Full audit fixpass: 93 defect fixes, 14 perf wins, vestigial cleanup

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

@@ -55,6 +55,7 @@ import it.unimi.dsi.fastutil.objects.Object2IntMap;
 import it.unimi.dsi.fastutil.shorts.ShortList;
 import net.bytebuddy.ByteBuddy;
 import net.bytebuddy.agent.builder.AgentBuilder;
+import net.bytebuddy.agent.builder.ResettableClassFileTransformer;
 import net.bytebuddy.asm.Advice;
 import net.bytebuddy.matcher.ElementMatchers;
 import net.minecraft.core.BlockPos;
@@ -172,6 +173,7 @@ public class NMSBinding implements INMSBinding {
     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 serverLevelTransformer;
     private final AtomicCache<MCAIdMapper<BlockState>> registryCache = new AtomicCache<>();
     private final AtomicCache<MCAPalette<BlockState>> globalCache = new AtomicCache<>();
     private final AtomicCache<RegistryAccess> registryAccess = new AtomicCache<>();
@@ -1523,7 +1525,7 @@ public class NMSBinding implements INMSBinding {
             }
             try {
                 IrisLogging.info("Injecting Bukkit");
-                new AgentBuilder.Default()
+                serverLevelTransformer = new AgentBuilder.Default()
                         .disableClassFormatChanges()
                         .with(AgentBuilder.RedefinitionStrategy.RETRANSFORMATION)
                         .type(ElementMatchers.is(ServerLevel.class))
@@ -1546,6 +1548,17 @@ 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;
+                serverLevelTransformer = null;
+                if (partial != null) {
+                    try {
+                        partial.reset(Agent.getInstrumentation(), AgentBuilder.RedefinitionStrategy.RETRANSFORMATION);
+                    } catch (Throwable ignored) {
+                    }
+                }
                 return false;
             }
         }
@@ -1562,6 +1575,24 @@ public class NMSBinding implements INMSBinding {
         }
     }
 
+    @Override
+    public void uninjectBukkit() {
+        synchronized (injected) {
+            ResettableClassFileTransformer transformer = serverLevelTransformer;
+            serverLevelTransformer = 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();
+            }
+        }
+    }
+
     @Override
     public KMap<Material, List<BlockProperty>> getBlockProperties() {
         KMap<Material, List<BlockProperty>> states = new KMap<>();
@@ -1624,24 +1655,56 @@ public class NMSBinding implements INMSBinding {
             if (dimensionKey == null)
                 return;
 
+            // This advice is inlined into every ServerLevel construction on the server. Until a
+            // world is proven Iris-owned, every failure must fail OPEN (keep the vanilla stem):
+            // Iris being unloaded or half-loaded must never break other plugins' world creation.
+            String levelId;
+            ClassLoader pluginClassLoader;
+            Class<?> generatorType;
+            Class<?> stagingType;
             try {
-                String levelId = dimensionKey.identifier().getPath();
+                levelId = dimensionKey.identifier().getPath();
                 if (levelId == null || levelId.isBlank()) {
                     return;
                 }
 
-                ClassLoader pluginClassLoader = Bukkit.getPluginManager().getPlugin("Iris").getClass().getClassLoader();
-                Class<?> generatorType = Class.forName("art.arcane.iris.engine.platform.PlatformChunkGenerator", true, pluginClassLoader);
+                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) {
+                // Iris absent or half-loaded: fail OPEN for a world we cannot prove ours.
+                return;
+            }
+
+            // From here Iris is present and its classes resolve; a failure resolving the
+            // staged generator must fail LOUD — silently handing a possibly-staged Iris world
+            // the vanilla stem corrupts generation.
+            ChunkGenerator gen = null;
+            try {
                 Object generator = generatorType.isInstance(constructorGenerator) ? constructorGenerator : null;
                 if (generator == null) {
-                    generator = Class.forName("art.arcane.iris.core.lifecycle.WorldLifecycleStaging", true, pluginClassLoader)
+                    generator = stagingType
                             .getDeclaredMethod("consumeStemGenerator", String.class)
                             .invoke(null, levelId);
                 }
-                if (!(generator instanceof ChunkGenerator gen) || !gen.getClass().getPackageName().startsWith("art.arcane.iris")) {
-                    return;
+                if (generator instanceof ChunkGenerator owned && owned.getClass().getPackageName().startsWith("art.arcane.iris")) {
+                    gen = owned;
                 }
+            } catch (Throwable e) {
+                throw new RuntimeException("Iris failed to resolve the staged world generator",
+                        e instanceof InvocationTargetException ex ? ex.getCause() : e);
+            }
+            if (gen == null) {
+                return;
+            }
 
+            // Past the ownership gate the world is Iris-owned; silently handing back the
+            // vanilla stem would corrupt generation, so failures from here rethrow.
+            try {
                 Object bindings = Class.forName("art.arcane.iris.core.nms.INMS", true, pluginClassLoader)
                         .getDeclaredMethod("get")
                         .invoke(null);

adapters/bukkit/plugin/build.gradle

@@ -14,6 +14,9 @@ dependencies {
         transitive = false
     }
     compileOnly(libs.paper.api)
+    // LogFilterSVC (constructed in Iris.enable's explicit service list) implements the
+    // log4j-core Filter interface, so its constructor reference needs the type resolvable.
+    compileOnly(libs.log4j.core)
     testImplementation('junit:junit:4.13.2')
     testImplementation('org.mockito:mockito-core:5.23.0')
     testImplementation(libs.paper.api)

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

@@ -51,9 +51,27 @@ import art.arcane.iris.core.link.MultiverseCoreLink;
 import art.arcane.iris.core.nms.INMS;
 import art.arcane.iris.core.gui.BukkitGuiHost;
 import art.arcane.iris.core.gui.PregeneratorJob;
+import art.arcane.iris.core.service.BoardSVC;
+import art.arcane.iris.core.service.CommandSVC;
+import art.arcane.iris.core.service.DatapackStructureScopeSVC;
 import art.arcane.iris.core.service.EditSVC;
+import art.arcane.iris.core.service.EntityRiseSVC;
+import art.arcane.iris.core.service.ExternalDataSVC;
+import art.arcane.iris.core.service.GlobalCacheSVC;
+import art.arcane.iris.core.service.IrisApiEventSVC;
+import art.arcane.iris.core.service.IrisEngineSVC;
+import art.arcane.iris.core.service.IrisIntegrationService;
+import art.arcane.iris.core.service.IrisProtocolService;
+import art.arcane.iris.core.service.IrisTerrainSVC;
+import art.arcane.iris.core.service.JigsawStudioService;
+import art.arcane.iris.core.service.LogFilterSVC;
+import art.arcane.iris.core.service.ObjectSVC;
+import art.arcane.iris.core.service.ObjectStudioSaveService;
 import art.arcane.iris.core.service.PreservationSVC;
 import art.arcane.iris.core.service.StudioSVC;
+import art.arcane.iris.core.service.TreeFellerSVC;
+import art.arcane.iris.core.service.TreeSVC;
+import art.arcane.iris.core.service.WandSVC;
 import art.arcane.iris.core.tools.IrisToolbelt;
 import art.arcane.iris.engine.EnginePanic;
 import art.arcane.iris.engine.framework.BlockEditAccess;
@@ -80,7 +98,6 @@ import art.arcane.volmlib.util.hud.HudBossBarLane;
 import art.arcane.volmlib.util.hud.HudSlotService;
 import art.arcane.volmlib.util.io.IO;
 import art.arcane.volmlib.util.io.InstanceState;
-import art.arcane.volmlib.util.io.JarScanner;
 import art.arcane.volmlib.util.math.M;
 import art.arcane.volmlib.util.math.RNG;
 import art.arcane.iris.util.common.misc.Bindings;
@@ -98,7 +115,6 @@ import org.bukkit.Bukkit;
 import org.bukkit.GameMode;
 import org.bukkit.Location;
 import org.bukkit.World;
-import org.bukkit.block.data.BlockData;
 import org.bukkit.command.Command;
 import org.bukkit.command.CommandSender;
 import org.bukkit.entity.Player;
@@ -115,9 +131,9 @@ import org.jetbrains.annotations.Nullable;
 import java.io.File;
 import java.io.FileOutputStream;
 import java.io.PrintWriter;
-import java.lang.annotation.Annotation;
 import java.lang.reflect.Modifier;
 import java.util.ArrayList;
+import java.util.concurrent.CopyOnWriteArrayList;
 import java.util.Date;
 import java.util.List;
 import java.util.Map;
@@ -165,6 +181,9 @@ public class Iris extends VolmitPlugin implements Listener, ReloadAware {
     private volatile IrisPapiListener papiListener;
     private volatile IrisPapiState papiState;
     private KMap<Class<? extends IrisService>, IrisService> services;
+    // Copy-on-write: mutated on the main thread during enable() and iterated by the JVM
+    // shutdown-hook thread during teardown; a plain list would CME and abort the teardown.
+    private final List<IrisService> enabledServices = new CopyOnWriteArrayList<>();
     private final IrisWorldGeneratorResolver generatorResolver = new IrisWorldGeneratorResolver(this);
     private final BukkitWorldReconciler worldReconciler = new BukkitWorldReconciler(this);
     private final PendingWorldDeleteQueue pendingWorldDeletes = new PendingWorldDeleteQueue(this);
@@ -206,28 +225,6 @@ public class Iris extends VolmitPlugin implements Listener, ReloadAware {
         }
     }
 
-    private static <T> KList<T> initialize(String s, Class<T> requiredType) {
-        JarScanner js = new JarScanner(instance.getJarFile(), s);
-        KList<T> v = new KList<>();
-        J.attempt(js::scan);
-        for (Class<?> i : js.getClasses()) {
-            if (!isConcreteImplementation(i, requiredType)) {
-                continue;
-            }
-            try {
-                v.add(requiredType.cast(i.getDeclaredConstructor().newInstance()));
-            } catch (Throwable ex) {
-                Iris.warn("Skipped class initialization for %s: %s%s",
-                        i.getName(),
-                        ex.getClass().getSimpleName(),
-                        ex.getMessage() == null ? "" : " - " + ex.getMessage());
-                Iris.reportError(ex);
-            }
-        }
-
-        return v;
-    }
-
     static boolean isConcreteImplementation(Class<?> candidate, Class<?> requiredType) {
         int modifiers = candidate.getModifiers();
         return requiredType.isAssignableFrom(candidate)
@@ -235,27 +232,6 @@ public class Iris extends VolmitPlugin implements Listener, ReloadAware {
                 && !Modifier.isAbstract(modifiers);
     }
 
-    public static KList<Class<?>> getClasses(String s, Class<? extends Annotation> slicedClass) {
-        JarScanner js = new JarScanner(instance.getJarFile(), s);
-        KList<Class<?>> v = new KList<>();
-        J.attempt(js::scan);
-        for (Class<?> i : js.getClasses()) {
-            if (slicedClass == null || i.isAnnotationPresent(slicedClass)) {
-                try {
-                    v.add(i);
-                } catch (Throwable ex) {
-                    Iris.warn("Skipped class discovery entry for %s: %s%s",
-                            i.getName(),
-                            ex.getClass().getSimpleName(),
-                            ex.getMessage() == null ? "" : " - " + ex.getMessage());
-                    Iris.reportError(ex);
-                }
-            }
-        }
-
-        return v;
-    }
-
     public static void sq(Runnable r) {
         synchronized (syncJobs) {
             syncJobs.queue(r);
@@ -538,7 +514,21 @@ public class Iris extends VolmitPlugin implements Listener, ReloadAware {
         }
     }
 
-    private void enable() {
+    /**
+     * @return false when the bootstrap was aborted (unsupported server version); the caller
+     * must bail out of onEnable without touching any further setup.
+     */
+    private boolean enable() {
+        if (!INMS.isBound()) {
+            Throwable bindFailure = INMS.bindFailure();
+            Iris.error("Iris cannot start: " + (bindFailure == null
+                    ? "no NMS binding is available for this server version."
+                    : bindFailure.getMessage()));
+            // Deferred one tick: disablePlugin from inside onEnable re-enters onDisable
+            // synchronously and the loader then continues registering the half-enabled plugin.
+            J.s(() -> Bukkit.getPluginManager().disablePlugin(this), 1);
+            return false;
+        }
         alreadyDrained.set(false);
         servicesDisabled.set(false);
         sharedRuntimeClosed.set(false);
@@ -551,25 +541,50 @@ public class Iris extends VolmitPlugin implements Listener, ReloadAware {
         setupAudience();
         BukkitPlatform.hostHud(new HudSlotService(this), new HudBossBarLane());
         Bindings.setupSentry();
-        initialize("art.arcane.iris.core.service", IrisService.class).forEach((i) -> {
+        // Explicit, ordered service list: the previous reflective jar scan gave hash-ordered
+        // enable/disable and paid a full-jar class sweep at boot. Infrastructure first,
+        // engine/world services next, commands last.
+        List<IrisService> orderedServices = List.of(
+                new PreservationSVC(),
+                new GlobalCacheSVC(),
+                new LogFilterSVC(),
+                new ExternalDataSVC(),
+                new EditSVC(),
+                new ObjectSVC(),
+                new ObjectStudioSaveService(),
+                new JigsawStudioService(),
+                new StudioSVC(),
+                new DatapackStructureScopeSVC(),
+                new IrisEngineSVC(),
+                new IrisTerrainSVC(),
+                new TreeSVC(),
+                new TreeFellerSVC(),
+                new EntityRiseSVC(),
+                new WandSVC(),
+                new BoardSVC(),
+                new IrisIntegrationService(),
+                new IrisProtocolService(),
+                new IrisApiEventSVC(),
+                new CommandSVC()
+        );
+        for (IrisService i : orderedServices) {
             Class<? extends IrisService> serviceType = i.getClass().asSubclass(IrisService.class);
             services.put(serviceType, i);
             IrisServices.register(serviceType, i);
-        });
+        }
         IrisServices.register(BlockEditAccess.class, services.get(EditSVC.class));
         IrisServices.register(PreservationRegistry.class, services.get(PreservationSVC.class));
-        IO.delete(new File("iris"));
         compat = IrisCompat.configured(getDataFile("compat.json"));
         IrisServices.register(IrisCompat.class, compat);
         ServerConfigurator.configure();
-        IrisToolbelt.applyPregenPerformanceProfile();
         StartupValidationOutcome datapackValidation = DatapackIngestService.validateOnStartup();
         if (datapackValidation == StartupValidationOutcome.READY) {
             generatorResolver.validateAllPacks();
         }
         IrisSafeguard.execute();
         getSender().setTag(getTag());
-        splash();
+        // A cosmetic banner must never abort the bootstrap.
+        J.attempt(this::splash);
         IrisSafeguard.printReports();
         IrisSafeguard.printFooter();
         tickets = new ChunkTickets();
@@ -594,20 +609,54 @@ public class Iris extends VolmitPlugin implements Listener, ReloadAware {
         // packs through cache/temp on an async thread, and a concurrent delete of that folder
         // truncated pack imports mid-copy (partial packs/<key> without dimensions/).
         IO.delete(getTemp());
-        services.values().forEach(IrisService::onEnable);
-        services.values().forEach(this::registerListener);
+        // One throwing service must not abort the bootstrap: the steps after this loop
+        // (listeners, shutdown hook, replacement journals) are the safety-critical ones.
+        // Only services that actually enabled get listeners and a later onDisable.
+        enabledServices.clear();
+        IrisService firstFailedService = null;
+        for (IrisService service : orderedServices) {
+            try {
+                service.onEnable();
+                enabledServices.add(service);
+            } catch (Throwable e) {
+                if (firstFailedService == null) {
+                    firstFailedService = service;
+                }
+                Iris.reportError("Failed to enable " + service.getClass().getSimpleName() + "; continuing with a degraded runtime.", e);
+                // A failed service is excluded from the teardown loop, so clean up whatever
+                // its partial onEnable started right here, best-effort.
+                try {
+                    service.onDisable();
+                } catch (Throwable cleanup) {
+                    Iris.reportError("Failed to clean up partially enabled " + service.getClass().getSimpleName() + ".", cleanup);
+                }
+            }
+        }
+        if (firstFailedService != null) {
+            IrisStartupValidation.markDatapacksInvalid("Iris service "
+                    + firstFailedService.getClass().getSimpleName()
+                    + " failed to enable; world creation and player admission are locked. Check the log above.");
+        }
+        for (IrisService service : enabledServices) {
+            try {
+                registerListener(service);
+            } catch (Throwable e) {
+                Iris.reportError("Failed to register listener for " + service.getClass().getSimpleName() + ".", e);
+            }
+        }
         addShutdownHook();
         pendingWorldReplacements.processPendingStartupReplacements();
         pendingWorldDeletes.processPendingStartupWorldDeletes();
-        WorldLifecycleService.get();
-        WorldRuntimeControlService.get();
 
         if (J.isFolia() && IrisStartupValidation.isReady()) {
             J.s(() -> worldReconciler.checkForBukkitWorlds(s -> true), 1);
         }
 
