d

adapters/bukkit/nms/v26_2_R1/src/main/java/art/arcane/iris/core/nms/v26_2_R1/CurrentPaperWorldDataWriter.java

@@ -0,0 +1,130 @@
+package art.arcane.iris.core.nms.v26_2_R1;
+
+import art.arcane.iris.core.lifecycle.WorldReplacementSeed;
+import art.arcane.iris.util.common.scheduling.J;
+import io.papermc.paper.world.saveddata.PaperLevelOverrides;
+import io.papermc.paper.world.saveddata.PaperWorldMetadata;
+import net.minecraft.server.MinecraftServer;
+import net.minecraft.world.level.storage.PrimaryLevelData;
+import net.minecraft.world.level.storage.SavedDataStorage;
+import org.bukkit.Bukkit;
+import org.bukkit.craftbukkit.CraftServer;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.LinkOption;
+import java.nio.file.Path;
+import java.util.List;
+import java.util.UUID;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
+
+final class CurrentPaperWorldDataWriter {
+    private static final long SNAPSHOT_TIMEOUT_SECONDS = 30L;
+
+    private CurrentPaperWorldDataWriter() {
+    }
+
+    static void write(
+            Path sourceWorldDirectory,
+            Path targetWorldDirectory,
+            long seed
+    ) throws IOException {
+        CraftServer craftServer = (CraftServer) Bukkit.getServer();
+        MinecraftServer server = craftServer.getHandle().getServer();
+        PaperLevelOverrides levelOverrides = captureLevelOverrides(craftServer, server);
+
+        Path targetWorld = targetWorldDirectory.toAbsolutePath().normalize();
+        UUID metadataUuid = UUID.randomUUID();
+        WorldReplacementSeed.copyWithAuthoritativeSeed(sourceWorldDirectory, targetWorld, seed);
+        try (SavedDataStorage savedDataStorage = new SavedDataStorage(
+                targetWorld.resolve("data"),
+                server.getFixerUpper(),
+                server.registryAccess()
+        )) {
+            savedDataStorage.set(PaperWorldMetadata.TYPE, new PaperWorldMetadata(metadataUuid));
+            savedDataStorage.set(PaperLevelOverrides.TYPE, levelOverrides);
+        }
+
+        List<Path> requiredDataFiles = List.of(
+                targetWorld.resolve("data/minecraft/world_gen_settings.dat"),
+                targetWorld.resolve("data/paper/metadata.dat"),
+                targetWorld.resolve("data/paper/level_overrides.dat")
+        );
+        for (Path requiredDataFile : requiredDataFiles) {
+            if (!Files.isRegularFile(requiredDataFile, LinkOption.NOFOLLOW_LINKS)) {
+                throw new IOException("Current Paper world data was not written: " + requiredDataFile);
+            }
+        }
+
+        long writtenSeed = WorldReplacementSeed.readAuthoritativeSeed(targetWorld);
+        if (writtenSeed != seed) {
+            throw new IOException("Current Paper world data did not retain the requested seed.");
+        }
+
+        try (SavedDataStorage verificationStorage = new SavedDataStorage(
+                targetWorld.resolve("data"),
+                server.getFixerUpper(),
+                server.registryAccess()
+        )) {
+            PaperWorldMetadata metadata = verificationStorage.get(PaperWorldMetadata.TYPE);
+            if (metadata == null || !metadataUuid.equals(metadata.uuid())) {
+                throw new IOException("Current Paper world metadata could not be verified.");
+            }
+            PaperLevelOverrides overrides = verificationStorage.get(PaperLevelOverrides.TYPE);
+            if (overrides == null || overrides.isInitialized()) {
+                throw new IOException("Current Paper level overrides could not be verified.");
+            }
+        }
+    }
+
+    private static PaperLevelOverrides captureLevelOverrides(
+            CraftServer craftServer,
+            MinecraftServer server
+    ) throws IOException {
+        if (craftServer.isGlobalTickThread()) {
+            return createLevelOverrides(craftServer, server);
+        }
+        if (J.isFolia() && J.isPrimaryThread()) {
+            throw new IOException("Current Paper world data cannot be staged from a Folia region tick thread.");
+        }
+
+        CompletableFuture<PaperLevelOverrides> captured = new CompletableFuture<>();
+        boolean scheduled = J.runGlobal(() -> {
+            try {
+                captured.complete(createLevelOverrides(craftServer, server));
+            } catch (Throwable failure) {
+                captured.completeExceptionally(failure);
+            }
+        });
+        if (!scheduled) {
+            throw new IOException("Could not schedule the current Paper level-data snapshot on the global thread.");
+        }
+
+        try {
+            return captured.get(SNAPSHOT_TIMEOUT_SECONDS, TimeUnit.SECONDS);
+        } catch (InterruptedException failure) {
+            Thread.currentThread().interrupt();
+            throw new IOException("Interrupted while capturing current Paper level data.", failure);
+        } catch (ExecutionException failure) {
+            throw new IOException("Could not capture current Paper level data.", failure.getCause());
+        } catch (TimeoutException failure) {
+            throw new IOException("Timed out while capturing current Paper level data.", failure);
+        }
+    }
+
+    private static PaperLevelOverrides createLevelOverrides(
+            CraftServer craftServer,
+            MinecraftServer server
+    ) throws IOException {
+        if (!craftServer.isGlobalTickThread()) {
+            throw new IOException("Current Paper level data must be captured on the global tick thread.");
+        }
+        if (!(server.getWorldData().overworldData() instanceof PrimaryLevelData primaryLevelData)) {
+            throw new IOException("Paper primary level data is unavailable for current world data staging.");
+        }
+        return PaperLevelOverrides.createFromLiveLevelData(primaryLevelData);
+    }
+}

adapters/bukkit/nms/v26_2_R1/src/main/java/art/arcane/iris/core/nms/v26_2_R1/DatapackStructureStateFilter.java

@@ -7,7 +7,6 @@ import net.minecraft.core.Holder;
 import net.minecraft.core.HolderOwner;
 import net.minecraft.core.Vec3i;
 import net.minecraft.resources.ResourceKey;
-import net.minecraft.world.level.chunk.ChunkGeneratorStructureState;
 import net.minecraft.world.level.levelgen.structure.StructureSet;
 import net.minecraft.world.level.levelgen.structure.placement.ConcentricRingsStructurePlacement;
 import net.minecraft.world.level.levelgen.structure.placement.RandomSpreadStructurePlacement;
@@ -41,16 +40,31 @@ final class DatapackStructureStateFilter {
             DatapackStructureScopeIndex scopeIndex,
             Set<String> declaredSources,
             IrisImportedStructureControl importedStructures
+    ) {
+        return filter(
+                structureSets,
+                scopeIndex,
+                declaredSources,
+                importedStructures,
+                keyIndex(structureSets));
+    }
+
+    static Selection filter(
+            List<Holder<StructureSet>> structureSets,
+            DatapackStructureScopeIndex scopeIndex,
+            Set<String> declaredSources,
+            IrisImportedStructureControl importedStructures,
+            StructureSetKeyIndex keyIndex
     ) {
         if (scopeIndex.isEmpty()) {
             return new Selection(
-                    scaleFrequencyOverrides(structureSets, importedStructures),
+                    scaleFrequencyOverrides(structureSets, importedStructures, keyIndex),
                     0,
                     0);
         }
         Map<String, Holder<StructureSet>> holdersByKey = new HashMap<>();
         for (Holder<StructureSet> holder : structureSets) {
-            String key = structureSetKey(holder);
+            String key = structureSetKey(holder, keyIndex);
             if (key != null) {
                 holdersByKey.putIfAbsent(key, holder);
             }
@@ -61,7 +75,7 @@ final class DatapackStructureStateFilter {
         int retainedManagedSets = 0;
         int excludedManagedSets = 0;
         for (Holder<StructureSet> holder : structureSets) {
-            String setKey = structureSetKey(holder);
+            String setKey = structureSetKey(holder, keyIndex);
             boolean managedSet = setKey != null && scopeIndex.isManagedStructureSet(setKey);
             Holder<StructureSet> scopedHolder = scopeHolder(
                     holder,
@@ -69,7 +83,8 @@ final class DatapackStructureStateFilter {
                     declaredSources,
                     holdersByKey,
                     scopedByIdentity,
-                    visiting);
+                    visiting,
+                    keyIndex);
             if (scopedHolder == null) {
                 if (managedSet) {
                     excludedManagedSets++;
@@ -82,21 +97,29 @@ final class DatapackStructureStateFilter {
             filteredSets.add(scopedHolder);
         }
         return new Selection(
-                scaleFrequencyOverrides(List.copyOf(filteredSets), importedStructures),
+                scaleFrequencyOverrides(
+                        List.copyOf(filteredSets), importedStructures, keyIndex),
                 retainedManagedSets,
                 excludedManagedSets);
     }
 
     static String structureSetKey(Holder<StructureSet> holder) {
-        Optional<ResourceKey<StructureSet>> key = holder.unwrapKey();
-        if (key.isPresent()) {
-            return key.get().identifier().toString();
-        }
-        if (holder.value().placement()
-                instanceof ChunkGeneratorStructureState.KeyedRandomSpreadStructurePlacement keyedPlacement) {
-            return keyedPlacement.key.identifier().toString();
-        }
-        return null;
+        return structureSetKey(holder, keyIndex(List.of(holder)));
+    }
+
+    static StructureSetKeyIndex keyIndex(
+            Iterable<? extends Holder<StructureSet>> registeredStructureSets
+    ) {
+        return StructureSetKeyIndex.create(registeredStructureSets);
+    }
+
+    private static String structureSetKey(
+            Holder<StructureSet> holder,
+            StructureSetKeyIndex keyIndex
+    ) {
+        return keyIndex.resolve(holder)
+                .map(key -> key.identifier().toString())
+                .orElse(null);
     }
 
     private static List<StructureSet.StructureSelectionEntry> filterEntries(
@@ -122,7 +145,8 @@ final class DatapackStructureStateFilter {
             Set<String> declaredSources,
             Map<String, Holder<StructureSet>> holdersByKey,
             Map<Holder<StructureSet>, Holder<StructureSet>> scopedByIdentity,
-            Set<Holder<StructureSet>> visiting
+            Set<Holder<StructureSet>> visiting,
+            StructureSetKeyIndex keyIndex
     ) {
         if (scopedByIdentity.containsKey(holder)) {
             return scopedByIdentity.get(holder);
@@ -131,7 +155,7 @@ final class DatapackStructureStateFilter {
             return null;
         }
         try {
-            String setKey = structureSetKey(holder);
+            String setKey = structureSetKey(holder, keyIndex);
             if (setKey != null && scopeIndex.isManagedStructureSet(setKey)
                     && !scopeIndex.allowsStructureSet(setKey, declaredSources)) {
                 scopedByIdentity.put(holder, null);
@@ -150,14 +174,15 @@ final class DatapackStructureStateFilter {
                     declaredSources,
                     holdersByKey,
                     scopedByIdentity,
-                    visiting);
+                    visiting,
+                    keyIndex);
             if (entries.size() == originalSet.structures().size()
                     && placement == originalSet.placement()) {
                 scopedByIdentity.put(holder, holder);
                 return holder;
             }
             Holder<StructureSet> scoped = replacementHolder(
-                    holder, new StructureSet(entries, placement));
+                    holder, new StructureSet(entries, placement), keyIndex);
             scopedByIdentity.put(holder, scoped);
             return scoped;
         } finally {
@@ -184,7 +209,8 @@ final class DatapackStructureStateFilter {
             Set<String> declaredSources,
             Map<String, Holder<StructureSet>> holdersByKey,
             Map<Holder<StructureSet>, Holder<StructureSet>> scopedByIdentity,
-            Set<Holder<StructureSet>> visiting
+            Set<Holder<StructureSet>> visiting,
+            StructureSetKeyIndex keyIndex
     ) {
         Optional<StructurePlacement.ExclusionZone> currentZone = exclusionZone(placement);
         if (currentZone.isEmpty()) {
@@ -192,7 +218,7 @@ final class DatapackStructureStateFilter {
         }
 
         Holder<StructureSet> target = currentZone.get().otherSet();
-        String targetKey = structureSetKey(target);
+        String targetKey = structureSetKey(target, keyIndex);
         if (targetKey != null) {
             target = holdersByKey.getOrDefault(targetKey, target);
         }
@@ -202,7 +228,8 @@ final class DatapackStructureStateFilter {
                 declaredSources,
                 holdersByKey,
                 scopedByIdentity,
-                visiting);
+                visiting,
+                keyIndex);
         Optional<StructurePlacement.ExclusionZone> scopedZone = Optional.empty();
         if (scopedTarget != null) {
             scopedZone = Optional.of(new StructurePlacement.ExclusionZone(
@@ -217,14 +244,15 @@ final class DatapackStructureStateFilter {
 
     private static List<Holder<StructureSet>> scaleFrequencyOverrides(
             List<Holder<StructureSet>> structureSets,
-            IrisImportedStructureControl importedStructures
+            IrisImportedStructureControl importedStructures,
+            StructureSetKeyIndex keyIndex
     ) {
         if (!importedStructures.hasFrequencyOverrides()) {
             return structureSets;
         }
         Map<String, Holder<StructureSet>> holdersByKey = new HashMap<>();
         for (Holder<StructureSet> holder : structureSets) {
-            String key = structureSetKey(holder);
+            String key = structureSetKey(holder, keyIndex);
             if (key != null) {
                 holdersByKey.putIfAbsent(key, holder);
             }
@@ -234,7 +262,11 @@ final class DatapackStructureStateFilter {
         boolean changed = false;
         for (Holder<StructureSet> holder : structureSets) {
             Holder<StructureSet> scaled = scaleFrequencyHolder(
-                    holder, importedStructures, holdersByKey, scaledByIdentity);
+                    holder,
+                    importedStructures,
+                    holdersByKey,
+                    scaledByIdentity,
+                    keyIndex);
             scaledSets.add(scaled);
             changed |= scaled != holder;
         }
@@ -245,17 +277,19 @@ final class DatapackStructureStateFilter {
             Holder<StructureSet> holder,
             IrisImportedStructureControl importedStructures,
             Map<String, Holder<StructureSet>> holdersByKey,
-            Map<Holder<StructureSet>, Holder<StructureSet>> scaledByIdentity
+            Map<Holder<StructureSet>, Holder<StructureSet>> scaledByIdentity,
+            StructureSetKeyIndex keyIndex
     ) {
         if (scaledByIdentity.containsKey(holder)) {
             return scaledByIdentity.get(holder);
         }
-        if (!dependsOnFrequencyOverride(holder, importedStructures, holdersByKey)) {
+        if (!dependsOnFrequencyOverride(
+                holder, importedStructures, holdersByKey, keyIndex)) {
             scaledByIdentity.put(holder, holder);
             return holder;
         }
 
-        ResourceKey<StructureSet> holderKey = structureSetResourceKey(holder).orElseThrow(() ->
+        ResourceKey<StructureSet> holderKey = keyIndex.resolve(holder).orElseThrow(() ->
                 new IllegalStateException(
                         "An affected native structure-set exclusion graph has an unkeyed holder"));
         ReboundStructureSetHolder scaledHolder = new ReboundStructureSetHolder(holderKey);
@@ -267,16 +301,21 @@ final class DatapackStructureStateFilter {
         Optional<StructurePlacement.ExclusionZone> scaledZone = originalZone;
         if (originalZone.isPresent()) {
             Holder<StructureSet> target = canonicalHolder(
-                    originalZone.get().otherSet(), holdersByKey);
+                    originalZone.get().otherSet(), holdersByKey, keyIndex);
             Holder<StructureSet> scaledTarget = scaleFrequencyHolder(
-                    target, importedStructures, holdersByKey, scaledByIdentity);
+                    target,
+                    importedStructures,
+                    holdersByKey,
+                    scaledByIdentity,
+                    keyIndex);
             if (scaledTarget != originalZone.get().otherSet()) {
                 scaledZone = Optional.of(new StructurePlacement.ExclusionZone(
                         scaledTarget, originalZone.get().chunkCount()));
             }
         }
 
-        double multiplier = importedStructures.frequencyMultiplier(structureSetKey(holder));
+        double multiplier = importedStructures.frequencyMultiplier(
+                structureSetKey(holder, keyIndex));
         StructurePlacement scaledPlacement = multiplier == 1D && scaledZone.equals(originalZone)
                 ? originalPlacement
                 : copyPlacement(originalPlacement, scaledZone, multiplier);
@@ -287,12 +326,14 @@ final class DatapackStructureStateFilter {
     private static boolean dependsOnFrequencyOverride(
             Holder<StructureSet> holder,
             IrisImportedStructureControl importedStructures,
-            Map<String, Holder<StructureSet>> holdersByKey
+            Map<String, Holder<StructureSet>> holdersByKey,
+            StructureSetKeyIndex keyIndex
     ) {
         Set<Holder<StructureSet>> visited = Collections.newSetFromMap(new IdentityHashMap<>());
         Holder<StructureSet> current = holder;
         while (visited.add(current)) {
-            if (importedStructures.frequencyMultiplier(structureSetKey(current)) != 1D) {
+            if (importedStructures.frequencyMultiplier(
+                    structureSetKey(current, keyIndex)) != 1D) {
                 return true;
             }
             Optional<StructurePlacement.ExclusionZone> zone =
@@ -300,24 +341,26 @@ final class DatapackStructureStateFilter {
             if (zone.isEmpty()) {
                 return false;
             }
-            current = canonicalHolder(zone.get().otherSet(), holdersByKey);
+            current = canonicalHolder(zone.get().otherSet(), holdersByKey, keyIndex);
         }
         return false;
     }
 
     private static Holder<StructureSet> canonicalHolder(
             Holder<StructureSet> holder,
-            Map<String, Holder<StructureSet>> holdersByKey
+            Map<String, Holder<StructureSet>> holdersByKey,
+            StructureSetKeyIndex keyIndex
     ) {
-        String key = structureSetKey(holder);
+        String key = structureSetKey(holder, keyIndex);
         return key == null ? holder : holdersByKey.getOrDefault(key, holder);
     }
 
     private static Holder<StructureSet> replacementHolder(
             Holder<StructureSet> original,
-            StructureSet replacement
+            StructureSet replacement,
+            StructureSetKeyIndex keyIndex
     ) {
-        Optional<ResourceKey<StructureSet>> key = structureSetResourceKey(original);
+        Optional<ResourceKey<StructureSet>> key = keyIndex.resolve(original);
         if (key.isEmpty()) {
             return Holder.direct(replacement);
         }
@@ -326,20 +369,6 @@ final class DatapackStructureStateFilter {
         return holder;
     }
 
-    private static Optional<ResourceKey<StructureSet>> structureSetResourceKey(
-            Holder<StructureSet> holder
-    ) {
-        Optional<ResourceKey<StructureSet>> key = holder.unwrapKey();
-        if (key.isPresent()) {
-            return key;
-        }
-        if (holder.value().placement()
-                instanceof ChunkGeneratorStructureState.KeyedRandomSpreadStructurePlacement keyedPlacement) {
-            return Optional.of(keyedPlacement.key);
-        }
-        return Optional.empty();
-    }
-
     private static StructurePlacement copyPlacement(
             StructurePlacement placement,
             Optional<StructurePlacement.ExclusionZone> exclusionZone,
@@ -357,26 +386,7 @@ final class DatapackStructureStateFilter {
         int salt = (int) declaredFieldValue(
                 StructurePlacement.class, placement, int.class);
 
-        if (placement.getClass()
-                == ChunkGeneratorStructureState.KeyedRandomSpreadStructurePlacement.class) {
-            ChunkGeneratorStructureState.KeyedRandomSpreadStructurePlacement keyedPlacement =
-                    (ChunkGeneratorStructureState.KeyedRandomSpreadStructurePlacement) placement;
-            NativeStructureFrequencyScale scale = NativeStructureFrequencyScale.randomSpread(
-                    frequency, keyedPlacement.spacing(), keyedPlacement.separation(), frequencyMultiplier);
-            return new ChunkGeneratorStructureState.KeyedRandomSpreadStructurePlacement(
-                    keyedPlacement.key,
-                    locateOffset,
-                    frequencyReductionMethod,
-                    scale.frequency(),
-                    salt,
-                    exclusionZone,
-                    scale.spacing(),
-                    keyedPlacement.separation(),
-                    keyedPlacement.spreadType());
-        }
-        if (placement.getClass() == RandomSpreadStructurePlacement.class) {
-            RandomSpreadStructurePlacement randomSpread =
-                    (RandomSpreadStructurePlacement) placement;
+        if (placement instanceof RandomSpreadStructurePlacement randomSpread) {
             NativeStructureFrequencyScale scale = NativeStructureFrequencyScale.randomSpread(
                     frequency, randomSpread.spacing(), randomSpread.separation(), frequencyMultiplier);
             return new RandomSpreadStructurePlacement(
@@ -439,6 +449,46 @@ final class DatapackStructureStateFilter {
         }
     }
 
+    static final class StructureSetKeyIndex {
+        private final Map<List<StructureSet.StructureSelectionEntry>, ResourceKey<StructureSet>>
+                keysByEntries;
+
+        private StructureSetKeyIndex(
+                Map<List<StructureSet.StructureSelectionEntry>, ResourceKey<StructureSet>>
+                        keysByEntries
+        ) {
+            this.keysByEntries = keysByEntries;
+        }
+
+        private static StructureSetKeyIndex create(
+                Iterable<? extends Holder<StructureSet>> registeredStructureSets
+        ) {
+            Map<List<StructureSet.StructureSelectionEntry>, ResourceKey<StructureSet>> keys =
+                    new IdentityHashMap<>();
+            for (Holder<StructureSet> holder : registeredStructureSets) {
+                Optional<ResourceKey<StructureSet>> key = holder.unwrapKey();
+                if (key.isEmpty()) {
+                    continue;
+                }
+                List<StructureSet.StructureSelectionEntry> entries = holder.value().structures();
+                ResourceKey<StructureSet> previous = keys.put(entries, key.get());
+                if (previous != null && !previous.equals(key.get())) {
+                    throw new IllegalStateException(
+                            "Multiple registered structure sets share the same entry list");
+                }
+            }
+            return new StructureSetKeyIndex(keys);
+        }
+
+        private Optional<ResourceKey<StructureSet>> resolve(Holder<StructureSet> holder) {
+            Optional<ResourceKey<StructureSet>> key = holder.unwrapKey();
+            if (key.isPresent()) {
+                return key;
+            }
+            return Optional.ofNullable(keysByEntries.get(holder.value().structures()));
+        }
+    }
+
     record Selection(
             List<Holder<StructureSet>> structureSets,
             int retainedManagedSets,

adapters/bukkit/nms/v26_2_R1/src/main/java/art/arcane/iris/core/nms/v26_2_R1/NMSBinding.java

