdedBiomePolicy<H, S> implements NativeModdedBiomePolicy<H, S> {
                 }
                 boolean monumentQuery = isMonumentSurfaceBiomeQuery(
                         y, radius, engine.getMinHeight(), engine.getDimension().getFluidHeight());
-                surfaceQuery = monumentQuery || isGuaranteedSurfaceBiome(minQuartY, engine.getMinHeight());
+                surfaceQuery = monumentQuery || isGuaranteedSurfaceBiome(engine, minQuartY);
             }
             if (!surfaceQuery) {
                 return query.fallback().get();
@@ -701,6 +701,11 @@ final class ModdedBiomePolicy<H, S> implements NativeModdedBiomePolicy<H, S> {
         int blockZ = quartZ << 2;
         int internalY = blockY - engine.getMinHeight();
         int caveSwitchY = Math.max(-8 - engine.getMinHeight(), 40);
+        IrisBiome featureBiome = engine.getSubterrainBiome(blockX, internalY, blockZ);
+        if (featureBiome != null) {
+            return createBiomeResolution(engine, featureBiome, true, engine.getDimension(), engine.getData(),
+                    blockX, blockY, blockZ);
+        }
         DimensionStackLayout.Layer stackLayer = includeDimensionStack
                 ? stackLayout == null
                         ? resolveDimensionStackLayer(engine, blockX, internalY, blockZ)
@@ -846,7 +851,13 @@ final class ModdedBiomePolicy<H, S> implements NativeModdedBiomePolicy<H, S> {
         return configuredBiomeKeys;
     }
 
-    static boolean isGuaranteedSurfaceBiome(int quartY, int minHeight) {
+    static boolean isGuaranteedSurfaceBiome(Engine engine, int quartY) {
+        IrisDimension dimension = engine.getDimension();
+        if (dimension != null && dimension.allowsSubterrainFeatures()
+                && !dimension.getSubterrainFeatures().isEmpty()) {
+            return false;
+        }
+        int minHeight = engine.getMinHeight();
         int internalY = (quartY << 2) - minHeight;
         int caveSwitchY = Math.max(-8 - minHeight, 40);
         return internalY > caveSwitchY;

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

@@ -50,7 +50,7 @@ public final class ModdedDecoratorHooks implements DecoratorPlatformHooks.FaceFi
             int xx = rX + dx;
             int yy = y + dy;
             int zz = rZ + dz;
-            return xx < 0 || xx > 15 || zz < 0 || zz > 15 || yy < 0 || yy > hunk.getHeight()
+            return xx < 0 || xx > 15 || zz < 0 || zz > 15 || yy < 0 || yy >= hunk.getHeight()
                     ? null : hunk.get(xx, yy, zz);
         }
     }

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

@@ -70,6 +70,7 @@ import art.arcane.iris.modded.service.ModdedEngineMaintenanceService;
 import art.arcane.iris.modded.service.ModdedEntitySpawnService;
 import art.arcane.iris.modded.service.ModdedLogFilterService;
 import art.arcane.iris.modded.service.ModdedPreservationService;
+import art.arcane.iris.modded.service.ModdedPackUpdateService;
 import art.arcane.iris.modded.service.ModdedSettingsHotloadService;
 import art.arcane.iris.modded.service.ModdedStudioHotloadService;
 import art.arcane.iris.modded.service.ModdedTreeFellerService;
@@ -477,6 +478,7 @@ public final class ModdedEngineBootstrap {
                 createdServices.register(ModdedLogFilterService.class, new ModdedLogFilterService());
                 createdServices.register(ModdedEngineMaintenanceService.class, new ModdedEngineMaintenanceService());
                 createdServices.register(ModdedSettingsHotloadService.class, new ModdedSettingsHotloadService());
+                createdServices.register(ModdedPackUpdateService.class, new ModdedPackUpdateService());
                 ModdedStudioHotloadService studioHotloadService = createdServices.register(
                         ModdedStudioHotloadService.class, new ModdedStudioHotloadService());
                 createdServices.register(ModdedChunkUpdateService.class, new ModdedChunkUpdateService());

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(irisEntity, entity, forcePersist());
-        applyPersistence(entity, persistent);
 
         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) {
+    static void applyPersistence(IrisEntity options, NativeSpawnedEntity entity, boolean forcePersistence) {
-        if (!entity.persistence(persistent)) {
+        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/ModdedGenPool.java

@@ -27,7 +27,6 @@ import java.util.concurrent.RejectedExecutionException;
 import java.util.concurrent.ThreadPoolExecutor;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicInteger;
-import java.util.concurrent.atomic.AtomicReference;
 
 /**
  * Owns the Iris generation pool and the single decision of whether this loader already runs chunk
@@ -43,7 +42,7 @@ public final class ModdedGenPool {
     private static final long SHUTDOWN_DRAIN_MILLIS = 2_000L;
     private static final AtomicInteger GEN_THREAD_SEQ = new AtomicInteger();
     private static final ChunkSystem CHUNK_SYSTEM = detectChunkSystem();
-    private static final AtomicReference<ExecutorService> GEN_POOL = new AtomicReference<>(createGenPool());
+    private static ExecutorService generationPool = createGenPool();
 
     private ModdedGenPool() {
     }
@@ -63,39 +62,32 @@ public final class ModdedGenPool {
         return CHUNK_SYSTEM.description();
     }
 
-    static ExecutorService pool() {
+    static synchronized ExecutorService pool() {
-        ExecutorService pool = GEN_POOL.get();
+        if (generationPool.isShutdown()) {
-        if (pool != null && !pool.isShutdown()) {
-            return pool;
-        }
-        start();
-        ExecutorService restarted = GEN_POOL.get();
-        if (restarted == null) {
             throw new RejectedExecutionException("Iris gen pool is shut down");
         }
-        return restarted;
+        return generationPool;
     }
 
-    static void start() {
+    static synchronized void start() {
-        while (true) {
+        if (!generationPool.isShutdown()) {
-            ExecutorService current = GEN_POOL.get();
-            if (current != null && !current.isShutdown()) {
             return;
         }
-            ExecutorService created = createGenPool();
+        if (!generationPool.isTerminated()) {
-            if (GEN_POOL.compareAndSet(current, created)) {
+            throw new IllegalStateException("Iris gen pool cannot restart while prior workers are still active");
-                return;
-            }
-            created.shutdownNow();
         }
+        generationPool = createGenPool();
     }
 
     static void shutdown() {
-        ExecutorService pool = GEN_POOL.getAndSet(null);
+        ExecutorService pool;
-        if (pool == null) {
+        synchronized (ModdedGenPool.class) {
+            pool = generationPool;
+            if (pool.isTerminated()) {
                 return;
             }
             pool.shutdown();
+        }
         try {
             if (pool.awaitTermination(SHUTDOWN_DRAIN_MILLIS, TimeUnit.MILLISECONDS)) {
                 return;

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

@@ -6,10 +6,9 @@ import art.arcane.volmlib.nativelib.terrain.NativeWorld;
 import art.arcane.iris.pack.loading.IrisData;
 import art.arcane.iris.configuration.IrisSettings;
 import art.arcane.iris.pack.BrokenPackException;
-import art.arcane.iris.pack.PackValidationCache;
+import art.arcane.iris.pack.PackFingerprints;
 import art.arcane.iris.pack.PackValidationRegistry;
 import art.arcane.iris.pack.PackValidationResult;
-import art.arcane.iris.pack.PackValidator;
 import art.arcane.iris.world.history.GenerationEpoch;
 import art.arcane.iris.world.history.GenerationEpochContractFactory;
 import art.arcane.iris.world.history.GenerationHistory;
@@ -174,7 +173,7 @@ final class ModdedGenerationHistoryStorage {
     static ActivePack resolveActive(GenerationHistory history) throws IOException {
         GenerationEpoch epoch = history.activeEpoch();
         Path packRoot = normalize(history.activePackRoot());
-        validatePack(packRoot, epoch.packFingerprint());
+        validatePack(packRoot);
         validateDimension(packRoot, epoch);
         return new ActivePack(
                 packRoot,
@@ -184,13 +183,16 @@ final class ModdedGenerationHistoryStorage {
         );
     }
 
-    private static void validatePack(Path packRoot, String fingerprint) {
+    static PackValidationResult validatePack(Path packRoot) {
-        String contextFingerprint = PackValidationCache.contextFingerprint();
+        PackValidationResult validation = PackValidationRegistry.getMatching(
-        PackValidationResult validation = PackValidator.validate(packRoot.toFile());
+                packRoot, PackFingerprints.computePackTreeFingerprint(packRoot.toFile()));
-        PackValidationRegistry.publish(packRoot, validation, fingerprint, contextFingerprint);
+        if (validation == null) {
+            validation = ModdedStartup.validatePack(packRoot.toFile());
+        }
         if (!validation.isLoadable()) {
             throw new BrokenPackException(packRoot.toString(), validation.getBlockingErrors());
         }
+        return validation;
     }
 
     private static void validateDimension(

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

@@ -20,13 +20,11 @@ package art.arcane.iris.modded;
 
 import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeModdedLoader;
 