         J.s(() -> {
-            pendingWorldReplacements.verifyLoadedPublishedWorlds();
+            pendingWorldReplacements.captureVanillaLevelContext();
+            // Off-main: the verify body takes the replacement-manager monitor and SHA-hashes
+            // whole pack trees; neither belongs on the tick thread.
+            J.a(pendingWorldReplacements::verifyLoadedPublishedWorlds);
             J.a(this::bstats);
             J.ar(() -> settingsHotloadWatch.checkConfigHotload(configHotloadEngine), 60);
             J.sr(this::tickQueue, 0);
@@ -620,20 +669,15 @@ public class Iris extends VolmitPlugin implements Listener, ReloadAware {
                 worldReconciler.checkForBukkitWorlds(s -> true);
             }
             IrisToolbelt.retainMantleDataForSlice(String.class.getCanonicalName());
-            IrisToolbelt.retainMantleDataForSlice(BlockData.class.getCanonicalName());
+            // The mantle stores block values as PlatformBlockState, so a BlockData retention can never
+            // match a slice type; the block-state slice is deliberately never retainable (regenerable, huge).
             IrisToolbelt.retainMantleDataForSlice(TreeBlockMaterial.class.getCanonicalName());
         });
+        return true;
     }
 
     public void addShutdownHook() {
-        if (shutdownHook != null) {
-            try {
-                Runtime.getRuntime().removeShutdownHook(shutdownHook);
-            } catch (IllegalStateException ex) {
-                Iris.debug("Skipping shutdown hook replacement because JVM shutdown is already in progress.");
-                return;
-            }
-        }
+        removeShutdownHook();
         shutdownHook = new Thread(() -> teardownRuntime("shutdown-hook", 30L), "Iris-ShutdownHook");
         try {
             Runtime.getRuntime().addShutdownHook(shutdownHook);
@@ -642,6 +686,24 @@ public class Iris extends VolmitPlugin implements Listener, ReloadAware {
         }
     }
 
+    /**
+     * The static-field guard in addShutdownHook is dead across a plugin reload (fresh
+     * classloader, fresh static), so onDisable must deregister the hook explicitly or each
+     * reload stacks another hook pinning the previous plugin classloader for the JVM's life.
+     */
+    public void removeShutdownHook() {
+        Thread hook = shutdownHook;
+        shutdownHook = null;
+        if (hook == null) {
+            return;
+        }
+        try {
+            Runtime.getRuntime().removeShutdownHook(hook);
+        } catch (IllegalStateException ignored) {
+            Iris.debug("Skipping shutdown hook removal because JVM shutdown is already in progress.");
+        }
+    }
+
     public BukkitWorldReconciler worldReconciler() {
         return worldReconciler;
     }
@@ -692,16 +754,20 @@ public class Iris extends VolmitPlugin implements Listener, ReloadAware {
         IrisStartupValidation.begin();
         Bukkit.getPluginManager().registerEvents(new IrisStartupAdmissionListener(), this);
         Bukkit.getPluginManager().registerEvents(pendingWorldReplacements, this);
-        enable();
+        boolean enabled = enable();
+        if (!enabled) {
+            return;
+        }
         BukkitGuiHost.install();
+        // super.onEnable() already registers this instance as a listener.
         super.onEnable();
-        Bukkit.getPluginManager().registerEvents(this, this);
     }
 
     public void onDisable() {
         teardownPapi();
-        if (IrisSafeguard.isForceShutdown()) return;
         teardownRuntime("onDisable", 30L);
+        removeShutdownHook();
+        J.attempt(() -> INMS.get().uninjectBukkit());
         if (BukkitPlatform.hasHud()) {
             BukkitPlatform.hudSlots().shutdown();
             BukkitPlatform.hudLanes().shutdown();
@@ -710,12 +776,9 @@ public class Iris extends VolmitPlugin implements Listener, ReloadAware {
             configHotloadEngine.clear();
             configHotloadEngine = null;
         }
-        J.cancelPluginTasks();
-        HandlerList.unregisterAll((Plugin) this);
         runPostShutdown();
+        // super.onDisable() cancels plugin tasks and unregisters every listener.
         super.onDisable();
-
-        J.attempt(new JarScanner(instance.getJarFile(), "", false)::scanAll);
         IrisPlatforms.unbind();
     }
 
@@ -753,7 +816,9 @@ public class Iris extends VolmitPlugin implements Listener, ReloadAware {
             }
 
             if (services != null && servicesDisabled.compareAndSet(false, true)) {
-                for (IrisService service : services.values()) {
+                // Only services whose onEnable actually completed; disabling a service that
+                // never initialized runs teardown against uninitialized state.
+                for (IrisService service : enabledServices) {
                     try {
                         service.onDisable();
                     } catch (Throwable e) {
@@ -768,6 +833,7 @@ public class Iris extends VolmitPlugin implements Listener, ReloadAware {
 
             J.attempt(MultiBurst.burst::close);
             J.attempt(MultiBurst.ioBurst::close);
+            clearQueues();
             IrisServices.clear();
         }
     }

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

@@ -169,7 +169,7 @@ public final class IrisWorldGeneratorResolver {
         IrisDimension dimension = pack.isDirectory() ? IrisData.get(pack).getDimensionLoader().load(id) : null;
         if (dimension == null) dimension = IrisData.loadAnyDimension(id, null);
         if (dimension == null) {
-            File packsRoot = IrisPlatforms.get().dataFolderNoCreate(StudioSVC.WORKSPACE_NAME);
+            File packsRoot = IrisPlatforms.get().packsFolderNoCreate();
             if (PackDownloader.isPackPresent(packsRoot, id)) {
                 Iris.error("Pack '" + id + "' exists at " + new File(packsRoot, id).getPath()
                         + " but its dimension failed to load; not redownloading. Fix or delete the pack folder.");

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

@@ -254,7 +254,10 @@ public final class PendingWorldReplacementManager implements Listener {
     @EventHandler(priority = EventPriority.MONITOR)
     public void onWorldLoad(WorldLoadEvent event) {
         World world = event.getWorld();
-        J.s(() -> verifyPublishedWorldIfPending(world), 1);
+        // One tick to let the load settle, then verify off-main: the body takes the manager
+        // monitor (held across pack staging by async threads) and SHA-hashes the whole pack
+        // tree — blocking the main thread on either froze the server.
+        J.s(() -> J.a(() -> verifyPublishedWorldIfPending(world)), 1);
     }
 
     private synchronized void verifyPublishedWorldIfPending(World world) {
@@ -506,10 +509,46 @@ public final class PendingWorldReplacementManager implements Listener {
         }
     }
 
+    /**
+     * Captures the primary level context on the main thread at startup. resolveEffectiveSeed
+     * reads this snapshot so staging never blocks on a main-thread hop while holding the
+     * manager monitor — that inversion froze the server for the full 30s hop timeout whenever
+     * another world loaded during staging. The context is stable for the process lifetime:
+     * slot replacements only commit across a restart.
+     */
+    public void captureVanillaLevelContext() {
+        try {
+            vanillaLevelContext = new VanillaLevelContext(
+                    WorldIdentity.resolve(NamespacedKey.minecraft("overworld"))
+                            .orElseThrow(() -> new IllegalStateException("The configured primary world is not loaded."))
+                            .getSeed(),
+                    Iris.instance.getServer().getAllowNether(),
+                    Iris.instance.getServer().getAllowEnd()
+            );
+        } catch (Throwable failure) {
+            Iris.debug("Could not capture the primary level context yet: " + detail(failure));
+        }
+    }
+
     private static long resolveEffectiveSeed(SlotKind slotKind, long requestedSeed) throws IOException {
         if (slotKind == SlotKind.IRIS_MANAGED) {
             return requestedSeed;
         }
+        VanillaLevelContext context = vanillaLevelContext;
+        if (context == null) {
+            context = resolveVanillaLevelContext();
+            vanillaLevelContext = context;
+        }
+        if (slotKind == SlotKind.VANILLA_NETHER && !context.allowNether()) {
+            throw new IOException("allow-nether must be true before the vanilla Nether can be replaced.");
+        }
+        if (slotKind == SlotKind.VANILLA_END && !context.allowEnd()) {
+            throw new IOException("Bukkit allow-end must be true before the vanilla End can be replaced.");
+        }
+        return context.seed();
+    }
+
+    private static VanillaLevelContext resolveVanillaLevelContext() throws IOException {
         CompletableFuture<VanillaLevelContext> contextFuture = J.sfut(() -> new VanillaLevelContext(
                 WorldIdentity.resolve(NamespacedKey.minecraft("overworld"))
                         .orElseThrow(() -> new IllegalStateException("The configured primary world is not loaded."))
@@ -521,14 +560,7 @@ public final class PendingWorldReplacementManager implements Listener {
             throw new IOException("Could not schedule primary level-seed resolution.");
         }
         try {
-            VanillaLevelContext context = contextFuture.get(30L, TimeUnit.SECONDS);
-            if (slotKind == SlotKind.VANILLA_NETHER && !context.allowNether()) {
-                throw new IOException("allow-nether must be true before the vanilla Nether can be replaced.");
-            }
-            if (slotKind == SlotKind.VANILLA_END && !context.allowEnd()) {
-                throw new IOException("Bukkit allow-end must be true before the vanilla End can be replaced.");
-            }
-            return context.seed();
+            return contextFuture.get(30L, TimeUnit.SECONDS);
         } catch (InterruptedException failure) {
             Thread.currentThread().interrupt();
             throw new IOException("Primary level-seed resolution was interrupted.", failure);
@@ -580,6 +612,8 @@ public final class PendingWorldReplacementManager implements Listener {
         }
     }
 
+    private static volatile VanillaLevelContext vanillaLevelContext;
+
     private record VanillaLevelContext(long seed, boolean allowNether, boolean allowEnd) {
     }
 

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

@@ -394,7 +394,7 @@ public class CommandDeveloper implements DirectorExecutor {
         }
     }
 
-    @Director(name = "goldenhash", aliases = {"gold"}, description = "Generate chunks into buffers (no world writes) and hash blocks+biomes; captures a golden file or verifies against an existing one. Resets mantle in the scanned area - use on disposable test worlds.", descriptionKey = "iris.director.commanddeveloper.director.generate_chunks_into_buffers_no_world_writes_hash_blocks_biomes_captures_golden", origin = DirectorOrigin.BOTH)
+    @Director(name = "goldenhash", aliases = {"gold"}, description = "Generate chunks into buffers (no world writes) and hash blocks+biomes; captures a golden file or verifies against an existing one. Deletes the world's entire mantle - use on disposable test worlds.", descriptionKey = "iris.director.commanddeveloper.director.generate_chunks_into_buffers_no_world_writes_hash_blocks_biomes_captures_golden", origin = DirectorOrigin.BOTH)
     public void goldenhash(
             @Param(description = "The world to scan", descriptionKey = "iris.director.commanddeveloper.param.world_scan", contextual = true)
             World world,
@@ -404,7 +404,7 @@ public class CommandDeveloper implements DirectorExecutor {
             int centerX,
             @Param(name = "center-z", description = "Center chunk Z", descriptionKey = "iris.director.commanddeveloper.param.center_chunk_z_2", defaultValue = "0")
             int centerZ,
-            @Param(name = "reset-mantle", description = "Delete mantle data in the scan area first for full regeneration from scratch", descriptionKey = "iris.director.commanddeveloper.param.delete_mantle_data_scan_area_first_full_regeneration_from_scratch", defaultValue = "true")
+            @Param(name = "reset-mantle", description = "Delete the world's entire mantle folder first for full regeneration from scratch", descriptionKey = "iris.director.commanddeveloper.param.delete_mantle_data_scan_area_first_full_regeneration_from_scratch", defaultValue = "true")
             boolean resetMantle,
             @Param(name = "threads", description = "Concurrent chunk generations; 1 = strictly serial for order-dependence testing", descriptionKey = "iris.director.commanddeveloper.param.concurrent_chunk_generations_1_strictly_serial_order_dependence_testing", defaultValue = "8")
             int threads,

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

@@ -705,7 +705,7 @@ public class CommandIris implements DirectorExecutor {
     public void download(
             @Param(name = "pack", description = "The pack to download", descriptionKey = "iris.director.commandiris.param.pack_download", aliases = "project")
             String pack,
-            @Param(name = "branch", description = "The branch to download from", descriptionKey = "iris.director.commandiris.param.branch_download_from", defaultValue = "stable")
+            @Param(name = "branch", description = "The branch to download from", descriptionKey = "iris.director.commandiris.param.branch_download_from", defaultValue = PackDownloader.DEFAULT_BRANCH)
             String branch,
             @Param(name = "overwrite", description = "Whether or not to overwrite the pack with the downloaded one", descriptionKey = "iris.director.commandiris.param.whether_not_overwrite_pack_with_downloaded_one", aliases = "force", defaultValue = "false")
             boolean overwrite
@@ -803,7 +803,7 @@ public class CommandIris implements DirectorExecutor {
                     });
             guardUnloadCompletion(sequence, terminalTimeout, world.getName())
                     .whenComplete((unloaded, throwable) -> {
-                        IrisToolbelt.endWorldMaintenance(world, "world-unload");
+                        IrisToolbelt.endWorldMaintenance(world, "world-unload", true);
                         lease.close();
                         Runnable response = () -> reportUnloadResult(responseSender, world, unloaded, throwable);
                         if (responseSender.isPlayer() && J.runEntity(responseSender.player(), response)) {
@@ -812,7 +812,7 @@ public class CommandIris implements DirectorExecutor {
                         J.s(response);
                     });
         } catch (Exception e) {
-            IrisToolbelt.endWorldMaintenance(world, "world-unload");
+            IrisToolbelt.endWorldMaintenance(world, "world-unload", true);
             lease.close();
             responseSender.sendMessage(IrisLanguage.text(BukkitCommandMessagesExtended.COMMAND_IRIS_FAILED_UNLOAD_WORLD_3, MessageArgument.untrusted("value", String.valueOf(e.getMessage()))));
             Iris.reportError("Failed to unload world \"" + world.getName() + "\".", e);

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

@@ -37,7 +37,6 @@ import art.arcane.iris.engine.object.IrisObject;
 import art.arcane.iris.engine.object.IrisObjectPlacement;
 import art.arcane.iris.engine.object.IrisObjectPlacementScaleInterpolator;
 import art.arcane.iris.engine.object.IrisObjectRotation;
-import art.arcane.iris.engine.object.StudioMode;
 import art.arcane.iris.engine.object.TileData;
 import art.arcane.iris.platform.bukkit.BukkitBlockState;
 import art.arcane.iris.spi.PlatformBlockState;
@@ -144,7 +143,8 @@ public class CommandObject implements DirectorExecutor {
             return;
         }
 