@@ -15,7 +15,6 @@ import art.arcane.iris.core.nms.container.BiomeColor;
 import art.arcane.iris.core.nms.container.Pair;
 import art.arcane.iris.core.nms.container.BlockProperty;
 import art.arcane.iris.core.nms.datapack.DataVersion;
-import art.arcane.iris.core.lifecycle.WorldReplacementSeed;
 import art.arcane.iris.engine.data.cache.AtomicCache;
 import art.arcane.iris.engine.data.chunk.TerrainChunk;
 import art.arcane.iris.engine.framework.Engine;
@@ -55,8 +54,6 @@ import art.arcane.volmlib.util.nbt.tag.CompoundTag;
 import art.arcane.iris.util.common.scheduling.J;
 import it.unimi.dsi.fastutil.objects.Object2IntMap;
 import it.unimi.dsi.fastutil.shorts.ShortList;
-import io.papermc.paper.world.saveddata.PaperLevelOverrides;
-import io.papermc.paper.world.saveddata.PaperWorldMetadata;
 import net.bytebuddy.ByteBuddy;
 import net.bytebuddy.agent.builder.AgentBuilder;
 import net.bytebuddy.agent.builder.ResettableClassFileTransformer;
@@ -119,14 +116,14 @@ import net.minecraft.world.level.levelgen.XoroshiroRandomSource;
 import net.minecraft.world.level.levelgen.structure.StructureCheck;
 import net.minecraft.world.level.levelgen.structure.BoundingBox;
 import net.minecraft.world.level.levelgen.structure.Structure;
+import net.minecraft.world.level.levelgen.structure.StructureSet;
 import net.minecraft.world.level.levelgen.structure.structures.JigsawStructure;
-import net.minecraft.world.level.storage.PrimaryLevelData;
-import net.minecraft.world.level.storage.SavedDataStorage;
 import net.minecraft.world.level.levelgen.feature.AbstractHugeMushroomFeature;
 import net.minecraft.world.level.levelgen.feature.ConfiguredFeature;
 import net.minecraft.world.level.levelgen.feature.FallenTreeFeature;
 import net.minecraft.world.level.levelgen.feature.Feature;
 import net.minecraft.world.level.levelgen.feature.TreeFeature;
+import net.minecraft.world.level.storage.LevelStorageSource;
 import net.minecraft.world.level.levelgen.flat.FlatLayerInfo;
 import net.minecraft.world.level.levelgen.flat.FlatLevelGeneratorSettings;
 import org.bukkit.Bukkit;
@@ -162,8 +159,6 @@ import java.lang.reflect.Field;
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
 import java.lang.reflect.Modifier;
-import java.nio.file.Files;
-import java.nio.file.LinkOption;
 import java.nio.file.Path;
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -173,23 +168,18 @@ import java.util.Map;
 import java.util.Optional;
 import java.util.List;
 import java.util.Set;
-import java.util.UUID;
-import java.util.concurrent.CompletableFuture;
-import java.util.concurrent.ExecutionException;
 import java.util.concurrent.Executor;
 import java.util.concurrent.TimeUnit;
-import java.util.concurrent.TimeoutException;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
 
 public class NMSBinding implements INMSBinding {
-    private static final long CURRENT_WORLD_DATA_SNAPSHOT_TIMEOUT_SECONDS = 30L;
-
     private final KMap<Biome, Object> baseBiomeCache = new KMap<>();
     private volatile DataVersion dataVersion;
     private final BlockData AIR = Material.AIR.createBlockData();
     private final AtomicCache<MCAIdMap<net.minecraft.world.level.biome.Biome>> biomeMapCache = new AtomicCache<>();
     private final AtomicBoolean injected = new AtomicBoolean();
+    private volatile ResettableClassFileTransformer levelStorageAccessTransformer;
     private volatile ResettableClassFileTransformer serverLevelTransformer;
     private final AtomicCache<MCAIdMapper<BlockState>> registryCache = new AtomicCache<>();
     private final AtomicCache<MCAPalette<BlockState>> globalCache = new AtomicCache<>();
@@ -1249,8 +1239,15 @@ public class NMSBinding implements INMSBinding {
         ChunkGeneratorStructureState currentState = level.getChunkSource().getGeneratorState();
         net.minecraft.world.level.chunk.ChunkGenerator generator = level.getChunkSource().getGenerator();
         ChunkGeneratorStructureState scopedState = createStructureState(level, generator, currentState);
+        Registry<StructureSet> structureSetRegistry =
+                level.registryAccess().lookupOrThrow(Registries.STRUCTURE_SET);
         DatapackStructureStateFilter.Selection selection = DatapackStructureStateFilter.filter(
-                scopedState.possibleStructureSets(), scopeIndex, declaredSources, importedStructures);
+                scopedState.possibleStructureSets(),
+                scopeIndex,
+                declaredSources,
+                importedStructures,
+                DatapackStructureStateFilter.keyIndex(
+                        structureSetRegistry.listElements().toList()));
 
         Field possibleSetsField = getField(scopedState.getClass(), List.class);
         possibleSetsField.setAccessible(true);
@@ -1328,7 +1325,7 @@ public class NMSBinding implements INMSBinding {
                 level.registryAccess().lookupOrThrow(Registries.STRUCTURE_SET),
                 currentState.randomState(),
                 currentState.getLevelSeed(),
-                currentState.conf);
+                level.spigotConfig);
     }
 
     private void initializeAndPublishStructureState(
@@ -1542,6 +1539,18 @@ public class NMSBinding implements INMSBinding {
             }
             try {
                 IrisLogging.info("Injecting Bukkit");
+                levelStorageAccessTransformer = new AgentBuilder.Default()
+                        .disableClassFormatChanges()
+                        .with(AgentBuilder.RedefinitionStrategy.RETRANSFORMATION)
+                        .type(ElementMatchers.is(LevelStorageSource.LevelStorageAccess.class))
+                        .transform((builder, typeDescription, classLoader, module, protectionDomain) ->
+                                builder.visit(Advice.to(LevelStorageAccessAdvice.class).on(ElementMatchers.isConstructor()
+                                        .and(ElementMatchers.takesArguments(4))
+                                        .and(ElementMatchers.takesArgument(0, LevelStorageSource.class))
+                                        .and(ElementMatchers.takesArgument(1, String.class))
+                                        .and(ElementMatchers.takesArgument(2, Path.class))
+                                        .and(ElementMatchers.takesArgument(3, ResourceKey.class)))))
+                        .installOn(Agent.getInstrumentation());
                 serverLevelTransformer = new AgentBuilder.Default()
                         .disableClassFormatChanges()
                         .with(AgentBuilder.RedefinitionStrategy.RETRANSFORMATION)
@@ -1549,8 +1558,7 @@ public class NMSBinding implements INMSBinding {
                         .transform((builder, typeDescription, classLoader, module, protectionDomain) ->
                                 builder.visit(Advice.to(ServerLevelAdvice.class).on(ElementMatchers.isConstructor()
                                         .and(ElementMatchers.takesArgument(0, MinecraftServer.class))
-                                        .and(ElementMatchers.takesArgument(5, LevelStem.class))
-                                        .and(ElementMatchers.takesArgument(12, ChunkGenerator.class)))))
+                                        .and(ElementMatchers.takesArgument(5, LevelStem.class)))))
                         .installOn(Agent.getInstrumentation());
                 ByteBuddy buddy = new ByteBuddy();
                 for (Class<?> clazz : List.of(ChunkAccess.class, ProtoChunk.class)) {
@@ -1565,12 +1573,17 @@ public class NMSBinding implements INMSBinding {
             } catch (Throwable e) {
                 IrisLogging.error(C.RED + "Failed to inject Bukkit");
                 e.printStackTrace();
-                // The ServerLevel transformer may already be installed when the ChunkAccess
-                // redefine throws; remove it or a retry would stack a second one and orphan
-                // this one permanently.
-                ResettableClassFileTransformer partial = serverLevelTransformer;
+                ResettableClassFileTransformer partialServerLevel = serverLevelTransformer;
+                ResettableClassFileTransformer partialStorageAccess = levelStorageAccessTransformer;
                 serverLevelTransformer = null;
-                if (partial != null) {
+                levelStorageAccessTransformer = null;
+                for (ResettableClassFileTransformer partial : new ResettableClassFileTransformer[]{
+                        partialServerLevel,
+                        partialStorageAccess
+                }) {
+                    if (partial == null) {
+                        continue;
+                    }
                     try {
                         partial.reset(Agent.getInstrumentation(), AgentBuilder.RedefinitionStrategy.RETRANSFORMATION);
                     } catch (Throwable ignored) {
@@ -1586,26 +1599,36 @@ public class NMSBinding implements INMSBinding {
         if (!injected.get())
             return;
         try {
-            Agent.getInstrumentation().retransformClasses(ServerLevel.class);
+            Agent.getInstrumentation().retransformClasses(
+                    LevelStorageSource.LevelStorageAccess.class,
+                    ServerLevel.class
+            );
         } catch (Throwable e) {
-            IrisLogging.error(C.RED + "Failed to re-apply ServerLevel injection");
+            IrisLogging.error(C.RED + "Failed to re-apply Bukkit world lifecycle injection");
         }
     }
 
     @Override
     public void uninjectBukkit() {
         synchronized (injected) {
-            ResettableClassFileTransformer transformer = serverLevelTransformer;
+            ResettableClassFileTransformer activeServerLevel = serverLevelTransformer;
+            ResettableClassFileTransformer activeStorageAccess = levelStorageAccessTransformer;
             serverLevelTransformer = null;
+            levelStorageAccessTransformer = null;
             injected.set(false);
-            if (transformer == null) {
-                return;
-            }
-            try {
-                transformer.reset(Agent.getInstrumentation(), AgentBuilder.RedefinitionStrategy.RETRANSFORMATION);
-            } catch (Throwable e) {
-                IrisLogging.error(C.RED + "Failed to remove ServerLevel injection");
-                e.printStackTrace();
+            for (ResettableClassFileTransformer transformer : new ResettableClassFileTransformer[]{
+                    activeServerLevel,
+                    activeStorageAccess
+            }) {
+                if (transformer == null) {
+                    continue;
+                }
+                try {
+                    transformer.reset(Agent.getInstrumentation(), AgentBuilder.RedefinitionStrategy.RETRANSFORMATION);
+                } catch (Throwable e) {
+                    IrisLogging.error(C.RED + "Failed to remove Bukkit world lifecycle injection");
+                    e.printStackTrace();
+                }
             }
         }
     }
@@ -1616,103 +1639,7 @@ public class NMSBinding implements INMSBinding {
             Path targetWorldDirectory,
             long seed
     ) throws IOException {
-        CraftServer craftServer = (CraftServer) Bukkit.getServer();
-        MinecraftServer server = craftServer.getHandle().getServer();
-        PaperLevelOverrides levelOverrides = captureCurrentPaperLevelOverrides(craftServer, server);
-
-        Path targetWorld = targetWorldDirectory.toAbsolutePath().normalize();
-        UUID metadataUuid = UUID.randomUUID();
-        WorldReplacementSeed.copyWithAuthoritativeSeed(sourceWorldDirectory, targetWorld, seed);
-        try (SavedDataStorage savedDataStorage = new SavedDataStorage(
-                targetWorld.resolve("data"),
-                server.getFixerUpper(),
-                server.registryAccess()
-        )) {
-            savedDataStorage.set(PaperWorldMetadata.TYPE, new PaperWorldMetadata(metadataUuid));
-            savedDataStorage.set(
-                    PaperLevelOverrides.TYPE,
-                    levelOverrides
-            );
-        }
-
-        List<Path> requiredDataFiles = List.of(
-                targetWorld.resolve("data/minecraft/world_gen_settings.dat"),
-                targetWorld.resolve("data/paper/metadata.dat"),
-                targetWorld.resolve("data/paper/level_overrides.dat")
-        );
-        for (Path requiredDataFile : requiredDataFiles) {
-            if (!Files.isRegularFile(requiredDataFile, LinkOption.NOFOLLOW_LINKS)) {
-                throw new IOException("Current Paper world data was not written: " + requiredDataFile);
-            }
-        }
-
-        long writtenSeed = WorldReplacementSeed.readAuthoritativeSeed(targetWorld);
-        if (writtenSeed != seed) {
-            throw new IOException("Current Paper world data did not retain the requested seed.");
-        }
-
-        try (SavedDataStorage verificationStorage = new SavedDataStorage(
-                targetWorld.resolve("data"),
-                server.getFixerUpper(),
-                server.registryAccess()
-        )) {
-            PaperWorldMetadata metadata = verificationStorage.get(PaperWorldMetadata.TYPE);
-            if (metadata == null || !metadataUuid.equals(metadata.uuid())) {
-                throw new IOException("Current Paper world metadata could not be verified.");
-            }
-            PaperLevelOverrides overrides = verificationStorage.get(PaperLevelOverrides.TYPE);
-            if (overrides == null || overrides.isInitialized()) {
-                throw new IOException("Current Paper level overrides could not be verified.");
-            }
-        }
-    }
-
-    private PaperLevelOverrides captureCurrentPaperLevelOverrides(
-            CraftServer craftServer,
-            MinecraftServer server
-    ) throws IOException {
-        if (craftServer.isGlobalTickThread()) {
-            return createCurrentPaperLevelOverrides(craftServer, server);
-        }
-        if (J.isFolia() && J.isPrimaryThread()) {
-            throw new IOException("Current Paper world data cannot be staged from a Folia region tick thread.");
-        }
-
-        CompletableFuture<PaperLevelOverrides> captured = new CompletableFuture<>();
-        boolean scheduled = J.runGlobal(() -> {
-            try {
-                captured.complete(createCurrentPaperLevelOverrides(craftServer, server));
-            } catch (Throwable failure) {
-                captured.completeExceptionally(failure);
-            }
-        });
-        if (!scheduled) {
-            throw new IOException("Could not schedule the current Paper level-data snapshot on the global thread.");
-        }
-
-        try {
-            return captured.get(CURRENT_WORLD_DATA_SNAPSHOT_TIMEOUT_SECONDS, TimeUnit.SECONDS);
-        } catch (InterruptedException failure) {
-            Thread.currentThread().interrupt();
-            throw new IOException("Interrupted while capturing current Paper level data.", failure);
-        } catch (ExecutionException failure) {
-            throw new IOException("Could not capture current Paper level data.", failure.getCause());
-        } catch (TimeoutException failure) {
-            throw new IOException("Timed out while capturing current Paper level data.", failure);
-        }
-    }
-
-    private PaperLevelOverrides createCurrentPaperLevelOverrides(
-            CraftServer craftServer,
-            MinecraftServer server
-    ) throws IOException {
-        if (!craftServer.isGlobalTickThread()) {
-            throw new IOException("Current Paper level data must be captured on the global tick thread.");
-        }
-        if (!(server.getWorldData().overworldData() instanceof PrimaryLevelData primaryLevelData)) {
-            throw new IOException("Paper primary level data is unavailable for current world data staging.");
-        }
-        return PaperLevelOverrides.createFromLiveLevelData(primaryLevelData);
+        CurrentPaperWorldDataWriter.write(sourceWorldDirectory, targetWorldDirectory, seed);
     }
 
     @Override
@@ -1777,13 +1704,76 @@ public class NMSBinding implements INMSBinding {
         }
     }
 
+    private static class LevelStorageAccessAdvice {
+        @Advice.OnMethodEnter
+        static void enter(
+                @Advice.Argument(1) String levelId,
+                @Advice.Argument(value = 3, readOnly = false) ResourceKey<LevelStem> dimensionType
+        ) {
+            if (levelId == null || levelId.isBlank()) {
+                return;
+            }
+
+            ClassLoader pluginClassLoader;
+            Class<?> generatorType;
+            Class<?> stagingType;
+            try {
+                org.bukkit.plugin.Plugin irisPlugin = Bukkit.getPluginManager().getPlugin("Iris");
+                if (irisPlugin == null) {
+                    return;
+                }
+                pluginClassLoader = irisPlugin.getClass().getClassLoader();
+                generatorType = Class.forName("art.arcane.iris.engine.platform.PlatformChunkGenerator", true, pluginClassLoader);
+                stagingType = Class.forName("art.arcane.iris.core.lifecycle.WorldLifecycleStaging", true, pluginClassLoader);
+            } catch (Throwable ignored) {
+                return;
+            }
+
+            Object generator;
+            try {
+                generator = stagingType
+                        .getDeclaredMethod("peekStemGenerator", String.class)
+                        .invoke(null, levelId);
+            } catch (Throwable e) {
+                throw new RuntimeException("Iris failed to inspect the staged world generator",
+                        e instanceof InvocationTargetException ex ? ex.getCause() : e);
+            }
+            if (generator == null || !generatorType.isInstance(generator)) {
+                return;
+            }
+
+            try {
+                Object target = generatorType.getMethod("getTarget").invoke(generator);
+                if (target == null) {
+                    throw new IllegalStateException("Iris generator has no engine target.");
+                }
+                Object world = target.getClass().getMethod("getWorld").invoke(target);
+                if (world == null) {
+                    throw new IllegalStateException("Iris generator target has no world identity.");
+                }
+                Object rawIdentity = world.getClass().getMethod("identity").invoke(world);
+                String worldIdentity = rawIdentity == null ? "" : rawIdentity.toString().trim();
+                Identifier worldIdentifier = Identifier.parse(worldIdentity);
+                if (!"iris".equals(worldIdentifier.getNamespace())
+                        && !"minecraft".equals(worldIdentifier.getNamespace())) {
+                    throw new IllegalStateException(
+                            "Iris generator has an unmanaged world identity: " + worldIdentity);
+                }
+                dimensionType = ResourceKey.create(Registries.LEVEL_STEM, worldIdentifier);
+            } catch (Throwable e) {
+                throw new RuntimeException("Iris failed to bind the staged world storage identity",
+                        e instanceof InvocationTargetException ex ? ex.getCause() : e);
+            }
+        }
+    }
+
     private static class ServerLevelAdvice {
         @Advice.OnMethodEnter
         static void enter(
                 @Advice.Argument(0) MinecraftServer server,
-                @Advice.Argument(4) ResourceKey<Level> dimensionKey,
+                @Advice.Argument(value = 4, readOnly = false) ResourceKey<Level> dimensionKey,
                 @Advice.Argument(value = 5, readOnly = false) LevelStem levelStem,
-                @Advice.Argument(12) ChunkGenerator constructorGenerator
+                @Advice.AllArguments Object[] constructorArguments
         ) {
             if (dimensionKey == null)
                 return;
@@ -1818,6 +1808,13 @@ public class NMSBinding implements INMSBinding {
             // the vanilla stem corrupts generation.
             ChunkGenerator gen = null;
             try {
+                ChunkGenerator constructorGenerator = null;
+                for (Object argument : constructorArguments) {
+                    if (argument instanceof ChunkGenerator candidate) {
+                        constructorGenerator = candidate;
+                        break;
+                    }
+                }
                 Object generator = generatorType.isInstance(constructorGenerator) ? constructorGenerator : null;
                 if (generator == null) {
                     generator = stagingType
@@ -1855,10 +1852,27 @@ public class NMSBinding implements INMSBinding {
                 if (stemMethod == null) {
                     throw new IllegalStateException("Iris binding is missing createRuntimeLevelStem.");
                 }
+                Object target = generatorType.getMethod("getTarget").invoke(gen);
+                if (target == null) {
+                    throw new IllegalStateException("Iris generator has no engine target.");
+                }
+                Object world = target.getClass().getMethod("getWorld").invoke(target);
+                if (world == null) {
+                    throw new IllegalStateException("Iris generator target has no world identity.");
+                }
+                Object rawIdentity = world.getClass().getMethod("identity").invoke(world);
+                String worldIdentity = rawIdentity == null ? "" : rawIdentity.toString().trim();
+                Identifier worldIdentifier = Identifier.parse(worldIdentity);
+                if (!"iris".equals(worldIdentifier.getNamespace())
+                        && !"minecraft".equals(worldIdentifier.getNamespace())) {
+                    throw new IllegalStateException(
+                            "Iris generator has an unmanaged world identity: " + worldIdentity);
+                }
                 Object resolvedStem = stemMethod.invoke(bindings, server.registryAccess(), gen);
                 if (!(resolvedStem instanceof LevelStem runtimeStem)) {
                     throw new IllegalStateException("Iris runtime LevelStem binding returned " + (resolvedStem == null ? "null" : resolvedStem.getClass().getName()) + ".");
                 }
+                dimensionKey = ResourceKey.create(Registries.DIMENSION, worldIdentifier);
                 levelStem = runtimeStem;
             } catch (Throwable e) {
                 throw new RuntimeException("Iris failed to replace the levelStem", e instanceof InvocationTargetException ex ? ex.getCause() : e);

adapters/bukkit/nms/v26_2_R1/src/main/java/art/arcane/iris/core/nms/v26_2_R1/NativeStructureWorldgenAccess.java

@@ -215,6 +215,14 @@ final class NativeStructureWorldgenAccess implements WorldGenLevel {
         }
     }
 
+    @Override
+    public ChunkAccess getChunk(int chunkX, int chunkZ) {
+        if (isInsideGenerationRegion(chunkX, chunkZ)) {
+            return delegate.getChunk(chunkX, chunkZ);
+        }
+        return outsideChunk(chunkX, chunkZ);
+    }
+
     @Override
     public ChunkAccess getChunk(int chunkX, int chunkZ, ChunkStatus status, boolean create) {
         if (isInsideGenerationRegion(chunkX, chunkZ)) {

adapters/bukkit/nms/v26_2_R1/src/test/java/art/arcane/iris/core/nms/v26_2_R1/NMSBindingCurrentPaperWorldDataContractTest.java

@@ -3,29 +3,54 @@ package art.arcane.iris.core.nms.v26_2_R1;
 import art.arcane.iris.core.nms.INMSBinding;
 import org.junit.Test;
 
+import java.io.InputStream;
 import java.lang.reflect.InvocationHandler;
 import java.lang.reflect.Proxy;
+import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.nio.file.Path;
 
 import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertThrows;
 import static org.junit.Assert.assertTrue;
 
 public class NMSBindingCurrentPaperWorldDataContractTest {
     @Test
-    public void stagesAllCurrentPaperWorldDataFromLiveServerState() throws Exception {
-        String source = Files.readString(Path.of(System.getProperty("iris.nmsBindingSource")));
+    public void bindingDelegatesWithoutLinkingPaperSavedDataClasses() throws Exception {
+        String bindingSource = Files.readString(bindingSourcePath());
         String writer = section(
-                source,
+                bindingSource,
                 "public void writeCurrentPaperWorldData(",
-                "public KMap<Material, List<BlockProperty>> getBlockProperties()"
+                "public boolean awaitServerShutdownBoundary("
         );
 