-import art.arcane.iris.spi.IrisPlatforms;
 import art.arcane.iris.configuration.IrisSettings;
 import art.arcane.iris.diagnostics.splash.IrisSplashComposer;
 import art.arcane.iris.diagnostics.splash.IrisSplashRenderer;
 import art.arcane.iris.spi.IrisLogging;
 
-import java.io.File;
 
 public final class ModdedIrisSplash {
 
@@ -34,18 +32,11 @@ public final class ModdedIrisSplash {
     }
 
     public static void print(NativeModdedLoader loader) {
-        printPacks(loader);
         if (isLogoEnabled()) {
             printLogo(loader);
         }
     }
 
-    private static void printPacks(NativeModdedLoader loader) {
-        File packFolder = IrisPlatforms.get().packsFolderNoCreate();
-        IrisSplashComposer.composePackLines(packFolder, IrisLogging::reportError)
-                .thenAccept(lines -> lines.forEach(IrisLogging::info));
-    }
-
     private static void printLogo(NativeModdedLoader loader) {
         String serverLine = loader.platformName() + " / Minecraft " + loader.minecraftVersion();
         String[] splash = IrisSplashRenderer.renderPlain();

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

@@ -45,6 +45,9 @@ public final class ModdedMixinAudit {
     private static final AtomicBoolean AUDITED = new AtomicBoolean(false);
 
     static final List<ExpectedMixin> EXPECTED = List.of(
+            new ExpectedMixin(ENTITY_CONFIG, "RegistryClientNamesMixin",
+                    NativeMixinTarget.REGISTRY_PACKET, "volmlib$clientRegistryNames",
+                    false, NativeMixinFlags::registryClientNamesRan),
             new ExpectedMixin(ENTITY_CONFIG, "EntityPersistenceMixin",
                     NativeMixinTarget.ENTITY, "iris$applyGeneratedPersistence",
                     false, NativeMixinFlags::entityPersistenceRan),
@@ -108,7 +111,7 @@ public final class ModdedMixinAudit {
             ModdedIrisLog.error("  missing: {}", entry);
         }
         ModdedIrisLog.error("The mixin config was not registered for this loader (fabric.mod.json mixins, neoforge.mods.toml [[mixins]], forge MixinConfigs manifest attribute).");
-        ModdedIrisLog.error("Entity persistence, custom mob loot, parallel structure safety, or Iris world-type labels are disabled until this is fixed.");
+        ModdedIrisLog.error("Entity persistence, custom mob loot, parallel structure safety, readable biome identifiers, or Iris world-type labels are disabled until this is fixed.");
         ModdedIrisLog.error("===============================================================");
     }
 

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

@@ -122,17 +122,6 @@ final class ModdedNativeStructurePolicy implements NativeModdedStructureStage.Po
         return ((IrisMaterialPalette) source).get(rng, x, y, z, generator.engine().getData());
     }
 
-    @Override
-    public RuntimeException structuresDisabled(int chunkX, int chunkZ) {
-        return new IllegalStateException("Iris cannot generate native structures in chunk "
-                + chunkX + "," + chunkZ
-                + " because generate-structures=false disables them outside the pack. That flag is fixed when "
-                + "the world is created (server.properties generate-structures, or the Generate Structures "
-                + "toggle in singleplayer), so it cannot be changed for this world: create a new world with "
-                + "structures enabled, then deny families through importedStructures.disabled or complete keys "
-                + "through importedStructures.disabledExact");
-    }
-
     @Override
     public String generationLabel(String structureId) {
         return "Iris native structure " + structureId;

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

@@ -27,16 +27,15 @@ 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.CompletableFuture;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
 
 public final class ModdedPrimaryWorldRouter {
     private static final int TICK_INTERVAL = 20;
 
-    private static final Set<UUID> routed = ConcurrentHashMap.newKeySet();
+    private static final ConcurrentMap<UUID, CompletableFuture<Boolean>> routes = new ConcurrentHashMap<>();
-    private static final Set<UUID> inFlight = ConcurrentHashMap.newKeySet();
     private static int tickCounter = 0;
     private static volatile String loginRefusal;
     private static volatile String absentPrimary;
@@ -45,8 +44,12 @@ public final class ModdedPrimaryWorldRouter {
     }
 
     public static void clear() {
-        routed.clear();
+        routes.forEach((id, route) -> {
-        inFlight.clear();
+            if (routes.remove(id, route)) {
+                route.cancel(false);
+            }
+        });
+        tickCounter = 0;
         loginRefusal = null;
         absentPrimary = null;
     }
@@ -57,8 +60,10 @@ public final class ModdedPrimaryWorldRouter {
      */
     public static void forget(UUID player) {
         if (player != null) {
-            routed.remove(player);
+            CompletableFuture<Boolean> route = routes.remove(player);
-            inFlight.remove(player);
+            if (route != null) {
+                route.cancel(false);
+            }
         }
     }
 
@@ -110,36 +115,52 @@ public final class ModdedPrimaryWorldRouter {
             return;
         }
 
-        server.forEachPlayer(player -> {
+        server.forEachPlayer(player -> routePlayer(server, player, overworld, target, primary));
+    }
+
+    private static void routePlayer(NativeModdedServer server, NativeProtocolPlayer player,
+                                    NativeWorld overworld, NativeWorld target, String primary) {
         UUID id = player.id();
-            if (routed.contains(id) || !inFlight.add(id)) {
+        if (routes.containsKey(id)) {
             return;
         }
+        CompletableFuture<Boolean> route = new CompletableFuture<>();
+        if (routes.putIfAbsent(id, route) != null) {
+            return;
+        }
+        route.whenComplete((success, failure) -> {
+            if (!Boolean.TRUE.equals(success)) {
+                routes.remove(id, route);
+            }
+        });
         if (!player.isInWorld(overworld)) {
-                inFlight.remove(id);
+            route.complete(true);
-                routed.add(id);
             return;
         }
         try {
             CompletableFuture<Boolean> teleport = NativeWorldTeleport.teleport(player,
                     new NativeWorldTeleport.Destination(server, target, player.x(), Double.MIN_VALUE, player.z(),
                             ModdedTeleportDeadline.fromNow()));
-                teleport.whenComplete((success, failure) -> {
+            route.whenComplete((success, failure) -> {
-                    inFlight.remove(id);
+                if (!Boolean.TRUE.equals(success) && !teleport.isDone()) {
-                    if (Boolean.TRUE.equals(success) && failure == null) {
+                    teleport.cancel(false);
-                        routed.add(id);
-                        return;
                 }
+            });
+            teleport.whenComplete((success, failure) -> {
                 if (failure != null) {
+                    if (route.completeExceptionally(failure)) {
                         ModdedIrisLog.error("Iris failed to route player {} to primary world '{}'",
                                 id, primary, failure);
                     }
-                });
+                } else {
-            } catch (Throwable e) {
+                    route.complete(Boolean.TRUE.equals(success));
-                inFlight.remove(id);
-                ModdedIrisLog.error("Iris failed to route player {} to primary world '{}'", id, primary, e);
                 }
             });
+        } catch (Throwable failure) {
+            if (route.completeExceptionally(failure)) {
+                ModdedIrisLog.error("Iris failed to route player {} to primary world '{}'", id, primary, failure);
+            }
+        }
     }
 
     /**

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

@@ -31,6 +31,7 @@ import art.arcane.iris.platform.protocol.IrisVisionRequestService;
 import art.arcane.iris.generation.runtime.Engine;
 import art.arcane.iris.spi.IrisServices;
 import art.arcane.iris.spi.protocol.IrisProtocol;
+import art.arcane.iris.modded.service.ModdedPackUpdateService;
 
 import java.util.Objects;
 import java.util.UUID;
@@ -128,6 +129,10 @@ public final class ModdedProtocolHandler {
         }
         String sessionId = sessionId(player);
         ModdedStartup.warnStartupFailuresTo(player);
+        ModdedPackUpdateService packUpdates = ModdedEngineBootstrap.services().service(ModdedPackUpdateService.class);
+        if (packUpdates != null) {
+            packUpdates.notifyPlayer(player);
+        }
         IrisSessionRegistry current = registry;
         ModdedProtocolTransport currentTransport = transport;
         if (current == null || currentTransport == null) {

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

@@ -18,10 +18,13 @@
 
 package art.arcane.iris.modded;
 
+import art.arcane.iris.pack.PackFingerprints;
+
 import art.arcane.iris.pack.BrokenPackException;
 import art.arcane.iris.pack.PackDirectoryResolver;
 import art.arcane.iris.pack.PackDownloader;
 import art.arcane.iris.pack.PackValidationRegistry;
+import art.arcane.iris.pack.PackValidationCache;
 import art.arcane.iris.pack.PackValidationResult;
 import art.arcane.iris.pack.PackValidator;
 import art.arcane.iris.modded.command.ModdedPackCommands;
@@ -31,15 +34,11 @@ import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeModdedServer;
 import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeProtocolPlayer;
 
 import java.io.File;
-import java.io.IOException;
-import java.nio.file.Files;
 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;
 
 public final class ModdedStartup {
     private static final int COMPAT_BOOT_KEY_CAP = 3;
@@ -60,36 +59,9 @@ public final class ModdedStartup {
         if (!PREPARED.compareAndSet(false, true)) {
             return;
         }
-        reportLegacyPacksDirectory();
         validateAllPacks();
     }
 