-        hostDimension.setStudioMode(StudioMode.OBJECT_BUFFET);
+        // ObjectStudioActivation carries the buffet state; mutating the shared cached
+        // IrisDimension here leaked OBJECT_BUFFET into later pack exports of this dimension.
         ObjectStudioActivation.activate(hostDimension.getLoadKey());
         ObjectStudioActivation.setSources(hostDimension.getLoadKey(), sources);
 
@@ -637,6 +637,7 @@ public class CommandObject implements DirectorExecutor {
         } catch (IOException e) {
             sender().sendMessage(IrisLanguage.text(BukkitCommandMessagesExtended.COMMAND_OBJECT_FAILED_SAVE_OBJECT_BECAUSE_IOEXCEPTION, MessageArgument.untrusted("value", String.valueOf(e.getMessage()))));
             Iris.reportError(e);
+            return;
         }
 
         sender().playSound(Sound.BLOCK_ENCHANTMENT_TABLE_USE, 1f, 1.5f);

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

@@ -42,9 +42,18 @@ import art.arcane.volmlib.util.localization.MessageArgument;
 import art.arcane.iris.core.localization.BukkitRuntimeMessages;
 @Director(name = "pack", aliases = {"pk"}, description = "Pack validation and maintenance", descriptionKey = "iris.director.commandpack.director.pack_validation_maintenance")
 public class CommandPack implements DirectorExecutor {
+    /**
+     * Director treats a blank defaultValue as "required", which made the all-packs branch
+     * unreachable from chat. The "*" sentinel keeps the parameter genuinely optional; a blank
+     * value (the documented "pack=" escape hatch) still means every pack.
+     */
+    static boolean wantsAllPacks(String pack) {
+        return pack == null || pack.isBlank() || "*".equals(pack.trim());
+    }
+
     @Director(description = "Validate a pack (or all packs) and re-publish results", descriptionKey = "iris.director.commandpack.director.validate_pack_all_packs_re_publish_results", aliases = {"v"})
     public void validate(
-            @Param(description = "The pack folder name to validate (leave empty for all)", descriptionKey = "iris.director.commandpack.param.pack_folder_name_validate_leave_empty_all", defaultValue = "")
+            @Param(description = "The pack folder name to validate, or * for every pack", descriptionKey = "iris.director.commandpack.param.pack_folder_name_validate_leave_empty_all", defaultValue = "*")
             String pack
     ) {
         VolmitSender s = sender();
@@ -54,7 +63,7 @@ public class CommandPack implements DirectorExecutor {
             return;
         }
 
-        if (pack == null || pack.isBlank()) {
+        if (wantsAllPacks(pack)) {
             List<File> dirs = PackDirectoryResolver.listVisiblePackDirectories(packsRoot);
             if (dirs.isEmpty()) {
                 s.sendMessage(IrisLanguage.text(BukkitRuntimeMessages.COMMAND_PACK_NO_PACKS_VALIDATE));
@@ -196,11 +205,11 @@ public class CommandPack implements DirectorExecutor {
 
     @Director(description = "Show cached validation status for a pack", descriptionKey = "iris.director.commandpack.director.show_cached_validation_status_pack", aliases = {"s"})
     public void status(
-            @Param(description = "The pack folder name", descriptionKey = "iris.director.commandpack.param.pack_folder_name", defaultValue = "")
+            @Param(description = "The pack folder name, or * for every pack", descriptionKey = "iris.director.commandpack.param.pack_folder_name", defaultValue = "*")
             String pack
     ) {
         VolmitSender s = sender();
-        if (pack == null || pack.isBlank()) {
+        if (wantsAllPacks(pack)) {
             if (PackValidationRegistry.snapshot().isEmpty()) {
                 s.sendMessage(IrisLanguage.text(BukkitRuntimeMessages.COMMAND_PACK_NO_VALIDATION_RESULTS_RECORDED_RUN_IRIS_PACK_VALIDATE_FIRST));
                 return;

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

@@ -33,6 +33,7 @@ import org.bukkit.util.Vector;
 
 import art.arcane.iris.core.localization.IrisLanguage;
 import art.arcane.iris.core.localization.BukkitCommandMessagesExtended;
+import art.arcane.iris.core.localization.ModdedCommandMessages;
 import art.arcane.iris.core.localization.RuntimeUiMessages;
 import art.arcane.volmlib.util.localization.MessageArgument;
 @Director(name = "pregen", aliases = "pregenerate", description = "Pregenerate your Iris worlds!", descriptionKey = "iris.director.commandpregen.director.pregenerate_your_iris_worlds")
@@ -59,6 +60,12 @@ public class CommandPregen implements DirectorExecutor {
             return;
         }
 
+        if (PregeneratorJob.getInstance() != null) {
+            // Reject like the modded adapter does; never silently kill a running job.
+            sender().sendMessage(IrisLanguage.text(ModdedCommandMessages.IRIS_MODDED_COMMANDS_PREGENERATION_TASK_IS_ALREADY_RUNNING_STOP_IT_FIRST_WITH_IRIS));
+            return;
+        }
+
         try {
             if (sender().isPlayer() && access() == null) {
                 sender().sendMessage(IrisLanguage.text(BukkitCommandMessagesExtended.COMMAND_PREGEN_ENGINE_ACCESS_THIS_WORLD_IS_NULL));

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

@@ -328,35 +328,50 @@ public class CommandStudio implements DirectorExecutor {
             sender().sendMessage(IrisLanguage.text(BukkitCommandMessagesExtended.COMMAND_STUDIO_ONLY_WORKS_IRIS_WORLD));
             return;
         }
+        if (radius <= 0 || radius > 2048) {
+            sender().sendMessage(IrisLanguage.text(BukkitCommandMessagesExtended.COMMAND_STUDIO_ONLY_WORKS_IRIS_WORLD));
+            sender().sendMessage("Radius must be between 1 and 2048 chunks.");
+            return;
+        }
         var sender = sender();
         var player = player();
         Thread.ofVirtual()
                 .start(() -> {
                     int d = radius * 2;
                     KMap<String, AtomicInteger> data = new KMap<>();
+                    // Everything acquired below is released in the finally: a throw mid-scan
+                    // previously leaked the whole sampler ForkJoinPool, the self-rescheduling
+                    // progress task and both HUD claims for the rest of the server's uptime.
+                    MultiBurst multiBurst = null;
+                    HudSlotClaim titleClaim = null;
+                    HudSlotClaim barClaim = null;
+                    int c = -1;
+                    try {
                     engine.getDimension().getRegions().forEach(key -> data.put(key, new AtomicInteger(0)));
-                    var multiBurst = new MultiBurst("Region Sampler");
-                    var executor = multiBurst.burst(radius * radius);
+                    multiBurst = new MultiBurst("Region Sampler");
+                    var executor = multiBurst.burst(Math.min(radius * radius, 1 << 20));
                     sender.sendMessage(IrisLanguage.text(BukkitCommandMessages.COMMAND_STUDIO_GENERATING_DATA));
                     var loc = player.getLocation();
                     int totalTasks = d * d;
                     AtomicInteger completedTasks = new AtomicInteger(0);
-                    HudSlotClaim titleClaim = BukkitPlatform.hudSlots().open(player, new HudSlotRequest("iris:job", HudPriority.PROGRESS, 1200L, List.of(HudSurface.TITLE)));
-                    HudSlotClaim barClaim = BukkitPlatform.hudSlots().open(player, new HudSlotRequest("iris:job", HudPriority.PROGRESS, 1200L, List.of(HudSurface.ACTION_BAR, HudSurface.BOSS_BAR)));
+                    titleClaim = BukkitPlatform.hudSlots().open(player, new HudSlotRequest("iris:job", HudPriority.PROGRESS, 1200L, List.of(HudSurface.TITLE)));
+                    barClaim = BukkitPlatform.hudSlots().open(player, new HudSlotRequest("iris:job", HudPriority.PROGRESS, 1200L, List.of(HudSurface.ACTION_BAR, HudSurface.BOSS_BAR)));
+                    HudSlotClaim finalTitleClaim = titleClaim;
+                    HudSlotClaim finalBarClaim = barClaim;
                     AtomicLong lastResolveMs = new AtomicLong(0L);
-                    int c = J.ar(() -> {
+                    c = J.ar(() -> {
                         long now = System.currentTimeMillis();
                         if (now - lastResolveMs.get() >= 250L) {
                             lastResolveMs.set(now);
-                            titleClaim.resolve();
-                            barClaim.resolve();
+                            finalTitleClaim.resolve();
+                            finalBarClaim.resolve();
                         }
                         double jobProgress = (double) completedTasks.get() / totalTasks;
-                        HudSurface barSurface = barClaim.granted();
+                        HudSurface barSurface = finalBarClaim.granted();
                         sender.sendProgress(
                                 jobProgress,
                                 IrisLanguage.text(RuntimeUiMessages.FINDING_REGIONS),
-                                titleClaim.granted(),
+                                finalTitleClaim.granted(),
                                 barSurface
                         );
                         if (barSurface == HudSurface.BOSS_BAR) {
@@ -372,15 +387,28 @@ public class CommandStudio implements DirectorExecutor {
                         completedTasks.incrementAndGet();
                     })).setOffset(loc.getBlockX(), loc.getBlockZ()).drain();
                     executor.complete();
-                    multiBurst.close();
-                    J.car(c);
-                    titleClaim.release();
-                    barClaim.release();
-                    BukkitPlatform.hudLanes().hide(player, "iris:job");
 
                     sender.sendMessage(IrisLanguage.text(BukkitCommandMessages.COMMAND_STUDIO_DONE));
                     var loader = engine.getData().getRegionLoader();
                     data.forEach((k, v) -> sender.sendMessage(IrisLanguage.text(BukkitCommandMessages.COMMAND_STUDIO_MESSAGE, MessageArgument.untrusted("k", k), MessageArgument.untrusted("value", loader.load(k).getRarity()), MessageArgument.untrusted("value2", Form.f((double) v.get() / totalTasks * 100, 2)))));
+                    } catch (Throwable e) {
+                        Iris.reportError(e);
+                        sender.sendMessage(IrisLanguage.text(BukkitCommandMessagesExtended.COMMAND_STUDIO_ONLY_WORKS_IRIS_WORLD));
+                    } finally {
+                        if (c != -1) {
+                            J.car(c);
+                        }
+                        if (titleClaim != null) {
+                            titleClaim.release();
+                        }
+                        if (barClaim != null) {
+                            barClaim.release();
+                            BukkitPlatform.hudLanes().hide(player, "iris:job");
+                        }
+                        if (multiBurst != null) {
+                            multiBurst.close();
+                        }
+                    }
                 });
     }
 
@@ -437,7 +465,6 @@ public class CommandStudio implements DirectorExecutor {
         KMap<InterpolationMethod, Double> interpolatorTimings = new KMap<>();
         KMap<String, Double> generatorTimings = new KMap<>();
         KMap<String, Double> biomeTimings = new KMap<>();
-        KMap<String, Double> regionTimings = new KMap<>();
 
         sender().sendMessage(IrisLanguage.text(BukkitCommandMessagesExtended.COMMAND_STUDIO_CALCULATING_PERFORMANCE_METRICS_NOISE_GENERATORS));
 
@@ -561,23 +588,6 @@ public class CommandStudio implements DirectorExecutor {
 
         fileText.add("");
 
-        for (String i : data.getRegionLoader().getPossibleKeys()) {
-            IrisRegion b = data.getRegionLoader().load(i);
-            double score = 0;
-
-            score += styleTimings.get(b.getLakeStyle().getStyle());
-            score += styleTimings.get(b.getRiverStyle().getStyle());
-            regionTimings.put(i, score);
-        }
-
-        fileText.add("Project Region Performance Impacts: ");
-
-        for (String i : regionTimings.sortKNumber()) {
-            fileText.add(i + ": " + regionTimings.get(i));
-        }
-
-        fileText.add("");
-
         double m = 0;
         for (double i : biomeTimings.v()) {
             m += i;
@@ -589,12 +599,6 @@ public class CommandStudio implements DirectorExecutor {
         }
         mm /= generatorTimings.size();
         m += mm;
-        double mmm = 0;
-        for (double i : regionTimings.v()) {
-            mmm += i;
-        }
-        mmm /= regionTimings.size();
-        m += mmm;
 
         fileText.add("Average Score: " + m);
         sender().sendMessage(IrisLanguage.text(BukkitCommandMessagesExtended.COMMAND_STUDIO_SCORE, MessageArgument.untrusted("value", Form.duration(m, 0))));
@@ -763,9 +767,8 @@ public class CommandStudio implements DirectorExecutor {
         }
 
         sender().sendMessage(IrisLanguage.text(BukkitCommandMessagesExtended.COMMAND_STUDIO_CAPTURING_IGENDATA_FROM_NEARBY_CHUNKS, MessageArgument.untrusted("value", chunks.size())));
-        try {
-            File ff = Iris.instance.getDataFile("reports/" + M.ms() + ".txt");
-            PrintWriter pw = new PrintWriter(ff);
+        File ff = Iris.instance.getDataFile("reports/" + M.ms() + ".txt");
+        try (PrintWriter pw = new PrintWriter(ff)) {
             pw.println("=== Iris Chunk Report ===");
             pw.println("== General Info ==");
             pw.println("Iris Version: " + Iris.instance.getDescription().getVersion());
@@ -820,7 +823,8 @@ public class CommandStudio implements DirectorExecutor {
                 }
             }
 
-            regions = Objects.requireNonNull(new File(world.getWorldFolder().getPath() + "/region").list()).length;
+            String[] regionFiles = new File(world.getWorldFolder(), "region").list();
+            regions = regionFiles == null ? 0 : regionFiles.length;
 
             pw.println();
             pw.println("== World Info ==");
@@ -854,10 +858,9 @@ public class CommandStudio implements DirectorExecutor {
             }
 
             pw.println();
-            pw.close();
 
             sender().sendMessage(IrisLanguage.text(BukkitCommandMessagesExtended.COMMAND_STUDIO_REPORTED, MessageArgument.untrusted("value", ff.getPath())));
-        } catch (FileNotFoundException e) {
+        } catch (Throwable e) {
             e.printStackTrace();
             Iris.reportError(e);
         }

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

@@ -26,7 +26,10 @@ import art.arcane.iris.core.edit.BlockSignal;
 import art.arcane.iris.core.nms.INMS;
 import art.arcane.iris.core.tools.IrisToolbelt;
 import art.arcane.iris.engine.framework.Engine;
+import art.arcane.iris.engine.framework.GenerationSessionException;
+import art.arcane.iris.engine.framework.GenerationSessionLease;
 import art.arcane.iris.engine.platform.EngineBukkitOps;
+import art.arcane.iris.util.project.context.IrisContext;
 import art.arcane.iris.engine.object.IrisBiome;
 import art.arcane.iris.engine.object.IrisRegion;
 import art.arcane.iris.util.common.director.DirectorExecutor;
@@ -36,8 +39,10 @@ import art.arcane.volmlib.util.director.DirectorOrigin;
 import art.arcane.volmlib.util.director.annotations.Director;
 import art.arcane.volmlib.util.director.annotations.Param;
 import art.arcane.iris.util.common.format.C;
+import art.arcane.volmlib.util.collection.KList;
 import art.arcane.volmlib.util.matter.MatterMarker;
 import org.bukkit.Chunk;
+import org.bukkit.Location;
 import org.bukkit.FluidCollisionMode;
 import org.bukkit.Material;
 import org.bukkit.NamespacedKey;
@@ -47,7 +52,6 @@ import org.bukkit.block.data.BlockData;
 import org.bukkit.entity.Player;
 
 import java.lang.reflect.Method;
-import java.util.concurrent.atomic.AtomicInteger;
 
 import art.arcane.iris.core.localization.IrisLanguage;
 import art.arcane.iris.core.localization.BukkitCommandMessagesExtended;
@@ -172,35 +176,73 @@ public class CommandWhat implements DirectorExecutor {
         });
     }
 