+        assertTrue(writer.contains("CurrentPaperWorldDataWriter.write("));
+        assertFalse(bindingSource.contains("PaperWorldMetadata"));
+        assertFalse(bindingSource.contains("PaperLevelOverrides"));
+        assertFalse(bindingSource.contains("io.papermc.paper.world.saveddata"));
+
+        InputStream classResource = NMSBindingCurrentPaperWorldDataContractTest.class
+                .getResourceAsStream("NMSBinding.class");
+        assertNotNull(classResource);
+        try (InputStream input = classResource) {
+            String classFile = new String(input.readAllBytes(), StandardCharsets.ISO_8859_1);
+            assertFalse(classFile.contains("PaperWorldMetadata"));
+            assertFalse(classFile.contains("PaperLevelOverrides"));
+            assertFalse(classFile.contains("io/papermc/paper/world/saveddata"));
+        }
+    }
+
+    @Test
+    public void stagesAllCurrentPaperWorldDataFromLiveServerState() throws Exception {
+        String writer = Files.readString(writerSourcePath());
+
         assertTrue(writer.contains("WorldReplacementSeed.copyWithAuthoritativeSeed("));
         assertTrue(writer.contains("UUID metadataUuid = UUID.randomUUID()"));
         assertTrue(writer.contains("new PaperWorldMetadata(metadataUuid)"));
-        assertTrue(writer.contains("captureCurrentPaperLevelOverrides(craftServer, server)"));
+        assertTrue(writer.contains("captureLevelOverrides(craftServer, server)"));
+        assertTrue(writer.indexOf("captureLevelOverrides(craftServer, server)")
+                < writer.indexOf("WorldReplacementSeed.copyWithAuthoritativeSeed("));
         assertTrue(writer.contains("new SavedDataStorage("));
         assertTrue(writer.contains("server.getFixerUpper()"));
         assertTrue(writer.contains("server.registryAccess()"));
@@ -44,23 +69,23 @@ public class NMSBindingCurrentPaperWorldDataContractTest {
 
     @Test
     public void capturesOnlyLiveLevelOverridesOnTheGlobalThread() throws Exception {
-        String source = Files.readString(Path.of(System.getProperty("iris.nmsBindingSource")));
+        String source = Files.readString(writerSourcePath());
         String capture = section(
                 source,
-                "private PaperLevelOverrides captureCurrentPaperLevelOverrides(",
-                "private PaperLevelOverrides createCurrentPaperLevelOverrides("
+                "private static PaperLevelOverrides captureLevelOverrides(",
+                "private static PaperLevelOverrides createLevelOverrides("
         );
         String create = section(
                 source,
-                "private PaperLevelOverrides createCurrentPaperLevelOverrides(",
-                "public KMap<Material, List<BlockProperty>> getBlockProperties()"
+                "private static PaperLevelOverrides createLevelOverrides(",
+                "\n    }\n}"
         );
 
         assertTrue(capture.contains("craftServer.isGlobalTickThread()"));
         assertTrue(capture.contains("J.isFolia() && J.isPrimaryThread()"));
         assertTrue(capture.contains("J.runGlobal("));
-        assertTrue(capture.contains("createCurrentPaperLevelOverrides(craftServer, server)"));
-        assertTrue(capture.contains("captured.get(CURRENT_WORLD_DATA_SNAPSHOT_TIMEOUT_SECONDS"));
+        assertTrue(capture.contains("createLevelOverrides(craftServer, server)"));
+        assertTrue(capture.contains("captured.get(SNAPSHOT_TIMEOUT_SECONDS"));
         assertTrue(capture.contains("Thread.currentThread().interrupt()"));
         assertTrue(create.contains("if (!craftServer.isGlobalTickThread())"));
         assertTrue(create.indexOf("if (!craftServer.isGlobalTickThread())")
@@ -89,6 +114,14 @@ public class NMSBindingCurrentPaperWorldDataContractTest {
         assertTrue(error.getMessage().contains("does not support current Paper world data staging"));
     }
 
+    private static Path bindingSourcePath() {
+        return Path.of(System.getProperty("iris.nmsBindingSource"));
+    }
+
+    private static Path writerSourcePath() {
+        return bindingSourcePath().resolveSibling("CurrentPaperWorldDataWriter.java");
+    }
+
     private static String section(String source, String startMarker, String endMarker) {
         int start = source.indexOf(startMarker);
         int end = source.indexOf(endMarker, start);

adapters/bukkit/nms/v26_2_R1/src/test/java/art/arcane/iris/core/nms/v26_2_R1/NMSBindingDatapackStructureScopeTest.java

@@ -27,6 +27,8 @@ import org.junit.Test;
 import org.junit.BeforeClass;
 
 import java.io.IOException;
+import java.io.InputStream;
+import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.List;
@@ -38,8 +40,8 @@ import java.util.stream.Stream;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotSame;
+import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertSame;
-import static org.junit.Assert.assertThrows;
 import static org.junit.Assert.assertTrue;
 
 public class NMSBindingDatapackStructureScopeTest {
@@ -108,28 +110,56 @@ public class NMSBindingDatapackStructureScopeTest {
     }
 
     @Test
-    public void spigotDirectHolderRetainsItsStructureSetKey() {
+    public void spigotDirectHolderRecoversItsRegistryKeyFromSharedEntries() {
         ResourceKey<StructureSet> key = ResourceKey.create(
                 Registries.STRUCTURE_SET,
-                Identifier.parse("minecraft:villages"));
-        ChunkGeneratorStructureState.KeyedRandomSpreadStructurePlacement placement =
-                new ChunkGeneratorStructureState.KeyedRandomSpreadStructurePlacement(
-                        key,
-                        Vec3i.ZERO,
-                        StructurePlacement.FrequencyReductionMethod.DEFAULT,
-                        1.0F,
-                        10387312,
-                        Optional.empty(),
-                        34,
-                        8,
-                        RandomSpreadType.LINEAR);
-        StructureSet structureSet = new StructureSet(
-                List.of(new StructureSet.StructureSelectionEntry(
-                        structureHolder("minecraft:village_plains"), 1)),
-                placement);
+                Identifier.parse("managed:illager_barracks"));
+        List<StructureSet.StructureSelectionEntry> entries = List.of(
+                new StructureSet.StructureSelectionEntry(
+                        structureHolder("minecraft:pillager_outpost"), 1));
+        Holder<StructureSet> registered = new KeyedHolder<>(key, new StructureSet(
+                entries,
+                new RandomSpreadStructurePlacement(
+                        34, 8, RandomSpreadType.LINEAR, 10387312)));
+        Holder<StructureSet> spigotDirect = Holder.direct(new StructureSet(
+                entries,
+                new RandomSpreadStructurePlacement(
+                        34, 8, RandomSpreadType.LINEAR, 14357620)));
+        DatapackStructureScopeIndex scopeIndex = index(
+                List.of(), List.of("managed:illager_barracks"));
+        DatapackStructureStateFilter.StructureSetKeyIndex keyIndex =
+                DatapackStructureStateFilter.keyIndex(List.of(registered));
 
-        assertEquals("minecraft:villages",
-                DatapackStructureStateFilter.structureSetKey(Holder.direct(structureSet)));
+        DatapackStructureStateFilter.Selection excluded =
+                DatapackStructureStateFilter.filter(
+                        List.of(spigotDirect),
+                        scopeIndex,
+                        Set.of(),
+                        new IrisImportedStructureControl(),
+                        keyIndex);
+        DatapackStructureStateFilter.Selection retained =
+                DatapackStructureStateFilter.filter(
+                        List.of(spigotDirect),
+                        scopeIndex,
+                        scopeIndex.declaredSources(List.of(SOURCE)),
+                        new IrisImportedStructureControl(),
+                        keyIndex);
+
+        assertEquals(0, excluded.structureSets().size());
+        assertEquals(1, excluded.excludedManagedSets());
+        assertSame(spigotDirect, retained.structureSets().getFirst());
+        assertEquals(1, retained.retainedManagedSets());
+    }
+
+    @Test
+    public void structureScopeDoesNotLinkPaperOnlyPlacementClasses() throws IOException {
+        InputStream classResource = NMSBindingDatapackStructureScopeTest.class
+                .getResourceAsStream("DatapackStructureStateFilter.class");
+        assertNotNull(classResource);
+        try (InputStream input = classResource) {
+            String classFile = new String(input.readAllBytes(), StandardCharsets.ISO_8859_1);
+            assertFalse(classFile.contains("KeyedRandomSpreadStructurePlacement"));
+        }
     }
 
     @Test
@@ -271,7 +301,7 @@ public class NMSBindingDatapackStructureScopeTest {
     }
 
     @Test
-    public void affectedRandomSpreadSubclassFailsInsteadOfLosingSubtypeBehavior() {
+    public void randomSpreadSubtypeUsesTheCanonicalPlacementContract() {
         Holder<StructureSet> custom = structureSetHolder(
                 "example:custom",
                 new CustomRandomSpreadPlacement(),
@@ -283,8 +313,12 @@ public class NMSBindingDatapackStructureScopeTest {
         IrisImportedStructureControl control = new IrisImportedStructureControl()
                 .setFrequencyOverrides(overrides);
 
-        assertThrows(IllegalStateException.class, () -> DatapackStructureStateFilter.filter(
-                List.of(custom), index(List.of(), List.of()), Set.of(), control));
+        DatapackStructureStateFilter.Selection selection = DatapackStructureStateFilter.filter(
+                List.of(custom), index(List.of(), List.of()), Set.of(), control);
+        StructurePlacement placement = selection.structureSets().getFirst().value().placement();
+
+        assertEquals(RandomSpreadStructurePlacement.class, placement.getClass());
+        assertEquals(26, ((RandomSpreadStructurePlacement) placement).spacing());
     }
 
     @Test
@@ -395,6 +429,21 @@ public class NMSBindingDatapackStructureScopeTest {
         assertTrue(structureRetarget > identityGate);
     }
 
+    @Test
+    public void structureStateRecreationUsesTheWorldOwnedSpigotConfiguration() throws IOException {
+        Path chunkGeneratorSource = Path.of(System.getProperty("iris.nmsChunkGeneratorSource"));
+        String source = Files.readString(chunkGeneratorSource.resolveSibling("NMSBinding.java"));
+        int methodStart = source.indexOf("private ChunkGeneratorStructureState createStructureState(");
+        int methodEnd = source.indexOf(
+                "\n    private void initializeAndPublishStructureState(", methodStart);
+
+        assertTrue(methodStart >= 0);
+        assertTrue(methodEnd > methodStart);
+        String method = source.substring(methodStart, methodEnd);
+        assertTrue(method.contains("level.spigotConfig"));
+        assertFalse(method.contains("currentState.conf"));
+    }
+
     private static DatapackStructureScopeIndex index(
             List<String> structureKeys,
             List<String> structureSetKeys

adapters/bukkit/nms/v26_2_R1/src/test/java/art/arcane/iris/core/nms/v26_2_R1/NMSBindingServerLevelAdviceContractTest.java

@@ -0,0 +1,103 @@
+package art.arcane.iris.core.nms.v26_2_R1;
+
+import org.junit.Test;
+
+import java.nio.file.Files;
+import java.nio.file.Path;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+public class NMSBindingServerLevelAdviceContractTest {
+    @Test
+    public void serverLevelAdviceSupportsCurrentSpigotAndPaperConstructorLayouts() throws Exception {
+        String source = Files.readString(
+                Path.of(System.getProperty("iris.nmsBindingSource")));
+        String transformer = section(
+                source,
+                "public boolean injectBukkit()",
+                "public void ensureServerLevelInjection()");
+        String advice = section(
+                source,
+                "private static class ServerLevelAdvice",
+                "\n    }\n}");
+
+        assertTrue(transformer.contains("takesArgument(0, MinecraftServer.class)"));
+        assertTrue(transformer.contains("takesArgument(5, LevelStem.class)"));
+        assertFalse(transformer.contains("takesArgument(12, ChunkGenerator.class)"));
+        assertFalse(transformer.contains("takesArgument(13, ChunkGenerator.class)"));
+        assertTrue(advice.contains("@Advice.AllArguments Object[] constructorArguments"));
+        assertTrue(advice.contains("argument instanceof ChunkGenerator candidate"));
+        assertFalse(advice.contains("@Advice.Argument(12)"));
+        assertFalse(advice.contains("@Advice.Argument(13)"));
+    }
+
+    @Test
+    public void currentSpigotStorageAccessReceivesManagedIdentityBeforeConstruction() throws Exception {
+        String source = Files.readString(
+                Path.of(System.getProperty("iris.nmsBindingSource")));
+        String transformer = section(
+                source,
+                "public boolean injectBukkit()",
+                "public void ensureServerLevelInjection()");
+        String advice = section(
+                source,
+                "private static class LevelStorageAccessAdvice",
+                "private static class ServerLevelAdvice");
+
+        assertTrue(transformer.contains(
+                ".type(ElementMatchers.is(LevelStorageSource.LevelStorageAccess.class))"));
+        assertTrue(transformer.contains("Advice.to(LevelStorageAccessAdvice.class)"));
+        assertTrue(transformer.contains("ElementMatchers.takesArguments(4)"));
+        assertTrue(transformer.contains(
+                "ElementMatchers.takesArgument(0, LevelStorageSource.class)"));
+        assertTrue(transformer.contains("ElementMatchers.takesArgument(1, String.class)"));
+        assertTrue(transformer.contains("ElementMatchers.takesArgument(2, Path.class)"));
+        assertTrue(transformer.contains("ElementMatchers.takesArgument(3, ResourceKey.class)"));
+        assertTrue(advice.contains("@Advice.Argument(1) String levelId"));
+        assertTrue(advice.contains(
+                "@Advice.Argument(value = 3, readOnly = false) ResourceKey<LevelStem> dimensionType"));
+        assertTrue(advice.contains("getDeclaredMethod(\"peekStemGenerator\", String.class)"));
+        assertTrue(advice.contains(".invoke(null, levelId)"));
+        assertTrue(advice.contains(
+                "dimensionType = ResourceKey.create(Registries.LEVEL_STEM, worldIdentifier);"));
+        assertFalse(advice.contains("dimensionRoot("));
+        assertFalse(advice.contains("Files.copy"));
+    }
+
+    @Test
+    public void ownedWorldPublishesItsManagedIdentityAndRuntimeStemTogether() throws Exception {
+        String source = Files.readString(
+                Path.of(System.getProperty("iris.nmsBindingSource")));
+        String advice = section(
+                source,
+                "private static class ServerLevelAdvice",
+                "\n    }\n}");
+
+        assertTrue(advice.contains(
+                "@Advice.Argument(value = 4, readOnly = false) ResourceKey<Level> dimensionKey"));
+        assertTrue(advice.contains("getMethod(\"getTarget\")"));
+        assertTrue(advice.contains("getMethod(\"getWorld\")"));
+        assertTrue(advice.contains("getMethod(\"identity\")"));
+        assertTrue(advice.contains("\"iris\".equals(worldIdentifier.getNamespace())"));
+        assertTrue(advice.contains("\"minecraft\".equals(worldIdentifier.getNamespace())"));
+
+        int resolvedStem = advice.indexOf("Object resolvedStem = stemMethod.invoke(");
+        int validatedStem = advice.indexOf("resolvedStem instanceof LevelStem runtimeStem");
+        int identityPublication = advice.indexOf(
+                "dimensionKey = ResourceKey.create(Registries.DIMENSION, worldIdentifier);");
+        int stemPublication = advice.indexOf("levelStem = runtimeStem;");
+        assertTrue(resolvedStem >= 0);
+        assertTrue(validatedStem > resolvedStem);
+        assertTrue(identityPublication > validatedStem);
+        assertTrue(stemPublication > identityPublication);
+    }
+
+    private static String section(String source, String startMarker, String endMarker) {
+        int start = source.indexOf(startMarker);
+        int end = source.indexOf(endMarker, start);
+        assertTrue("Missing source section starting with " + startMarker, start >= 0);
+        assertTrue("Missing source section ending with " + endMarker, end > start);
+        return source.substring(start, end);
+    }
+}

adapters/bukkit/nms/v26_2_R1/src/test/java/art/arcane/iris/core/nms/v26_2_R1/NativeStructureWorldgenAccessTest.java

@@ -135,6 +135,18 @@ public class NativeStructureWorldgenAccessTest {
         assertEquals(1, recording.blockTicks.count());
     }
 
+    @Test
+    public void statuslessChunkReadsPreserveWorldgenDelegateSemantics() {
+        RecordingDelegate recording = new RecordingDelegate();
+        NativeStructureWorldgenAccess access = access(recording);
+        ChunkPos generationCenter = generationCenter();
+
+        assertNull(access.getChunk(generationCenter.getWorldPosition()));
+
+        assertEquals(1, recording.statuslessChunkReads);
+        assertEquals(0, recording.statusChunkReads);
+    }
+
     @Test
     public void entityQueriesRejectDisjointAreasAndClampOverlaps() {
         RecordingDelegate recording = new RecordingDelegate();
@@ -187,6 +199,8 @@ public class NativeStructureWorldgenAccessTest {
         private int terrainReads;
         private int heightReads;
         private int chunkReads;
+        private int statuslessChunkReads;
+        private int statusChunkReads;
         private int mutations;
         private int events;
 
@@ -240,7 +254,16 @@ public class NativeStructureWorldgenAccessTest {
                 terrainReads++;
                 return Blocks.WATER.defaultBlockState().getFluidState();
             }
-            if (name.equals("getChunk") || name.equals("getChunkIfLoadedImmediately")) {
+            if (name.equals("getChunk")) {
+                chunkReads++;
+                if (arguments.length == 2) {
+                    statuslessChunkReads++;
+                } else {
+                    statusChunkReads++;
+                }
+                return null;
+            }
+            if (name.equals("getChunkIfLoadedImmediately")) {
                 chunkReads++;
                 return null;
             }

adapters/bukkit/plugin/build.gradle

@@ -3,7 +3,7 @@ def mainClass = 'art.arcane.iris.Iris'
 def bootstrapperClass = 'art.arcane.iris.IrisBootstrap'
 
 String volmLibCoordinate = providers.gradleProperty('volmLibCoordinate')
-    .orElse('com.github.VolmitSoftware:VolmLib:d9026a7c8ebc391c8109f401ce79a0ce65df3969')
+    .orElse('com.github.VolmitSoftware:VolmLib:5486ac97ad6d6833e27275dc768222d377721522')
     .get()
 
 dependencies {

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

@@ -756,6 +756,7 @@ public class Iris extends VolmitPlugin implements Listener, ReloadAware {
         IrisStartupValidation.begin();
         Bukkit.getPluginManager().registerEvents(new IrisStartupAdmissionListener(), this);
         Bukkit.getPluginManager().registerEvents(pendingWorldReplacements, this);
+        pendingWorldReplacements.registerPlatformEntryListener();
         boolean enabled = enable();
         if (!enabled) {
             return;

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

@@ -22,13 +22,13 @@ import art.arcane.iris.Iris;
 import art.arcane.iris.core.lifecycle.BukkitWorldConfiguration;
 import art.arcane.iris.core.lifecycle.LifecycleOperationCoordinator;
 import art.arcane.iris.core.nms.INMS;
-import art.arcane.iris.core.pack.PackValidationRegistry;
 import art.arcane.iris.core.tools.IrisToolbelt;
 import art.arcane.iris.engine.object.IrisDimension;
 import art.arcane.iris.platform.bukkit.BukkitEnvironment;
 import art.arcane.iris.util.common.format.C;
 import art.arcane.iris.util.common.misc.ServerProperties;
 import art.arcane.volmlib.util.bukkit.WorldIdentity;
+import org.bukkit.Bukkit;
 import org.bukkit.NamespacedKey;
 import org.bukkit.World;
 import org.bukkit.WorldCreator;
@@ -698,16 +698,17 @@ public final class BukkitWorldReconciler {
         @Override
         public CompletableFuture<World> createWorld(NamespacedKey worldKey, String dimension, Long seed) {
             try {
-                String worldName = IrisWorldStorage.logicalName(worldKey);
-                Iris.info("Loading World: %s | Generator: %s", worldName, dimension);
-                ChunkGenerator generator = plugin.getDefaultWorldGenerator(worldName, dimension);
-                IrisDimension irisDimension = IrisWorldGeneratorResolver.loadDimension(worldName, dimension);
+                String logicalWorldName = IrisWorldStorage.logicalName(worldKey);
+                String configuredWorldName = configuredWorldName(worldKey);
+                Iris.info("Loading World: %s | Generator: %s", logicalWorldName, dimension);
+                ChunkGenerator generator = plugin.getDefaultWorldGenerator(configuredWorldName, dimension);
+                IrisDimension irisDimension = IrisWorldGeneratorResolver.loadDimension(configuredWorldName, dimension);
                 if (generator == null || irisDimension == null) {
                     throw new IllegalStateException("Could not resolve the Iris generator or dimension \"" + dimension + "\".");
                 }
 
-                Iris.info(C.LIGHT_PURPLE + "Preparing Spawn for " + worldName + " using Iris:" + dimension + "...");
-                WorldCreator creator = WorldCreatorCompat.ofKey(worldKey)
+                Iris.info(C.LIGHT_PURPLE + "Preparing Spawn for " + logicalWorldName + " using Iris:" + dimension + "...");
+                WorldCreator creator = WorldCreatorCompat.ofPersistentKey(worldKey)
                         .generator(generator)
                         .environment(BukkitEnvironment.from(irisDimension.getEnvironment()));
                 if (seed != null) {
@@ -726,7 +727,7 @@ public final class BukkitWorldReconciler {
 
         @Override
         public DimensionResolution resolveDimension(NamespacedKey worldKey) {
-            File dimensionsDirectory = new File(IrisWorldStorage.packRoot(worldKey), "dimensions");
+            File dimensionsDirectory = new File(snapshotRoot(worldKey), "dimensions");
             if (!dimensionsDirectory.isDirectory()) {
                 return DimensionResolution.failed(new IllegalStateException("The world has no Iris dimensions directory."));
             }
@@ -764,19 +765,30 @@ public final class BukkitWorldReconciler {
 
         @Override
         public void requireDimensionLoadable(NamespacedKey worldKey, String dimension) {
-            File snapshotRoot = IrisWorldStorage.packRoot(worldKey);
-            boolean snapshotPresent = snapshotRoot.isDirectory();
-            if (snapshotPresent) {
-                IrisWorldGeneratorResolver.requireSnapshotLoadable(snapshotRoot);
-            }
-            String worldName = IrisWorldStorage.logicalName(worldKey);
-            IrisDimension irisDimension = IrisWorldGeneratorResolver.loadDimension(worldName, dimension);
+            File snapshotRoot = snapshotRoot(worldKey);
+            IrisWorldGeneratorResolver.requireSnapshotLoadable(snapshotRoot);
+            String configuredWorldName = configuredWorldName(worldKey);
+            IrisDimension irisDimension = IrisWorldGeneratorResolver.loadDimension(configuredWorldName, dimension);
             if (irisDimension == null) {
                 throw new IllegalStateException("Could not resolve the Iris dimension \"" + dimension + "\".");
             }
-            if (!snapshotPresent) {
-                PackValidationRegistry.requireLoadable(irisDimension.getLoader().getDataFolder().getName());
+        }
+
+        private File snapshotRoot(NamespacedKey worldKey) {
+            File levelRoot = IrisWorldStorage.levelRoot();
+            File dimensionRoot = IrisWorldStorage.requireFrozenDimensionRoot(
+                    Bukkit.getWorldContainer(),
+                    levelRoot,
+                    configuredWorldName(worldKey),
+                    worldKey
+            );
+            File expectedRoot = WorldCreatorCompat.persistentDimensionRoot(worldKey);
+            if (!dimensionRoot.toPath().toAbsolutePath().normalize()
+                    .equals(expectedRoot.toPath().toAbsolutePath().normalize())) {
+                throw new IllegalStateException("Iris world storage does not match the current platform layout for "
+                        + worldKey + ".");
             }
+            return IrisWorldStorage.requireFrozenPackRoot(dimensionRoot);
         }
     }
 }

adapters/bukkit/plugin/src/main/java/art/arcane/iris/core/IrisStartupAdmissionListener.java