-    /**
-     * Older builds mkdir'd (and stale guidance sometimes populated) config/iris/packs, but modded
-     * packs live under config/irisworldgen/packs. Never auto-move user content: warn loudly when
-     * the legacy directory holds packs, and quietly remove it when it is empty.
-     */
-    private static void reportLegacyPacksDirectory() {
-        try {
-            File legacy = ModdedEngineBootstrap.loader().configDir().resolve("iris").resolve("packs").toFile();
-            if (!legacy.isDirectory()) {
-                return;
-            }
-            if (!PackDirectoryResolver.listVisiblePackDirectories(legacy).isEmpty()) {
-                File real = art.arcane.iris.spi.IrisPlatforms.get().packsFolderNoCreate();
-                ModdedIrisLog.warn("Iris found packs under the legacy directory {} - modded packs load from {} only. Move them there.",
-                        legacy.getAbsolutePath(), real.getAbsolutePath());
-                return;
-            }
-            String[] entries = legacy.list();
-            if (entries == null || entries.length == 0) {
-                legacy.delete();
-            }
-        } catch (Throwable e) {
-            ModdedIrisLog.debug("Iris legacy packs directory check failed", e);
-        }
-    }
-
     /**
      * Boot trigger for the forced datapack. Runs on its own daemon thread rather than the Iris scheduler:
      * ModdedEngineBootstrap.start clears the async queue at SERVER_STARTING, which would silently drop this
@@ -140,8 +112,7 @@ public final class ModdedStartup {
         }
         for (File packDir : packDirs) {
             try {
-                PackValidationResult result = PackValidator.validate(packDir);
+                PackValidationResult result = validatePack(packDir);
-                PackValidationRegistry.publish(result);
                 String minecraftVersion = IrisPlatforms.isBound() ? IrisPlatforms.get().minecraftVersion() : null;
                 String compatSummary = PackValidator.compatSummary(result, minecraftVersion);
                 String compatSuffix = compatSummary.isEmpty() ? "" : " " + compatSummary;
@@ -184,16 +155,15 @@ public final class ModdedStartup {
             throw new BrokenPackException(pack, List.of(
                     "Pack folder does not exist under " + ModdedPackCommands.packsRoot().getAbsolutePath() + "."));
         }
-        PackValidationResult cached = PackValidationRegistry.get(pack);
+        Path packRoot = packDir.toPath();
-        if (cached != null && cached.getValidatedAtMillis() >= newestModificationMillis(packDir.toPath())) {
-            // prepareForStartup already validated this pack and nothing in it changed since; re-validating per
-            // persistent dimension at boot costs a full pack parse each time.
-            return PackValidationRegistry.requireLoadable(pack);
-        }
         try {
-            PackValidationResult result = PackValidator.validate(packDir);
+            PackValidationResult cached = PackValidationRegistry.getMatching(
-            PackValidationRegistry.publish(result);
+                    packRoot, PackFingerprints.computePackTreeFingerprint(packDir));
-            return PackValidationRegistry.requireLoadable(pack);
+            if (cached != null) {
+                return PackValidationRegistry.requireLoadable(packRoot);
+            }
+            validatePack(packDir);
+            return PackValidationRegistry.requireLoadable(packRoot);
         } catch (BrokenPackException e) {
             throw e;
         } catch (Throwable e) {
@@ -212,6 +182,42 @@ public final class ModdedStartup {
         }
     }
 
+    public static PackValidationResult validatePack(File packDir) {
+        Path packRoot = packDir.toPath();
+        PackValidationRegistry.ValidationTicket ticket = PackValidationRegistry.tryBeginValidation(packRoot);
+        if (ticket == null) {
+            throw new BrokenPackException(packDir.getName(), List.of("Pack content is currently being changed."));
+        }
+        String contentFingerprint = PackFingerprints.computePackTreeFingerprint(packDir);
+        String contextFingerprint = PackValidationCache.contextFingerprint();
+        PackValidationResult result;
+        try {
+            result = PackValidator.validate(packDir);
+        } catch (Throwable failure) {
+            ModdedIrisLog.error("Iris pack validation failed for '{}'", packDir.getName(), failure);
+            String detail = failure.getMessage();
+            if (detail == null || detail.isBlank()) {
+                detail = failure.getClass().getSimpleName();
+            }
+            result = new PackValidationResult(
+                    packDir.getName(),
+                    List.of("Pack validation failed with " + failure.getClass().getSimpleName() + ": " + detail),
+                    List.of(),
+                    System.currentTimeMillis());
+        }
+        if (!contentFingerprint.equals(PackFingerprints.computePackTreeFingerprint(packDir))
+                || !contextFingerprint.equals(PackValidationCache.contextFingerprint())) {
+            PackValidationRegistry.remove(packRoot);
+            PackValidationRegistry.remove(packDir.getName());
+            throw new BrokenPackException(packDir.getName(), List.of("Pack content or validation context changed during validation."));
+        }
+        if (!PackValidationRegistry.publishIfCurrent(ticket, result, contentFingerprint, contextFingerprint)) {
+            throw new BrokenPackException(packDir.getName(), List.of("Pack content changed during validation."));
+        }
+        PackValidationRegistry.publish(result);
+        return result;
+    }
+
     static void reinjectPersistentDimensions(NativeModdedServer server) {
         List<ModdedDimensionRegistryStore.PersistentDimension> dimensions =
                 ModdedDimensionRegistryStore.loadForStartup(server);
@@ -266,23 +272,6 @@ public final class ModdedStartup {
                 + GenerationRefusalNotice.summary(failure));
     }
 
-    private static long newestModificationMillis(Path root) {
-        long newest = 0L;
-        try (Stream<Path> walk = Files.walk(root)) {
-            for (Path path : (Iterable<Path>) walk::iterator) {
-                BasicFileAttributes attributes = Files.readAttributes(path, BasicFileAttributes.class);
-                long modified = attributes.lastModifiedTime().toMillis();
-                if (modified > newest) {
-                    newest = modified;
-                }
-            }
-        } catch (IOException | RuntimeException unreadable) {
-            ModdedIrisLog.debug("Iris could not stat {} for validation reuse; revalidating", root, unreadable);
-            return Long.MAX_VALUE;
-        }
-        return newest;
-    }
-
     /**
      * 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.
@@ -296,7 +285,7 @@ public final class ModdedStartup {
      * 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()) {
+        if (player == null || (!player.isGameMaster() && !player.isServerOwner())) {
             return;
         }
         for (String failure : DIMENSION_FAILURES) {

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

@@ -44,6 +44,8 @@ import art.arcane.iris.pack.value.IrisPosition;
 import art.arcane.iris.pack.value.IrisRange;
 import art.arcane.iris.world.entity.IrisSpawnGroup;
 import art.arcane.iris.world.entity.IrisSpawner;
+import art.arcane.iris.world.entity.EntitySpawnSeed;
+import art.arcane.iris.world.entity.IrisEntitySpawn.SpawnContext;
 import art.arcane.iris.generation.decoration.IrisSurface;
 import art.arcane.iris.spi.IrisLogging;
 import art.arcane.volmlib.util.collection.KList;
@@ -55,11 +57,14 @@ 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.HashMap;
 import java.util.HashSet;
 import java.util.List;
 import java.util.ArrayList;
 import java.util.Optional;
 import java.util.Set;
+import java.util.Comparator;
 import java.util.concurrent.ArrayBlockingQueue;
 import java.util.concurrent.BlockingQueue;
 import java.util.concurrent.ConcurrentHashMap;
@@ -234,6 +239,10 @@ public final class ModdedWorldManager implements EngineWorldManager {
     }
 
     boolean initialSpawnChunk(NativeWorld level, int chunkX, int chunkZ) {
+        if (!isEntitySpawningEnabledForCurrentWorld()
+                || !NativeSpawnQueries.ambientAllowed(level, chunkX, chunkZ, true)) {
+            return false;
+        }
         if (!ModdedEntitySpawner.chunksSafe(entityRuntime(level), chunkX, chunkZ)) {
             return false;
         }
@@ -248,54 +257,25 @@ public final class ModdedWorldManager implements EngineWorldManager {
         MantleChunk<Matter> chunk = mantle.useChunk(chunkX, chunkZ);
         try {
             List<PreparedMarkerSpawn> markers = markerSystemEnabled()
-                    ? prepareMarkerSpawns(level, chunkX, chunkZ, chunk) : List.of();
+                    ? prepareMarkerSpawns(level, chunkX, chunkZ, chunk, true) : List.of();
             Optional<BiomeEnvironment> environment = ambientSystemEnabled()
                     ? resolveSurfaceEnvironment(chunkX, chunkZ) : Optional.empty();
-            chunk.raiseFlagUnchecked(INITIAL_SPAWN_COMPLETION_FLAG, () -> {
+            if (ambientSystemEnabled() && engine.getComplex() == null) {
+                return false;
+            }
             spawnPreparedMarkers(level, markers, true);
             if (environment.isPresent()) {
-                    scheduleInitialFollowUp(level, chunkX, chunkZ, environment.get());
+                try (BiomeEnvironment.Scope ignored = engine.openBiomeEnvironmentScope(environment.get())) {
+                    spawnAmbient(level, chunkX, chunkZ, true, environment.get());
                 }
-            });
+            }
+            chunk.raiseFlagUnchecked(INITIAL_SPAWN_COMPLETION_FLAG, () -> {});
         } finally {
             chunk.release();
         }
         return true;
     }
 