+    // Matches ModdedWhatCommands.MAX_MARKERS so both loaders truncate identically.
+    private static final int MAX_MARKER_HITS = 8_192;
+    private static final int MARKER_SIGNAL_BATCH = 128;
+
     @Director(description = "Show markers in chunk", descriptionKey = "iris.director.commandwhat.director.show_markers_chunk", origin = DirectorOrigin.PLAYER)
     public void markers(@Param(description = "Marker name such as cave_floor or cave_ceiling", descriptionKey = "iris.director.commandwhat.param.marker_name_such_as_cave_floor_cave_ceiling") String marker) {
         VolmitSender commandSender = sender();
         Player player = player();
+        if (player == null) {
+            return;
+        }
 
-        // Chunk lookup plus the block signals both need the thread owning the player's chunk.
+        // Only the chunk coordinates need the owning thread; the 81-chunk mantle sweep loads
+        // tectonic plates from disk and must never run on the tick thread (the modded adapter
+        // already scans async, leased and capped — mirror it).
         onPlayerThread(player, () -> {
+            World world = player.getWorld();
             Chunk c = player.getLocation().getChunk();
+            int chunkX = c.getX();
+            int chunkZ = c.getZ();
 
-            if (IrisToolbelt.isIrisWorld(c.getWorld())) {
-                AtomicInteger v = new AtomicInteger(0);
+            if (!IrisToolbelt.isIrisWorld(world)) {
+                commandSender.sendMessage(IrisLanguage.text(BukkitCommandMessagesExtended.COMMAND_WHAT_IRIS_WORLDS_ONLY_2));
+                return;
+            }
+            Engine engine = IrisToolbelt.access(world).getEngine();
 
-                for (int xxx = c.getX() - 4; xxx <= c.getX() + 4; xxx++) {
-                    for (int zzz = c.getZ() - 4; zzz <= c.getZ() + 4; zzz++) {
-                        IrisToolbelt.access(c.getWorld()).getEngine().getMantle().findMarkers(xxx, zzz, new MatterMarker(marker))
-                                .convert((i) -> BukkitPlatform.toLocation(i, c.getWorld())).forEach((i) -> {
-                                    BlockSignal.of(i.getWorld(), i.getBlockX(), i.getBlockY(), i.getBlockZ(), 100);
-                                    v.incrementAndGet();
-                                });
+            J.a(() -> {
+                KList<Location> hits = new KList<>();
+                MatterMarker matterMarker = new MatterMarker(marker);
+                try (GenerationSessionLease lease = engine.acquireGenerationLease("bukkit_what_markers");
+                     IrisContext.Scope ignored = IrisContext.open(engine, lease.sessionId(), null)) {
+                    scan:
+                    for (int xxx = chunkX - 4; xxx <= chunkX + 4; xxx++) {
+                        for (int zzz = chunkZ - 4; zzz <= chunkZ + 4; zzz++) {
+                            for (Location i : engine.getMantle().findMarkers(xxx, zzz, matterMarker)
+                                    .convert((p) -> BukkitPlatform.toLocation(p, world))) {
+                                hits.add(i);
+                                if (hits.size() >= MAX_MARKER_HITS) {
+                                    break scan;
+                                }
+                            }
+                        }
                     }
+                } catch (GenerationSessionException e) {
+                    commandSender.sendMessage(IrisLanguage.text(BukkitCommandMessagesExtended.COMMAND_WHAT_IRIS_WORLDS_ONLY_2));
+                    return;
                 }
 
-                commandSender.sendMessage(IrisLanguage.text(BukkitCommandMessagesExtended.COMMAND_WHAT_FOUND_NEARBY_MARKERS, MessageArgument.untrusted("value", v.get()), MessageArgument.untrusted("marker", marker)));
-            } else {
-                commandSender.sendMessage(IrisLanguage.text(BukkitCommandMessagesExtended.COMMAND_WHAT_IRIS_WORLDS_ONLY_2));
-            }
+                commandSender.sendMessage(IrisLanguage.text(BukkitCommandMessagesExtended.COMMAND_WHAT_FOUND_NEARBY_MARKERS, MessageArgument.untrusted("value", hits.size()), MessageArgument.untrusted("marker", marker)));
+                emitMarkerSignals(player, engine, hits, 0);
+            });
         });
     }
 
+    private void emitMarkerSignals(Player player, Engine engine, KList<Location> hits, int from) {
+        if (from >= hits.size() || !player.isOnline() || engine.isClosed() || engine.isClosing()) {
+            return;
+        }
+        int to = Math.min(from + MARKER_SIGNAL_BATCH, hits.size());
+        for (int i = from; i < to; i++) {
+            Location at = hits.get(i);
+            BlockSignal.of(at.getWorld(), at.getBlockX(), at.getBlockY(), at.getBlockZ(), 100);
+        }
+        J.s(() -> emitMarkerSignals(player, engine, hits, to), 1);
+    }
+
     /**
      * Runs the body on the thread owning the player, reporting when the hop cannot be scheduled.
      */

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

@@ -1,5 +1,6 @@
 package art.arcane.iris.core.service;
 
+import art.arcane.iris.core.IrisStartupValidation;
 import art.arcane.iris.core.datapack.DatapackIngestService;
 import art.arcane.iris.core.datapack.DatapackStructureScopeIndex;
 import art.arcane.iris.core.nms.DatapackStructureScopeResult;
@@ -29,13 +30,26 @@ public final class DatapackStructureScopeSVC implements IrisService {
             scopeIndex = DatapackStructureScopeIndex.create(
                     DatapackIngestService.installedStructureScopeResources());
         } catch (IOException e) {
-            throw new IllegalStateException(
-                    "Iris could not establish ownership for installed datapack structure sets", e);
+            // A missing manifest entry is the condition validateOnStartup already classified as
+            // non-fatal; degrade to an empty scope and lock world creation instead of aborting
+            // the whole plugin bootstrap (which would skip listeners and journal reconciliation).
+            scopeIndex = DatapackStructureScopeIndex.create(null);
+            IrisLogging.error("Could not establish ownership for installed datapack structure sets; "
+                    + "datapack structure scoping is disabled until the manifest is repaired: " + e.getMessage());
+            IrisStartupValidation.markDatapacksInvalid(
+                    "Iris could not establish ownership for installed datapack structure sets: " + e.getMessage());
         }
         for (World world : Bukkit.getWorlds()) {
-            IrisImportedStructureControl importedStructures = importedStructures(world);
-            if (!scopeIndex.isEmpty() || importedStructures != null && importedStructures.hasFrequencyOverrides()) {
-                applyScope(world, importedStructures);
+            try {
+                IrisImportedStructureControl importedStructures = importedStructures(world);
+                if (!scopeIndex.isEmpty() || importedStructures != null && importedStructures.hasFrequencyOverrides()) {
+                    applyScope(world, importedStructures);
+                }
+            } catch (Throwable e) {
+                // Per-world containment: one world's scoping failure must not abort the
+                // service enable (and with it the whole bootstrap's containment contract).
+                IrisLogging.error("Could not scope datapack structures for world '" + world.getName() + "'.");
+                IrisLogging.reportError(e);
             }
         }
     }

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

@@ -35,7 +35,6 @@ import org.bukkit.event.world.WorldUnloadEvent;
 public class EditSVC implements IrisService, BlockEditAccess<World, BlockData, Biome> {
     private KMap<World, BlockEditor> editors;
     private int updateTaskId = -1;
-    public static boolean deletingWorld = false;
 
     @Override
     public void onEnable() {
@@ -84,7 +83,7 @@ public class EditSVC implements IrisService, BlockEditAccess<World, BlockData, B
         if (editors == null) {
             return;
         }
-        if (editors.containsKey(e.getWorld()) && !deletingWorld) {
+        if (editors.containsKey(e.getWorld())) {
             editors.remove(e.getWorld()).close();
         }
     }

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

@@ -22,7 +22,7 @@ public class IrisStartupOrderingTest {
     @Test
     public void externalDatapacksValidateBeforeDimensionPacks() throws Exception {
         String source = Files.readString(Path.of(System.getProperty("iris.startupSource")));
-        String enable = section(source, "private void enable()", "public void addShutdownHook()");
+        String enable = section(source, "private boolean enable()", "public void addShutdownHook()");
 
         assertOrdered(enable,
                 "DatapackIngestService.validateOnStartup();",

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

@@ -0,0 +1,20 @@
+package art.arcane.iris.core.commands;
+
+import org.junit.Test;
+
+import java.nio.file.Files;
+import java.nio.file.Path;
+
+import static org.junit.Assert.assertTrue;
+
+public class CommandIrisDownloadDefaultTest {
+    @Test
+    public void downloadBranchParamDefaultsToTheCoreConstant() throws Exception {
+        String source = Files.readString(Path.of("src/main/java/art/arcane/iris/core/commands/CommandIris.java"));
+        int branchParam = source.indexOf("name = \"branch\"");
+        assertTrue("CommandIris must declare the branch param", branchParam >= 0);
+        String declaration = source.substring(branchParam, source.indexOf(')', branchParam));
+        assertTrue("branch param default must be PackDownloader.DEFAULT_BRANCH, not a literal",
+                declaration.contains("defaultValue = PackDownloader.DEFAULT_BRANCH"));
+    }
+}

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

@@ -0,0 +1,63 @@
+package art.arcane.iris.core.commands;
+
+import art.arcane.volmlib.util.director.compat.DirectorAnnotationCompatibility;
+import art.arcane.volmlib.util.director.runtime.DirectorNodeDescriptor;
+import art.arcane.volmlib.util.director.runtime.DirectorParameterDescriptor;
+import org.junit.Test;
+
+import java.util.List;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+public class CommandPackOptionalPackContractTest {
+    private static DirectorParameterDescriptor packParam(String method) throws Exception {
+        DirectorNodeDescriptor node = DirectorAnnotationCompatibility
+                .fromMethod(CommandPack.class.getDeclaredMethod(method, String.class))
+                .orElseThrow();
+        DirectorParameterDescriptor pack = node.getParameters().get(0);
+        assertEquals("pack", pack.getName());
+        return pack;
+    }
+
+    @Test
+    public void bareValidateAndStatusAreInvocableWithoutAPackArgument() throws Exception {
+        for (String method : List.of("validate", "status")) {
+            DirectorParameterDescriptor pack = packParam(method);
+            assertFalse(method + " must not require a pack", pack.isRequired());
+            assertFalse(method + " needs a non-blank default for Director to treat it as optional",
+                    pack.getDefaultValue().isBlank());
+        }
+    }
+
+    @Test
+    public void cleanupAndRestoreStillRequireAPack() throws Exception {
+        for (String method : List.of("cleanup", "restore")) {
+            DirectorNodeDescriptor node = DirectorAnnotationCompatibility
+                    .fromMethod(findMethod(method))
+                    .orElseThrow();
+            DirectorParameterDescriptor pack = node.getParameters().get(0);
+            assertEquals("pack", pack.getName());
+            assertTrue(method + " must keep requiring a pack", pack.isRequired());
+        }
+    }
+
+    @Test
+    public void allPacksPredicateAcceptsSentinelBlankAndNull() {
+        assertTrue(CommandPack.wantsAllPacks(null));
+        assertTrue(CommandPack.wantsAllPacks(""));
+        assertTrue(CommandPack.wantsAllPacks(" "));
+        assertTrue(CommandPack.wantsAllPacks("*"));
+        assertFalse(CommandPack.wantsAllPacks("overworld"));
+    }
+
+    private static java.lang.reflect.Method findMethod(String name) {
+        for (java.lang.reflect.Method method : CommandPack.class.getDeclaredMethods()) {
+            if (method.getName().equals(name)) {
+                return method;
+            }
+        }
+        throw new AssertionError("CommandPack must declare " + name);
+    }
+}

adapters/client-common/src/main/java/art/arcane/iris/client/IrisClientPregenState.java

@@ -46,7 +46,10 @@ public final class IrisClientPregenState {
         jobs.remove(jobId);
         Long current = activeJobId;
         if (current != null && current == jobId) {
-            activeJobId = jobs.keySet().stream().findFirst().orElse(null);
+            // Promote nothing: the server runs a single live job, so any remaining entry is
+            // dead or orphaned — and the access-ordered map's head is the STALEST entry,
+            // which is what the HUD used to promote.
+            activeJobId = null;
         }
     }
 

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

@@ -161,7 +161,9 @@ public final class NativeStructureVegetationClearer {
         if (state.is(BlockTags.LOGS) || state.is(BlockTags.LEAVES)) {
             return true;
         }
-        String path = BuiltInRegistries.BLOCK.getKey(state.getBlock()).getPath();
+        // Field reads instead of a registry byValue map hit — this predicate runs per block
+        // probe on the hottest native-structure scans.
+        String path = state.getBlock().builtInRegistryHolder().key().identifier().getPath();
         return path.endsWith("_log") || path.endsWith("_wood")
                 || path.endsWith("_stem") || path.endsWith("_hyphae")
                 || path.endsWith("_leaves");

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

@@ -815,10 +815,10 @@ public final class IrisModdedChunkGenerator extends ChunkGenerator {
                     int localY = blockY & 15;
                     for (int z = 0; z < 16; z++) {
                         for (int x = 0; x < 16; x++) {
-                            if (blocks.isAir(x, bufferY, z)) {
+                            PlatformBlockState state = blocks.rawOrNull(x, bufferY, z);
+                            if (state == null) {
                                 continue;
                             }
-                            PlatformBlockState state = blocks.getRaw(x, bufferY, z);
                             BlockState blockState = (BlockState) state.nativeHandle();
                             section.setBlockState(x, localY, z, blockState, false);
                             if (blockState.hasBlockEntity()) {

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

@@ -40,6 +40,14 @@ public final class ModdedBlockBuffer implements Hunk<PlatformBlockState> {
         return data[index(x, y, z)] == null;
     }
 
+    /**
+     * Direct slot read, null when unset — lets writeBlocks pay one index + one array load per
+     * block instead of the isAir + getRaw pair.
+     */
+    public PlatformBlockState rawOrNull(int x, int y, int z) {
+        return data[index(x, y, z)];
+    }
+
     @Override
     public int getWidth() {
         return 16;

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

@@ -226,6 +226,8 @@ public final class ModdedDimensionManager {
                 ModdedWorldEngines.evictOrThrow(level);
                 level.save(null, true, false);
                 serverAccess.removeLevel(server, key);
+                // Undo snapshots pin the ServerLevel and could replay into the dead level.
+                art.arcane.iris.modded.command.ModdedObjectUndo.forget(level);
                 level.close();
                 HANDLES.remove(dimensionId);
                 if (wipeStorage) {