@@ -1,6 +1,5 @@
 package art.arcane.iris.core;
 
-import net.kyori.adventure.text.Component;
 import org.bukkit.event.EventHandler;
 import org.bukkit.event.EventPriority;
 import org.bukkit.event.Listener;
@@ -11,6 +10,6 @@ public final class IrisStartupAdmissionListener implements Listener {
     public void onAsyncPlayerPreLogin(AsyncPlayerPreLoginEvent event) {
         IrisStartupValidation.denialReason().ifPresent(reason -> event.disallow(
                 AsyncPlayerPreLoginEvent.Result.KICK_OTHER,
-                Component.text(reason + " Check the server console, correct the reported Iris state, and restart.")));
+                reason + " Check the server console, correct the reported Iris state, and restart."));
     }
 }

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

@@ -29,12 +29,12 @@ import art.arcane.iris.core.pack.PackValidationRegistry;
 import art.arcane.iris.core.pack.PackValidationResult;
 import art.arcane.iris.core.pack.PackValidator;
 import art.arcane.iris.spi.IrisPlatforms;
-import art.arcane.iris.core.service.StudioSVC;
 import art.arcane.iris.engine.object.IrisDimension;
 import art.arcane.iris.engine.object.IrisWorld;
 import art.arcane.iris.engine.platform.BukkitChunkGenerator;
 import art.arcane.iris.util.common.plugin.VolmitPlugin;
 import lombok.NonNull;
+import org.bukkit.Bukkit;
 import org.bukkit.NamespacedKey;
 import org.bukkit.generator.BiomeProvider;
 import org.bukkit.generator.ChunkGenerator;
@@ -231,9 +231,18 @@ public final class IrisWorldGeneratorResolver {
 
     @Nullable
     public static IrisDimension loadDimension(@NonNull String worldName, @NonNull String id) {
-        NamespacedKey worldKey = configuredWorldKey(worldName, IrisWorldStorage.levelRoot().getName());
-        File pack = IrisWorldStorage.packRoot(worldKey);
-        IrisDimension dimension = pack.isDirectory() ? IrisData.get(pack).getDimensionLoader().load(id) : null;
+        File levelRoot = IrisWorldStorage.levelRoot();
+        NamespacedKey worldKey = configuredWorldKey(worldName, levelRoot.getName());
+        String configuredWorldName = IrisWorldStorage.configuredWorldName(worldKey, levelRoot.getName());
+        File pack = IrisWorldStorage.frozenDimensionRoot(
+                        Bukkit.getWorldContainer(),
+                        levelRoot,
+                        configuredWorldName,
+                        worldKey
+                )
+                .map(IrisWorldStorage::requireFrozenPackRoot)
+                .orElse(null);
+        IrisDimension dimension = pack == null ? null : IrisData.get(pack).getDimensionLoader().load(id);
         if (dimension == null) dimension = IrisData.loadAnyDimension(id, null);
         if (dimension == null) {
             File packsRoot = IrisPlatforms.get().packsFolderNoCreate();
@@ -279,57 +288,63 @@ public final class IrisWorldGeneratorResolver {
         if (id == null || id.isEmpty()) id = IrisSettings.get().getGenerator().getDefaultWorldType();
         Iris.debug("Generator ID: " + id + " requested by bukkit/plugin");
 
-        IrisDimension dim = loadDimension(worldName, id);
-        if (dim == null) {
-            throw new RuntimeException("Can't find dimension " + id + "!");
-        }
-        NamespacedKey worldKey = configuredWorldKey(worldName, IrisWorldStorage.levelRoot().getName());
-        File snapshotRoot = IrisWorldStorage.packRoot(worldKey);
-        File dimensionPackRoot = dim.getLoader().getDataFolder();
-        String packName = dimensionPackRoot.getName();
         try {
-            if (snapshotRoot.toPath().toAbsolutePath().normalize()
-                    .equals(dimensionPackRoot.toPath().toAbsolutePath().normalize())) {
-                requireSnapshotLoadable(snapshotRoot);
-            } else {
-                PackValidationRegistry.requireLoadable(packName);
-            }
+            return resolveFrozenWorldGenerator(worldName, id);
+        } catch (RuntimeException failure) {
+            Iris.reportError("Refusing to load configured Iris world '" + worldName
+                    + "' because its frozen world-local pack snapshot could not be used.", failure);
+            Bukkit.shutdown();
+            throw failure;
+        }
+    }
+
+    private ChunkGenerator resolveFrozenWorldGenerator(String worldName, String id) {
+        File levelRoot = IrisWorldStorage.levelRoot();
+        NamespacedKey worldKey = configuredWorldKey(worldName, levelRoot.getName());
+        File dimensionRoot = IrisWorldStorage.requireFrozenDimensionRoot(
+                Bukkit.getWorldContainer(),
+                levelRoot,
+                worldName,
+                worldKey
+        );
+        File expectedDimensionRoot = WorldCreatorCompat.persistentDimensionRoot(worldKey);
+        if (!dimensionRoot.toPath().toAbsolutePath().normalize()
+                .equals(expectedDimensionRoot.toPath().toAbsolutePath().normalize())) {
+            throw new IllegalStateException("Frozen Iris world storage does not match the current platform layout for "
+                    + worldKey + ".");
+        }
+        File snapshotRoot = IrisWorldStorage.requireFrozenPackRoot(dimensionRoot);
+        try {
+            requireSnapshotLoadable(snapshotRoot);
         } catch (BrokenPackException exception) {
-            Iris.error("Refusing to create world '" + worldName + "' using broken pack '" + packName + "':");
+            Iris.error("Refusing to create world '" + worldName + "' using broken snapshot at '"
+                    + snapshotRoot + "':");
             for (String reason : exception.getReasons()) {
                 Iris.error("  - " + reason);
             }
             throw exception;
         }
 
-        Iris.debug("Assuming IrisDimension: " + dim.getName());
+        IrisDimension dimension = IrisData.get(snapshotRoot).getDimensionLoader().load(id, false);
+        if (dimension == null) {
+            throw new IllegalStateException("Frozen Iris pack snapshot at " + snapshotRoot
+                    + " does not contain dimension " + id + ".");
+        }
 
-        IrisWorld w = IrisWorld.builder()
+        Iris.debug("Assuming IrisDimension: " + dimension.getName());
+
+        IrisWorld world = IrisWorld.builder()
                 .platformIdentity(worldKey.toString())
                 .name(worldName)
                 .seed(1337)
-                .worldFolder(IrisWorldStorage.dimensionRoot(worldKey))
-                .minHeight(dim.getMinHeight())
-                .maxHeight(dim.getMaxHeight())
+                .worldFolder(dimensionRoot)
+                .minHeight(dimension.getMinHeight())
+                .maxHeight(dimension.getMaxHeight())
                 .build();
 
-        Iris.debug("Generator Config: " + w.toString());
+        Iris.debug("Generator Config: " + world);
 
-        File ff = new File(w.worldFolder(), "iris/pack");
-        IrisDimension installedDimension = ff.isDirectory()
-                ? IrisData.get(ff).getDimensionLoader().load(dim.getLoadKey(), false)
-                : null;
-        if (installedDimension == null) {
-            dim = Iris.service(StudioSVC.class).replaceIntoWorld(Iris.getSender(), dim, w.worldFolder());
-            if (dim == null) {
-                throw new IllegalStateException("Failed to install dimension pack for " + id);
-            }
-        } else {
-            dim = installedDimension;
-        }
-        requireSnapshotLoadable(ff);
-
-        return new BukkitChunkGenerator(w, false, ff, dim.getLoadKey());
+        return new BukkitChunkGenerator(world, false, snapshotRoot, dimension.getLoadKey());
     }
 
     private record FreshValidation(

adapters/bukkit/plugin/src/main/java/art/arcane/iris/core/PaperWorldReplacementEntryListener.java

@@ -0,0 +1,54 @@
+package art.arcane.iris.core;
+
+import io.papermc.paper.event.player.AsyncPlayerSpawnLocationEvent;
+import net.kyori.adventure.text.Component;
+import org.bukkit.Location;
+import org.bukkit.event.EventHandler;
+import org.bukkit.event.EventPriority;
+import org.bukkit.event.Listener;
+
+import java.util.Objects;
+import java.util.UUID;
+
+public final class PaperWorldReplacementEntryListener implements Listener {
+    private final PendingWorldReplacementManager manager;
+
+    public PaperWorldReplacementEntryListener(PendingWorldReplacementManager manager) {
+        this.manager = Objects.requireNonNull(manager, "manager");
+    }
+
+    @EventHandler(priority = EventPriority.HIGHEST)
+    public void onAsyncPlayerSpawnLocation(AsyncPlayerSpawnLocationEvent event) {
+        UUID playerId = event.getConnection().getProfile().getId();
+        if (playerId == null) {
+            return;
+        }
+        try {
+            PendingWorldReplacementManager.ReplacementEntryRedirect redirect = manager.prepareReplacementEntry(
+                    playerId,
+                    event.getSpawnLocation(),
+                    event.isNewPlayer()
+            );
+            if (redirect == null) {
+                return;
+            }
+            Location location = redirect.location();
+            event.setSpawnLocation(location);
+            if (redirect.acknowledgementRequired()) {
+                manager.expectReplacementEntryAcknowledgement(playerId, redirect.transactionId());
+            }
+        } catch (InterruptedException failure) {
+            Thread.currentThread().interrupt();
+            refuseUnsafeEntry(event, playerId, failure);
+        } catch (Throwable failure) {
+            refuseUnsafeEntry(event, playerId, failure);
+        }
+    }
+
+    private void refuseUnsafeEntry(AsyncPlayerSpawnLocationEvent event, UUID playerId, Throwable failure) {
+        manager.reportUnsafeEntry(playerId, failure);
+        event.getConnection().disconnect(Component.text(
+                "Iris could not verify a safe login location after the Overworld replacement. Retry after startup completes."
+        ));
+    }
+}

adapters/bukkit/plugin/src/main/java/art/arcane/iris/core/PendingWorldDeleteQueue.java

@@ -451,18 +451,51 @@ public final class PendingWorldDeleteQueue implements WorldDeletionQueue {
 
             if (type == QueueEntryType.EXACT) {
                 NamespacedKey key = IrisWorldStorage.managedKeyFromName(storedName, levelRoot.getName());
-                Path path = IrisWorldStorage.requireSafeManagedDimensionRoot(levelRoot, key).toPath();
+                Path path = currentStorageRoot(levelRoot, key);
                 return List.of(new DeleteTarget(key, path));
             }
 
             ArrayList<DeleteTarget> targets = new ArrayList<>(3);
             for (String familyWorldName : TransientWorldCleanupSupport.worldFamilyNames(storedName)) {
                 NamespacedKey key = IrisWorldStorage.managedKeyFromName(familyWorldName, levelRoot.getName());
-                Path path = IrisWorldStorage.requireSafeManagedDimensionRoot(levelRoot, key).toPath();
+                Path path = currentStorageRoot(levelRoot, key);
                 targets.add(new DeleteTarget(key, path));
             }
             return targets;
         }
+
+        private static Path currentStorageRoot(File levelRoot, NamespacedKey key) {
+            File worldContainer = levelRoot.getAbsoluteFile().getParentFile();
+            if (worldContainer == null) {
+                throw new IllegalArgumentException("Selected level root has no world container: " + levelRoot);
+            }
+            String configuredWorldName = IrisWorldStorage.configuredWorldName(key, levelRoot.getName());
+            Path directRoot = IrisWorldStorage.requireSafeManagedDimensionRoot(levelRoot, key)
+                    .toPath()
+                    .toAbsolutePath()
+                    .normalize();
+            Path dimensionRoot = IrisWorldStorage.frozenDimensionRoot(
+                    worldContainer,
+                    levelRoot,
+                    configuredWorldName,
+                    key
+            ).map(file -> file.toPath().toAbsolutePath().normalize()).orElse(directRoot);
+            if (dimensionRoot.equals(directRoot)) {
+                return directRoot;
+            }
+            Path configuredDimensionRoot = IrisWorldStorage.configuredDimensionRoot(
+                    worldContainer,
+                    levelRoot,
+                    key
+            ).toPath().toAbsolutePath().normalize();
+            if (!dimensionRoot.equals(configuredDimensionRoot)) {
+                throw new IllegalStateException("Iris world storage does not match the current platform layout.");
+            }
+            return IrisWorldStorage.configuredLevelRoot(worldContainer, levelRoot, key)
+                    .toPath()
+                    .toAbsolutePath()
+                    .normalize();
+        }
     }
 
     private static Path requireSafeQuarantinePath(File levelRoot, String quarantineName) throws IOException {

adapters/bukkit/plugin/src/main/java/art/arcane/iris/core/PendingWorldReplacementManager.java

@@ -8,6 +8,7 @@ import art.arcane.iris.core.lifecycle.BukkitWorldConfiguration.WorldGeneratorSna
 import art.arcane.iris.core.lifecycle.LifecycleOperationCoordinator;
 import art.arcane.iris.core.lifecycle.WorldReplacementBootstrap;
 import art.arcane.iris.core.lifecycle.WorldReplacementBootstrapMarker;
+import art.arcane.iris.core.lifecycle.WorldReplacementEntryGuard;
 import art.arcane.iris.core.lifecycle.WorldReplacementFilesystem;
 import art.arcane.iris.core.lifecycle.WorldReplacementFilesystem.ReplacementPaths;
 import art.arcane.iris.core.lifecycle.WorldReplacementJournal;
@@ -15,24 +16,32 @@ import art.arcane.iris.core.lifecycle.WorldReplacementJournal.Phase;
 import art.arcane.iris.core.lifecycle.WorldReplacementJournal.Transaction;
 import art.arcane.iris.core.lifecycle.WorldReplacementSeed;
 import art.arcane.iris.core.pack.PackValidationRegistry;
+import art.arcane.iris.core.runtime.WorldRuntimeControlService;
 import art.arcane.iris.core.service.StudioSVC;
 import art.arcane.iris.core.tools.IrisToolbelt;
 import art.arcane.iris.engine.object.IrisDimension;
 import art.arcane.iris.engine.object.IrisEnvironment;
+import art.arcane.iris.engine.platform.BukkitChunkGenerator;
 import art.arcane.iris.engine.platform.PlatformChunkGenerator;
 import art.arcane.iris.util.common.misc.ServerProperties;
 import art.arcane.iris.util.common.plugin.VolmitSender;
 import art.arcane.iris.util.common.scheduling.J;
 import art.arcane.volmlib.util.bukkit.WorldIdentity;
+import org.bukkit.Bukkit;
+import org.bukkit.Chunk;
+import org.bukkit.Location;
 import org.bukkit.NamespacedKey;
 import org.bukkit.World;
 import org.bukkit.event.EventHandler;
 import org.bukkit.event.EventPriority;
 import org.bukkit.event.Listener;
+import org.bukkit.event.player.PlayerJoinEvent;
 import org.bukkit.event.world.WorldLoadEvent;
 
 import java.io.File;
 import java.io.IOException;
+import java.lang.reflect.Constructor;
+import java.lang.reflect.InvocationTargetException;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.ArrayList;
@@ -40,23 +49,60 @@ import java.util.HashSet;
 import java.util.List;
 import java.util.Locale;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.OptionalLong;
 import java.util.Set;
 import java.util.UUID;
 import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.TimeoutException;
 
 public final class PendingWorldReplacementManager implements Listener {
+    private static final WorldSlotKey OVERWORLD_KEY = WorldSlotKey.minecraft("overworld");
+    private static final long SAFE_ENTRY_TIMEOUT_SECONDS = 30L;
+
     private final Iris plugin;
     private final Set<UUID> cleanupInFlight = new HashSet<>();
     private final Set<UUID> verificationInFlight = new HashSet<>();
+    private final ConcurrentHashMap<UUID, UUID> pendingEntryAcknowledgements = new ConcurrentHashMap<>();
+    private volatile WorldReplacementEntryGuard.Entry overworldEntryGuard;
+    private volatile Path overworldEntryWorldDirectory;
+    private volatile CompletableFuture<Location> overworldSafeEntry;
+    private volatile UUID overworldEntryAwaitingVerification;
+    private volatile World overworldEntryWorld;
+    private volatile boolean paperEntryListenerRegistered;
 
     public PendingWorldReplacementManager(Iris plugin) {
         this.plugin = Objects.requireNonNull(plugin, "plugin");
     }
 