-    private void scheduleInitialFollowUp(NativeWorld level, int chunkX, int chunkZ, BiomeEnvironment environment) {
-        ModdedScheduler scheduler = ModdedEngineBootstrap.schedulerOrNull();
-        if (scheduler == null) {
-            IrisLogging.error("Iris could not schedule the initial entity-spawn follow-up because the modded scheduler is unavailable.");
-            return;
-        }
-        scheduler.laterGlobal(
-                () -> EngineLifecycleTasks.run(
-                        engine,
-                        "modded_world_manager_initial_spawn_followup",
-                        () -> runInitialFollowUp(level, chunkX, chunkZ, environment)),
-                RNG.r.i(5, 200));
-    }
-
-    private void runInitialFollowUp(NativeWorld level, int chunkX, int chunkZ, BiomeEnvironment environment) {
-        Mantle<Matter> mantle = engine.getMantle().getMantle();
-        if (closed || engine.isClosed() || mantle.isClosed() || !isEntitySpawningEnabledForCurrentWorld()) {
-            return;
-        }
-        if (!level.isChunkLoaded(chunkX, chunkZ) || !mantle.isChunkLoaded(chunkX, chunkZ)) {
-            return;
-        }
-        if (engine.getComplex() == null) {
-            return;
-        }
-
-        if (ambientSystemEnabled()) {
-            try (BiomeEnvironment.Scope ignored = engine.openBiomeEnvironmentScope(environment)) {
-                spawnAmbient(level, chunkX, chunkZ, true, environment);
-            }
-        }
-    }
-
     private void warmupMantleChunkAsync(long key, int chunkX, int chunkZ) {
         if (closed || !mantleWarmups.add(key)) {
             return;
@@ -379,11 +359,14 @@ public final class ModdedWorldManager implements EngineWorldManager {
         if (!mantle.isChunkLoaded(chunkX, chunkZ)) {
             return;
         }
+        if (!mantle.hasFlag(chunkX, chunkZ, INITIAL_SPAWN_COMPLETION_FLAG)) {
+            return;
+        }
 
         MantleChunk<Matter> chunk = mantle.useChunk(chunkX, chunkZ);
         try {
             if (markerSystemEnabled()) {
-                spawnPreparedMarkers(level, prepareMarkerSpawns(level, chunkX, chunkZ, chunk), false);
+                spawnPreparedMarkers(level, prepareMarkerSpawns(level, chunkX, chunkZ, chunk, false), false);
             }
             if (ambientSystemEnabled()) {
                 spawnAmbient(level, chunkX, chunkZ, false);
@@ -393,7 +376,7 @@ public final class ModdedWorldManager implements EngineWorldManager {
         }
     }
 
-    private List<PreparedMarkerSpawn> prepareMarkerSpawns(NativeWorld level, int chunkX, int chunkZ, MantleChunk<Matter> chunk) {
+    private List<PreparedMarkerSpawn> prepareMarkerSpawns(NativeWorld level, int chunkX, int chunkZ, MantleChunk<Matter> chunk, boolean initial) {
         int minHeight = engine.getWorld().minHeight();
         KList<IrisPosition> obstructed = new KList<>();
         List<PreparedMarkerSpawn> prepared = new ArrayList<>();
@@ -428,62 +411,71 @@ public final class ModdedWorldManager implements EngineWorldManager {
             if (spawners.isEmpty()) {
                 return;
             }
-            IrisSpawner chosen = spawners.getRandom();
+            if (initial) {
+                spawners.sort(Comparator.comparing(IrisSpawner::getLoadKey, Comparator.nullsFirst(Comparator.naturalOrder())));
+            }
+            RNG markerRng = initial ? EntitySpawnSeed.marker(engine.getSeedManager().getEntity(), worldX, worldY, worldZ)
+                    : new RNG(RNG.r.nextLong());
+            IrisSpawner chosen = spawners.getRandom(markerRng);
             if (chosen == null) {
                 return;
             }
-            prepared.add(new PreparedMarkerSpawn(new IrisPosition(worldX, worldY, worldZ), chosen, environment));
+            prepared.add(new PreparedMarkerSpawn(new IrisPosition(worldX, worldY, worldZ), chosen, resolved, markerRng, environment));
         });
         Mantle<Matter> mantle = engine.getMantle().getMantle();
         for (IrisPosition position : obstructed) {
             mantle.remove(position.getX(), position.getY(), position.getZ(), MatterMarker.class);
         }
+        if (initial) {
+            prepared.sort(Comparator.comparingInt((PreparedMarkerSpawn marker) -> marker.position().getX())
+                    .thenComparingInt(marker -> marker.position().getY())
+                    .thenComparingInt(marker -> marker.position().getZ()));
+        }
         return List.copyOf(prepared);
     }
 
     private KList<IrisSpawner> resolveMarkerSpawners(IrisMarker marker, BiomeEnvironment environment) {
         KList<IrisSpawner> spawners = new KList<>();
+        Set<IrisSpawner> seen = new HashSet<>();
         for (String key : marker.getSpawners()) {
             IrisSpawner spawner = environment.data().getSpawnerLoader().load(key);
             if (spawner == null) {
                 IrisLogging.error("Cannot load spawner: " + key + " for marker on " + engine.getName());
                 continue;
             }
-            spawner.setReferenceMarker(marker);
+            if (!spawner.isCompatExcluded() && seen.add(spawner)) {
                 spawners.add(spawner);
             }
+        }
         return spawners;
     }
 
     private void spawnPreparedMarkers(NativeWorld level, List<PreparedMarkerSpawn> markers, boolean initial) {
         for (PreparedMarkerSpawn marker : markers) {
             try (BiomeEnvironment.Scope ignored = engine.openBiomeEnvironmentScope(marker.environment())) {
-                spawnFromSpawner(level, marker.position(), marker.spawner(), initial);
+                spawnFromSpawner(level, marker.position(), marker.rng(), new SpawnContext(marker.spawner(), marker.marker(), initial));
             }
         }
     }
 
-    private void spawnFromSpawner(NativeWorld level, IrisPosition position, IrisSpawner spawner, boolean initial) {
+    private void spawnFromSpawner(NativeWorld level, IrisPosition position, RNG rng, SpawnContext context) {
-        KList<IrisEntitySpawn> spawns = initial ? spawner.getInitialSpawns() : spawner.getSpawns();
+        IrisSpawner spawner = context.spawner();
+        KList<IrisEntitySpawn> spawns = context.initial() ? spawner.getInitialSpawns() : spawner.getSpawns();
         if (spawns.isEmpty()) {
             return;
         }
-        for (IrisEntitySpawn entry : spawns) {
+        IrisEntitySpawn chosen = rarityPick(spawns, rng);
-            entry.setReferenceSpawner(spawner);
-            entry.setReferenceMarker(spawner.getReferenceMarker());
-        }
-        IrisEntitySpawn chosen = rarityPick(spawns);
         if (chosen == null) {
             return;
         }
 
         int chunkX = position.getX() >> 4;
         int chunkZ = position.getZ() >> 4;
-        if (!canSpawn(spawner, chunkX, chunkZ)) {
+        if (!canSpawn(spawner, chunkX, chunkZ, context.initial())) {
             return;
         }
-        int spawned = spawnEntryAt(level, chosen, spawner, position);
+        int spawned = spawnEntryAt(level, chosen, position, rng, context);
-        if (spawned > 0) {
+        if (spawned > 0 && !context.initial()) {
             spawner.spawn(engine, chunkX, chunkZ);
         }
     }
@@ -511,60 +503,177 @@ 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 = new HashMap<>(initial ? Map.of()
+                : NativeSpawnQueries.livingEntityCategories(level, chunkX, chunkZ));
+        RNG rng = initial ? EntitySpawnSeed.chunk(engine.getSeedManager().getEntity(), chunkX, chunkZ)
+                : new RNG(RNG.r.nextLong());
 