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

@@ -47,6 +47,7 @@ import art.arcane.iris.modded.service.ModdedTreeFellerService;
 import art.arcane.iris.spi.IrisPlatform;
 import art.arcane.iris.spi.IrisPlatforms;
 import art.arcane.iris.spi.IrisServices;
+import art.arcane.iris.util.common.parallel.MultiBurst;
 import net.minecraft.core.BlockPos;
 import net.minecraft.server.MinecraftServer;
 import net.minecraft.server.level.ServerLevel;
@@ -99,6 +100,11 @@ public final class ModdedEngineBootstrap {
         captureInitialSpawn(server);
         currentServer = server;
         bind();
+        // Pair of the stop() burst-pools stage. Load-bearing on integrated servers: once
+        // closed, MultiBurst falls back to a same-thread executor, so a second world load
+        // without reopen() would silently run every burst inline.
+        MultiBurst.burst.reopen();
+        MultiBurst.ioBurst.reopen();
         ModdedScheduler scheduler = schedulerOrNull();
         if (scheduler != null) {
             scheduler.reset();
@@ -170,6 +176,7 @@ public final class ModdedEngineBootstrap {
         failure = runStopStage(failure, "wand service", ModdedWandService::clearAll);
         failure = runStopStage(failure, "block break handler", ModdedBlockBreakHandler::clear);
         failure = runStopStage(failure, "studio commands", ModdedStudioCommands::clear);
+        failure = runStopStage(failure, "gui host", ModdedGuiHost::clear);
         failure = runStopStage(failure, "services", () -> services().disableAll());
         failure = runStopStage(failure, "world engines", ModdedWorldEngines::shutdown);
         failure = runStopStage(failure, "primary world router", ModdedPrimaryWorldRouter::clear);
@@ -183,6 +190,10 @@ public final class ModdedEngineBootstrap {
             failure = runStopStage(failure, "level snapshot", ModdedServerLevels::forget);
         }
         failure = runStopStage(failure, "generation pool", IrisModdedChunkGenerator::shutdownGenPool);
+        failure = runStopStage(failure, "burst pools", () -> {
+            MultiBurst.burst.close();
+            MultiBurst.ioBurst.close();
+        });
         failure = runStopStage(failure, "sentry", ModdedSentry::flush);
         failure = runStopStage(failure, "startup state", ModdedStartup::reset);
         failure = runStopStage(failure, "server state", () -> {
@@ -386,7 +397,12 @@ public final class ModdedEngineBootstrap {
                 ModdedCustomContentRegistry.Discovery customContentDiscovery =
                         ModdedCustomContentRegistry.discover();
                 rollback.add(customContentDiscovery::rollback);
-                ModdedIrisSplash.print(boundLoader);
+                try {
+                    ModdedIrisSplash.print(boundLoader);
+                } catch (Throwable splashFailure) {
+                    // A cosmetic banner must never roll back the platform bind.
+                    LOGGER.warn("Iris splash could not be printed", splashFailure);
+                }
                 createdServices.enableAll();
                 runtime = new BoundRuntime(created, createdServices);
                 rollback.clear();

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

@@ -18,6 +18,7 @@
 
 package art.arcane.iris.modded;
 
+import art.arcane.iris.spi.IrisPlatforms;
 import art.arcane.iris.core.loader.IrisData;
 import art.arcane.iris.core.localization.IrisLanguage;
 import art.arcane.iris.core.localization.RuntimeUiMessages;
@@ -734,7 +735,7 @@ public final class ModdedForcedDatapack {
     }
 
     private static Path packsRoot() {
-        return ModdedEngineBootstrap.loader().configDir().resolve("irisworldgen").resolve("packs");
+        return IrisPlatforms.get().packsFolderNoCreate().toPath();
     }
 
     private record PublishedState(Path directory, String packsHash) {

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

@@ -18,6 +18,7 @@
 
 package art.arcane.iris.modded;
 
+import art.arcane.iris.spi.IrisPlatforms;
 import art.arcane.iris.core.IrisSettings;
 import art.arcane.iris.core.splash.IrisSplashComposer;
 import art.arcane.iris.core.splash.IrisSplashRenderer;
@@ -38,7 +39,7 @@ public final class ModdedIrisSplash {
     }
 
     private static void printPacks(ModdedLoader loader) {
-        File packFolder = loader.configDir().resolve("irisworldgen").resolve("packs").toFile();
+        File packFolder = IrisPlatforms.get().packsFolderNoCreate();
         for (String line : IrisSplashComposer.composePackLines(packFolder, IrisLogging::reportError)) {
             IrisLogging.info(line);
         }

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

@@ -116,13 +116,68 @@ public final class ModdedPlatform implements IrisPlatform {
         return folder;
     }
 
+    /**
+     * Modded packs live under config/irisworldgen/packs, not the config/iris data folder. The
+     * packsFolder overrides are the source of truth; the dataFolder/dataFile overrides below
+     * re-root any path whose FIRST segment is exactly "packs" so no call site can regress onto
+     * the empty config/iris/packs directory. Settings, worlds.json, parity/, cache/ and every
+     * other name stay under config/iris.
+     */
+    @Override
+    public File packsFolder(String... sub) {
+        File folder = packsFolderNoCreate(sub);
+        folder.mkdirs();
+        return folder;
+    }
+
+    @Override
+    public File packsFolderNoCreate(String... sub) {
+        File root = loader.configDir().resolve("irisworldgen").resolve("packs").toFile();
+        if (sub == null || sub.length == 0) {
+            return root;
+        }
+        return new File(root, String.join(File.separator, sub));
+    }
+
+    @Override
+    public File dataFolder(String... path) {
+        if (isPacksPath(path)) {
+            return packsFolder(stripPacksSegment(path));
+        }
+        return IrisPlatform.super.dataFolder(path);
+    }
+
+    @Override
+    public File dataFolderNoCreate(String... path) {
+        if (isPacksPath(path)) {
+            return packsFolderNoCreate(stripPacksSegment(path));
+        }
+        return IrisPlatform.super.dataFolderNoCreate(path);
+    }
+
     @Override
     public File dataFile(String... path) {
+        if (isPacksPath(path)) {
+            File file = packsFolderNoCreate(stripPacksSegment(path));
+            file.getParentFile().mkdirs();
+            return file;
+        }
         File file = new File(dataFolder(), String.join(File.separator, path));
         file.getParentFile().mkdirs();
         return file;
     }
 
+    private static boolean isPacksPath(String... path) {
+        // Exact-segment match only: "packbenchmarks" and "packsx" must stay under config/iris.
+        return path != null && path.length > 0 && "packs".equals(path[0]);
+    }
+
+    private static String[] stripPacksSegment(String... path) {
+        String[] sub = new String[path.length - 1];
+        System.arraycopy(path, 1, sub, 0, sub.length);
+        return sub;
+    }
+
     @Override
     public File pluginJar() {
         File jar = loader.modJar();

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

@@ -50,6 +50,11 @@ final class ModdedSpawnTableMerger {
     }
 
     void initializeVanillaSpawnBiomes(Registry<Biome> registry) {
+        // Volatile fast path BEFORE the monitor: this runs per mob category per spawn attempt
+        // on the server thread, and the generator monitor is contended by binds/hotloads.
+        if (vanillaSpawnBiomesInitialized) {
+            return;
+        }
         synchronized (generator) {
             if (vanillaSpawnBiomesInitialized) {
                 return;

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

@@ -59,9 +59,36 @@ public final class ModdedStartup {
         if (!PREPARED.compareAndSet(false, true)) {
             return;
         }
+        reportLegacyPacksDirectory();
         validateAllPacks();
     }
 
+    /**
+     * Older builds mkdir'd (and stale guidance sometimes populated) config/iris/packs, but modded
+     * packs live under config/irisworldgen/packs. Never auto-move user content: warn loudly when
+     * the legacy directory holds packs, and quietly remove it when it is empty.
+     */
+    private static void reportLegacyPacksDirectory() {
+        try {
+            File legacy = ModdedEngineBootstrap.loader().configDir().resolve("iris").resolve("packs").toFile();
+            if (!legacy.isDirectory()) {
+                return;
+            }
+            if (!PackDirectoryResolver.listVisiblePackDirectories(legacy).isEmpty()) {
+                File real = art.arcane.iris.spi.IrisPlatforms.get().packsFolderNoCreate();
+                LOGGER.warn("Iris found packs under the legacy directory {} - modded packs load from {} only. Move them there.",
+                        legacy.getAbsolutePath(), real.getAbsolutePath());
+                return;
+            }
+            String[] entries = legacy.list();
+            if (entries == null || entries.length == 0) {
+                legacy.delete();
+            }
+        } catch (Throwable e) {
+            LOGGER.debug("Iris legacy packs directory check failed", e);
+        }
+    }
+
     /**
      * Boot trigger for the forced datapack. Runs on its own daemon thread rather than the Iris scheduler:
      * ModdedEngineBootstrap.start clears the async queue at SERVER_STARTING, which would silently drop this

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

@@ -18,6 +18,7 @@
 
 package art.arcane.iris.modded;
 
+import art.arcane.iris.spi.IrisPlatforms;
 import art.arcane.iris.core.loader.IrisData;
 import art.arcane.iris.core.pack.PackValidationRegistry;
 import art.arcane.iris.engine.IrisEngine;
@@ -26,6 +27,7 @@ import art.arcane.iris.engine.framework.EngineTarget;
 import art.arcane.iris.engine.object.IrisDimension;
 import art.arcane.iris.engine.object.IrisDimensionRuntimeContract;
 import art.arcane.iris.engine.object.IrisWorld;
+import art.arcane.iris.modded.command.ModdedGuiHost;
 import net.minecraft.server.level.ServerLevel;
 import net.minecraft.world.level.dimension.DimensionType;
 import net.minecraft.world.level.storage.LevelResource;
@@ -76,6 +78,8 @@ public final class ModdedWorldEngines {
         if (removed[0] == null) {
             return;
         }
+        // The GUI host holds strong Engine/ServerLevel references with no other remove path.
+        ModdedGuiHost.unbind(removed[0]);
         LOGGER.info("Iris engine evicted for {}", level.dimension().identifier());
     }
 
@@ -89,6 +93,7 @@ public final class ModdedWorldEngines {
         ENGINES.compute(activeLevel, (ServerLevel ignored, Engine current) -> {
             if (current != null && current != activeReplacement) {
                 close(current);
+                ModdedGuiHost.unbind(current);
             }
             return activeReplacement;
         });
@@ -96,6 +101,7 @@ public final class ModdedWorldEngines {
 
     static void closeUnregistered(Engine engine) {
         close(engine);
+        ModdedGuiHost.unbind(engine);
     }
 
     private static Engine create(ServerLevel level, String pack, String dimensionKey, long seedOverride) {
@@ -167,11 +173,7 @@ public final class ModdedWorldEngines {
     }
 
     public static File packFolder(String pack) {
-        return ModdedEngineBootstrap.loader().configDir()
-                .resolve("irisworldgen")
-                .resolve("packs")
-                .resolve(pack)
-                .toFile();
+        return IrisPlatforms.get().packsFolderNoCreate(pack);
     }
 
     static File resolvePack(String pack, String dimensionKey) {
@@ -200,10 +202,18 @@ public final class ModdedWorldEngines {
             ServerLevel level = entry.getKey();
             Engine engine = entry.getValue();
             try {
-                close(engine);
-                if (!ENGINES.remove(level, engine) && ENGINES.containsKey(level)) {
-                    throw new IllegalStateException("Iris engine mapping changed during shutdown for "
-                            + level.dimension().identifier());
+                // Latch the generator's unloading flag BEFORE closing (unbindEngine sets it,
+                // then evicts): chunk-system drain work running after this stage would
+                // otherwise see a closed engine and silently rebuild a fresh engine + Mantle
+                // that no teardown stage ever closes, writing plates after the final save.
+                if (level.getChunkSource().getGenerator() instanceof IrisModdedChunkGenerator generator) {
+                    generator.unbindEngine(level);
+                } else {
+                    close(engine);
+                    if (!ENGINES.remove(level, engine) && ENGINES.containsKey(level)) {
+                        throw new IllegalStateException("Iris engine mapping changed during shutdown for "
+                                + level.dimension().identifier());
+                    }
                 }
                 LOGGER.info("Iris engine closed for {}", level.dimension().identifier());
             } catch (Throwable e) {

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

@@ -565,9 +565,7 @@ public final class ModdedWorldManager implements EngineWorldManager {
             if (worldY <= level.getMinY() || worldY >= level.getMaxY()) {
                 continue;
             }
-            if (!LootResolver.oneIn(entityRng, entry.getRarity())) {
-                continue;
-            }
+            // Rarity is applied exactly once, as pool weighting in rarityPick - never re-rolled per position (Bukkit parity).
             if (!lightAllowed(spawner, level, worldX, worldY, worldZ)) {
                 continue;
             }
@@ -605,9 +603,7 @@ public final class ModdedWorldManager implements EngineWorldManager {
         int worldZ = position.getZ();
         int spawned = 0;
         for (int i = 0; i < count; i++) {
-            if (!LootResolver.oneIn(entityRng, entry.getRarity())) {
-                continue;
-            }
+            // Rarity is applied exactly once, as pool weighting in rarityPick - never re-rolled per position (Bukkit parity).
             if (!lightAllowed(spawner, level, worldX, worldY, worldZ)) {
                 continue;
             }
@@ -774,18 +770,8 @@ public final class ModdedWorldManager implements EngineWorldManager {
     }
 
     private IrisEntitySpawn rarityPick(KList<IrisEntitySpawn> entries) {
-        int totalRarity = 0;
-        for (IrisEntitySpawn entry : entries) {
-            totalRarity += IRare.get(entry);
-        }
-        if (totalRarity <= 0) {
-            return entries.getRandom();
-        }
-        KList<IrisEntitySpawn> weighted = new KList<>();
-        for (IrisEntitySpawn entry : entries) {
-            weighted.addMultiple(entry, totalRarity / IRare.get(entry));
-        }
-        return weighted.getRandom();
+        KList<IrisEntitySpawn> weighted = IRare.expandWeighted(entries);
+        return weighted.isEmpty() ? entries.getRandom() : weighted.getRandom();
     }
 
     private static long pack(int x, int z) {

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

@@ -178,10 +178,16 @@ public final class IrisModdedAPI {
     /**
      * Declares that mantle slices of {@code sliceType} must be kept rather than discarded.
      * <p>
-     * Iris drops slices it does not need once a region's generation data has served its purpose. Any type a mod
-     * writes with {@link #setMantleData(ServerLevel, int, int, int, Object)} and expects to read back later must be
+     * Iris drops slices it does not need once a region's generation data has served its purpose - both the
+     * normal per-chunk trim and pregeneration's forced cleanup honor this registry. Any type a mod writes
+     * with {@link #setMantleData(ServerLevel, int, int, int, Object)} and expects to read back later must be
      * declared here first. Registration is by canonical class name, process-wide across every Iris world, and
-     * cannot be undone - declare it once during mod setup. A null {@code sliceType} is ignored.
+     * cannot be undone - declare it once during mod setup. A null {@code sliceType} is ignored, and the
+     * block-state slice can never be retained.
+     * <p>
+     * Retained data lives for the world's lifetime: it persists into the mantle region files and unloads
+     * with them, so region files grow with everything you retain. The mod owns the cleanup - call
+     * {@code deleteMantleData} when a value is no longer needed.
      */
     public static void retainMantleDataForSlice(Class<?> sliceType) {
         if (sliceType == null) {

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

@@ -18,6 +18,7 @@
 
 package art.arcane.iris.modded.command;
 
+import art.arcane.iris.spi.IrisPlatforms;
 import art.arcane.iris.core.pack.PackDirectoryResolver;
 import art.arcane.iris.engine.framework.Engine;
 import art.arcane.iris.engine.framework.IrisStructureLocator;
@@ -230,7 +231,7 @@ final class ModdedCommandSuggestions {
         Set<String> names = new TreeSet<>();
         names.add("overworld");
         try {
-            File packs = ModdedEngineBootstrap.loader().configDir().resolve("irisworldgen").resolve("packs").toFile();
+            File packs = IrisPlatforms.get().packsFolderNoCreate();
             for (File child : PackDirectoryResolver.listVisiblePackDirectories(packs)) {
                 String packName = child.getName();
                 names.add(packName);

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

@@ -18,6 +18,7 @@
 
 package art.arcane.iris.modded.command;
 