+    public void registerPlatformEntryListener() {
+        ClassLoader loader = getClass().getClassLoader();
+        try {
+            Class.forName("io.papermc.paper.event.player.AsyncPlayerSpawnLocationEvent", false, loader);
+        } catch (ClassNotFoundException | LinkageError unavailable) {
+            return;
+        }
+        try {
+            Class<?> listenerType = Class.forName(
+                    "art.arcane.iris.core.PaperWorldReplacementEntryListener",
+                    true,
+                    loader
+            );
+            Constructor<?> constructor = listenerType.getConstructor(PendingWorldReplacementManager.class);
+            Listener listener = (Listener) constructor.newInstance(this);
+            Bukkit.getPluginManager().registerEvents(listener, plugin);
+            paperEntryListenerRegistered = true;
+        } catch (InvocationTargetException failure) {
+            Throwable cause = failure.getCause() == null ? failure : failure.getCause();
+            throw new IllegalStateException("Paper replacement entry listener registration failed.", cause);
+        } catch (ReflectiveOperationException | LinkageError failure) {
+            throw new IllegalStateException("Paper replacement entry listener is unavailable.", failure);
+        }
+    }
+
     public NamespacedKey resolveRequestedWorldKey(String requestedName) {
         NamespacedKey worldKey = IrisWorldStorage.replacementKeyFromName(
                 requestedName,
@@ -129,6 +175,9 @@ public final class PendingWorldReplacementManager implements Listener {
                         paths.stage(),
                         seedSelection
                 );
+                if (target.slotKind() == SlotKind.VANILLA_OVERWORLD) {
+                    WorldReplacementEntryGuard.stage(target.levelRoot(), paths.stage(), transactionId);
+                }
                 File stagedPack = paths.stage().resolve("iris/pack").toFile();
                 IrisWorldGeneratorResolver.requireSnapshotLoadable(stagedPack);
                 String packFingerprint = WorldReplacementFilesystem.fingerprintPack(stagedPack.toPath());
@@ -205,6 +254,20 @@ public final class PendingWorldReplacementManager implements Listener {
     public synchronized void processPendingStartupReplacements() {
         ArrayList<String> failures = new ArrayList<>();
         ArrayList<String> restartBoundaries = new ArrayList<>();
+        try {
+            loadOverworldEntryGuard();
+        } catch (Throwable failure) {
+            String message = "Iris could not load the Overworld replacement entry guard: " + detail(failure);
+            Iris.reportError(message, failure);
+            IrisStartupValidation.markPacksInvalid(List.of(message));
+            return;
+        }
+        if (overworldEntryGuard != null && !paperEntryListenerRegistered) {
+            String message = "A pending Overworld replacement requires the Paper safe-entry capability.";
+            Iris.error(message);
+            IrisStartupValidation.markPacksInvalid(List.of(message));
+            return;
+        }
         List<Transaction> transactions;
         try {
             transactions = loadTransactions();
@@ -215,6 +278,9 @@ public final class PendingWorldReplacementManager implements Listener {
             return;
         }
         for (Transaction transaction : transactions) {
+            if (OVERWORLD_KEY.equals(transaction.worldKey()) && transaction.phase() == Phase.PUBLISHED) {
+                overworldEntryAwaitingVerification = transaction.id();
+            }
             try {
                 inspectStartupTransaction(transaction);
             } catch (RestartBoundaryRequired boundary) {
@@ -229,6 +295,7 @@ public final class PendingWorldReplacementManager implements Listener {
                 Iris.reportError(message, failure);
             }
         }
+        scheduleLoadedOverworldEntryPreparation();
         if (!failures.isEmpty()) {
             IrisStartupValidation.markPacksInvalid(failures);
         }
@@ -258,6 +325,245 @@ public final class PendingWorldReplacementManager implements Listener {
                 scheduleRuntimeCapture(transaction, 0);
             }
         }
+        scheduleLoadedOverworldEntryPreparation();
+    }
+
+    private void scheduleLoadedOverworldEntryPreparation() {
+        if (overworldEntryGuard == null) {
+            return;
+        }
+        try {
+            J.s(this::prepareLoadedOverworldEntry);
+        } catch (Throwable failure) {
+            failOverworldEntryPreparation(failure);
+        }
+    }
+
+    private void prepareLoadedOverworldEntry() {
+        World world;
+        try {
+            world = WorldIdentity.resolve(toNamespacedKey(OVERWORLD_KEY)).orElse(null);
+        } catch (Throwable failure) {
+            failOverworldEntryPreparation(failure);
+            return;
+        }
+        if (world != null) {
+            prepareOverworldEntry(world);
+        }
+    }
+
+    private void prepareOverworldEntry(World world) {
+        WorldReplacementEntryGuard.Entry guard = overworldEntryGuard;
+        if (guard == null
+                || guard.transactionId().equals(overworldEntryAwaitingVerification)
+                || !OVERWORLD_KEY.equals(toWorldSlotKey(WorldIdentity.key(world)))) {
+            return;
+        }
+        CompletableFuture<Location> targetFuture;
+        synchronized (this) {
+            if (overworldSafeEntry != null) {
+                return;
+            }
+            targetFuture = new CompletableFuture<>();
+            overworldSafeEntry = targetFuture;
+            overworldEntryWorld = world;
+        }
+        try {
+            PlatformChunkGenerator generator = IrisToolbelt.access(world);
+            if (!(generator instanceof BukkitChunkGenerator bukkitGenerator)) {
+                throw new IOException("The replaced Overworld does not have a Bukkit Iris generator.");
+            }
+            Location anchor = bukkitGenerator.getInitialSpawnLocation(world);
+            int chunkX = anchor.getBlockX() >> 4;
+            int chunkZ = anchor.getBlockZ() >> 4;
+            WorldRuntimeControlService runtime = WorldRuntimeControlService.get();
+            CompletableFuture<Chunk> chunkFuture = runtime.requestChunkAsync(world, chunkX, chunkZ, true);
+            if (chunkFuture == null) {
+                throw new IOException("The replacement spawn chunk request was not accepted.");
+            }
+            chunkFuture
+                    .thenCompose(chunk -> runtime.resolveSafeEntry(world, anchor))
+                    .thenCompose(this::applyOverworldSpawn)
+                    .thenCompose(this::persistOverworldSpawn)
+                    .whenComplete((safeEntry, failure) -> {
+                        if (failure != null) {
+                            targetFuture.completeExceptionally(failure);
+                            Iris.reportError("Could not prepare a safe spawn for the replaced Overworld.", failure);
+                            return;
+                        }
+                        targetFuture.complete(safeEntry.clone());
+                        retireOverworldEntryIfComplete(guard.transactionId());
+                    });
+        } catch (Throwable failure) {
+            targetFuture.completeExceptionally(failure);
+            Iris.reportError("Could not prepare a safe spawn for the replaced Overworld.", failure);
+        }
+    }
+
+    private CompletableFuture<Location> applyOverworldSpawn(Location safeEntry) {
+        Location requiredSafeEntry = Objects.requireNonNull(safeEntry, "safeEntry").clone();
+        World world = Objects.requireNonNull(requiredSafeEntry.getWorld(), "safeEntry.world");
+        CompletableFuture<Location> applied = new CompletableFuture<>();
+        int chunkX = requiredSafeEntry.getBlockX() >> 4;
+        int chunkZ = requiredSafeEntry.getBlockZ() >> 4;
+        boolean scheduled = J.runRegion(world, chunkX, chunkZ, () -> {
+            try {
+                if (!world.setSpawnLocation(requiredSafeEntry)) {
+                    throw new IOException("The server rejected the replacement spawn location.");
+                }
+                applied.complete(requiredSafeEntry.clone());
+            } catch (Throwable failure) {
+                applied.completeExceptionally(failure);
+            }
+        });
+        if (!scheduled) {
+            applied.completeExceptionally(new IOException("Could not schedule the replacement spawn update."));
+        }
+        return applied;
+    }
+
+    private CompletableFuture<Location> persistOverworldSpawn(Location safeEntry) {
+        Location requiredSafeEntry = Objects.requireNonNull(safeEntry, "safeEntry").clone();
+        World world = Objects.requireNonNull(requiredSafeEntry.getWorld(), "safeEntry.world");
+        CompletableFuture<Location> persisted = new CompletableFuture<>();
+        boolean scheduled = J.runGlobal(() -> {
+            try {
+                world.save();
+                persisted.complete(requiredSafeEntry.clone());
+            } catch (Throwable failure) {
+                persisted.completeExceptionally(failure);
+            }
+        });
+        if (!scheduled) {
+            persisted.completeExceptionally(new IOException("Could not schedule replacement spawn persistence."));
+        }
+        return persisted;
+    }
+
+    private CompletableFuture<Boolean> inspectLoginCollision(Location location) {
+        Location requiredLocation = Objects.requireNonNull(location, "location").clone();
+        World world = Objects.requireNonNull(requiredLocation.getWorld(), "location.world");
+        int chunkX = requiredLocation.getBlockX() >> 4;
+        int chunkZ = requiredLocation.getBlockZ() >> 4;
+        WorldRuntimeControlService runtime = WorldRuntimeControlService.get();
+        CompletableFuture<Chunk> chunkFuture = runtime.requestChunkAsync(world, chunkX, chunkZ, true);
+        if (chunkFuture == null) {
+            return CompletableFuture.failedFuture(new IOException("The saved login chunk request was not accepted."));
+        }
+        return chunkFuture.thenCompose(chunk -> inspectLoadedLoginCollision(requiredLocation));
+    }
+
+    private CompletableFuture<Boolean> inspectLoadedLoginCollision(Location location) {
+        World world = Objects.requireNonNull(location.getWorld(), "location.world");
+        CompletableFuture<Boolean> inspected = new CompletableFuture<>();
+        int chunkX = location.getBlockX() >> 4;
+        int chunkZ = location.getBlockZ() >> 4;
+        boolean scheduled = J.runRegion(world, chunkX, chunkZ, () -> {
+            try {
+                int blockY = location.getBlockY();
+                if (blockY < world.getMinHeight() || blockY + 1 >= world.getMaxHeight()) {
+                    inspected.complete(false);
+                    return;
+                }
+                boolean feetPassable = world.getBlockAt(location.getBlockX(), blockY, location.getBlockZ())
+                        .isPassable();
+                boolean headPassable = world.getBlockAt(location.getBlockX(), blockY + 1, location.getBlockZ())
+                        .isPassable();
+                inspected.complete(feetPassable && headPassable);
+            } catch (Throwable failure) {
+                inspected.completeExceptionally(failure);
+            }
+        });
+        if (!scheduled) {
+            inspected.completeExceptionally(new IOException("Could not schedule the saved login collision check."));
+        }
+        return inspected;
+    }
+
+    private void completeOverworldEntry(UUID playerId, UUID transactionId) {
+        try {
+            J.a(() -> completeOverworldEntryAsync(playerId, transactionId));
+        } catch (Throwable failure) {
+            Iris.reportError("Could not record a completed Overworld replacement entry for " + playerId + ".", failure);
+        }
+    }
+
+    private void completeOverworldEntryAsync(UUID playerId, UUID transactionId) {
+        boolean retire = false;
+        try {
+            synchronized (this) {
+                WorldReplacementEntryGuard.Entry current = overworldEntryGuard;
+                Path worldDirectory = overworldEntryWorldDirectory;
+                if (current == null
+                        || worldDirectory == null
+                        || !current.transactionId().equals(transactionId)
+                        || !current.pendingPlayers().contains(playerId)) {
+                    return;
+                }
+                Optional<WorldReplacementEntryGuard.Entry> updated = WorldReplacementEntryGuard.completePlayer(
+                        worldDirectory,
+                        transactionId,
+                        playerId
+                );
+                overworldEntryGuard = updated.orElse(null);
+                retire = overworldEntryGuard != null && overworldEntryGuard.pendingPlayers().isEmpty();
+            }
+        } catch (Throwable failure) {
+            Iris.reportError("Could not record a completed Overworld replacement entry for " + playerId + ".", failure);
+            return;
+        }
+        if (retire) {
+            retireOverworldEntryIfCompleteAsync(transactionId);
+        }
+    }
+
+    private void retireOverworldEntryIfComplete(UUID transactionId) {
+        try {
+            J.a(() -> retireOverworldEntryIfCompleteAsync(transactionId));
+        } catch (Throwable failure) {
+            Iris.reportError("Could not schedule Overworld replacement entry marker retirement.", failure);
+        }
+    }
+
+    private synchronized void retireOverworldEntryIfCompleteAsync(UUID transactionId) {
+        WorldReplacementEntryGuard.Entry current = overworldEntryGuard;
+        Path worldDirectory = overworldEntryWorldDirectory;
+        CompletableFuture<Location> safeEntry = overworldSafeEntry;
+        if (current == null
+                || worldDirectory == null
+                || !current.transactionId().equals(transactionId)
+                || !current.pendingPlayers().isEmpty()
+                || safeEntry == null
+                || !safeEntry.isDone()
+                || safeEntry.isCompletedExceptionally()) {
+            return;
+        }
+        try {
+            if (!WorldReplacementEntryGuard.retireIfEmpty(worldDirectory, transactionId)) {
+                return;
+            }
+            overworldEntryGuard = null;
+            overworldEntryWorldDirectory = null;
+            overworldSafeEntry = null;
+            overworldEntryWorld = null;
+            pendingEntryAcknowledgements.entrySet().removeIf(entry -> entry.getValue().equals(transactionId));
+        } catch (Throwable failure) {
+            Iris.reportError("Could not retire the completed Overworld replacement entry marker.", failure);
+        }
+    }
+
+    void reportUnsafeEntry(UUID playerId, Throwable failure) {
+        Iris.reportError("Refused unsafe Overworld replacement entry for " + playerId + ".", failure);
+    }
+
+    private synchronized void failOverworldEntryPreparation(Throwable failure) {
+        CompletableFuture<Location> future = overworldSafeEntry;
+        if (future == null) {
+            future = new CompletableFuture<>();
+            overworldSafeEntry = future;
+        }
+        future.completeExceptionally(failure);
+        Iris.reportError("Could not prepare a safe spawn for the replaced Overworld.", failure);
     }
 
     @EventHandler(priority = EventPriority.MONITOR)
@@ -269,9 +575,81 @@ public final class PendingWorldReplacementManager implements Listener {
             Iris.reportError("Failed to capture a loaded world identity for replacement verification.", failure);
             return;
         }
+        if (OVERWORLD_KEY.equals(worldKey)) {
+            prepareOverworldEntry(event.getWorld());
+        }
         J.a(() -> discoverLoadedWorldTransaction(worldKey));
     }
 
+    ReplacementEntryRedirect prepareReplacementEntry(UUID playerId, Location savedLocation, boolean newPlayer)
+            throws IOException, InterruptedException, ExecutionException, TimeoutException {
+        WorldReplacementEntryGuard.Entry guard = overworldEntryGuard;
+        if (guard == null || playerId == null) {
+            return null;
+        }
+        boolean pendingPlayer = guard.pendingPlayers().contains(playerId);
+        if (!pendingPlayer && !newPlayer) {
+            return null;
+        }
+        Location requiredSavedLocation = Objects.requireNonNull(savedLocation, "savedLocation").clone();
+        World replacementWorld = overworldEntryWorld;
+        if (replacementWorld == null) {
+            throw new IOException("The replacement Overworld is not ready.");
+        }
+        if (requiredSavedLocation.getWorld() != replacementWorld) {
+            if (pendingPlayer) {
+                completeOverworldEntry(playerId, guard.transactionId());
+            }
+            return null;
+        }
+        if (!newPlayer) {
+            boolean collisionSafe = inspectLoginCollision(requiredSavedLocation)
+                    .get(SAFE_ENTRY_TIMEOUT_SECONDS, TimeUnit.SECONDS);
+            if (collisionSafe) {
+                completeOverworldEntry(playerId, guard.transactionId());
+                return null;
+            }
+        }
+        CompletableFuture<Location> safeEntry = overworldSafeEntry;
+        if (safeEntry == null) {
+            throw new IOException("The replacement safe spawn is not ready.");
+        }
+        Location prepared = safeEntry.get(SAFE_ENTRY_TIMEOUT_SECONDS, TimeUnit.SECONDS).clone();
+        prepared.setYaw(requiredSavedLocation.getYaw());
+        prepared.setPitch(requiredSavedLocation.getPitch());
+        return new ReplacementEntryRedirect(guard.transactionId(), prepared, pendingPlayer);
+    }
+
+    void expectReplacementEntryAcknowledgement(UUID playerId, UUID transactionId) throws IOException {
+        WorldReplacementEntryGuard.Entry guard = overworldEntryGuard;
+        if (guard == null
+                || !guard.transactionId().equals(transactionId)
+                || !guard.pendingPlayers().contains(playerId)) {
+            throw new IOException("The Overworld replacement entry receipt is no longer active.");
+        }
+        pendingEntryAcknowledgements.put(playerId, transactionId);
+    }
+
+    @EventHandler(priority = EventPriority.MONITOR)
+    public void onPlayerJoin(PlayerJoinEvent event) {
+        UUID playerId = event.getPlayer().getUniqueId();
+        UUID transactionId = pendingEntryAcknowledgements.remove(playerId);
+        if (transactionId == null) {
+            return;
+        }
+        boolean scheduled = J.runEntity(event.getPlayer(), () -> {
+            try {
+                event.getPlayer().saveData();
+                completeOverworldEntry(playerId, transactionId);
+            } catch (Throwable failure) {
+                Iris.reportError("Could not persist safe Overworld replacement entry for " + playerId + ".", failure);
+            }
+        });
+        if (!scheduled) {
+            Iris.error("Could not schedule safe Overworld replacement entry persistence for " + playerId + ".");
+        }
+    }
+
     private void discoverLoadedWorldTransaction(WorldSlotKey worldKey) {
         Transaction transaction;
         try {
@@ -412,6 +790,10 @@ public final class PendingWorldReplacementManager implements Listener {
         try {
             writeTransaction(committed);
             Iris.success("Committed Iris world replacement for " + transaction.worldKey() + ".");
+            if (OVERWORLD_KEY.equals(transaction.worldKey())) {
+                overworldEntryAwaitingVerification = null;
+                scheduleLoadedOverworldEntryPreparation();
+            }
             scheduleCommittedCleanup(committed);
         } catch (Throwable failure) {
             Iris.reportError("The replacement for " + transaction.worldKey()
@@ -456,6 +838,9 @@ public final class PendingWorldReplacementManager implements Listener {
     private void initiateRollback(Transaction transaction, Throwable failure) {
         Iris.reportError("Iris world replacement verification failed for " + transaction.worldKey()
                 + "; the retained world will be restored on restart.", failure);
+        if (OVERWORLD_KEY.equals(transaction.worldKey())) {
+            clearOverworldEntryGuard();
+        }
         try {
             Transaction rollback = transaction.withPhase(Phase.ROLLBACK_PENDING);
             writeTransaction(rollback);
@@ -608,6 +993,24 @@ public final class PendingWorldReplacementManager implements Listener {
         return plugin.getDataFolder().toPath().toAbsolutePath().normalize();
     }
 
+    private synchronized void loadOverworldEntryGuard() throws IOException {
+        ExactWorldSlotPathPolicy.Target target = resolveTarget(OVERWORLD_KEY);
+        Optional<WorldReplacementEntryGuard.Entry> loaded = WorldReplacementEntryGuard.load(target.worldDirectory());
+        overworldEntryGuard = loaded.orElse(null);
+        overworldEntryWorldDirectory = loaded.isPresent() ? target.worldDirectory() : null;
+        overworldSafeEntry = null;
+        overworldEntryAwaitingVerification = null;
+    }
+
+    private synchronized void clearOverworldEntryGuard() {
+        overworldEntryGuard = null;
+        overworldEntryWorldDirectory = null;
+        overworldSafeEntry = null;
+        overworldEntryAwaitingVerification = null;
+        overworldEntryWorld = null;
+        pendingEntryAcknowledgements.clear();
+    }
+
     private ExactWorldSlotPathPolicy.Target resolveTransactionTarget(Transaction transaction) throws IOException {
         return WorldReplacementJournal.resolveTarget(transaction, IrisWorldStorage.levelRoot().toPath());
     }
@@ -738,6 +1141,22 @@ public final class PendingWorldReplacementManager implements Listener {
     private record VanillaLevelContext(boolean allowNether, boolean allowEnd) {
     }
 
+    record ReplacementEntryRedirect(
+            UUID transactionId,
+            Location location,
+            boolean acknowledgementRequired
+    ) {
+        ReplacementEntryRedirect {
+            Objects.requireNonNull(transactionId, "transactionId");
+            location = Objects.requireNonNull(location, "location").clone();
+        }
+
+        @Override
+        public Location location() {
+            return location.clone();
+        }
+    }
+
     private static final class RestartBoundaryRequired extends IOException {
         private RestartBoundaryRequired(String message) {
             super(message);

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

@@ -801,8 +801,14 @@ public class CommandIris implements DirectorExecutor {
     }
 
     boolean doesWorldExist(String worldName) {
-        File worldDirectory = IrisWorldStorage.dimensionRoot(worldName);
-        return worldDirectory.exists() && worldDirectory.isDirectory();
+        NamespacedKey worldKey = IrisWorldStorage.managedKeyFromName(worldName);
+        File levelRoot = IrisWorldStorage.levelRoot();
+        return IrisWorldStorage.frozenDimensionRoot(
+                Bukkit.getWorldContainer(),
+                levelRoot,
+                IrisWorldStorage.configuredWorldName(worldKey, levelRoot.getName()),
+                worldKey
+        ).isPresent();
     }
 
     public static class ManagedWorldNameHandler implements DirectorParameterHandler<String> {

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

@@ -93,6 +93,61 @@ public class IrisWorldGeneratorResolverTest {
         );
     }
 
+    @Test
+    public void configuredWorldResolutionUsesOnlyFrozenWorldLocalSnapshot() throws Exception {
+        String source = Files.readString(Path.of(
+                "src/main/java/art/arcane/iris/core/IrisWorldGeneratorResolver.java"));
+        int resolverStart = source.indexOf("private ChunkGenerator resolveFrozenWorldGenerator(");
+        int resolverEnd = source.indexOf("private record FreshValidation", resolverStart);
+        String resolver = source.substring(resolverStart, resolverEnd);
+
+        int dimensionRoot = resolver.indexOf("IrisWorldStorage.requireFrozenDimensionRoot(");
+        int currentPlatformRoot = resolver.indexOf("WorldCreatorCompat.persistentDimensionRoot(worldKey)");
+        int layoutRefusal = resolver.indexOf(
+                "Frozen Iris world storage does not match the current platform layout",
+                currentPlatformRoot
+        );
+        int snapshotRoot = resolver.indexOf("IrisWorldStorage.requireFrozenPackRoot(dimensionRoot)");
+        int validation = resolver.indexOf("requireSnapshotLoadable(snapshotRoot)");
+        int exactLoad = resolver.indexOf(
+                "IrisData.get(snapshotRoot).getDimensionLoader().load(id, false)"
+        );
+        int canonicalIdentity = resolver.indexOf(".platformIdentity(worldKey.toString())");
+        int resolvedStorage = resolver.indexOf(".worldFolder(dimensionRoot)");
+
+        assertTrue(dimensionRoot >= 0);
+        assertTrue(currentPlatformRoot > dimensionRoot);
+        assertTrue(layoutRefusal > currentPlatformRoot);
+        assertTrue(snapshotRoot > layoutRefusal);
+        assertTrue(validation > snapshotRoot);
+        assertTrue(exactLoad > validation);
+        assertTrue(canonicalIdentity > exactLoad);
+        assertTrue(resolvedStorage > canonicalIdentity);
+        assertFalse(resolver.contains("loadDimension("));
+        assertFalse(resolver.contains("loadAnyDimension("));
+        assertFalse(resolver.contains("replaceIntoWorld("));
+        assertFalse(resolver.contains("installIntoWorld("));
+    }
+
+    @Test
+    public void configuredWorldSnapshotFailureStopsStartupAndRethrows() throws Exception {
+        String source = Files.readString(Path.of(
+                "src/main/java/art/arcane/iris/core/IrisWorldGeneratorResolver.java"));
+        int resolverStart = source.indexOf("public ChunkGenerator resolveDefaultWorldGenerator(");
+        int resolverEnd = source.indexOf("private ChunkGenerator resolveFrozenWorldGenerator(", resolverStart);
+        String resolver = source.substring(resolverStart, resolverEnd);
+
+        int failureCapture = resolver.indexOf("catch (RuntimeException failure)");
+        int report = resolver.indexOf("Iris.reportError(", failureCapture);
+        int shutdown = resolver.indexOf("Bukkit.shutdown()", report);
+        int rethrow = resolver.indexOf("throw failure", shutdown);
+
+        assertTrue(failureCapture >= 0);
+        assertTrue(report > failureCapture);
+        assertTrue(shutdown > report);
+        assertTrue(rethrow > shutdown);
+    }
+
     private static void writeValidPack(Path packRoot) throws Exception {
         Files.createDirectories(packRoot.resolve("dimensions"));
         Files.createDirectories(packRoot.resolve("regions"));

adapters/bukkit/plugin/src/test/java/art/arcane/iris/core/PendingWorldDeleteQueueTest.java

@@ -174,6 +174,19 @@ public class PendingWorldDeleteQueueTest {
         ), family);
     }
 
+    @Test
+    public void exactLogicalEntryResolvesCurrentCraftBukkitLevelStorage() throws IOException {
+        Path worldContainer = temporaryFolder.newFolder("configured-delete-server").toPath();
+        File levelRoot = Files.createDirectory(worldContainer.resolve("world")).toFile();
+        Path configuredLevelRoot = worldContainer.resolve("world_iris_alpha");
+        Files.createDirectories(configuredLevelRoot.resolve("dimensions/iris/alpha"));
+
+        assertEquals(
+                List.of(configuredLevelRoot.toAbsolutePath().normalize()),
+                PendingWorldDeleteQueue.resolveQueueEntryPaths(levelRoot, "exact:alpha")
+        );
+    }
+
     @Test
     public void failedSafeDeletionSignalsQueueRetentionAndSucceedsOnRetry() throws IOException {
         File levelRoot = temporaryFolder.newFolder("retry-world");

adapters/bukkit/plugin/src/test/java/art/arcane/iris/core/PendingWorldReplacementThreadAffinityTest.java

@@ -164,6 +164,84 @@ public class PendingWorldReplacementThreadAffinityTest {
         assertFalse(irisSource.contains("J.a(pendingWorldReplacements::verifyLoadedPublishedWorlds)"));
     }
 
+    @Test
+    public void paperLoginHookIsIsolatedFromAlwaysLoadedSpigotClasses() throws Exception {
+        String managerSource = Files.readString(Path.of(
+                "src/main/java/art/arcane/iris/core/PendingWorldReplacementManager.java"));
+        String irisSource = Files.readString(Path.of("src/main/java/art/arcane/iris/Iris.java"));
+        String listenerSource = Files.readString(Path.of(
+                "src/main/java/art/arcane/iris/core/PaperWorldReplacementEntryListener.java"));
+        String registration = method(managerSource, "public void registerPlatformEntryListener()");
+
+        assertFalse(managerSource.contains("import io.papermc.paper.event.player.AsyncPlayerSpawnLocationEvent"));
+        assertFalse(managerSource.contains("AsyncPlayerSpawnLocationEvent event"));
+        assertFalse(irisSource.contains("AsyncPlayerSpawnLocationEvent"));
+        assertTrue(registration.contains("Class.forName(\"io.papermc.paper.event.player.AsyncPlayerSpawnLocationEvent\""));
+        assertTrue(registration.contains("Class.forName("));
+        assertTrue(registration.contains("PaperWorldReplacementEntryListener"));
+        assertTrue(irisSource.contains("pendingWorldReplacements.registerPlatformEntryListener();"));
+        assertTrue(listenerSource.contains("onAsyncPlayerSpawnLocation(AsyncPlayerSpawnLocationEvent event)"));
+    }
+
+    @Test
+    public void redirectedPlayerReceiptSurvivesUntilTheMaterializedPositionIsSaved() throws Exception {
+        String managerSource = Files.readString(Path.of(
+                "src/main/java/art/arcane/iris/core/PendingWorldReplacementManager.java"));
+        String listenerSource = Files.readString(Path.of(
+                "src/main/java/art/arcane/iris/core/PaperWorldReplacementEntryListener.java"));
+        String preparation = method(
+                managerSource,
+                "ReplacementEntryRedirect prepareReplacementEntry(UUID playerId, Location savedLocation, boolean newPlayer)"
+        );
+        String acknowledgement = method(
+                managerSource,
+                "void expectReplacementEntryAcknowledgement(UUID playerId, UUID transactionId)"
+        );
+        String join = method(managerSource, "public void onPlayerJoin(PlayerJoinEvent event)");
+        String listener = method(
+                listenerSource,
+                "public void onAsyncPlayerSpawnLocation(AsyncPlayerSpawnLocationEvent event)"
+        );
+
+        assertTrue(preparation.contains("return new ReplacementEntryRedirect(guard.transactionId(), prepared, pendingPlayer)"));
+        assertFalse(preparation.substring(preparation.indexOf("CompletableFuture<Location> safeEntry"))
+                .contains("completeOverworldEntry("));
+        assertBefore(listener, "event.setSpawnLocation(location)",
+                "manager.expectReplacementEntryAcknowledgement(playerId, redirect.transactionId())");
+        assertTrue(acknowledgement.contains("pendingEntryAcknowledgements.put(playerId, transactionId)"));
+        assertBefore(join, "event.getPlayer().saveData()", "completeOverworldEntry(playerId, transactionId)");
+    }
+
+    @Test
+    public void replacementSpawnIsPersistedBeforeFinalMarkerRetirement() throws Exception {
+        String managerSource = Files.readString(Path.of(
+                "src/main/java/art/arcane/iris/core/PendingWorldReplacementManager.java"));
+        String listenerSource = Files.readString(Path.of(
+                "src/main/java/art/arcane/iris/core/PaperWorldReplacementEntryListener.java"));
+        String preparation = method(managerSource, "private void prepareOverworldEntry(World world)");
+        String persistence = method(managerSource, "private CompletableFuture<Location> persistOverworldSpawn(Location safeEntry)");
+        String retirement = method(
+                managerSource,
+                "private synchronized void retireOverworldEntryIfCompleteAsync(UUID transactionId)"
+        );
+        String listener = method(
+                listenerSource,
+                "public void onAsyncPlayerSpawnLocation(AsyncPlayerSpawnLocationEvent event)"
+        );
+        String generatorSource = Files.readString(Path.of(System.getProperty("iris.bukkitChunkGeneratorSource")));
+
+        assertBefore(preparation, ".thenCompose(this::applyOverworldSpawn)",
+                ".thenCompose(this::persistOverworldSpawn)");
+        assertBefore(preparation, "targetFuture.complete(safeEntry.clone())",
+                "retireOverworldEntryIfComplete(guard.transactionId())");
+        assertTrue(persistence.contains("world.save()"));
+        assertTrue(retirement.contains("!current.pendingPlayers().isEmpty()"));
+        assertTrue(retirement.contains("!safeEntry.isDone()"));
+        assertTrue(retirement.contains("safeEntry.isCompletedExceptionally()"));
+        assertTrue(listener.contains("event.isNewPlayer()"));
+        assertTrue(generatorSource.contains("world.getHighestBlockYAt(initialSpawn) + 1"));
+    }
+
     private static PendingWorldReplacementManager.PublishedWorldRuntimeState runtimeState(
             WorldSlotKey worldKey,
             long seed,