-        KList<IrisEntitySpawn> pool = new KList<>();
+        KList<SpawnCandidate> pool = new KList<>();
-        collectSpawns(pool, environment.data().getSpawnerLoader().loadAll(environment.dimension().getEntitySpawners()), biome, chunkX, chunkZ, chunkMobs, initial);
+        collectSpawns(pool, environment.data().getSpawnerLoader().loadAll(environment.dimension().getEntitySpawners()), biome, chunkX, chunkZ, chunkMobs, initial, false);
-        collectSpawns(pool, environment.data().getSpawnerLoader().loadAll(environment.region().getEntitySpawners()), null, chunkX, chunkZ, chunkMobs, initial);
+        collectSpawns(pool, environment.data().getSpawnerLoader().loadAll(environment.region().getEntitySpawners()), null, chunkX, chunkZ, chunkMobs, initial, false);
-        collectSpawns(pool, environment.data().getSpawnerLoader().loadAll(biome.getEntitySpawners()), null, chunkX, chunkZ, chunkMobs, initial);
+        collectSpawns(pool, environment.data().getSpawnerLoader().loadAll(biome.getEntitySpawners()), null, chunkX, chunkZ, chunkMobs, initial, false);
+        if (environment.dimension().hasUndergroundSpawners(engine)) {
+            spawnUnderground(level, chunkX, chunkZ, initial, chunkMobs, rng.nextParallelRNG(0x5A17D3B48269C0EFL));
+        }
         if (pool.isEmpty()) {
             return;
         }
 
-        IrisEntitySpawn chosen = rarityPick(pool);
+        SpawnCandidate chosen = rarityPick(pool, rng);
-        if (chosen == null || chosen.getReferenceSpawner() == null) {
+        if (chosen == null) {
             return;
         }
-        IrisSpawner spawner = chosen.getReferenceSpawner();
+        IrisSpawner spawner = chosen.spawner();
-        if (!canSpawn(spawner, chunkX, chunkZ)) {
+        if (!canSpawn(spawner, chunkX, chunkZ, initial)) {
             return;
         }
-        int spawned = spawnEntry(level, chosen, spawner, chunkX, chunkZ);
+        int spawned = spawnEntry(level, chosen.entry(), chunkX, chunkZ,
-        if (spawned > 0) {
+                remainingCapacity(chosen.entry(), spawner, chunkMobs), rng, new SpawnContext(spawner, null, initial));
+        recordSpawned(chosen.entry(), chunkMobs, spawned);
+        if (spawned > 0 && !initial) {
             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 spawnUnderground(NativeWorld level, int chunkX, int chunkZ, boolean initial,
-        for (IrisSpawner spawner : spawners) {
+                                  Map<String, Integer> chunkMobs, RNG random) {
-            if (spawner == null) {
+        for (IrisSurface surface : List.of(IrisSurface.LAND, IrisSurface.WATER, IrisSurface.LAVA)) {
+            IrisPosition candidate = findUndergroundCandidate(level, chunkX, chunkZ,
+                    random.nextParallelRNG(surface.ordinal()), surface);
+            if (candidate == null) {
                 continue;
             }
-            if (spawner.getMaxEntitiesPerChunk() <= chunkMobs) {
+            BiomeEnvironment environment;
+            try {
+                environment = engine.getBiomeOrMantleEnvironment(candidate.getX(),
+                        candidate.getY() - engine.getWorld().minHeight(), candidate.getZ());
+            } catch (SavedBiomeUnavailableException unavailable) {
+                continue;
+            }
+            try (BiomeEnvironment.Scope ignored = engine.openBiomeEnvironmentScope(environment)) {
+                KList<SpawnCandidate> pool = new KList<>();
+                collectSpawns(pool, environment.data().getSpawnerLoader().loadAll(environment.dimension().getEntitySpawners()),
+                        environment.biome(), chunkX, chunkZ, chunkMobs, initial, true);
+                collectSpawns(pool, environment.data().getSpawnerLoader().loadAll(environment.region().getEntitySpawners()),
+                        null, chunkX, chunkZ, chunkMobs, initial, true);
+                collectSpawns(pool, environment.data().getSpawnerLoader().loadAll(environment.biome().getEntitySpawners()),
+                        null, chunkX, chunkZ, chunkMobs, initial, true);
+                pool.removeIf(selection -> !matchesUndergroundSurface(selection.entry(), surface));
+                SpawnCandidate selected = rarityPick(pool, random);
+                if (selected == null) {
+                    continue;
+                }
+                int capacity = remainingCapacity(selected.entry(), selected.spawner(), chunkMobs);
+                int spawned = spawnUndergroundEntry(level, candidate, selected, capacity, random, initial);
+                recordSpawned(selected.entry(), chunkMobs, spawned);
+                if (spawned > 0 && !initial) {
+                    selected.spawner().spawn(engine, chunkX, chunkZ);
+                }
+                return;
+            }
+        }
+    }
+
+    private boolean matchesUndergroundSurface(IrisEntitySpawn entry, IrisSurface surface) {
+        IrisEntity entity = entry.getRealEntity(engine);
+        return entity != null && entity.getSurface().isFluid() == surface.isFluid()
+                && (!surface.isFluid() || entity.getSurface() == surface);
+    }
+
+    static IrisPosition findUndergroundCandidate(NativeWorld level, int chunkX, int chunkZ, RNG random, IrisSurface surface) {
+        int minimumY = level.minHeight() + 1;
+        for (int attempt = 0; attempt < 8; attempt++) {
+            int x = (chunkX << 4) + random.i(1, 15);
+            int z = (chunkZ << 4) + random.i(1, 15);
+            int maximumY = Math.min(level.maxHeight() - 3, NativeSpawnQueries.surfaceHeight(level, x, z, true) - 1);
+            if (maximumY < minimumY) {
+                continue;
+            }
+            int span = maximumY - minimumY + 1;
+            int startY = LootResolver.inclusive(random, minimumY, maximumY);
+            for (int sample = 0; sample < Math.min(span, 128); sample++) {
+                int y = minimumY + Math.floorMod(startY - minimumY - sample, span);
+                NativeBlockState state = level.getBlock(x, y, z);
+                boolean acceptable = surface.isFluid() ? matchesSurface(surface, state)
+                        : state != null && state.isAir() && NativeSpawnQueries.solid(level.getBlock(x, y - 1, z))
+                        && level.getBlock(x, y + 1, z).isAir();
+                if (acceptable) {
+                    return new IrisPosition(x, y, z);
+                }
+            }
+        }
+        return null;
+    }
+
+    private int spawnUndergroundEntry(NativeWorld level, IrisPosition candidate, SpawnCandidate selection,
+                                      int capacity, RNG random, boolean initial) {
+        IrisEntity entity = selection.entry().getRealEntity(engine);
+        if (entity == null) {
+            return 0;
+        }
+        int x = candidate.getX();
+        int y = candidate.getY();
+        int z = candidate.getZ();
+        int count = Math.min(Math.max(0, capacity), LootResolver.inclusive(random,
+                selection.entry().getMinSpawns(), selection.entry().getMaxSpawns()));
+        int spawned = 0;
+        for (int ordinal = 0; ordinal < count; ordinal++) {
+            if (!initial && !lightAllowed(selection.spawner(), level, x, y, z)
+                    || !surfaceMatches(entity.getSurface(), level, x, y, z)
+                    || !ModdedEntitySpawner.isAreaClearForSpawn(entityRuntime(level), entity, x, y, z)) {
+                continue;
+            }
+            if (ModdedEntitySpawner.spawn(engine, entity, entityRuntime(level), x, y, z,
+                    EntitySpawnSeed.entity(random.getSeed(), ordinal)) != null) {
+                spawned++;
+            }
+        }
+        return spawned;
+    }
+
+    private void collectSpawns(KList<SpawnCandidate> pool, KList<IrisSpawner> spawners, IrisBiome biomeFilter, int chunkX, int chunkZ, Map<String, Integer> chunkMobs, boolean initial, boolean underground) {
+        for (IrisSpawner spawner : spawners) {
+            if (spawner == null || (spawner.getGroup() == IrisSpawnGroup.CAVE) != underground) {
                 continue;
             }
             if (biomeFilter != null && !spawner.isValid(biomeFilter)) {
                 continue;
             }
-            if (!canSpawn(spawner, chunkX, chunkZ)) {
+            if (!canSpawn(spawner, chunkX, chunkZ, initial)) {
                 continue;
             }
             KList<IrisEntitySpawn> spawns = initial ? spawner.getInitialSpawns() : spawner.getSpawns();
             for (IrisEntitySpawn entry : spawns) {
-                entry.setReferenceSpawner(spawner);
+                if (remainingCapacity(entry, spawner, chunkMobs) > 0) {
-                entry.setReferenceMarker(spawner.getReferenceMarker());
+                    pool.add(new SpawnCandidate(entry, spawner));
-                pool.add(entry);
+                }
             }
         }
     }
 
-    private int spawnEntry(NativeWorld level, IrisEntitySpawn entry, IrisSpawner spawner, int chunkX, int chunkZ) {
+    private void recordSpawned(IrisEntitySpawn entry, Map<String, Integer> counts, int spawned) {
+        IrisEntity entity = entry.getRealEntity(engine);
+        if (spawned > 0 && entity != null) {
+            counts.merge(entity.spawnCategory(), spawned, Integer::sum);
+        }
+    }
+
+    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, int chunkX, int chunkZ,
+                           int remainingCapacity, RNG rng, SpawnContext context) {
         IrisEntity irisEntity = entry.getRealEntity(engine);
         if (irisEntity == null) {
             return 0;
@@ -572,18 +681,24 @@ 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, min, max));
         if (count <= 0) {
             return 0;
         }
 