+import art.arcane.iris.core.pack.PackDownloader;
 import com.mojang.brigadier.arguments.BoolArgumentType;
 import com.mojang.brigadier.arguments.IntegerArgumentType;
 import com.mojang.brigadier.arguments.LongArgumentType;
@@ -190,15 +191,15 @@ final class ModdedCommandTree {
                 .then(Commands.argument("pack", StringArgumentType.word()).suggests(ModdedCommandSuggestions.PACK_NAMES)
                         .executes((CommandContext<CommandSourceStack> context) ->
                                 IrisModdedCommands.download(context.getSource(),
-                                        StringArgumentType.getString(context, "pack"), "stable", false))
+                                        StringArgumentType.getString(context, "pack"), PackDownloader.DEFAULT_BRANCH, false))
                         .then(Commands.literal("force")
                                 .executes((CommandContext<CommandSourceStack> context) ->
                                         IrisModdedCommands.download(context.getSource(),
-                                                StringArgumentType.getString(context, "pack"), "stable", true)))
+                                                StringArgumentType.getString(context, "pack"), PackDownloader.DEFAULT_BRANCH, true)))
                         .then(Commands.argument("overwrite", BoolArgumentType.bool())
                                 .executes((CommandContext<CommandSourceStack> context) ->
                                         IrisModdedCommands.download(context.getSource(),
-                                                StringArgumentType.getString(context, "pack"), "stable",
+                                                StringArgumentType.getString(context, "pack"), PackDownloader.DEFAULT_BRANCH,
                                                 BoolArgumentType.getBool(context, "overwrite"))))
                         .then(Commands.argument("branch", StringArgumentType.word())
                                 .executes((CommandContext<CommandSourceStack> context) ->

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

@@ -188,6 +188,9 @@ public final class ModdedDustRevealer {
     private static void revealBatch(ModdedScheduler scheduler, RevealRun run,
                                     List<BlockPos> hits, int from) {
         if (!active(run)) {
+            // Drop the registry entry on abort too, or the run record pins the player, level
+            // and engine until server stop. No-op if a newer run already replaced it.
+            ACTIVE_RUNS.remove(run.playerId(), run);
             return;
         }
         int to = Math.min(hits.size(), from + PARTICLE_BATCH_SIZE);

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

@@ -55,6 +55,29 @@ public final class ModdedGuiHost implements GuiHost.Provider {
         }
     }
 
+    /**
+     * Drops the GUI binding for an evicted engine. Without this the host pinned every
+     * GUI-bound Engine, its ServerLevel and transitively the MinecraftServer for the process
+     * lifetime — there was no remove path at all.
+     */
+    public static void unbind(Engine engine) {
+        if (engine == null) {
+            return;
+        }
+        INSTANCE.levels.remove(engine);
+        INSTANCE.openers.remove(engine);
+        if (INSTANCE.active == engine) {
+            INSTANCE.active = null;
+        }
+    }
+
+    public static void clear() {
+        INSTANCE.levels.clear();
+        INSTANCE.openers.clear();
+        INSTANCE.active = null;
+        INSTANCE.server = null;
+    }
+
     public static boolean isGuiLaunchable() {
         return GuiHost.isAvailable() && IrisSettings.get().getGui().isUseServerLaunchedGuis();
     }

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

@@ -543,6 +543,16 @@ final class ModdedLocateCommands {
 
     private static void teleportToLocateResult(CommandSourceStack source, ServerLevel level, Engine engine,
                                                 ServerPlayer player, String label, Position2 at) {
+        // Same liveness guards the structure completion path has: the search can take up to
+        // two minutes, and the captured ServerPlayer may be gone or elsewhere by then.
+        if (player.hasDisconnected() || player.isRemoved()) {
+            IrisModdedCommands.fail(source, IrisLanguage.plain(ModdedCommandMessages.IRIS_MODDED_COMMANDS_PLAYER_DISCONNECTED_BEFORE_STRUCTURE_SEARCH_COMPLETED));
+            return;
+        }
+        if (player.level() != level) {
+            IrisModdedCommands.fail(source, IrisLanguage.plain(ModdedCommandMessages.IRIS_MODDED_COMMANDS_YOU_CHANGED_DIMENSIONS_BEFORE_STRUCTURE_SEARCH_COMPLETED_RUN_COMMAND_AGAIN));
+            return;
+        }
         int blockX = (at.getX() << 4) + 8;
         int blockZ = (at.getZ() << 4) + 8;
         try (GenerationSessionLease lease = engine.acquireGenerationLease("modded_locator_teleport");

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

@@ -291,30 +291,35 @@ public final class ModdedObjectCommands {
         }
         int[] tilesSkipped = {0};
         int[] tilesSaved = {0};
+        // capture() must stay on the server thread (getBlockState/getBlockEntity are not
+        // async-safe), but the disk write of a local, unshared object is not tick work.
         IrisObject object = capture(level, min, max, w, h, d, tilesSkipped, tilesSaved);
-        File parent = file.getParentFile();
-        if (parent != null) {
-            parent.mkdirs();
-        }
-        try {
-            object.write(file);
-        } catch (IOException e) {
-            LOGGER.error("Iris object save failed for {}", file.getAbsolutePath(), e);
-            IrisModdedCommands.fail(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_OBJECT_COMMANDS_FAILED_SAVE_OBJECT, MessageArgument.untrusted("value", String.valueOf(e.getMessage()))));
-            return 0;
-        }
-        StringBuilder tileNote = new StringBuilder();
-        if (tilesSaved[0] > 0) {
-            tileNote.append(" (").append(tilesSaved[0]).append(" tile entity state(s) captured");
-            if (tilesSkipped[0] > 0) {
-                tileNote.append(", ").append(tilesSkipped[0]).append(" failed");
+        MinecraftServer server = source.getServer();
+        J.a(() -> {
+            File parent = file.getParentFile();
+            if (parent != null) {
+                parent.mkdirs();
             }
-            tileNote.append(")");
-        } else if (tilesSkipped[0] > 0) {
-            tileNote.append(" (").append(tilesSkipped[0]).append(" tile state(s) could not be captured)");
-        }
-        IrisModdedCommands.ok(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_OBJECT_COMMANDS_SAVED_OBJECTS_IOB_X_X_BLOCK_S, MessageArgument.untrusted("value", engine.getData().getDataFolder().getName()), MessageArgument.untrusted("name", name), MessageArgument.untrusted("w", w), MessageArgument.untrusted("h", h), MessageArgument.untrusted("d", d), MessageArgument.untrusted("value2", object.getBlocks().size()), MessageArgument.untrusted("tileNote", tileNote)));
-        LOGGER.info("Iris object save: {} {}x{}x{} blocks={} tilesSaved={} tilesSkipped={} -> {}", name, w, h, d, object.getBlocks().size(), tilesSaved[0], tilesSkipped[0], file.getAbsolutePath());
+            try {
+                object.write(file);
+            } catch (IOException e) {
+                LOGGER.error("Iris object save failed for {}", file.getAbsolutePath(), e);
+                server.execute(() -> IrisModdedCommands.fail(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_OBJECT_COMMANDS_FAILED_SAVE_OBJECT, MessageArgument.untrusted("value", String.valueOf(e.getMessage())))));
+                return;
+            }
+            StringBuilder tileNote = new StringBuilder();
+            if (tilesSaved[0] > 0) {
+                tileNote.append(" (").append(tilesSaved[0]).append(" tile entity state(s) captured");
+                if (tilesSkipped[0] > 0) {
+                    tileNote.append(", ").append(tilesSkipped[0]).append(" failed");
+                }
+                tileNote.append(")");
+            } else if (tilesSkipped[0] > 0) {
+                tileNote.append(" (").append(tilesSkipped[0]).append(" tile state(s) could not be captured)");
+            }
+            server.execute(() -> IrisModdedCommands.ok(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_OBJECT_COMMANDS_SAVED_OBJECTS_IOB_X_X_BLOCK_S, MessageArgument.untrusted("value", engine.getData().getDataFolder().getName()), MessageArgument.untrusted("name", name), MessageArgument.untrusted("w", w), MessageArgument.untrusted("h", h), MessageArgument.untrusted("d", d), MessageArgument.untrusted("value2", object.getBlocks().size()), MessageArgument.untrusted("tileNote", tileNote))));
+            LOGGER.info("Iris object save: {} {}x{}x{} blocks={} tilesSaved={} tilesSkipped={} -> {}", name, w, h, d, object.getBlocks().size(), tilesSaved[0], tilesSkipped[0], file.getAbsolutePath());
+        });
         return 1;
     }
 

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

@@ -19,6 +19,7 @@
 package art.arcane.iris.modded.command;
 
 import net.minecraft.core.BlockPos;
+import net.minecraft.server.MinecraftServer;
 import net.minecraft.server.level.ServerLevel;
 import net.minecraft.world.level.block.Block;
 import net.minecraft.world.level.block.state.BlockState;
@@ -88,10 +89,22 @@ public final class ModdedObjectUndo {
             if (entry == null) {
                 break;
             }
+            // Identity check, not just null: a studio closed and reopened under the same
+            // dimension id must never have blocks replayed into the dead ServerLevel.
+            MinecraftServer server = entry.level().getServer();
+            if (server == null || server.getLevel(entry.level().dimension()) != entry.level()) {
+                LOGGER.warn("Iris object undo: skipped a stale entry for removed dimension {}",
+                        entry.level().dimension().identifier());
+                continue;
+            }
             int writes = 0;
             for (Map.Entry<BlockPos, BlockState> block : entry.blocks().entrySet()) {
-                entry.level().setBlock(block.getKey(), block.getValue(), Block.UPDATE_CLIENTS | Block.UPDATE_KNOWN_SHAPE);
-                writes++;
+                try {
+                    entry.level().setBlock(block.getKey(), block.getValue(), Block.UPDATE_CLIENTS | Block.UPDATE_KNOWN_SHAPE);
+                    writes++;
+                } catch (Throwable e) {
+                    LOGGER.error("Iris object undo: failed to revert a block at {}", block.getKey(), e);
+                }
             }
             LOGGER.info("Iris object undo: reverted {} block(s) in {}", writes, entry.level().dimension().identifier());
             reverted++;
@@ -99,6 +112,23 @@ public final class ModdedObjectUndo {
         return reverted;
     }
 
+    /**
+     * Drops every entry recorded against the given level. Called on dimension removal so a
+     * closed studio releases its block snapshots and the ServerLevel reference.
+     */
+    public static void forget(ServerLevel level) {
+        if (level == null) {
+            return;
+        }
+        UNDOS.entrySet().removeIf((Map.Entry<UUID, Deque<Entry>> ownerEntry) -> {
+            Deque<Entry> queue = ownerEntry.getValue();
+            synchronized (queue) {
+                queue.removeIf((Entry entry) -> entry.level() == level);
+                return queue.isEmpty();
+            }
+        });
+    }
+
     public static void clearAll() {
         UNDOS.clear();
     }

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

@@ -18,6 +18,7 @@
 
 package art.arcane.iris.modded.command;
 
+import art.arcane.iris.spi.IrisPlatforms;
 import art.arcane.iris.core.pack.PackDirectoryResolver;
 import art.arcane.iris.core.pack.PackResourceCleanup;
 import art.arcane.iris.core.pack.PackValidationRegistry;
@@ -98,7 +99,7 @@ public final class ModdedPackCommands {
     }
 
     public static File packsRoot() {
-        return ModdedEngineBootstrap.loader().configDir().resolve("irisworldgen").resolve("packs").toFile();
+        return IrisPlatforms.get().packsFolderNoCreate();
     }
 
     private static int validate(CommandSourceStack source, String pack) {

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

@@ -23,6 +23,7 @@ import art.arcane.iris.core.gui.GuiHost;
 import art.arcane.iris.core.gui.NoiseExplorerGUI;
 import art.arcane.iris.core.gui.VisionGUI;
 import art.arcane.iris.core.loader.IrisData;
+import art.arcane.iris.core.pack.PackDownloader;
 import art.arcane.iris.core.pack.StructurePackageClosure;
 import art.arcane.iris.core.project.IrisProjectCopier;
 import art.arcane.iris.engine.framework.Engine;
@@ -31,7 +32,9 @@ import art.arcane.iris.engine.object.IrisBiomeGeneratorLink;
 import art.arcane.iris.engine.object.IrisDimension;
 import art.arcane.iris.engine.object.IrisEntitySpawn;
 import art.arcane.iris.engine.object.IrisGenerator;
-import art.arcane.iris.engine.object.IrisObjectPlacement;
+import art.arcane.iris.core.pack.PackExportClosure;
+import art.arcane.iris.engine.object.IrisEntity;
+import art.arcane.iris.engine.object.IrisMarker;
 import art.arcane.iris.engine.object.IrisRegion;
 import art.arcane.iris.engine.object.IrisSpawner;
 import art.arcane.iris.engine.object.IrisStructurePlacement;
@@ -383,7 +386,7 @@ public final class ModdedStudioCommands {
             File packFolder = new File(ModdedPackCommands.packsRoot(), pack);
             if (!new File(packFolder, "dimensions/" + pack + ".json").isFile()) {
                 server.execute(() -> IrisModdedCommands.ok(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_STUDIO_COMMANDS_PACK_MISSING_DOWNLOADING_IRISDIMENSIONS, MessageArgument.untrusted("pack", pack), MessageArgument.untrusted("pack2", pack))));
-                boolean installed = ModdedPackInstaller.install(ModdedEngineBootstrap.loader().configDir(), pack, "master", false, true,
+                boolean installed = ModdedPackInstaller.install(ModdedEngineBootstrap.loader().configDir(), pack, PackDownloader.DEFAULT_BRANCH, false, true,
                         (String line) -> server.execute(() -> IrisModdedCommands.ok(source, line)));
                 if (!installed || !new File(packFolder, "dimensions/" + pack + ".json").isFile()) {
                     server.execute(() -> IrisModdedCommands.fail(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_STUDIO_COMMANDS_PACK_COULD_NOT_BE_DOWNLOADED_CHECK_NAME_TRY_IRIS_DOWNLOAD, MessageArgument.untrusted("pack", pack), MessageArgument.untrusted("pack2", pack))));
@@ -467,7 +470,9 @@ public final class ModdedStudioCommands {
         ServerPlayer player = source.getPlayer();
         MinecraftServer server = source.getServer();
         UUID owner = player == null ? CONSOLE_OWNER : player.getUUID();
-        String dimensionId = STUDIOS.remove(owner);
+        // Commit the ownership drop only after removal succeeds: dropping it first orphaned a
+        // still-registered studio that no command could ever remove again.
+        String dimensionId = STUDIOS.get(owner);
         if (dimensionId == null) {
             IrisModdedCommands.fail(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_STUDIO_COMMANDS_YOU_DO_NOT_HAVE_OPEN_STUDIO_USE_IRIS_STUDIO_OPEN));
             return 0;
@@ -479,6 +484,7 @@ public final class ModdedStudioCommands {
             IrisModdedCommands.fail(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_STUDIO_COMMANDS_STUDIO_CLOSE_FAILED, MessageArgument.untrusted("value", e.getClass().getSimpleName()), MessageArgument.trusted("errorMessage", IrisLanguage.errorDetail(e))));
             return 0;
         }
+        STUDIOS.remove(owner, dimensionId);
         IrisModdedCommands.ok(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_STUDIO_COMMANDS_STUDIO_CLOSED_WAS_EVACUATED_UNLOADED_ITS_REGION_DATA_DELETED, MessageArgument.untrusted("dimensionId", dimensionId)));
         return 1;
     }
@@ -588,7 +594,7 @@ public final class ModdedStudioCommands {
                 File templateFolder = new File(packsRoot, template);
                 if (!new File(templateFolder, "dimensions/" + template + ".json").isFile()) {
                     server.execute(() -> IrisModdedCommands.ok(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_STUDIO_COMMANDS_TEMPLATE_IS_NOT_INSTALLED_DOWNLOADING_IRISDIMENSIONS, MessageArgument.untrusted("template", template), MessageArgument.untrusted("template2", template))));
-                    boolean installed = ModdedPackInstaller.install(ModdedEngineBootstrap.loader().configDir(), template, "master", false, true,
+                    boolean installed = ModdedPackInstaller.install(ModdedEngineBootstrap.loader().configDir(), template, PackDownloader.DEFAULT_BRANCH, false, true,
                             (String line) -> server.execute(() -> IrisModdedCommands.ok(source, line)));
                     if (!installed || !new File(templateFolder, "dimensions/" + template + ".json").isFile()) {
                         server.execute(() -> IrisModdedCommands.fail(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_STUDIO_COMMANDS_TEMPLATE_COULD_NOT_BE_DOWNLOADED_INSTALL_PACK_WITH_DIMENSIONS_JSON, MessageArgument.untrusted("template", template), MessageArgument.untrusted("template2", template))));
@@ -655,6 +661,7 @@ public final class ModdedStudioCommands {
         LinkedHashSet<String> generatorKeys = new LinkedHashSet<>();
         LinkedHashSet<String> lootKeys = new LinkedHashSet<>();
         LinkedHashSet<String> objectKeys = new LinkedHashSet<>();
+        LinkedHashSet<String> markerKeys = new LinkedHashSet<>();
         LinkedHashSet<String> structureKeys = new LinkedHashSet<>();
 