adapters/fabric/build.gradle

@@ -31,7 +31,7 @@ file('../../gradle.properties').withInputStream { InputStream stream -> rootProp
 String irisVersion = providers.gradleProperty('irisVersion').getOrElse(rootProperties.getProperty('irisVersion', '4.0.0-26.2'))
 String minecraftVersion = providers.gradleProperty('minecraftVersion').getOrElse(rootProperties.getProperty('minecraftVersion', '26.2'))
 String fabricLoaderVersion = providers.gradleProperty('fabricLoaderVersion').getOrElse(rootProperties.getProperty('fabricLoaderVersion', '0.19.3'))
-String volmLibCoordinate = providers.gradleProperty('volmLibCoordinate').getOrElse(rootProperties.getProperty('volmLibCoordinate', 'com.github.VolmitSoftware:VolmLib:d9026a7c8ebc391c8109f401ce79a0ce65df3969'))
+String volmLibCoordinate = providers.gradleProperty('volmLibCoordinate').getOrElse(rootProperties.getProperty('volmLibCoordinate', 'com.github.VolmitSoftware:VolmLib:5486ac97ad6d6833e27275dc768222d377721522'))
 Closure<String> irisArtifactName = { String platform, String targetVersion ->
     return "Iris v${project.version} [${platform}] ${targetVersion}.jar"
 }

adapters/forge/build.gradle

@@ -30,8 +30,8 @@ Properties rootProperties = new Properties()
 file('../../gradle.properties').withInputStream { InputStream stream -> rootProperties.load(stream) }
 String irisVersion = providers.gradleProperty('irisVersion').getOrElse(rootProperties.getProperty('irisVersion', '4.0.0-26.2'))
 String minecraftVersion = providers.gradleProperty('minecraftVersion').getOrElse(rootProperties.getProperty('minecraftVersion', '26.2'))
-String forgeVersion = providers.gradleProperty('forgeVersion').getOrElse(rootProperties.getProperty('forgeVersion', '26.2-65.0.4'))
-String volmLibCoordinate = providers.gradleProperty('volmLibCoordinate').getOrElse(rootProperties.getProperty('volmLibCoordinate', 'com.github.VolmitSoftware:VolmLib:d9026a7c8ebc391c8109f401ce79a0ce65df3969'))
+String forgeVersion = providers.gradleProperty('forgeVersion').getOrElse(rootProperties.getProperty('forgeVersion', '26.2-65.1.1'))
+String volmLibCoordinate = providers.gradleProperty('volmLibCoordinate').getOrElse(rootProperties.getProperty('volmLibCoordinate', 'com.github.VolmitSoftware:VolmLib:5486ac97ad6d6833e27275dc768222d377721522'))
 Closure<String> loaderDisplayVersion = { String loaderVersion ->
     String coordinatePrefix = "${minecraftVersion}-"
     if (loaderVersion.startsWith(coordinatePrefix)) {

adapters/minecraft-common/src/main/java/art/arcane/iris/nativegen/NativeStructureVolumeIndex.java

@@ -360,9 +360,8 @@ public final class NativeStructureVolumeIndex {
 
     private static void warnOnce(String structureId, Throwable error) {
         if (WARNED_RESOLUTION_FAILURES.add(structureId)) {
-            IrisLogging.warn("Native structure volume resolution failed for '" + structureId
-                    + "'; objects will not be vetoed against it: "
-                    + error.getClass().getSimpleName() + ":" + error.getMessage());
+            IrisLogging.reportError("Native structure volume resolution failed for '" + structureId
+                    + "'; objects will not be vetoed against it.", error);
         }
     }
 

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

@@ -53,6 +53,10 @@ public final class ModdedMixinAudit {
             new ExpectedMixin("MobAwarenessMixin", "entity",
                     "net.minecraft.world.entity.Mob", "iris$tickUnawareMob",
                     false, ModdedMixinFlags::mobAwarenessRan),
+            new ExpectedMixin("StructureTemplatePaletteConcurrencyMixin", "common",
+                    "net.minecraft.world.level.levelgen.structure.templatesystem.StructureTemplate$Palette",
+                    "iris$installConcurrentBlockCache",
+                    false, ModdedMixinFlags::structureTemplatePaletteRan),
             new ExpectedMixin("IrisWorldOpenFlowsMixin", "client",
                     "net.minecraft.client.gui.screens.worldselection.WorldOpenFlows",
                     "iris$openWorldCheckWorldStemCompatibility",
@@ -103,7 +107,7 @@ public final class ModdedMixinAudit {
             LOGGER.error("  missing: {}", entry);
         }
         LOGGER.error("The mixin config was not registered for this loader (fabric.mod.json mixins, neoforge.mods.toml [[mixins]], forge MixinConfigs manifest attribute).");
-        LOGGER.error("Entity persistence, custom mob loot and Iris world-type labels are disabled until this is fixed.");
+        LOGGER.error("Entity persistence, custom mob loot, parallel structure safety, or Iris world-type labels are disabled until this is fixed.");
         LOGGER.error("===============================================================");
     }
 

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

@@ -31,6 +31,7 @@ public final class ModdedMixinFlags {
     private static volatile boolean entityPersistenceRan;
     private static volatile boolean livingEntityLootRan;
     private static volatile boolean mobAwarenessRan;
+    private static volatile boolean structureTemplatePaletteRan;
     private static volatile boolean worldOpenFlowsRan;
     private static volatile boolean worldTypeEntryRan;
 
@@ -58,6 +59,12 @@ public final class ModdedMixinFlags {
         }
     }
 
+    public static void markStructureTemplatePalette() {
+        if (!structureTemplatePaletteRan) {
+            structureTemplatePaletteRan = true;
+        }
+    }
+
     public static void markWorldOpenFlows() {
         if (!worldOpenFlowsRan) {
             worldOpenFlowsRan = true;
@@ -82,6 +89,10 @@ public final class ModdedMixinFlags {
         return mobAwarenessRan;
     }
 
+    public static boolean structureTemplatePaletteRan() {
+        return structureTemplatePaletteRan;
+    }
+
     public static boolean worldOpenFlowsRan() {
         return worldOpenFlowsRan;
     }
@@ -94,6 +105,7 @@ public final class ModdedMixinFlags {
         entityPersistenceRan = false;
         livingEntityLootRan = false;
         mobAwarenessRan = false;
+        structureTemplatePaletteRan = false;
         worldOpenFlowsRan = false;
         worldTypeEntryRan = false;
     }

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

@@ -50,10 +50,12 @@ import net.minecraft.core.SectionPos;
 import net.minecraft.core.registries.Registries;
 import net.minecraft.resources.Identifier;
 import net.minecraft.server.level.ServerLevel;
+import net.minecraft.world.entity.ai.village.poi.PoiTypes;
 import net.minecraft.world.level.ChunkPos;
 import net.minecraft.world.level.LevelHeightAccessor;
 import net.minecraft.world.level.StructureManager;
 import net.minecraft.world.level.WorldGenLevel;
+import net.minecraft.world.level.block.Blocks;
 import net.minecraft.world.level.block.state.BlockState;
 import net.minecraft.world.level.biome.BiomeSource;
 import net.minecraft.world.level.chunk.ChunkAccess;
@@ -73,6 +75,7 @@ import java.util.Comparator;
 import java.util.List;
 import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.function.BiConsumer;
 import java.util.function.IntBinaryOperator;
 
 /**
@@ -346,6 +349,11 @@ final class ModdedNativeStructureStage {
                 index++;
             }
         }
+        if (!placementGroups.isEmpty()) {
+            ServerLevel level = world.getLevel();
+            visitExistingPois(chunk, (position, state) -> level.updatePOIOnBlockStateChange(
+                    position, Blocks.AIR.defaultBlockState(), state));
+        }
         try {
             int runtimeMinY = world.getMinY();
             WorldgenTerrainHeightmaps.primeStructurePlacement(
@@ -405,6 +413,10 @@ final class ModdedNativeStructureStage {
         }
     }
 
+    static void visitExistingPois(ChunkAccess chunk, BiConsumer<BlockPos, BlockState> visitor) {
+        chunk.findBlocks(PoiTypes::hasPoi, visitor);
+    }
+
     private static String nativeStructureBatchContext(List<NativePlacementGroup> placementGroups) {
         if (placementGroups.isEmpty()) {
             return "<no resolved native structures>";
@@ -423,9 +435,21 @@ final class ModdedNativeStructureStage {
                                        WorldgenRandom random, BoundingBox area, ChunkPos chunkPos,
                                        String structureId, StructureStart start,
                                        IrisNativeStructureDecision decision) {
-        NativeStructurePostProcessor.place(world, structureManager, generator, random, area, chunkPos,
-                structureId, start, decision, this::resolvePaletteBlock,
-                (x, z) -> generator.engine().getHeight(x, z, true) + generator.engine().getMinHeight());
+        Engine current = generator.engine();
+        int runtimeMinY = world.getMinY();
+        WorldGenLevel boundedWorld = ModdedNativeStructureWorldgenAccess.create(
+                world, chunkPos,
+                worldgenSurfaceHeight(current, runtimeMinY),
+                worldgenFloorHeight(current, runtimeMinY));
+        world.setCurrentlyGenerating(() -> "Iris native structure " + structureId);
+        try {
+            NativeStructurePostProcessor.place(
+                    boundedWorld, structureManager, generator, random, area, chunkPos,
+                    structureId, start, decision, this::resolvePaletteBlock,
+                    (x, z) -> current.getHeight(x, z, true) + current.getMinHeight());
+        } finally {
+            world.setCurrentlyGenerating(null);
+        }
     }
 
     private List<List<Structure>> structuresByStep(Registry<Structure> registry) {

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

@@ -0,0 +1,558 @@
+package art.arcane.iris.modded;
+
+import art.arcane.iris.nativegen.WorldgenTerrainHeightmaps;
+import it.unimi.dsi.fastutil.longs.Long2LongOpenHashMap;
+import it.unimi.dsi.fastutil.longs.Long2ObjectOpenHashMap;
+import net.minecraft.core.BlockPos;
+import net.minecraft.core.Direction;
+import net.minecraft.core.Holder;
+import net.minecraft.core.QuartPos;
+import net.minecraft.core.RegistryAccess;
+import net.minecraft.core.particles.ParticleOptions;
+import net.minecraft.server.MinecraftServer;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.sounds.SoundEvent;
+import net.minecraft.sounds.SoundSource;
+import net.minecraft.util.Mth;
+import net.minecraft.util.RandomSource;
+import net.minecraft.world.DifficultyInstance;
+import net.minecraft.world.attribute.EnvironmentAttributeReader;
+import net.minecraft.world.entity.Entity;
+import net.minecraft.world.entity.player.Player;
+import net.minecraft.world.flag.FeatureFlagSet;
+import net.minecraft.world.level.BlockGetter;
+import net.minecraft.world.level.ChunkPos;
+import net.minecraft.world.level.LightLayer;
+import net.minecraft.world.level.WorldGenLevel;
+import net.minecraft.world.level.biome.Biome;
+import net.minecraft.world.level.biome.BiomeManager;
+import net.minecraft.world.level.block.Block;
+import net.minecraft.world.level.block.Blocks;
+import net.minecraft.world.level.block.entity.BlockEntity;
+import net.minecraft.world.level.block.entity.BlockEntityType;
+import net.minecraft.world.level.block.state.BlockState;
+import net.minecraft.world.level.border.WorldBorder;
+import net.minecraft.world.level.chunk.ChunkAccess;
+import net.minecraft.world.level.chunk.ChunkSource;
+import net.minecraft.world.level.chunk.EmptyLevelChunk;
+import net.minecraft.world.level.chunk.status.ChunkStatus;
+import net.minecraft.world.level.dimension.DimensionType;
+import net.minecraft.world.level.entity.EntityTypeTest;
+import net.minecraft.world.level.gameevent.GameEvent;
+import net.minecraft.world.level.levelgen.Heightmap;
+import net.minecraft.world.level.lighting.LevelLightEngine;
+import net.minecraft.world.level.material.Fluid;
+import net.minecraft.world.level.material.FluidState;
+import net.minecraft.world.level.storage.LevelData;
+import net.minecraft.world.phys.AABB;
+import net.minecraft.world.phys.Vec3;
+import net.minecraft.world.ticks.LevelTickAccess;
+import net.minecraft.world.ticks.ScheduledTick;
+
+import java.util.List;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.function.IntBinaryOperator;
+import java.util.function.Predicate;
+import java.util.function.Supplier;
+
+final class ModdedNativeStructureWorldgenAccess implements WorldGenLevel {
+    private static final int WRITE_RADIUS = 1;
+
+    private final WorldGenLevel delegate;
+    private final ChunkPos generationCenter;
+    private final IntBinaryOperator surfaceFirstFreeY;
+    private final IntBinaryOperator floorFirstFreeY;
+    private final Holder<Biome> fallbackBiome;
+    private final BiomeManager biomeManager;
+    private final AABB generationBounds;
+    private final LevelTickAccess<Block> blockTicks;
+    private final LevelTickAccess<Fluid> fluidTicks;
+    private final Long2LongOpenHashMap terrainHeights;
+    private final Long2ObjectOpenHashMap<ChunkAccess> outsideChunks;
+
+    private ModdedNativeStructureWorldgenAccess(WorldGenLevel delegate, Boundary boundary) {
+        this.delegate = Objects.requireNonNull(delegate, "Native structure world access requires a delegate");
+        this.generationCenter = Objects.requireNonNull(
+                boundary.generationCenter(), "Native structure world access requires a generation center");
+        this.surfaceFirstFreeY = Objects.requireNonNull(
+                boundary.surfaceFirstFreeY(), "Native structure world access requires a surface resolver");
+        this.floorFirstFreeY = Objects.requireNonNull(
+                boundary.floorFirstFreeY(), "Native structure world access requires an ocean-floor resolver");
+        BlockPos biomeSample = generationCenter.getMiddleBlockPosition(delegate.getSeaLevel());
+        this.fallbackBiome = delegate.getBiome(biomeSample);
+        this.biomeManager = delegate.getBiomeManager().withDifferentSource(this);
+        this.generationBounds = new AABB(
+                generationCenter.getMinBlockX() - 16,
+                delegate.getMinY(),
+                generationCenter.getMinBlockZ() - 16,
+                generationCenter.getMaxBlockX() + 17,
+                delegate.getMinY() + delegate.getHeight(),
+                generationCenter.getMaxBlockZ() + 17);
+        this.blockTicks = new BoundedTickAccess<>(delegate.getBlockTicks(), this::isWritable);
+        this.fluidTicks = new BoundedTickAccess<>(delegate.getFluidTicks(), this::isWritable);
+        this.terrainHeights = new Long2LongOpenHashMap();
+        this.terrainHeights.defaultReturnValue(Long.MIN_VALUE);
+        this.outsideChunks = new Long2ObjectOpenHashMap<>();
+    }
+
+    static ModdedNativeStructureWorldgenAccess create(WorldGenLevel delegate, ChunkPos generationCenter,
+                                                IntBinaryOperator surfaceFirstFreeY,
+                                                IntBinaryOperator floorFirstFreeY) {
+        return new ModdedNativeStructureWorldgenAccess(delegate, new Boundary(
+                generationCenter, surfaceFirstFreeY, floorFirstFreeY));
+    }
+
+    @Override
+    public long getSeed() {
+        return delegate.getSeed();
+    }
+
+    @Override
+    public boolean ensureCanWrite(BlockPos position) {
+        return isWritable(position) && delegate.ensureCanWrite(position);
+    }
+
+    @Override
+    public void setCurrentlyGenerating(Supplier<String> description) {
+        delegate.setCurrentlyGenerating(description);
+    }
+
+    @Override
+    public ServerLevel getLevel() {
+        return delegate.getLevel();
+    }
+
+    @Override
+    public DifficultyInstance getCurrentDifficultyAt(BlockPos position) {
+        if (isReadable(position)) {
+            return delegate.getCurrentDifficultyAt(position);
+        }
+        return delegate.getCurrentDifficultyAt(generationCenter.getMiddleBlockPosition(
+                Mth.clamp(position.getY(), getMinY(), getMaxY() - 1)));
+    }
+
+    @Override
+    public long nextSubTickCount() {
+        return delegate.nextSubTickCount();
+    }
+
+    @Override
+    public LevelTickAccess<Block> getBlockTicks() {
+        return blockTicks;
+    }
+
+    @Override
+    public LevelTickAccess<Fluid> getFluidTicks() {
+        return fluidTicks;
+    }
+
+    @Override
+    public LevelData getLevelData() {
+        return delegate.getLevelData();
+    }
+
+    @Override
+    public MinecraftServer getServer() {
+        return delegate.getServer();
+    }
+
+    @Override
+    public ChunkSource getChunkSource() {
+        return delegate.getChunkSource();
+    }
+
+    @Override
+    public RandomSource getRandom() {
+        return delegate.getRandom();
+    }
+
+    @Override
+    public void updateNeighborsAt(BlockPos position, Block block) {
+        if (isWritableNeighbourhood(position)) {
+            delegate.updateNeighborsAt(position, block);
+        }
+    }
+
+    @Override
+    public void neighborShapeChanged(Direction direction, BlockPos position,
+                                     BlockPos neighbourPosition, BlockState neighbourState,
+                                     int updateFlags, int updateLimit) {
+        if (isWritable(position) && isWritable(neighbourPosition)) {
+            delegate.neighborShapeChanged(
+                    direction, position, neighbourPosition, neighbourState, updateFlags, updateLimit);
+        }
+    }
+
+    @Override
+    public void playSound(Entity source, BlockPos position, SoundEvent sound,
+                          SoundSource soundSource, float volume, float pitch) {
+        if (isWritable(position)) {
+            delegate.playSound(source, position, sound, soundSource, volume, pitch);
+        }
+    }
+
+    @Override
+    public void addParticle(ParticleOptions particle, double x, double y, double z,
+                            double velocityX, double velocityY, double velocityZ) {
+        if (isWritable(BlockPos.containing(x, y, z))) {
+            delegate.addParticle(particle, x, y, z, velocityX, velocityY, velocityZ);
+        }
+    }
+
+    @Override
+    public void levelEvent(Entity source, int eventId, BlockPos position, int data) {
+        if (isWritable(position)) {
+            delegate.levelEvent(source, eventId, position, data);
+        }
+    }
+
+    @Override
+    public void gameEvent(Holder<GameEvent> event, Vec3 position, GameEvent.Context context) {
+        if (isWritable(BlockPos.containing(position))) {
+            delegate.gameEvent(event, position, context);
+        }
+    }
+
+    @Override
+    public ChunkAccess getChunk(int chunkX, int chunkZ) {
+        if (isInsideGenerationRegion(chunkX, chunkZ)) {
+            return delegate.getChunk(chunkX, chunkZ);
+        }
+        return outsideChunk(chunkX, chunkZ);
+    }
+
+    @Override
+    public ChunkAccess getChunk(int chunkX, int chunkZ, ChunkStatus status, boolean create) {
+        if (isInsideGenerationRegion(chunkX, chunkZ)) {
+            return delegate.getChunk(chunkX, chunkZ, status, create);
+        }
+        return create ? outsideChunk(chunkX, chunkZ) : null;
+    }
+
+    @Override
+    public boolean hasChunk(int chunkX, int chunkZ) {
+        return isInsideGenerationRegion(chunkX, chunkZ) && delegate.hasChunk(chunkX, chunkZ);
+    }
+
+    @Override
+    public int getHeight(Heightmap.Types type, int x, int z) {
+        if (isInsideGenerationRegion(x >> 4, z >> 4)) {
+            return delegate.getHeight(type, x, z);
+        }
+        return height(type, x, z);
+    }
+
+    @Override
+    public int getSkyDarken() {
+        return delegate.getSkyDarken();
+    }
+
+    @Override
+    public BiomeManager getBiomeManager() {
+        return biomeManager;
+    }
+
+    @Override
+    public Holder<Biome> getNoiseBiome(int quartX, int quartY, int quartZ) {
+        return getUncachedNoiseBiome(quartX, quartY, quartZ);
+    }
+
+    @Override
+    public Holder<Biome> getUncachedNoiseBiome(int quartX, int quartY, int quartZ) {
+        if (isInsideGenerationRegion(QuartPos.toSection(quartX), QuartPos.toSection(quartZ))) {
+            return delegate.getUncachedNoiseBiome(quartX, quartY, quartZ);
+        }
+        return fallbackBiome;
+    }
+
+    @Override
+    public boolean isClientSide() {
+        return delegate.isClientSide();
+    }
+
+    @Override
+    public int getSeaLevel() {
+        return delegate.getSeaLevel();
+    }
+
+    @Override
+    public DimensionType dimensionType() {
+        return delegate.dimensionType();
+    }
+
+    @Override
+    public int getMinY() {
+        return delegate.getMinY();
+    }
+
+    @Override
+    public int getHeight() {
+        return delegate.getHeight();
+    }
+
+    @Override
+    public RegistryAccess registryAccess() {
+        return delegate.registryAccess();
+    }
+
+    @Override
+    public FeatureFlagSet enabledFeatures() {
+        return delegate.enabledFeatures();
+    }
+
+    @Override
+    public EnvironmentAttributeReader environmentAttributes() {
+        return delegate.environmentAttributes();
+    }
+
+    @Override
+    public LevelLightEngine getLightEngine() {
+        return delegate.getLightEngine();
+    }
+
+    @Override
+    public int getBrightness(LightLayer layer, BlockPos position) {
+        if (isReadable(position)) {
+            return delegate.getBrightness(layer, position);
+        }
+        return layer == LightLayer.SKY && canSeeSky(position) ? 15 : 0;
+    }
+
+    @Override
+    public int getRawBrightness(BlockPos position, int ambientDarkening) {
+        if (isReadable(position)) {
+            return delegate.getRawBrightness(position, ambientDarkening);
+        }
+        return Math.max(0, getBrightness(LightLayer.SKY, position) - ambientDarkening);
+    }
+
+    @Override
+    public boolean canSeeSky(BlockPos position) {
+        if (isReadable(position)) {
+            return delegate.canSeeSky(position);
+        }
+        return position.getY() >= height(Heightmap.Types.WORLD_SURFACE_WG, position.getX(), position.getZ());
+    }
+
+    @Override
+    public WorldBorder getWorldBorder() {
+        return delegate.getWorldBorder();
+    }
+
+    @Override
+    public BlockGetter getChunkForCollisions(int chunkX, int chunkZ) {
+        if (isInsideGenerationRegion(chunkX, chunkZ)) {
+            return delegate.getChunkForCollisions(chunkX, chunkZ);
+        }
+        return outsideChunk(chunkX, chunkZ);
+    }
+
+    @Override
+    public BlockEntity getBlockEntity(BlockPos position) {
+        return isReadable(position) ? delegate.getBlockEntity(position) : null;
+    }
+
+    @Override
+    public <T extends BlockEntity> Optional<T> getBlockEntity(
+            BlockPos position, BlockEntityType<T> type) {
+        return isReadable(position) ? delegate.getBlockEntity(position, type) : Optional.empty();
+    }
+
+    @Override
+    public BlockState getBlockState(BlockPos position) {
+        return isReadable(position) ? delegate.getBlockState(position) : terrainState(position);
+    }
+
+    @Override
+    public FluidState getFluidState(BlockPos position) {
+        return isReadable(position) ? delegate.getFluidState(position) : terrainState(position).getFluidState();
+    }
+
+    @Override
+    public List<Entity> getEntities(Entity source, AABB area, Predicate<? super Entity> predicate) {
+        AABB boundedArea = boundedArea(area);
+        return boundedArea == null ? List.of() : delegate.getEntities(source, boundedArea, predicate);
+    }
+
+    @Override
+    public <T extends Entity> List<T> getEntities(
+            EntityTypeTest<Entity, T> type,
+            AABB area, Predicate<? super T> predicate) {
+        AABB boundedArea = boundedArea(area);
+        return boundedArea == null ? List.of() : delegate.getEntities(type, boundedArea, predicate);
+    }
+
+    @Override
+    public List<? extends Player> players() {
+        return delegate.players();
+    }
+
+    @Override
+    public boolean isStateAtPosition(BlockPos position, Predicate<BlockState> predicate) {
+        return predicate.test(getBlockState(position));
+    }
+
+    @Override
+    public boolean isFluidAtPosition(BlockPos position, Predicate<FluidState> predicate) {
+        return predicate.test(getFluidState(position));
+    }
+
+    @Override
+    public BlockPos getHeightmapPos(Heightmap.Types type, BlockPos position) {
+        return position.atY(getHeight(type, position.getX(), position.getZ()));
+    }
+
+    @Override
+    public boolean setBlock(BlockPos position, BlockState state, int updateFlags, int updateLimit) {
+        return isWritable(position) && delegate.setBlock(position, state, updateFlags, updateLimit);
+    }
+
+    @Override
+    public boolean removeBlock(BlockPos position, boolean move) {
+        return isWritable(position) && delegate.removeBlock(position, move);
+    }
+
+    @Override
+    public boolean destroyBlock(BlockPos position, boolean drop, Entity source, int updateLimit) {
+        return isWritable(position) && delegate.destroyBlock(position, drop, source, updateLimit);
+    }
+
+    @Override
+    public boolean addFreshEntity(Entity entity) {
+        return isWritable(entity.blockPosition()) && delegate.addFreshEntity(entity);
+    }
+
+
+    private boolean isReadable(BlockPos position) {
+        return isInsideGenerationRegion(position.getX() >> 4, position.getZ() >> 4)
+                && !isOutsideBuildHeight(position);
+    }
+
+    private boolean isWritable(BlockPos position) {
+        return isReadable(position);
+    }
+
+    private boolean isWritableNeighbourhood(BlockPos position) {
+        return isWritable(position)
+                && isWritable(position.north())
+                && isWritable(position.south())
+                && isWritable(position.east())
+                && isWritable(position.west())
+                && isWritable(position.above())
+                && isWritable(position.below());
+    }
+
+    private AABB boundedArea(AABB area) {
+        double minX = Math.max(area.minX, generationBounds.minX);
+        double minY = Math.max(area.minY, generationBounds.minY);
+        double minZ = Math.max(area.minZ, generationBounds.minZ);
+        double maxX = Math.min(area.maxX, generationBounds.maxX);
+        double maxY = Math.min(area.maxY, generationBounds.maxY);
+        double maxZ = Math.min(area.maxZ, generationBounds.maxZ);
+        if (minX >= maxX || minY >= maxY || minZ >= maxZ) {
+            return null;
+        }
+        if (minX == area.minX && minY == area.minY && minZ == area.minZ
+                && maxX == area.maxX && maxY == area.maxY && maxZ == area.maxZ) {
+            return area;
+        }
+        return new AABB(minX, minY, minZ, maxX, maxY, maxZ);
+    }
+
+    boolean isInsideGenerationRegion(int chunkX, int chunkZ) {
+        return Math.abs(chunkX - generationCenter.x()) <= WRITE_RADIUS
+                && Math.abs(chunkZ - generationCenter.z()) <= WRITE_RADIUS;
+    }
+
+    @Override
+    public boolean isOutsideBuildHeight(BlockPos position) {
+        return position.getY() < getMinY() || position.getY() >= getMaxY();
+    }
+
+    private BlockState terrainState(BlockPos position) {
+        if (isOutsideBuildHeight(position)) {
+            return Blocks.VOID_AIR.defaultBlockState();
+        }
+        long heights = heights(position.getX(), position.getZ());
+        int surface = (int) (heights >> 32);
+        int floor = (int) heights;
+        if (position.getY() < floor) {
+            return Blocks.STONE.defaultBlockState();
+        }
+        if (position.getY() < surface) {
+            return Blocks.WATER.defaultBlockState();
+        }
+        return Blocks.AIR.defaultBlockState();
+    }
+
+    private int height(Heightmap.Types type, int x, int z) {
+        long heights = heights(x, z);
+        if (type == Heightmap.Types.OCEAN_FLOOR || type == Heightmap.Types.OCEAN_FLOOR_WG) {
+            return (int) heights;
+        }
+        return (int) (heights >> 32);
+    }
+
+    private long heights(int x, int z) {
+        long key = ((long) x << 32) ^ (z & 0xffffffffL);
+        long cached = terrainHeights.get(key);
+        if (cached != Long.MIN_VALUE) {
+            return cached;
+        }
+        int floor = Mth.clamp(floorFirstFreeY.applyAsInt(x, z), getMinY(), getMaxY());
+        int surface = Mth.clamp(surfaceFirstFreeY.applyAsInt(x, z), floor, getMaxY());
+        long heights = ((long) surface << 32) | (floor & 0xffffffffL);
+        terrainHeights.put(key, heights);
+        return heights;
+    }
+
+    private ChunkAccess outsideChunk(int chunkX, int chunkZ) {
+        long key = ChunkPos.pack(chunkX, chunkZ);
+        ChunkAccess cached = outsideChunks.get(key);
+        if (cached != null) {
+            return cached;
+        }
+        EmptyLevelChunk chunk = new EmptyLevelChunk(getLevel(), new ChunkPos(chunkX, chunkZ), fallbackBiome);
+        WorldgenTerrainHeightmaps.primeTerrain(chunk, surfaceFirstFreeY, floorFirstFreeY);
+        outsideChunks.put(key, chunk);
+        return chunk;
+    }
+
+    private record Boundary(ChunkPos generationCenter,
+                            IntBinaryOperator surfaceFirstFreeY,
+                            IntBinaryOperator floorFirstFreeY) {
+    }
+
+    private static final class BoundedTickAccess<T> implements LevelTickAccess<T> {
+        private final LevelTickAccess<T> delegate;
+        private final Predicate<BlockPos> writable;
+
+        private BoundedTickAccess(LevelTickAccess<T> delegate, Predicate<BlockPos> writable) {
+            this.delegate = delegate;
+            this.writable = writable;
+        }
+
+        @Override
+        public void schedule(ScheduledTick<T> tick) {
+            if (writable.test(tick.pos())) {
+                delegate.schedule(tick);
+            }
+        }
+
+        @Override
+        public boolean hasScheduledTick(BlockPos position, T type) {
+            return writable.test(position) && delegate.hasScheduledTick(position, type);
+        }
+
+        @Override
+        public int count() {
+            return delegate.count();
+        }
+
+        @Override
+        public boolean willTickThisTick(BlockPos position, T type) {
+            return writable.test(position) && delegate.willTickThisTick(position, type);
+        }
+    }
+}