-        RNG entityRng = entry.getRng().aquire(() -> new RNG(engine.getSeedManager().getEntity()));
+        IrisSpawner spawner = context.spawner();
         IrisSpawnGroup group = spawner.getGroup();
         KList<IrisPosition> caveFloors = group == IrisSpawnGroup.CAVE
                 ? engine.getMantle().findMarkers(chunkX, chunkZ, MarkerMatter.CAVE_FLOOR)
                 : new KList<>();
+        if (context.initial()) {
+            caveFloors.sort(Comparator.comparingInt(IrisPosition::getX)
+                    .thenComparingInt(IrisPosition::getY).thenComparingInt(IrisPosition::getZ));
+        }
         int spawned = 0;
         for (int i = 0; i < count; i++) {
+            RNG entityRng = EntitySpawnSeed.entity(rng.getSeed(), i);
+            RNG positionRng = entityRng.nextParallelRNG(0x632BE59BD9B4E019L);
             int worldX;
             int worldY;
             int worldZ;
@@ -591,16 +706,16 @@ public final class ModdedWorldManager implements EngineWorldManager {
                 if (caveFloors.isEmpty()) {
                     continue;
                 }
-                IrisPosition caveFloor = caveFloors.getRandom(RNG.r);
+                IrisPosition caveFloor = caveFloors.getRandom(positionRng);
                 worldX = caveFloor.getX();
-                worldY = caveFloor.getY() + 1;
+                worldY = caveFloor.getY();
                 worldZ = caveFloor.getZ();
             } else {
-                worldX = (chunkX << 4) + RNG.r.i(16);
+                worldX = (chunkX << 4) + positionRng.i(16);
-                worldZ = (chunkZ << 4) + RNG.r.i(16);
+                worldZ = (chunkZ << 4) + positionRng.i(16);
                 int surfaceY = NativeSpawnQueries.surfaceHeight(level, worldX, worldZ, false);
                 int solidY = NativeSpawnQueries.surfaceHeight(level, worldX, worldZ, true);
-                Integer selectedY = IrisEntitySpawn.selectSurfaceSpawnY(group, irisEntity.getSurface(), solidY, surfaceY, RNG.r);
+                Integer selectedY = IrisEntitySpawn.selectSurfaceSpawnY(group, irisEntity.getSurface(), solidY, surfaceY, positionRng);
                 if (selectedY == null) {
                     continue;
                 }
@@ -610,7 +725,7 @@ public final class ModdedWorldManager implements EngineWorldManager {
                 continue;
             }
             // Rarity is applied exactly once, as pool weighting in rarityPick - never re-rolled per position (Bukkit parity).
-            if (!lightAllowed(spawner, level, worldX, worldY, worldZ)) {
+            if (!context.initial() && !lightAllowed(spawner, level, worldX, worldY, worldZ)) {
                 continue;
             }
             if (!surfaceMatches(irisEntity.getSurface(), level, worldX, worldY, worldZ)) {
@@ -626,7 +741,7 @@ public final class ModdedWorldManager implements EngineWorldManager {
         return spawned;
     }
 
-    private int spawnEntryAt(NativeWorld level, IrisEntitySpawn entry, IrisSpawner spawner, IrisPosition position) {
+    private int spawnEntryAt(NativeWorld level, IrisEntitySpawn entry, IrisPosition position, RNG rng, SpawnContext context) {
         IrisEntity irisEntity = entry.getRealEntity(engine);
         if (irisEntity == null) {
             return 0;
@@ -634,21 +749,21 @@ public final class ModdedWorldManager implements EngineWorldManager {
 
         int min = entry.getMinSpawns();
         int max = entry.getMaxSpawns();
-        int count = LootResolver.inclusive(RNG.r, min, max);
+        int count = LootResolver.inclusive(rng, min, max);
         if (count <= 0) {
             return 0;
         }
 
-        exhaustMarker(spawner, position);
+        exhaustMarker(context.marker(), position, EntitySpawnSeed.entity(rng.getSeed(), -1));
 
-        RNG entityRng = entry.getRng().aquire(() -> new RNG(engine.getSeedManager().getEntity()));
         int worldX = position.getX();
         int worldY = position.getY() + 1;
         int worldZ = position.getZ();
         int spawned = 0;
         for (int i = 0; i < count; i++) {
+            RNG entityRng = EntitySpawnSeed.entity(rng.getSeed(), i);
             // Rarity is applied exactly once, as pool weighting in rarityPick - never re-rolled per position (Bukkit parity).
-            if (!lightAllowed(spawner, level, worldX, worldY, worldZ)) {
+            if (!context.initial() && !lightAllowed(context.spawner(), level, worldX, worldY, worldZ)) {
                 continue;
             }
             if (irisEntity.getSurface().isFluid()
@@ -663,16 +778,15 @@ public final class ModdedWorldManager implements EngineWorldManager {
         return spawned;
     }
 
-    private void exhaustMarker(IrisSpawner spawner, IrisPosition position) {
+    private void exhaustMarker(IrisMarker marker, IrisPosition position, RNG rng) {
-        IrisMarker marker = spawner.getReferenceMarker();
+        if (marker == null || !marker.shouldExhaust(rng)) {
-        if (marker == null || !marker.shouldExhaust()) {
             return;
         }
         engine.getMantle().getMantle().remove(position.getX(), position.getY() - engine.getWorld().minHeight(), position.getZ(), MatterMarker.class);
     }
 
-    private boolean canSpawn(IrisSpawner spawner, int chunkX, int chunkZ) {
+    private boolean canSpawn(IrisSpawner spawner, int chunkX, int chunkZ, boolean initial) {
-        return spawner.canSpawn(engine, chunkX, chunkZ);
+        return !spawner.isCompatExcluded() && (initial || spawner.canSpawn(engine, chunkX, chunkZ));
     }
 
     private boolean lightAllowed(IrisSpawner spawner, NativeWorld level, int worldX, int worldY, int worldZ) {
@@ -708,10 +822,6 @@ 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
@@ -791,9 +901,9 @@ public final class ModdedWorldManager implements EngineWorldManager {
         return !studio || studioSetting;
     }
 
-    private IrisEntitySpawn rarityPick(KList<IrisEntitySpawn> entries) {
+    private static <T extends Rarity> T rarityPick(KList<T> entries, RNG rng) {
-        KList<IrisEntitySpawn> weighted = Rarity.expandWeighted(entries);
+        KList<T> weighted = Rarity.expandWeighted(entries);
-        return weighted.isEmpty() ? entries.getRandom() : weighted.getRandom();
+        return weighted.isEmpty() ? entries.getRandom(rng) : weighted.getRandom(rng);
     }
 
     private static long pack(int x, int z) {
@@ -888,7 +998,14 @@ public final class ModdedWorldManager implements EngineWorldManager {
         return failure;
     }
 
-    private record PreparedMarkerSpawn(IrisPosition position, IrisSpawner spawner, BiomeEnvironment environment) {
+    private record PreparedMarkerSpawn(IrisPosition position, IrisSpawner spawner, IrisMarker marker, RNG rng, BiomeEnvironment environment) {
+    }
+
+    private record SpawnCandidate(IrisEntitySpawn entry, IrisSpawner spawner) implements Rarity {
+        @Override
+        public int getRarity() {
+            return entry.getRarity();
+        }
     }
 
     private NativeEntityRuntime entityRuntime(NativeWorld level) {

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

@@ -33,6 +33,7 @@ import art.arcane.iris.modded.IrisModdedChunkGenerator;
 import art.arcane.iris.modded.ModdedDimensionManager;
 import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeWorldTeleport;
 import art.arcane.iris.modded.ModdedEngineBootstrap;
+import art.arcane.iris.modded.service.ModdedPackUpdateService;
 import art.arcane.iris.modded.ModdedForcedDatapack;
 import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeModdedLoader;
 import art.arcane.iris.modded.ModdedScheduler;
@@ -445,6 +446,12 @@ public final class IrisModdedCommands {
                     );
             String completionMessage = downloadCompletionMessage(result);
             if (result != null) {
+                if (result.changed()) {
+                    ModdedPackUpdateService updates = ModdedEngineBootstrap.services().service(ModdedPackUpdateService.class);
+                    if (updates != null) {
+                        dispatchDownloadFeedback(source, updates::refresh);
+                    }
+                }
                 if (completionMessage != null) {
                     dispatchDownloadFeedback(source, () -> ok(source, completionMessage));
                 }