         regionKeys.addAll(dimension.getRegions());
@@ -675,6 +682,8 @@ public final class ModdedStudioCommands {
             lootKeys.addAll(region.getLoot().getTables());
             spawnerKeys.addAll(region.getEntitySpawners());
             collectStructureKeys(structureKeys, region.getStructures());
+            objectKeys.addAll(PackExportClosure.collectObjectKeys(region.getObjects()));
+            markerKeys.addAll(PackExportClosure.collectMarkerKeys(region.getObjects()));
         }
         for (String biomeKey : biomeKeys) {
             IrisBiome biome = dm.getBiomeLoader().load(biomeKey);
@@ -685,9 +694,15 @@ public final class ModdedStudioCommands {
             lootKeys.addAll(biome.getLoot().getTables());
             spawnerKeys.addAll(biome.getEntitySpawners());
             collectStructureKeys(structureKeys, biome.getStructures());
-            for (IrisObjectPlacement placement : biome.getObjects()) {
-                objectKeys.addAll(placement.getPlace());
+            objectKeys.addAll(PackExportClosure.collectObjectKeys(biome.getObjects()));
+            markerKeys.addAll(PackExportClosure.collectMarkerKeys(biome.getObjects()));
+        }
+        for (String markerKey : markerKeys) {
+            IrisMarker marker = dm.getMarkerLoader().load(markerKey);
+            if (marker == null) {
+                continue;
             }
+            spawnerKeys.addAll(marker.getSpawners());
         }
         for (String spawnerKey : spawnerKeys) {
             IrisSpawner spawner = dm.getSpawnerLoader().load(spawnerKey);
@@ -695,6 +710,14 @@ public final class ModdedStudioCommands {
                 continue;
             }
             spawner.getSpawns().forEach((IrisEntitySpawn spawn) -> entityKeys.add(spawn.getEntity()));
+            spawner.getInitialSpawns().forEach((IrisEntitySpawn spawn) -> entityKeys.add(spawn.getEntity()));
+        }
+        for (String entityKey : entityKeys) {
+            IrisEntity entity = dm.getEntityLoader().load(entityKey);
+            if (entity == null) {
+                continue;
+            }
+            lootKeys.addAll(entity.getLoot().getTables());
         }
 
         StringBuilder hashes = new StringBuilder();
@@ -732,6 +755,12 @@ public final class ModdedStudioCommands {
         for (String key : lootKeys) {
             hashes.append(copyJson(folder, "loot", key, dm.getLootLoader().findFile(key)));
         }
+        for (String key : spawnerKeys) {
+            hashes.append(copyJson(folder, "spawners", key, dm.getSpawnerLoader().findFile(key)));
+        }
+        for (String key : markerKeys) {
+            hashes.append(copyJson(folder, "markers", key, dm.getMarkerLoader().findFile(key)));
+        }
 
         JSONObject meta = new JSONObject();
         meta.put("hash", IO.hash(hashes.toString()));
@@ -794,14 +823,19 @@ public final class ModdedStudioCommands {
                 int totalTasks = diameter * diameter;
                 KMap<String, AtomicInteger> counts = new KMap<>();
                 engine.getDimension().getRegions().forEach((String key) -> counts.put(key, new AtomicInteger(0)));
+                // finally-scoped: a throw mid-scan previously leaked the sampler's whole
+                // ForkJoinPool (close() is the only thing that shuts it down).
                 MultiBurst burst = new MultiBurst("Region Sampler");
-                BurstExecutor executor = burst.burst(totalTasks);
-                new Spiraler(diameter, diameter, (int x, int z) -> executor.queue(() -> {
-                    IrisRegion region = engine.getRegion((x << 4) + 8, (z << 4) + 8);
-                    counts.computeIfAbsent(region.getLoadKey(), (String key) -> new AtomicInteger(0)).incrementAndGet();
-                })).setOffset(blockX >> 4, blockZ >> 4).drain();
-                executor.complete();
-                burst.close();
+                try {
+                    BurstExecutor executor = burst.burst(totalTasks);
+                    new Spiraler(diameter, diameter, (int x, int z) -> executor.queue(() -> {
+                        IrisRegion region = engine.getRegion((x << 4) + 8, (z << 4) + 8);
+                        counts.computeIfAbsent(region.getLoadKey(), (String key) -> new AtomicInteger(0)).incrementAndGet();
+                    })).setOffset(blockX >> 4, blockZ >> 4).drain();
+                    executor.complete();
+                } finally {
+                    burst.close();
+                }
                 server.execute(() -> counts.forEach((String key, AtomicInteger count) -> {
                     IrisRegion region = engine.getData().getRegionLoader().load(key);
                     String rarity = region == null ? "?" : String.valueOf(region.getRarity());

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

@@ -451,6 +451,9 @@ public final class ModdedWhatCommands {
                                           ModdedScheduler scheduler, MarkerRun run,
                                           List<BlockPos> hits, int from) {
         if (!active(run)) {
+            // Drop the registry entry on abort too, or the run record pins the player, level
+            // and engine until server stop. No-op if a newer run already replaced it.
+            ACTIVE_MARKER_RUNS.remove(run.playerId(), run);
             return;
         }
         int to = Math.min(hits.size(), from + MARKER_BATCH_SIZE);

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

@@ -20,6 +20,7 @@ package art.arcane.iris.modded.command;
 
 import art.arcane.iris.core.loader.IrisData;
 import art.arcane.iris.core.pack.BrokenPackException;
+import art.arcane.iris.core.pack.PackDownloader;
 import art.arcane.iris.core.pack.PackValidationRegistry;
 import art.arcane.iris.engine.object.IrisDimension;
 import art.arcane.iris.modded.IrisModdedChunkGenerator;
@@ -177,7 +178,7 @@ public final class ModdedWorldCommands {
         }
         IrisModdedCommands.ok(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_WORLD_COMMANDS_PACK_IS_NOT_INSTALLED_DOWNLOADING_IRISDIMENSIONS, MessageArgument.untrusted("pack", pack), MessageArgument.untrusted("pack2", pack)));
         Thread thread = new Thread(() -> {
-            boolean installed = ModdedPackInstaller.install(ModdedEngineBootstrap.loader().configDir(), pack, "master", false, true,
+            boolean installed = ModdedPackInstaller.install(ModdedEngineBootstrap.loader().configDir(), pack, PackDownloader.DEFAULT_BRANCH, false, true,
                     (String line) -> server.execute(() -> IrisModdedCommands.ok(source, line)));
             server.execute(() -> {
                 if (!installed || !packFolder.isDirectory()) {
@@ -280,7 +281,7 @@ public final class ModdedWorldCommands {
         }
         IrisModdedCommands.ok(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_WORLD_COMMANDS_PACK_IS_NOT_INSTALLED_DOWNLOADING_IRISDIMENSIONS_2, MessageArgument.untrusted("pack", pack), MessageArgument.untrusted("pack2", pack)));
         Thread thread = new Thread(() -> {
-            boolean installed = ModdedPackInstaller.install(ModdedEngineBootstrap.loader().configDir(), pack, "master", false, true,
+            boolean installed = ModdedPackInstaller.install(ModdedEngineBootstrap.loader().configDir(), pack, PackDownloader.DEFAULT_BRANCH, false, true,
                     (String line) -> server.execute(() -> IrisModdedCommands.ok(source, line)));
             server.execute(() -> {
                 if (!installed || !packFolder.isDirectory()) {

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

@@ -55,6 +55,7 @@ import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.RejectedExecutionException;
+import java.util.concurrent.TimeUnit;
 
 public final class ModdedChunkUpdateService implements ModdedTickableService {
     private static final long PASS_PERIOD_MILLIS = 3_000L;
@@ -84,7 +85,17 @@ public final class ModdedChunkUpdateService implements ModdedTickableService {
         ExecutorService active = warmupExecutor;
         warmupExecutor = null;
         if (active != null) {
-            active.shutdown();
+            // Drop queued warm-ups (pure prefetch) and AWAIT: the very next shutdown stage
+            // closes every Mantle, and an in-flight mantle.getChunk would fault a plate back
+            // in after the close-time flush.
+            active.shutdownNow();
+            try {
+                if (!active.awaitTermination(5L, TimeUnit.SECONDS)) {
+                    IrisLogging.warn("Iris mantle warm-up did not stop before engine close");
+                }
+            } catch (InterruptedException e) {
+                Thread.currentThread().interrupt();
+            }
         }
         warmupQueue.clear();
     }

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

@@ -0,0 +1,31 @@
+package art.arcane.iris.modded;
+
+import org.junit.Test;
+
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.List;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+public class ModdedDownloadBranchParityTest {
+    private static final List<String> DOWNLOAD_SOURCES = List.of(
+            "art/arcane/iris/modded/command/ModdedWorldCommands.java",
+            "art/arcane/iris/modded/command/ModdedStudioCommands.java",
+            "art/arcane/iris/modded/command/ModdedCommandTree.java");
+
+    @Test
+    public void implicitAndExplicitDownloadsShareTheCoreDefaultBranch() throws Exception {
+        for (String source : DOWNLOAD_SOURCES) {
+            Path path = Path.of(System.getProperty("iris.moddedCommonSources"), source);
+            String text = Files.readString(path);
+            assertFalse(source + " must not hardcode a \"master\" download branch",
+                    text.contains("\"master\""));
+            assertFalse(source + " must not hardcode a \"stable\" download branch",
+                    text.contains("\"stable\""));
+            assertTrue(source + " must use PackDownloader.DEFAULT_BRANCH",
+                    text.contains("PackDownloader.DEFAULT_BRANCH"));
+        }
+    }
+}

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

@@ -36,12 +36,12 @@ public class ModdedLootApplierTest {
     }
 
     @Test
-    public void clearRemovesNativeAndIrisSourcesBeforeAdding() {
+    public void clearRemovesEverythingAndContributesNothing() {
         List<String> sources = new ArrayList<>(List.of("placement-native", "dimension-iris"));
 
         LootResolver.injectSources(sources, List.of("biome-iris"), IrisLootMode.CLEAR, false);
 
-        assertEquals(List.of("biome-iris"), sources);
+        assertEquals(List.of(), sources);
     }
 
     @Test

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

@@ -0,0 +1,106 @@
+package art.arcane.iris.modded;
+
+import net.minecraft.core.BlockPos;
+import net.minecraft.server.MinecraftServer;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.level.block.state.BlockState;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.TemporaryFolder;
+
+import java.io.File;
+import java.nio.file.Path;
+
+import static org.junit.Assert.assertEquals;
+
+public class ModdedPlatformPathsTest {
+    @Rule
+    public TemporaryFolder temporaryFolder = new TemporaryFolder();
+
+    private ModdedPlatform platform() {
+        Path configDir = temporaryFolder.getRoot().toPath();
+        return new ModdedPlatform(new ModdedLoader() {
+            @Override
+            public String platformName() {
+                return "test";
+            }
+
+            @Override
+            public String minecraftVersion() {
+                return "26.2";
+            }
+
+            @Override
+            public String modVersion() {
+                return "0.0.0";
+            }
+
+            @Override
+            public MinecraftServer currentServer() {
+                return null;
+            }
+
+            @Override
+            public void invalidateLevelCache(MinecraftServer server) {
+            }
+
+            @Override
+            public boolean clientEnvironment() {
+                return false;
+            }
+
+            @Override
+            public Path configDir() {
+                return configDir;
+            }
+
+            @Override
+            public File modJar() {
+                return null;
+            }
+
+            @Override
+            public boolean hasTreeFellerPermission(ServerPlayer player) {
+                return false;
+            }
+
+            @Override
+            public boolean canTreeFellerBreak(ServerLevel level, ServerPlayer player, BlockPos position, BlockState state) {
+                return false;
+            }
+        });
+    }
+
+    @Test
+    public void packsResolveUnderIrisworldgen() {
+        ModdedPlatform platform = platform();
+        File root = temporaryFolder.getRoot();
+        File packsRoot = new File(new File(root, "irisworldgen"), "packs");
+
+        assertEquals(packsRoot, platform.packsFolder());
+        assertEquals(packsRoot, platform.dataFolder("packs"));
+        assertEquals(new File(packsRoot, "overworld"), platform.dataFolderNoCreate("packs", "overworld"));
+        assertEquals(new File(packsRoot, "overworld" + File.separator + "dimensions" + File.separator + "overworld.json"),
+                platform.dataFile("packs", "overworld", "dimensions", "overworld.json"));
+    }
+
+    @Test
+    public void everythingElseStaysUnderIris() {
+        ModdedPlatform platform = platform();
+        File iris = new File(temporaryFolder.getRoot(), "iris");
+
+        assertEquals(iris, platform.dataFolder());
+        assertEquals(new File(iris, "settings.json"), platform.dataFile("settings.json"));
+        assertEquals(new File(iris, "parity"), platform.dataFolder("parity"));
+    }
+
+    @Test
+    public void packsMatchIsExactSegmentOnly() {
+        ModdedPlatform platform = platform();
+        File iris = new File(temporaryFolder.getRoot(), "iris");
+
+        assertEquals(new File(iris, "packbenchmarks"), platform.dataFolder("packbenchmarks"));
+        assertEquals(new File(iris, "packsx"), platform.dataFolderNoCreate("packsx"));
+    }
+}