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

@@ -344,7 +344,7 @@ public final class IrisModdedCommands {
 
             execution = new PackDownloadExecution(
                     lease,
-                    cancellation -> executeDownload(source, request, target, downloadSource, scheduler, cancellation)
+                    cancellation -> executeDownload(source, request, target, downloadSource, cancellation)
             );
             PackDownloadExecution trackedExecution = execution;
             execution.onCompletion(() -> clearActiveDownload(trackedExecution));
@@ -384,7 +384,6 @@ public final class IrisModdedCommands {
             DownloadRequest request,
             String target,
             String downloadSource,
-            ModdedScheduler scheduler,
             PackDownloader.DownloadCancellation cancellation
     ) throws PackDownloader.PackDownloadCancelledException {
         File packs = ModdedPackCommands.packsRoot();
@@ -394,37 +393,41 @@ public final class IrisModdedCommands {
                             packs,
                             request.url(),
                             false,
-                            (String message) -> scheduler.global(() -> ok(source, message)),
+                            (String message) -> dispatchDownloadFeedback(source, () -> ok(source, message)),
                             cancellation
                     )
                     : PackDownloader.downloadBuiltIn(
                             packs,
                             request.pack(),
                             false,
-                            (String message) -> scheduler.global(() -> ok(source, message)),
+                            (String message) -> dispatchDownloadFeedback(source, () -> ok(source, message)),
                             cancellation
                     );
             String completionMessage = downloadCompletionMessage(result);
             if (result != null) {
                 if (completionMessage != null) {
-                    scheduler.global(() -> ok(source, completionMessage));
+                    dispatchDownloadFeedback(source, () -> ok(source, completionMessage));
                 }
                 return;
             }
         } catch (PackDownloader.PackDownloadCancelledException error) {
             throw error;
         } catch (PackDownloader.PackDownloadBusyException error) {
-            scheduler.global(() -> fail(source, error.getMessage()));
+            dispatchDownloadFeedback(source, () -> fail(source, error.getMessage()));
             return;
         } catch (IOException | RuntimeException error) {
             LOGGER.error("Iris pack download failed for {}", target, error);
         }
-        scheduler.global(() -> fail(source, IrisLanguage.plain(
+        dispatchDownloadFeedback(source, () -> fail(source, IrisLanguage.plain(
                 ModdedCommandMessages.IRIS_MODDED_COMMANDS_PACK_DOWNLOAD_FAILED_SEE_CONSOLE,
                 MessageArgument.untrusted("pack", target),
                 MessageArgument.untrusted("downloadSource", downloadSource))));
     }
 
+    private static void dispatchDownloadFeedback(CommandSourceStack source, Runnable feedback) {
+        source.getServer().execute(feedback);
+    }
+
     static String downloadBusyMessage(LifecycleOperationCoordinator.ActiveOperation operation) {
         if (operation.domain() == LifecycleOperationCoordinator.Domain.PACK_MUTATION
                 && operation.kind() == LifecycleOperationCoordinator.OperationKind.PACK_DOWNLOAD) {

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

@@ -51,7 +51,14 @@ final class ModdedPregenCommands {
             return 0;
         }
         boolean showGui = gui && ModdedGuiHost.isGuiLaunchable();
-        if (!ModdedPregenJob.start(source.getServer(), level, engine, radius, centerX, centerZ, showGui, sync, !nocache)) {
+        boolean started;
+        try {
+            started = ModdedPregenJob.start(source.getServer(), level, engine, radius, centerX, centerZ, showGui, sync, !nocache);
+        } catch (IllegalArgumentException failure) {
+            IrisModdedCommands.fail(source, failure.getMessage());
+            return 0;
+        }
+        if (!started) {
             IrisModdedCommands.fail(source, IrisLanguage.plain(ModdedCommandMessages.IRIS_MODDED_COMMANDS_PREGENERATION_TASK_IS_ALREADY_RUNNING_STOP_IT_FIRST_WITH_IRIS));
             return 0;
         }

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

@@ -55,13 +55,13 @@ public final class ModdedPregenJob {
             return false;
         }
 
-        PregenPerformanceProfile.apply(engine);
         PregenTask task = PregenTask.builder()
                 .gui(gui)
                 .center(new Position2(centerBlockX, centerBlockZ))
                 .radiusX(radiusBlocks)
                 .radiusZ(radiusBlocks)
                 .build();
+        PregenPerformanceProfile.apply(engine);
         ModdedPregenMethod moddedMethod = new ModdedPregenMethod(level, engine, sync);
         PregeneratorMethod method = moddedMethod;
         if (cached) {

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

@@ -73,6 +73,7 @@ public final class ModdedPregenMethod implements PregeneratorMethod {
     private final AtomicBoolean finalSaveCompleted = new AtomicBoolean(false);
     private final AtomicReference<FinalSaveRequest> queuedFinalSave = new AtomicReference<>();
     private final AtomicBoolean stallHintLogged = new AtomicBoolean(false);
+    private final AtomicBoolean failureDetailLogged = new AtomicBoolean(false);
     private final int timeoutSeconds;
     private final PregenMantleBackpressure backpressure;
     private final PauseWhenEmptyGuard pauseGuard;
@@ -350,7 +351,7 @@ public final class ModdedPregenMethod implements PregeneratorMethod {
             if (e instanceof TimeoutException) {
                 noteStallHint();
             }
-            LOGGER.warn("Iris pregen chunk {},{} failed: {}", x, z, e.toString());
+            logChunkFailure(x, z, e);
             listener.onChunkFailed(x, z);
         } finally {
             markFinished();
@@ -395,7 +396,7 @@ public final class ModdedPregenMethod implements PregeneratorMethod {
                     if (unwrap(error) instanceof TimeoutException) {
                         onTimeout();
                     }
-                    LOGGER.warn("Iris pregen chunk {},{} failed: {}", x, z, error.toString());
+                    logChunkFailure(x, z, error);
                     listener.onChunkFailed(x, z);
                     return;
                 }
@@ -421,6 +422,15 @@ public final class ModdedPregenMethod implements PregeneratorMethod {
         inFlightPeak.accumulateAndGet(current, Math::max);
     }
 
+    private void logChunkFailure(int x, int z, Throwable failure) {
+        Throwable cause = unwrap(failure);
+        if (failureDetailLogged.compareAndSet(false, true)) {
+            LOGGER.warn("Iris pregen chunk {},{} failed; first failure follows", x, z, cause);
+            return;
+        }
+        LOGGER.warn("Iris pregen chunk {},{} failed: {}", x, z, cause.toString());
+    }
+
     private void markFinished() {
         inFlight.decrementAndGet();
         if (sync) {

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

@@ -0,0 +1,31 @@
+package art.arcane.iris.modded.mixin;
+
+import art.arcane.iris.modded.ModdedMixinFlags;
+import net.minecraft.world.level.block.Block;
+import net.minecraft.world.level.levelgen.structure.templatesystem.StructureTemplate;
+import org.spongepowered.asm.mixin.Final;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Mutable;
+import org.spongepowered.asm.mixin.Shadow;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
+
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+
+@Mixin(StructureTemplate.Palette.class)
+public abstract class StructureTemplatePaletteConcurrencyMixin {
+    @Shadow
+    @Final
+    @Mutable
+    private Map<Block, List<StructureTemplate.StructureBlockInfo>> cache;
+
+    @Inject(method = "<init>(Ljava/util/List;)V", at = @At("RETURN"))
+    private void iris$installConcurrentBlockCache(List<StructureTemplate.StructureBlockInfo> blocks,
+                                                  CallbackInfo info) {
+        cache = new ConcurrentHashMap<>();
+        ModdedMixinFlags.markStructureTemplatePalette();
+    }
+}

adapters/modded-common/src/main/resources/irisworldgen.entity.mixins.json

@@ -6,7 +6,8 @@
   "mixins": [
     "EntityPersistenceMixin",
     "LivingEntityLootMixin",
-    "MobAwarenessMixin"
+    "MobAwarenessMixin",
+    "StructureTemplatePaletteConcurrencyMixin"
   ],
   "injectors": {
     "defaultRequire": 1

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

@@ -102,7 +102,12 @@ public class ModdedGenerationLeaseContractTest {
         String execution = method(source, "private static void executeDownload(");
         assertTrue(execution.contains("PackDownloader.DownloadCancellation cancellation"));
         assertTrue(execution.contains("catch (PackDownloader.PackDownloadCancelledException error)"));
+        assertTrue(execution.contains("dispatchDownloadFeedback(source,"));
+        assertFalse(execution.contains("scheduler.global("));
         assertFalse(execution.contains("lease.close();"));
+
+        String feedback = method(source, "private static void dispatchDownloadFeedback(");
+        assertTrue(feedback.contains("source.getServer().execute(feedback);"));
     }
 
     @Test
@@ -170,6 +175,34 @@ public class ModdedGenerationLeaseContractTest {
         assertTrue(pending.contains("queuedFinalSave.get() != null"));
     }
 
+    @Test
+    public void firstPregenChunkFailureRetainsItsFullCause() throws IOException {
+        String methodSource = source("art/arcane/iris/modded/command/ModdedPregenMethod.java");
+        String logFailure = method(methodSource, "private void logChunkFailure(");
+
+        assertTrue(methodSource.contains("AtomicBoolean failureDetailLogged"));
+        assertTrue(logFailure.contains("unwrap(failure)"));
+        assertTrue(logFailure.contains("failureDetailLogged.compareAndSet(false, true)"));
+        assertTrue(logFailure.contains("x, z, cause);"));
+        assertTrue(logFailure.contains("cause.toString()"));
+    }
+
+    @Test
+    public void invalidPregenBoundsFailBeforeRuntimeMutation() throws IOException {
+        String jobSource = source("art/arcane/iris/modded/command/ModdedPregenJob.java");
+        String start = method(jobSource, "public static boolean start(");
+        int taskConstruction = start.indexOf("PregenTask task = PregenTask.builder()");
+        int profileMutation = start.indexOf("PregenPerformanceProfile.apply(engine);");
+
+        assertTrue(taskConstruction >= 0);
+        assertTrue(profileMutation > taskConstruction);
+
+        String commandSource = source("art/arcane/iris/modded/command/ModdedPregenCommands.java");
+        String command = method(commandSource, "static int pregenStart(");
+        assertTrue(command.contains("catch (IllegalArgumentException failure)"));
+        assertTrue(command.contains("IrisModdedCommands.fail(source, failure.getMessage())"));
+    }
+
     private static String source(String relativePath) throws IOException {
         String root = System.getProperty(SOURCE_ROOT_PROPERTY);
         assertTrue("Missing system property " + SOURCE_ROOT_PROPERTY, root != null && !root.isBlank());

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

@@ -0,0 +1,169 @@
+package art.arcane.iris.modded;
+
+import com.mojang.serialization.Codec;
+import net.minecraft.SharedConstants;
+import net.minecraft.core.BlockPos;
+import net.minecraft.core.Holder;
+import net.minecraft.core.IdMapper;
+import net.minecraft.server.Bootstrap;
+import net.minecraft.world.entity.ai.village.poi.PoiSection;
+import net.minecraft.world.entity.ai.village.poi.PoiType;
+import net.minecraft.world.entity.ai.village.poi.PoiTypes;
+import net.minecraft.world.level.ChunkPos;
+import net.minecraft.world.level.LevelHeightAccessor;
+import net.minecraft.world.level.biome.Biome;
+import net.minecraft.world.level.biome.BiomeGenerationSettings;
+import net.minecraft.world.level.biome.BiomeSpecialEffects;
+import net.minecraft.world.level.biome.MobSpawnSettings;
+import net.minecraft.world.level.block.Block;
+import net.minecraft.world.level.block.Blocks;
+import net.minecraft.world.level.block.state.BlockState;
+import net.minecraft.world.level.chunk.PalettedContainer;
+import net.minecraft.world.level.chunk.PalettedContainerFactory;
+import net.minecraft.world.level.chunk.PalettedContainerRO;
+import net.minecraft.world.level.chunk.ProtoChunk;
+import net.minecraft.world.level.chunk.Strategy;
+import net.minecraft.world.level.chunk.UpgradeData;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import java.util.ArrayDeque;
+import java.util.Deque;
+import java.util.LinkedHashMap;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.concurrent.atomic.AtomicInteger;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
+
+public class ModdedNativeStructurePoiRegistrationTest {
+    @BeforeClass
+    public static void bootstrapMinecraftRegistries() {
+        SharedConstants.tryDetectVersion();
+        Bootstrap.bootStrap();
+    }
+
+    @Test
+    public void visitsOnlyExistingPoiBlocksBeforeNativePlacement() {
+        ProtoChunk chunk = newChunk();
+        BlockPos poiPosition = new BlockPos(3, 70, 5);
+        BlockPos ordinaryPosition = new BlockPos(4, 70, 5);
+        BlockState poiState = Blocks.BARREL.defaultBlockState();
+        chunk.setBlockState(poiPosition, poiState, 0);
+        chunk.setBlockState(ordinaryPosition, Blocks.STONE.defaultBlockState(), 0);
+        Map<BlockPos, BlockState> visited = new LinkedHashMap<>();
+
+        ModdedNativeStructureStage.visitExistingPois(
+                chunk, (position, state) -> visited.put(position.immutable(), state));
+
+        assertEquals(poiState, visited.get(poiPosition));
+        assertFalse(visited.containsKey(ordinaryPosition));
+        assertEquals(1, visited.size());
+    }
+
+    @Test
+    public void duplicatePrimingIsIdempotentForAnAlreadyRegisteredPoi() {
+        BlockPos position = new BlockPos(3, 70, 5);
+        Holder<PoiType> type = PoiTypes.forState(
+                Blocks.BARREL.defaultBlockState()).orElseThrow();
+        PoiSection section = new PoiSection(() -> { });
+
+        assertNotNull(section.add(position, type));
+        assertNull(section.add(position, type));
+        assertEquals(type, section.getType(position).orElseThrow());
+
+        section.remove(position);
+
+        assertTrue(section.getType(position).isEmpty());
+    }
+
+    @Test
+    public void worldgenPrimingQueuesBeforeTheLaterVanillaRemoval() {
+        ProtoChunk chunk = newChunk();
+        BlockPos position = new BlockPos(3, 70, 5);
+        BlockState poiState = Blocks.BARREL.defaultBlockState();
+        chunk.setBlockState(position, poiState, 0);
+        PoiSection section = new PoiSection(() -> { });
+        Deque<Runnable> serverQueue = new ArrayDeque<>();
+        AtomicInteger missingRemovals = new AtomicInteger();
+
+        ModdedNativeStructureStage.visitExistingPois(chunk,
+                (poiPosition, state) -> queuePoiTransition(
+                        serverQueue, section, poiPosition,
+                        Blocks.AIR.defaultBlockState(), state, missingRemovals));
+        assertTrue(section.getType(position).isEmpty());
+        queuePoiTransition(serverQueue, section, position,
+                poiState, Blocks.AIR.defaultBlockState(), missingRemovals);
+
+        while (!serverQueue.isEmpty()) {
+            serverQueue.removeFirst().run();
+        }
+
+        assertEquals(0, missingRemovals.get());
+        assertTrue(section.getType(position).isEmpty());
+    }
+
+    private static void queuePoiTransition(Deque<Runnable> serverQueue,
+                                           PoiSection section,
+                                           BlockPos position,
+                                           BlockState oldState,
+                                           BlockState newState,
+                                           AtomicInteger missingRemovals) {
+        Optional<Holder<PoiType>> oldType = PoiTypes.forState(oldState);
+        Optional<Holder<PoiType>> newType = PoiTypes.forState(newState);
+        if (Objects.equals(oldType, newType)) {
+            return;
+        }
+        BlockPos immutablePosition = position.immutable();
+        oldType.ifPresent(type -> serverQueue.addLast(() -> {
+            if (section.getType(immutablePosition).isEmpty()) {
+                missingRemovals.incrementAndGet();
+                return;
+            }
+            section.remove(immutablePosition);
+        }));
+        newType.ifPresent(type -> serverQueue.addLast(
+                () -> section.add(immutablePosition, type)));
+    }
+
+    private static ProtoChunk newChunk() {
+        return new ProtoChunk(
+                new ChunkPos(0, 0),
+                UpgradeData.EMPTY,
+                LevelHeightAccessor.create(-64, 384),
+                palettedContainerFactory(),
+                null);
+    }
+
+    private static PalettedContainerFactory palettedContainerFactory() {
+        Strategy<BlockState> blockStrategy = Strategy.createForBlockStates(Block.BLOCK_STATE_REGISTRY);
+        Codec<PalettedContainer<BlockState>> blockCodec = PalettedContainer.codecRW(
+                BlockState.CODEC, blockStrategy, Blocks.AIR.defaultBlockState());
+        Biome biome = new Biome.BiomeBuilder()
+                .hasPrecipitation(false)
+                .temperature(0.8F)
+                .downfall(0.4F)
+                .specialEffects(new BiomeSpecialEffects.Builder().waterColor(0x3F76E4).build())
+                .mobSpawnSettings(MobSpawnSettings.EMPTY)
+                .generationSettings(BiomeGenerationSettings.EMPTY)
+                .build();
+        Holder<Biome> biomeHolder = Holder.direct(biome);
+        IdMapper<Holder<Biome>> biomeIds = new IdMapper<>(1);
+        biomeIds.add(biomeHolder);
+        Strategy<Holder<Biome>> biomeStrategy = Strategy.createForBiomes(biomeIds);
+        Codec<PalettedContainerRO<Holder<Biome>>> biomeCodec = PalettedContainer.codecRO(
+                Biome.CODEC, biomeStrategy, biomeHolder);
+        return new PalettedContainerFactory(
+                blockStrategy,
+                Blocks.AIR.defaultBlockState(),
+                blockCodec,
+                biomeStrategy,
+                biomeHolder,
+                biomeCodec);
+    }
+}