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

@@ -31,6 +31,9 @@ import art.arcane.iris.generation.runtime.GenerationSessionException;
 import art.arcane.iris.generation.runtime.GenerationSessionLease;
 import art.arcane.iris.structure.placement.IrisStructureLocator;
 import art.arcane.iris.generation.locator.Locator;
+import art.arcane.iris.generation.locator.BiomeLocator;
+import art.arcane.iris.generation.subterrain.SubterrainPosition;
+import art.arcane.iris.world.history.SavedBiomeRuntime;
 import art.arcane.iris.structure.nativegen.NativeStructureGenerationPolicy;
 import art.arcane.iris.structure.placement.StructureReachability;
 import art.arcane.iris.generation.runtime.WrongEngineBroException;
@@ -82,7 +85,7 @@ final class ModdedLocateCommands {
             IrisModdedCommands.fail(source, IrisLanguage.plain(ModdedCommandMessages.IRIS_MODDED_COMMANDS_UNKNOWN_BIOME_2, MessageArgument.untrusted("key", key)));
             return 0;
         }
-        locate(source, level, engine, player, Locator.surfaceBiome(biome.getLoadKey()), "biome " + biome.getLoadKey());
+        locate(source, level, engine, player, BiomeLocator.forBiome(engine, biome.getLoadKey(), player.blockY()), "biome " + biome.getLoadKey());
         return 1;
     }
 
@@ -545,12 +548,12 @@ final class ModdedLocateCommands {
             previous.cancel(true);
         }
         search.whenComplete((Position2 at, Throwable error) -> completeLocate(
-                source, level, engine, player, label, server, playerId, search, at, error));
+                source, level, engine, player, label, server, playerId, search, locator, at, error));
     }
 
     private static void completeLocate(NativeCommandSource source, NativeWorld level, Engine engine,
                                        NativeProtocolPlayer player, String label, NativeModdedServer server, UUID playerId,
-                                       CompletableFuture<Position2> search, Position2 at, Throwable error) {
+                                       CompletableFuture<Position2> search, Locator<?> locator, Position2 at, Throwable error) {
         if (ACTIVE_LOCATE_REQUESTS.get(playerId) != search) {
             return;
         }
@@ -576,15 +579,77 @@ final class ModdedLocateCommands {
             });
             return;
         }
+        if (locator instanceof BiomeLocator caveLocator) {
+            prepareCaveLocate(new CaveLocateRequest(source, level, engine, player, label, server, playerId,
+                    search, caveLocator, at));
+            return;
+        }
         server.execute(() -> {
             if (ACTIVE_LOCATE_REQUESTS.remove(playerId, search)) {
-                teleportToLocateResult(source, level, engine, player, label, at);
+                teleportToLocateResult(source, level, engine, player, label, locator, at, Optional.empty());
             }
         });
     }
 
-    private static void teleportToLocateResult(NativeCommandSource source, NativeWorld level, Engine engine,
+    private static void prepareCaveLocate(CaveLocateRequest request) {
-                                                NativeProtocolPlayer player, String label, Position2 at) {
+        CompletableFuture.supplyAsync(() -> resolveCavePosition(request))
+                .whenComplete((target, error) -> request.server().execute(() -> loadCaveDestination(request, target, error)));
+    }
+
+    private static SubterrainPosition resolveCavePosition(CaveLocateRequest request) {
+        try (GenerationSessionLease lease = request.engine().acquireGenerationLease("modded_cave_position");
+             IrisContext.Scope ignored = IrisContext.open(request.engine(), lease.sessionId(), null)) {
+            return request.locator().position(request.engine(), request.at());
+        } catch (GenerationSessionException error) {
+            throw new CompletionException(error);
+        }
+    }
+
+    private static void loadCaveDestination(CaveLocateRequest request, SubterrainPosition target, Throwable error) {
+        if (ACTIVE_LOCATE_REQUESTS.get(request.playerId()) != request.search()) {
+            return;
+        }
+        if (error != null) {
+            failCaveLocate(request, error);
+            return;
+        }
+        if (target == null || !request.player().connected() || !request.player().inWorld(request.level())) {
+            if (ACTIVE_LOCATE_REQUESTS.remove(request.playerId(), request.search())) {
+                IrisModdedCommands.fail(request.source(), "The cave destination is no longer available.");
+            }
+            return;
+        }
+        try {
+            request.level().getBlock(target.x(), target.y(), target.z());
+            request.locator().prepareRead(request.engine(), new Position2(target.x() >> 4, target.z() >> 4))
+                    .whenComplete((read, failure) -> request.server().execute(() -> finishCaveLocate(request, target, read, failure)));
+        } catch (RuntimeException failure) {
+            failCaveLocate(request, failure);
+        }
+    }
+
+    private static void finishCaveLocate(CaveLocateRequest request, SubterrainPosition target,
+                                         Optional<SavedBiomeRuntime.ReadSession> read, Throwable error) {
+        if (error != null) {
+            failCaveLocate(request, error);
+            return;
+        }
+        if (ACTIVE_LOCATE_REQUESTS.remove(request.playerId(), request.search())) {
+            teleportToLocateResult(request.source(), request.level(), request.engine(), request.player(),
+                    request.label(), request.locator(), request.at(), Optional.of(new CaveDestination(target, read)));
+        }
+    }
+
+    private static void failCaveLocate(CaveLocateRequest request, Throwable error) {
+        ModdedIrisLog.error("Iris cave locate failed for {}", request.label(), error);
+        if (ACTIVE_LOCATE_REQUESTS.remove(request.playerId(), request.search())) {
+            IrisModdedCommands.fail(request.source(), "Could not prepare the cave destination. See the server log for details.");
+        }
+    }
+
+    static void teleportToLocateResult(NativeCommandSource source, NativeWorld level, Engine engine,
+                                                NativeProtocolPlayer player, String label, Locator<?> locator, Position2 at,
+                                        Optional<CaveDestination> caveDestination) {
         // Same liveness guards the structure completion path has: the search can take up to
         // two minutes, and the captured NativeProtocolPlayer may be gone or elsewhere by then.
         if (!player.connected()) {
@@ -600,6 +665,17 @@ final class ModdedLocateCommands {
         try (GenerationSessionLease lease = engine.acquireGenerationLease("modded_locator_teleport");
             IrisContext.Scope ignored = IrisContext.open(engine, lease.sessionId(), null)) {
             int blockY = engine.getMinHeight() + engine.getHeight(blockX, blockZ, false) + 2;
+            if (locator instanceof BiomeLocator caveLocator) {
+                CaveDestination prepared = caveDestination.orElseThrow();
+                SubterrainPosition landing = caveLocator.landing(engine, level, prepared.target(), prepared.read());
+                if (landing == null) {
+                    IrisModdedCommands.fail(source, "No safe cave landing found for " + label + ".");
+                    return;
+                }
+                blockX = landing.x();
+                blockY = landing.y();
+                blockZ = landing.z();
+            }
             boolean teleported = player.teleport(level, blockX + 0.5D, blockY, blockZ + 0.5D);
             if (!teleported) {
                 IrisModdedCommands.fail(source, IrisLanguage.plain(
@@ -611,7 +687,8 @@ final class ModdedLocateCommands {
                 return;
             }
             IrisModdedCommands.ok(source, IrisLanguage.plain(ModdedCommandMessages.IRIS_MODDED_COMMANDS_TELEPORTED_AT_2, MessageArgument.untrusted("label", label), MessageArgument.untrusted("blockX", blockX), MessageArgument.untrusted("blockY", blockY), MessageArgument.untrusted("blockZ", blockZ)));
-        } catch (GenerationSessionException e) {
+        } catch (GenerationSessionException | RuntimeException e) {
+            ModdedIrisLog.error("Iris locate teleport failed for {}", label, e);
             IrisModdedCommands.fail(source, IrisLanguage.plain(ModdedCommandMessages.IRIS_MODDED_COMMANDS_ENGINE_CHANGED_WHILE_LOCATING_TRY_AGAIN, MessageArgument.untrusted("label", label)));
         }
     }
@@ -635,6 +712,14 @@ final class ModdedLocateCommands {
         NO_PLACEMENT
     }
 
+    record CaveDestination(SubterrainPosition target, Optional<SavedBiomeRuntime.ReadSession> read) {
+    }
+
+    private record CaveLocateRequest(NativeCommandSource source, NativeWorld level, Engine engine,
+                                     NativeProtocolPlayer player, String label, NativeModdedServer server,
+                                     UUID playerId, CompletableFuture<Position2> search, BiomeLocator locator, Position2 at) {
+    }
+
     private record NativeStructureTarget(String key, NativeStructureQueries.Reference holder,
                                          NativeStructureAvailability availability) {
     }

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

@@ -18,6 +18,8 @@
 
 package art.arcane.iris.modded.command;
 