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

@@ -0,0 +1,323 @@
+package art.arcane.iris.modded;
+
+import net.minecraft.SharedConstants;
+import net.minecraft.core.BlockPos;
+import net.minecraft.core.Direction;
+import net.minecraft.core.Holder;
+import net.minecraft.server.Bootstrap;
+import net.minecraft.world.entity.Entity;
+import net.minecraft.world.level.ChunkPos;
+import net.minecraft.world.level.WorldGenLevel;
+import net.minecraft.world.level.biome.Biome;
+import net.minecraft.world.level.biome.BiomeManager;
+import net.minecraft.world.level.block.Block;
+import net.minecraft.world.level.block.Blocks;
+import net.minecraft.world.level.block.state.BlockState;
+import net.minecraft.world.level.chunk.status.ChunkStatus;
+import net.minecraft.world.level.entity.EntityTypeTest;
+import net.minecraft.world.level.levelgen.Heightmap;
+import net.minecraft.world.level.material.Fluid;
+import net.minecraft.world.level.material.FluidState;
+import net.minecraft.world.phys.AABB;
+import net.minecraft.world.phys.Vec3;
+import net.minecraft.world.ticks.LevelTickAccess;
+import net.minecraft.world.ticks.ScheduledTick;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import java.lang.reflect.InvocationHandler;
+import java.lang.reflect.Method;
+import java.lang.reflect.Proxy;
+import java.util.ArrayList;
+import java.util.List;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertSame;
+import static org.junit.Assert.assertTrue;
+
+public class ModdedNativeStructureWorldgenAccessTest {
+    private static final int GENERATION_CENTER_X = 60;
+    private static final int GENERATION_CENTER_Z = 15;
+    private static final int SURFACE_FIRST_FREE_Y = 80;
+    private static final int FLOOR_FIRST_FREE_Y = 70;
+
+    @BeforeClass
+    public static void bootstrapMinecraftRegistries() {
+        SharedConstants.tryDetectVersion();
+        Bootstrap.bootStrap();
+    }
+
+    @Test
+    public void distanceTwoTerrainReadsNeverReachTheDelegate() {
+        RecordingDelegate recording = new RecordingDelegate();
+        ModdedNativeStructureWorldgenAccess access = access(recording);
+        ChunkPos generationCenter = generationCenter();
+        int x = generationCenter.getMiddleBlockX();
+        int z = (generationCenter.z() + 2) << 4;
+
+        assertSame(Blocks.STONE, access.getBlockState(new BlockPos(x, FLOOR_FIRST_FREE_Y - 1, z)).getBlock());
+        assertSame(Blocks.WATER, access.getBlockState(new BlockPos(x, FLOOR_FIRST_FREE_Y, z)).getBlock());
+        assertSame(Blocks.AIR, access.getBlockState(new BlockPos(x, SURFACE_FIRST_FREE_Y, z)).getBlock());
+        assertSame(Blocks.WATER.defaultBlockState().getFluidState(),
+                access.getFluidState(new BlockPos(x, FLOOR_FIRST_FREE_Y, z)));
+        assertEquals(SURFACE_FIRST_FREE_Y, access.getHeight(Heightmap.Types.WORLD_SURFACE_WG, x, z));
+        assertEquals(FLOOR_FIRST_FREE_Y, access.getHeight(Heightmap.Types.OCEAN_FLOOR_WG, x, z));
+        assertNull(access.getChunk(generationCenter.x(), generationCenter.z() + 2, ChunkStatus.FEATURES, false));
+        List<BlockState> loadedOnly = access.getBlockStatesIfLoaded(new AABB(
+                x, FLOOR_FIRST_FREE_Y, z, x, FLOOR_FIRST_FREE_Y, z)).toList();
+        List<BlockState> streamed = access.getBlockStates(new AABB(
+                x, FLOOR_FIRST_FREE_Y, z, x, FLOOR_FIRST_FREE_Y, z)).toList();
+
+        assertTrue(loadedOnly.isEmpty());
+        assertEquals(1, streamed.size());
+        assertSame(Blocks.WATER, streamed.getFirst().getBlock());
+        assertEquals(0, recording.terrainReads);
+        assertEquals(0, recording.heightReads);
+        assertEquals(0, recording.chunkReads);
+    }
+
+    @Test
+    public void distanceTwoMutationsAndSideEffectsNeverReachTheDelegate() {
+        RecordingDelegate recording = new RecordingDelegate();
+        ModdedNativeStructureWorldgenAccess access = access(recording);
+        ChunkPos generationCenter = generationCenter();
+        BlockPos position = new BlockPos(
+                generationCenter.getMiddleBlockX(),
+                FLOOR_FIRST_FREE_Y,
+                (generationCenter.z() + 2) << 4);
+
+        assertFalse(access.ensureCanWrite(position));
+        assertFalse(access.setBlock(position, Blocks.DIRT.defaultBlockState(), 2));
+        assertFalse(access.removeBlock(position, false));
+        assertFalse(access.destroyBlock(position, false));
+        access.updateNeighborsAt(position, Blocks.DIRT);
+        access.neighborShapeChanged(
+                Direction.NORTH, position, position.north(),
+                Blocks.DIRT.defaultBlockState(), 2, 512);
+        access.levelEvent(null, 2001, position, 0);
+        access.gameEvent(null, Vec3.atCenterOf(position), null);
+        access.addParticle(null, position.getX(), position.getY(), position.getZ(), 0, 0, 0);
+        access.getBlockTicks().schedule(new ScheduledTick<>(
+                Blocks.DIRT, position, 1L, 0L));
+
+        assertEquals(0, recording.mutations);
+        assertEquals(0, recording.events);
+        assertEquals(0, recording.blockTicks.count());
+    }
+
+    @Test
+    public void radiusOneReadsWritesAndTicksRemainUnchanged() {
+        RecordingDelegate recording = new RecordingDelegate();
+        ModdedNativeStructureWorldgenAccess access = access(recording);
+        ChunkPos generationCenter = generationCenter();
+        BlockPos position = new BlockPos(
+                (generationCenter.x() + 1) << 4,
+                FLOOR_FIRST_FREE_Y,
+                (generationCenter.z() - 1) << 4);
+
+        assertTrue(access.isInsideGenerationRegion(
+                generationCenter.x() + 1, generationCenter.z() - 1));
+        assertSame(Blocks.DIRT, access.getBlockState(position).getBlock());
+        assertEquals(91, access.getHeight(
+                Heightmap.Types.WORLD_SURFACE_WG, position.getX(), position.getZ()));
+        assertTrue(access.ensureCanWrite(position));
+        assertTrue(access.setBlock(position, Blocks.STONE.defaultBlockState(), 2));
+        assertTrue(access.removeBlock(position, false));
+        assertTrue(access.destroyBlock(position, false));
+        access.getBlockTicks().schedule(new ScheduledTick<>(
+                Blocks.DIRT, position, 1L, 0L));
+
+        assertEquals(1, recording.terrainReads);
+        assertEquals(1, recording.heightReads);
+        assertEquals(4, recording.mutations);
+        assertEquals(1, recording.blockTicks.count());
+    }
+
+    @Test
+    public void statuslessChunkReadsPreserveWorldgenDelegateSemantics() {
+        RecordingDelegate recording = new RecordingDelegate();
+        ModdedNativeStructureWorldgenAccess access = access(recording);
+        ChunkPos generationCenter = generationCenter();
+
+        assertNull(access.getChunk(generationCenter.getWorldPosition()));
+
+        assertEquals(1, recording.statuslessChunkReads);
+        assertEquals(0, recording.statusChunkReads);
+    }
+
+    @Test
+    public void entityQueriesRejectDisjointAreasAndClampOverlaps() {
+        RecordingDelegate recording = new RecordingDelegate();
+        ModdedNativeStructureWorldgenAccess access = access(recording);
+        ChunkPos generationCenter = generationCenter();
+        int safeMaxX = generationCenter.getMaxBlockX() + 17;
+        int safeMinZ = generationCenter.getMinBlockZ() - 16;
+        int safeMaxZ = generationCenter.getMaxBlockZ() + 17;
+        AABB disjoint = new AABB(
+                safeMaxX, -64, safeMinZ,
+                safeMaxX + 16, 320, safeMaxZ);
+        AABB overlap = new AABB(
+                safeMaxX - 8, -128, safeMinZ - 8,
+                safeMaxX + 16, 400, safeMaxZ + 8);
+        EntityTypeTest<Entity, Entity> type = EntityTypeTest.forClass(Entity.class);
+
+        assertTrue(access.getEntities((Entity) null, disjoint, entity -> true).isEmpty());
+        assertTrue(access.getEntities(type, disjoint, entity -> true).isEmpty());
+        access.getEntities((Entity) null, overlap, entity -> true);
+        access.getEntities(type, overlap, entity -> true);
+
+        assertEquals(2, recording.entityAreas.size());
+        for (AABB delegatedArea : recording.entityAreas) {
+            assertEquals(safeMaxX - 8, delegatedArea.minX, 0D);
+            assertEquals(-64, delegatedArea.minY, 0D);
+            assertEquals(safeMinZ, delegatedArea.minZ, 0D);
+            assertEquals(safeMaxX, delegatedArea.maxX, 0D);
+            assertEquals(320, delegatedArea.maxY, 0D);
+            assertEquals(safeMaxZ, delegatedArea.maxZ, 0D);
+        }
+    }
+
+    private static ModdedNativeStructureWorldgenAccess access(RecordingDelegate recording) {
+        return ModdedNativeStructureWorldgenAccess.create(
+                recording.world(), generationCenter(),
+                (x, z) -> SURFACE_FIRST_FREE_Y,
+                (x, z) -> FLOOR_FIRST_FREE_Y);
+    }
+
+    private static ChunkPos generationCenter() {
+        return new ChunkPos(GENERATION_CENTER_X, GENERATION_CENTER_Z);
+    }
+
+    private static final class RecordingDelegate implements InvocationHandler {
+        private final Holder<Biome> biome;
+        private final BiomeManager biomeManager;
+        private final RecordingTicks<Block> blockTicks;
+        private final RecordingTicks<Fluid> fluidTicks;
+        private final List<AABB> entityAreas;
+        private int terrainReads;
+        private int heightReads;
+        private int chunkReads;
+        private int statuslessChunkReads;
+        private int statusChunkReads;
+        private int mutations;
+        private int events;
+
+        private RecordingDelegate() {
+            this.biome = Holder.direct((Biome) null);
+            this.biomeManager = new BiomeManager((x, y, z) -> biome, 13L);
+            this.blockTicks = new RecordingTicks<>();
+            this.fluidTicks = new RecordingTicks<>();
+            this.entityAreas = new ArrayList<>();
+        }
+
+        private WorldGenLevel world() {
+            return (WorldGenLevel) Proxy.newProxyInstance(
+                    WorldGenLevel.class.getClassLoader(),
+                    new Class<?>[]{WorldGenLevel.class}, this);
+        }
+
+        @Override
+        public Object invoke(Object proxy, Method method, Object[] arguments) {
+            String name = method.getName();
+            if (name.equals("getSeaLevel")) {
+                return 63;
+            }
+            if (name.equals("getBiome")) {
+                return biome;
+            }
+            if (name.equals("getBiomeManager")) {
+                return biomeManager;
+            }
+            if (name.equals("getBlockTicks")) {
+                return blockTicks;
+            }
+            if (name.equals("getFluidTicks")) {
+                return fluidTicks;
+            }
+            if (name.equals("getMinY")) {
+                return -64;
+            }
+            if (name.equals("getHeight") && arguments == null) {
+                return 384;
+            }
+            if (name.equals("getHeight")) {
+                heightReads++;
+                return 91;
+            }
+            if (name.equals("getBlockState")) {
+                terrainReads++;
+                return Blocks.DIRT.defaultBlockState();
+            }
+            if (name.equals("getFluidState")) {
+                terrainReads++;
+                return Blocks.WATER.defaultBlockState().getFluidState();
+            }
+            if (name.equals("getChunk")) {
+                chunkReads++;
+                if (arguments.length == 2) {
+                    statuslessChunkReads++;
+                } else {
+                    statusChunkReads++;
+                }
+                return null;
+            }
+            if (name.equals("getChunkIfLoadedImmediately")) {
+                chunkReads++;
+                return null;
+            }
+            if (name.equals("getEntities")) {
+                entityAreas.add((AABB) arguments[1]);
+                return List.of();
+            }
+            if (name.equals("ensureCanWrite") || name.equals("setBlock")
+                    || name.equals("removeBlock") || name.equals("destroyBlock")) {
+                mutations++;
+                return true;
+            }
+            if (name.equals("updateNeighborsAt") || name.equals("neighborShapeChanged")) {
+                mutations++;
+                return null;
+            }
+            if (name.equals("levelEvent") || name.equals("gameEvent") || name.equals("addParticle")) {
+                events++;
+                return null;
+            }
+            if (name.equals("hashCode")) {
+                return System.identityHashCode(proxy);
+            }
+            if (name.equals("equals")) {
+                return proxy == arguments[0];
+            }
+            if (name.equals("toString")) {
+                return "native-structure-worldgen-test-delegate";
+            }
+            throw new UnsupportedOperationException(method.toString());
+        }
+    }
+
+    private static final class RecordingTicks<T> implements LevelTickAccess<T> {
+        private int count;
+
+        @Override
+        public void schedule(ScheduledTick<T> tick) {
+            count++;
+        }
+
+        @Override
+        public boolean hasScheduledTick(BlockPos position, T type) {
+            return false;
+        }
+
+        @Override
+        public int count() {
+            return count;
+        }
+
+        @Override
+        public boolean willTickThisTick(BlockPos position, T type) {
+            return false;
+        }
+    }
+}

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

@@ -0,0 +1,77 @@
+package art.arcane.iris.modded;
+
+import org.junit.Test;
+
+import java.io.InputStream;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicInteger;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertTrue;
+
+public class ModdedStructureTemplateCacheTest {
+    @Test
+    public void concurrentCacheOwnsDistinctAndSharedMappingsExactlyOnce() throws Exception {
+        ConcurrentHashMap<String, Integer> cache = new ConcurrentHashMap<>();
+        ExecutorService executor = Executors.newFixedThreadPool(32);
+        CountDownLatch start = new CountDownLatch(1);
+        AtomicInteger mappingCalls = new AtomicInteger();
+        List<Future<Integer>> futures = new ArrayList<>();
+        try {
+            for (int task = 0; task < 256; task++) {
+                int value = task;
+                String key = task % 2 == 0 ? "shared" : "distinct-" + task;
+                futures.add(executor.submit(() -> {
+                    start.await();
+                    return cache.computeIfAbsent(key, ignored -> {
+                        mappingCalls.incrementAndGet();
+                        Thread.yield();
+                        return value;
+                    });
+                }));
+            }
+            start.countDown();
+            for (Future<Integer> future : futures) {
+                assertNotNull(future.get(10, TimeUnit.SECONDS));
+            }
+        } finally {
+            executor.shutdownNow();
+            assertTrue(executor.awaitTermination(10, TimeUnit.SECONDS));
+        }
+
+        assertEquals(129, cache.size());
+        assertEquals(129, mappingCalls.get());
+    }
+
+    @Test
+    public void requiredCommonMixinConfigRegistersPaletteConcurrencyFix() throws Exception {
+        InputStream resource = ModdedStructureTemplateCacheTest.class.getClassLoader()
+                .getResourceAsStream("irisworldgen.entity.mixins.json");
+        assertNotNull(resource);
+        String config;
+        try (InputStream input = resource) {
+            config = new String(input.readAllBytes(), StandardCharsets.UTF_8);
+        }
+        assertTrue(config.contains("\"StructureTemplatePaletteConcurrencyMixin\""));
+
+        Path source = Path.of(System.getProperty("iris.moddedCommonSources"))
+                .resolve("art/arcane/iris/modded/mixin/StructureTemplatePaletteConcurrencyMixin.java");
+        String mixin = Files.readString(source);
+        assertTrue(mixin.contains("@Mixin(StructureTemplate.Palette.class)"));
+        assertTrue(mixin.contains("@Shadow\n    @Final\n    @Mutable"));
+        assertTrue(mixin.contains("private Map<Block, List<StructureTemplate.StructureBlockInfo>> cache;"));
+        assertTrue(mixin.contains("@Inject(method = \"<init>(Ljava/util/List;)V\", at = @At(\"RETURN\"))"));
+        assertTrue(mixin.contains("cache = new ConcurrentHashMap<>();"));
+    }
+}

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

@@ -67,6 +67,11 @@ public class NativeStructureFailureContractTest {
         assertTrue(placement.contains("\"terrain preparation\""));
         assertTrue(placement.contains("\"foundation repair\""));
         assertFalse(placement.contains("\"terrain carving\""));
+        assertTrue(placement.contains("visitExistingPois(chunk"));
+        assertTrue(placement.contains("level.updatePOIOnBlockStateChange("));
+        assertTrue(placement.contains("Blocks.AIR.defaultBlockState(), state"));
+        assertTrue(placement.indexOf("visitExistingPois(chunk")
+                < placement.indexOf("WorldgenTerrainHeightmaps.primeStructurePlacement("));
         assertTrue(placement.contains("prepareSurfaceStructures"));
         assertTrue(placement.contains("clearIntersectingVegetation"));
         assertTrue(placement.indexOf("clearIntersectingVegetation")
@@ -95,6 +100,19 @@ public class NativeStructureFailureContractTest {
         assertTrue(source.contains("int minY = chunk.getMinY() + 1;"));
     }
 
+    @Test
+    public void nativeStructurePostProcessingUsesBoundedWorldgenAccess() throws IOException {
+        String source = moddedSource("ModdedNativeStructureStage.java");
+        int placementStart = source.indexOf("private void placeVanillaStructure");
+        int placementEnd = source.indexOf("private List<List<Structure>> structuresByStep", placementStart);
+        String placement = source.substring(placementStart, placementEnd);
+
+        assertTrue(placement.contains("ModdedNativeStructureWorldgenAccess.create("));
+        assertTrue(placement.contains("NativeStructurePostProcessor.place(\n                    boundedWorld"));
+        assertFalse(placement.contains("NativeStructurePostProcessor.place(world,"));
+        assertTrue(placement.contains("world.setCurrentlyGenerating(null);"));
+    }
+
     @Test
     public void structureFailurePreservesPhaseIdentityChunkAndCause() {
         IllegalArgumentException cause = new IllegalArgumentException("broken placement");

adapters/neoforge/build.gradle

@@ -30,8 +30,8 @@ Properties rootProperties = new Properties()
 file('../../gradle.properties').withInputStream { InputStream stream -> rootProperties.load(stream) }
 String irisVersion = providers.gradleProperty('irisVersion').getOrElse(rootProperties.getProperty('irisVersion', '4.0.0-26.2'))
 String minecraftVersion = providers.gradleProperty('minecraftVersion').getOrElse(rootProperties.getProperty('minecraftVersion', '26.2'))
-String neoForgeVersion = providers.gradleProperty('neoForgeVersion').getOrElse(rootProperties.getProperty('neoForgeVersion', '26.2.0.12-beta'))
-String volmLibCoordinate = providers.gradleProperty('volmLibCoordinate').getOrElse(rootProperties.getProperty('volmLibCoordinate', 'com.github.VolmitSoftware:VolmLib:d9026a7c8ebc391c8109f401ce79a0ce65df3969'))
+String neoForgeVersion = providers.gradleProperty('neoForgeVersion').getOrElse(rootProperties.getProperty('neoForgeVersion', '26.2.0.59'))
+String volmLibCoordinate = providers.gradleProperty('volmLibCoordinate').getOrElse(rootProperties.getProperty('volmLibCoordinate', 'com.github.VolmitSoftware:VolmLib:5486ac97ad6d6833e27275dc768222d377721522'))
 Closure<String> irisArtifactName = { String platform, String targetVersion ->
     return "Iris v${project.version} [${platform}] ${targetVersion}.jar"
 }