+import art.arcane.iris.modded.ModdedStartup;
+
 import art.arcane.iris.modded.ModdedIrisLog;
 import art.arcane.iris.pack.validation.PackCompatReport;
 import art.arcane.iris.spi.IrisPlatforms;
@@ -25,7 +27,6 @@ import art.arcane.iris.pack.PackDirectoryResolver;
 import art.arcane.iris.pack.PackResourceCleanup;
 import art.arcane.iris.pack.PackValidationRegistry;
 import art.arcane.iris.pack.PackValidationResult;
-import art.arcane.iris.pack.PackValidator;
 import art.arcane.iris.modded.ModdedEngineBootstrap;
 import com.mojang.brigadier.arguments.StringArgumentType;
 import com.mojang.brigadier.builder.LiteralArgumentBuilder;
@@ -138,8 +139,7 @@ public final class ModdedPackCommands {
             int broken = 0;
             for (File target : targets) {
                 try {
-                    PackValidationResult result = PackValidator.validate(target);
+                    PackValidationResult result = ModdedStartup.validatePack(target);
-                    PackValidationRegistry.publish(result);
                     if (!result.isLoadable()) {
                         broken++;
                     }

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

@@ -0,0 +1,138 @@
+package art.arcane.iris.modded.service;
+
+import art.arcane.iris.diagnostics.splash.IrisSplashPackScanner;
+import art.arcane.iris.diagnostics.splash.IrisSplashPackScanner.SplashPackMetadata;
+import art.arcane.iris.pack.BuiltInPackUpdates;
+import art.arcane.iris.spi.IrisLogging;
+import art.arcane.iris.spi.IrisPlatforms;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeModdedServer;
+import art.arcane.volmlib.nativelib.minecraft26_2.modded.NativeProtocolPlayer;
+
+import java.io.File;
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.UUID;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CompletionException;
+import java.util.function.Function;
+
+public final class ModdedPackUpdateService implements ModdedTickableService {
+    private final Function<File, CompletableFuture<PackCheck>> checker;
+    private final Set<UUID> notified = new HashSet<>();
+    private CompletableFuture<PackCheck> pending;
+    private List<String> notices = List.of();
+    private File packsFolder;
+    private boolean enabled;
+    private boolean started;
+
+    public ModdedPackUpdateService() {
+        this(ModdedPackUpdateService::checkPacks);
+    }
+
+    ModdedPackUpdateService(Function<File, CompletableFuture<PackCheck>> checker) {
+        this.checker = checker;
+    }
+
+    @Override
+    public void onEnable() {
+        enabled = true;
+    }
+
+    @Override
+    public void onDisable() {
+        enabled = false;
+        if (pending != null) {
+            pending.cancel(true);
+            pending = null;
+        }
+        started = false;
+        notices = List.of();
+        notified.clear();
+        packsFolder = null;
+    }
+
+    @Override
+    public void onServerTick(NativeModdedServer server) {
+        if (!enabled || server == null || !server.hasPlayerList()) {
+            return;
+        }
+        if (!started) {
+            started = true;
+            packsFolder = IrisPlatforms.get().packsFolderNoCreate().getAbsoluteFile();
+            pending = checker.apply(packsFolder);
+        }
+        if (pending == null || !pending.isDone()) {
+            return;
+        }
+        CompletableFuture<PackCheck> completed = pending;
+        pending = null;
+        try {
+            publish(completed.join());
+            server.forEachPlayer(this::notifyPlayer);
+        } catch (CompletionException error) {
+            IrisLogging.reportError("Iris pack update check failed", error);
+        }
+    }
+
+    public void refresh() {
+        if (!enabled) {
+            return;
+        }
+        if (pending != null) {
+            pending.cancel(true);
+            pending = null;
+        }
+        started = false;
+        notices = List.of();
+        notified.clear();
+    }
+
+    public void notifyPlayer(NativeProtocolPlayer player) {
+        if (!enabled || notices.isEmpty() || player == null || !player.connected()
+                || (!player.isGameMaster() && !player.isServerOwner()) || !notified.add(player.id())) {
+            return;
+        }
+        for (String notice : notices) {
+            player.sendMessage(notice);
+        }
+    }
+
+    private static CompletableFuture<PackCheck> checkPacks(File folder) {
+        return CompletableFuture.supplyAsync(() -> IrisSplashPackScanner.collect(folder, IrisLogging::reportError))
+                .thenCompose(packs -> BuiltInPackUpdates.check(packs.stream().map(SplashPackMetadata::name).toList())
+                        .thenApply(updates -> new PackCheck(packs, updates)));
+    }
+
+    private void publish(PackCheck result) {
+        List<String> updates = new ArrayList<>();
+        IrisLogging.info("Iris packs: " + packsFolder);
+        for (SplashPackMetadata pack : result.packs()) {
+            BuiltInPackUpdates.Update update = result.updates().get(pack.name());
+            String version = pack.version().matches("[0-9]+") ? "v" + pack.version() : "version unknown";
+            IrisLogging.info("  " + pack.name() + " " + version
+                    + (update == null ? "" : update.suffix(pack.version())));
+            if (update != null && update.newerThan(pack.version())) {
+                updates.add("Iris " + pack.name() + " release metadata is outdated: installed v" + pack.version()
+                        + ", latest built-in release v" + update.version() + ".");
+                updates.add("Back up and review custom edits in " + new File(packsFolder, pack.name())
+                        + "; close Studio, then update with /iris download pack=" + pack.name() + " overwrite=true.");
+                updates.add("Existing worlds retain their recorded production pack. Back up the complete world, then stage an update with /iris world update <dimension> "
+                        + pack.name() + " and restart the server to activate it.");
+            }
+        }
+        notices = List.copyOf(updates);
+        for (String notice : notices) {
+            IrisLogging.warn(notice);
+        }
+    }
+
+    record PackCheck(List<SplashPackMetadata> packs, Map<String, BuiltInPackUpdates.Update> updates) {
+        PackCheck {
+            packs = List.copyOf(packs);
+            updates = Map.copyOf(updates);
+        }
+    }
+}

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

@@ -57,6 +57,7 @@ import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.RejectedExecutionException;
+import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
 
 public final class ModdedStudioHotloadService implements ModdedTickableService, EnginePlatformHooks {
@@ -64,6 +65,8 @@ public final class ModdedStudioHotloadService implements ModdedTickableService,
     private static final long POLL_MILLIS = 250L;
     private static final long CHECK_LATCH_MILLIS = 1_000L;
     private static final long RECENT_GENERATION_HOLDOFF_MILLIS = 2_000L;
+    private static final long SHUTDOWN_TIMEOUT_SECONDS = 30L;
+    private static final long INTERRUPT_DRAIN_TIMEOUT_SECONDS = 5L;
 
     private final ConcurrentHashMap<String, Watch> watches = new ConcurrentHashMap<>();
     private volatile ExecutorService executor;
@@ -81,9 +84,13 @@ public final class ModdedStudioHotloadService implements ModdedTickableService,
 
     @Override
     public void onEnable() {
-        if (executor != null) {
+        ExecutorService current = executor;
+        if (current != null && !current.isTerminated()) {
+            if (!current.isShutdown()) {
                 return;
             }
+            throw new IllegalStateException("Iris Studio hotload cannot restart while prior workers are still active");
+        }
         executor = Executors.newSingleThreadExecutor((Runnable task) -> {
             Thread thread = new Thread(task, "Iris Studio Hotload");
             thread.setDaemon(true);
@@ -96,10 +103,10 @@ public final class ModdedStudioHotloadService implements ModdedTickableService,
     @Override
     public void onDisable() {
         ExecutorService active = executor;
-        executor = null;
+        if (!shutdownAndDrain(active)) {
-        if (active != null) {
+            throw new IllegalStateException("Iris Studio hotload worker remained active during service shutdown");
-            active.shutdownNow();
         }
+        executor = null;
         for (Watch watch : watches.values()) {
             watch.close();
         }
@@ -197,7 +204,7 @@ public final class ModdedStudioHotloadService implements ModdedTickableService,
     @Override
     public void onServerTick(NativeModdedServer server) {
         ExecutorService active = executor;
-        if (active == null) {
+        if (active == null || active.isShutdown()) {
             return;
         }
         long now = System.currentTimeMillis();
@@ -284,6 +291,30 @@ public final class ModdedStudioHotloadService implements ModdedTickableService,
                 && !isPregeneratorActive(engine);
     }
 
+    private static boolean shutdownAndDrain(ExecutorService active) {
+        if (active == null) {
+            return true;
+        }
+        active.shutdown();
+        try {
+            if (active.awaitTermination(SHUTDOWN_TIMEOUT_SECONDS, TimeUnit.SECONDS)) {
+                return true;
+            }
+            active.shutdownNow();
+            if (active.awaitTermination(INTERRUPT_DRAIN_TIMEOUT_SECONDS, TimeUnit.SECONDS)) {
+                return true;
+            }
+            ModdedIrisLog.error("Iris Studio hotload worker did not stop after shutdownNow",
+                    new IllegalStateException("Iris Studio hotload worker is still active"));
+            return false;
+        } catch (InterruptedException exception) {
+            active.shutdownNow();
+            Thread.currentThread().interrupt();
+            ModdedIrisLog.error("Interrupted while draining Iris Studio hotload", exception);
+            return false;
+        }
+    }
+
     private boolean throttled(IrisModdedChunkGenerator generator, Engine engine, long now) {
         if (now - generator.lastChunkGenAt() < RECENT_GENERATION_HOLDOFF_MILLIS) {
             return true;