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

@@ -0,0 +1,75 @@
+package art.arcane.iris.modded;
+
+import art.arcane.iris.engine.object.IRare;
+import art.arcane.iris.engine.object.IrisEntitySpawn;
+import art.arcane.volmlib.util.collection.KList;
+import org.junit.Test;
+
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.List;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+public class ModdedSpawnerRarityParityTest {
+    private static IrisEntitySpawn spawn(int rarity) {
+        IrisEntitySpawn spawn = new IrisEntitySpawn();
+        spawn.setRarity(rarity);
+        return spawn;
+    }
+
+    @Test
+    public void rarityIsAppliedOnceAsPoolWeightOnly() {
+        IrisEntitySpawn common = spawn(1);
+        IrisEntitySpawn rare = spawn(4);
+
+        KList<IrisEntitySpawn> expanded = IRare.expandWeighted(List.of(common, rare));
+
+        // totalRarity 5 -> common appears 5/1 = 5 times, rare 5/4 = 1 time.
+        assertEquals(6, expanded.size());
+        assertEquals(5, expanded.stream().filter(entry -> entry == common).count());
+        assertEquals(1, expanded.stream().filter(entry -> entry == rare).count());
+    }
+
+    @Test
+    public void rarityZeroAndNegativeAreClampedToOne() {
+        assertEquals(1, IRare.get(spawn(0)));
+        assertEquals(1, IRare.get(spawn(-5)));
+        assertEquals(3, IRare.get(spawn(3)));
+    }
+
+    @Test
+    public void perPositionSpawnLoopsDoNotRerollEntryRarity() throws Exception {
+        String source = Files.readString(Path.of(System.getProperty("iris.moddedCommonSources"),
+                "art/arcane/iris/modded/ModdedWorldManager.java"));
+
+        for (String method : List.of("private int spawnEntry(", "private int spawnEntryAt(")) {
+            String body = methodBody(source, method);
+            assertFalse(method + " must not re-roll rarity per position; rarityPick already weighted the pool",
+                    body.contains("getRarity()"));
+            assertTrue(method + " must keep the min/max spawn-count roll",
+                    body.contains("LootResolver.inclusive("));
+        }
+    }
+
+    private static String methodBody(String source, String declaration) {
+        int start = source.indexOf(declaration);
+        assertTrue("ModdedWorldManager must declare " + declaration, start >= 0);
+        int open = source.indexOf('{', start);
+        int depth = 0;
+        for (int index = open; index < source.length(); index++) {
+            char character = source.charAt(index);
+            if (character == '{') {
+                depth++;
+            } else if (character == '}') {
+                depth--;
+                if (depth == 0) {
+                    return source.substring(open + 1, index);
+                }
+            }
+        }
+        throw new AssertionError(declaration + " is not brace balanced");
+    }
+}

core/src/main/java/art/arcane/iris/core/IrisSettings.java

@@ -41,7 +41,7 @@ public class IrisSettings {
     private IrisSettingsGUI gui = new IrisSettingsGUI();
     private IrisSettingsAutoconfiguration autoConfiguration = new IrisSettingsAutoconfiguration();
     private IrisSettingsGenerator generator = new IrisSettingsGenerator();
-    private IrisSettingsConcurrency concurrency = new IrisSettingsConcurrency();
+    private transient IrisSettingsConcurrency concurrency = new IrisSettingsConcurrency();
     private IrisSettingsStudio studio = new IrisSettingsStudio();
     private IrisSettingsPerformance performance = new IrisSettingsPerformance();
     private IrisSettingsPregen pregen = new IrisSettingsPregen();

core/src/main/java/art/arcane/iris/core/IrisWorlds.java

@@ -222,7 +222,7 @@ public class IrisWorlds {
             dimension = IrisData.loadAnyDimension(id, null);
         }
         if (dimension == null) {
-            File packsRoot = IrisPlatforms.get().dataFolderNoCreate(StudioSVC.WORKSPACE_NAME);
+            File packsRoot = IrisPlatforms.get().packsFolderNoCreate();
             if (PackDownloader.isPackPresent(packsRoot, id)) {
                 IrisLogging.error("Pack '" + id + "' exists at " + new File(packsRoot, id).getPath()
                         + " but its dimension failed to load; not redownloading. Fix or delete the pack folder.");

core/src/main/java/art/arcane/iris/core/ServerConfigurator.java

@@ -892,7 +892,7 @@ public class ServerConfigurator {
 
     public static Stream<IrisData> allPacks() {
         Stream<File> locals = PackDirectoryResolver.listVisiblePackDirectories(
-                IrisPlatforms.get().dataFolder("packs")
+                IrisPlatforms.get().packsFolder()
         ).stream();
         return Stream.concat(locals
                 .filter(base -> {

core/src/main/java/art/arcane/iris/core/datapack/DatapackIngestService.java

@@ -175,7 +175,7 @@ public final class DatapackIngestService {
         if (autoIngest && !configured.isEmpty()) {
             IrisLogging.info("Validating " + configured.size()
                     + " configured external datapack import(s) before player admission...");
-            Report report = ingest(null, configured, true);
+            Report report = ingest(null, configured, true, true);
             if (!report.getFailed().isEmpty()) {
                 String failure = report.getFailed().getFirst();
                 IrisStartupValidation.markDatapacksInvalid(failure);
@@ -513,15 +513,35 @@ public final class DatapackIngestService {
     }
 
     public static Report ingest(VolmitSender sender, KList<String> urls, boolean restart) {
-        IrisStartupValidation.beginDatapackValidation();
+        return ingest(sender, urls, restart, false);
+    }
+
+    /**
+     * Only startup validation owns the global player-admission gate (gateAdmission=true). The
+     * runtime admin command must never flip it: a transient download failure there would lock
+     * every login until restart, and the PENDING window would close logins for the whole
+     * (potentially very slow) download. World-creation safety on the ungated path is carried
+     * by the loaded-runtime invalidation plus requireDatapackRestart when files change.
+     */
+    private static Report ingest(VolmitSender sender, KList<String> urls, boolean restart, boolean gateAdmission) {
+        if (gateAdmission) {
+            IrisStartupValidation.beginDatapackValidation();
+        }
         ServerConfigurator.LoadedDatapackRuntimeInvalidation invalidation =
                 ServerConfigurator.invalidateLoadedDatapackRuntime();
         Report report;
+        boolean settled = false;
         TRANSACTION_LOCK.lock();
         try {
             report = ingestLocked(sender, urls, restart);
+            settled = true;
         } finally {
             TRANSACTION_LOCK.unlock();
+            if (!settled && gateAdmission) {
+                // Never strand the admission gate at PENDING on an unexpected throw.
+                IrisStartupValidation.markDatapacksInvalid(
+                        "External datapack ingest failed unexpectedly; check the log above.");
+            }
         }
         if (!report.changed() && report.getFailed().isEmpty()) {
             ServerConfigurator.restoreLoadedDatapackRuntimeIfUnchanged(invalidation);
@@ -532,10 +552,12 @@ public final class DatapackIngestService {
                 ServerConfigurator.requireDatapackRestart();
             }
         }
-        if (!report.getFailed().isEmpty()) {
-            IrisStartupValidation.markDatapacksInvalid(report.getFailed().getFirst());
-        } else if (!report.changed()) {
-            IrisStartupValidation.markDatapacksReady();
+        if (gateAdmission) {
+            if (!report.getFailed().isEmpty()) {
+                IrisStartupValidation.markDatapacksInvalid(report.getFailed().getFirst());
+            } else if (!report.changed()) {
+                IrisStartupValidation.markDatapacksReady();
+            }
         }
         return report;
     }
@@ -944,45 +966,61 @@ public final class DatapackIngestService {
         }
     }
 
+    enum RemoveOutcome {
+        REMOVED,
+        REJECTED,
+        FAILED_AFTER_MUTATION
+    }
+
     public static boolean remove(VolmitSender sender, String id) {
-        ServerConfigurator.invalidateLoadedDatapackRuntime();
-        boolean removed;
+        ServerConfigurator.LoadedDatapackRuntimeInvalidation invalidation =
+                ServerConfigurator.invalidateLoadedDatapackRuntime();
+        RemoveOutcome outcome;
         TRANSACTION_LOCK.lock();
         try {
-            removed = removeLocked(sender, id);
+            outcome = removeOutcomeLocked(sender, id);
         } finally {
             TRANSACTION_LOCK.unlock();
         }
-        if (removed) {
+        if (outcome == RemoveOutcome.REMOVED) {
             ServerConfigurator.requireDatapackRestart();
+        } else if (outcome == RemoveOutcome.REJECTED) {
+            // Rejected before any mutation: nothing on disk changed, so the loaded runtime is
+            // still valid. Leaving it invalidated forced a full datapack reinstall on every
+            // later world creation for the rest of the session.
+            ServerConfigurator.restoreLoadedDatapackRuntimeIfUnchanged(invalidation);
         }
-        return removed;
+        return outcome == RemoveOutcome.REMOVED;
     }
 
-    private static boolean removeLocked(VolmitSender sender, String id) {
+    private static RemoveOutcome removeOutcomeLocked(VolmitSender sender, String id) {
         File root = IrisPlatforms.get().dataFolder("datapacks");
-        return removeLocked(sender, id, root, ServerConfigurator.getDatapacksFolder());
+        return removeOutcomeLocked(sender, id, root, ServerConfigurator.getDatapacksFolder());
     }
 
     static boolean removeLocked(VolmitSender sender, String id, File root, List<File> worldFolders) {
+        return removeOutcomeLocked(sender, id, root, worldFolders) == RemoveOutcome.REMOVED;
+    }
+
+    static RemoveOutcome removeOutcomeLocked(VolmitSender sender, String id, File root, List<File> worldFolders) {
         String requested = id == null ? "" : id.trim().toLowerCase(Locale.ROOT);
         String cleaned = sanitizeId(id);
         if (requested.isBlank() || !requested.equals(cleaned) || RESERVED_IDS.contains(cleaned)) {
             message(sender, C.RED + "Invalid Iris-managed datapack id '" + requested + "'. Run /iris datapack list and use the exact listed id.");
-            return false;
+            return RemoveOutcome.REJECTED;
         }
         try {
             recoverTransactions(root, worldFolders);
         } catch (IOException e) {
             message(sender, C.RED + "Datapack removal blocked by incomplete transaction recovery: " + e.getMessage());
             IrisLogging.reportError(e);
-            return false;
+            return RemoveOutcome.REJECTED;
         }
         Manifest manifest = readManifest(root);
         Entry ownedEntry = manifest.findById(cleaned);
         if (ownedEntry == null) {
             message(sender, C.YELLOW + "No Iris-managed datapack named '" + cleaned + "'. Unmanaged world datapacks are never removed by Iris.");
-            return false;
+            return RemoveOutcome.REJECTED;
         }
 
         List<File> targets;
@@ -991,7 +1029,7 @@ public final class DatapackIngestService {
         } catch (IOException e) {
             message(sender, C.RED + "Refused to remove datapack '" + cleaned + "': " + e.getMessage());
             IrisLogging.reportError(e);
-            return false;
+            return RemoveOutcome.REJECTED;
         }
 
         EditableImportRemoval editableRemoval = null;
@@ -1017,7 +1055,7 @@ public final class DatapackIngestService {
                         removalFailure);
                 message(sender, C.GREEN + "Removed datapack '" + C.WHITE + cleaned + C.GREEN
                         + "'. Restart for it to stop generating, and delete its URL from the pack's datapackImports to keep it gone.");
-                return true;
+                return RemoveOutcome.REMOVED;
             }
             boolean restored = rollbackRemoval(manifestWrite, directoryRemoval, editableRemoval, removalFailure);
             if (restored && coordinator != null) {
@@ -1030,12 +1068,14 @@ public final class DatapackIngestService {
             message(sender, C.RED + "Failed to remove datapack '" + cleaned
                     + "'; Iris attempted to restore every prior location: " + removalFailure.getMessage());
             IrisLogging.reportError(removalFailure);
-            return false;
+            // A mutation was attempted; even a successful rollback is not provably identical
+            // (the fingerprint does not cover datapacks/), so stay conservatively invalidated.
+            return RemoveOutcome.FAILED_AFTER_MUTATION;
         }
         finishCommittedRemoval(cleaned, manifestWrite, directoryRemoval, editableRemoval, coordinator, null);
         message(sender, C.GREEN + "Removed datapack '" + C.WHITE + cleaned + C.GREEN
                 + "'. Restart for it to stop generating, and delete its URL from the pack's datapackImports to keep it gone.");
-        return true;
+        return RemoveOutcome.REMOVED;
     }
 
     private static void finishCommittedRemoval(

core/src/main/java/art/arcane/iris/core/datapack/ModrinthResolver.java

@@ -358,15 +358,18 @@ public final class ModrinthResolver {
         connection.setReadTimeout(20000);
         connection.setInstanceFollowRedirects(true);
 
-        int code = connection.getResponseCode();
-        if (code != 200) {
-            connection.disconnect();
-            throw new IOException("HTTP " + code + " from " + url);
-        }
+        // Everything past openConnection under one finally: a timeout/DNS/TLS throw inside
+        // getResponseCode abandoned the connection undisconnected.
+        try {
+            int code = connection.getResponseCode();
+            if (code != 200) {
+                throw new IOException("HTTP " + code + " from " + url);
+            }
 
-        try (InputStream input = connection.getInputStream();
-             InputStreamReader reader = new InputStreamReader(input, StandardCharsets.UTF_8)) {
-            return readBoundedApiResponse(reader, url, MAX_API_RESPONSE_CHARS);
+            try (InputStream input = connection.getInputStream();
+                 InputStreamReader reader = new InputStreamReader(input, StandardCharsets.UTF_8)) {
+                return readBoundedApiResponse(reader, url, MAX_API_RESPONSE_CHARS);
+            }
         } finally {
             connection.disconnect();
         }

core/src/main/java/art/arcane/iris/core/edit/BlockSignal.java

@@ -36,9 +36,17 @@ public class BlockSignal {
     public static final AtomicInteger active = new AtomicInteger(0);
 
     public BlockSignal(Block block, int ticks) {
-        active.incrementAndGet();
+        // Count only after the entity actually exists, and release unconditionally: a refused
+        // Folia schedule or a spawn failure must not inflate the throttle counter forever.
         Location tg = block.getLocation().clone().add(0.5, 0, 0.5);
-        FallingBlock e = block.getWorld().spawnFallingBlock(tg, block.getBlockData());
+        FallingBlock e;
+        try {
+            e = block.getWorld().spawnFallingBlock(tg, block.getBlockData());
+        } catch (Throwable spawnFailure) {
+            sendBlockRefresh(block);
+            throw spawnFailure;
+        }
+        active.incrementAndGet();
         e.setGravity(false);
         e.setInvulnerable(true);
         e.setGlowing(true);
@@ -55,10 +63,11 @@ public class BlockSignal {
             active.decrementAndGet();
             sendBlockRefresh(block);
         };
-        if (!J.runAt(blockLocation, removeTask, ticks)) {
-            if (!J.isFolia()) {
-                J.s(removeTask, ticks);
-            }
+        boolean scheduled = J.runAt(blockLocation, removeTask, ticks);
+        if (!scheduled && !J.isFolia()) {
+            J.s(removeTask, ticks);
+        } else if (!scheduled) {
+            removeTask.run();
         }
     }
 

core/src/main/java/art/arcane/iris/core/edit/DustRevealer.java

@@ -36,7 +36,6 @@ import art.arcane.volmlib.util.math.RNG;
 import art.arcane.volmlib.util.localization.MessageArgument;
 import art.arcane.iris.util.common.plugin.VolmitSender;
 import art.arcane.iris.util.common.scheduling.J;
-import lombok.Data;
 import org.bukkit.Location;
 import org.bukkit.Sound;
 import org.bukkit.World;
@@ -47,74 +46,83 @@ import net.kyori.adventure.text.event.ClickEvent;
 import net.kyori.adventure.text.event.HoverEvent;
 import net.kyori.adventure.text.format.NamedTextColor;
 
+import java.util.ArrayDeque;
+import java.util.HashSet;
 import java.util.Set;
 import java.util.function.Supplier;
 
-@SuppressWarnings("ALL")
-@Data
 public class DustRevealer {
-    private final Engine engine;
-    private final World world;
-    private final BlockPosition block;
-    private final String key;
-    private final KList<BlockPosition> hits;
+    // Matches the modded twin (ModdedDustRevealer) so both platforms truncate identically.
+    private static final int MAX_HITS = 2_048;
+    private static final int PARTICLE_BATCH_SIZE = 64;
 
-    public DustRevealer(Engine engine, World world, BlockPosition block, String key, KList<BlockPosition> hits) {
-        this.engine = engine;
-        this.world = world;
-        this.block = block;
-        this.key = key;
-        this.hits = hits;
+    /**
+     * Bounded, single-threaded flood fill over the object's placement key, followed by batched
+     * particle playback on the owning threads. The previous shape recursively spawned one
+     * scheduler task + one burst task per matched block, all mutating one unsynchronized
+     * ArrayList and sleep-spinning MultiBurst workers — unbounded fan-out on large objects.
+     */
+    private static void reveal(Engine engine, World world, BlockPosition origin, String key) {
+        KList<BlockPosition> hits = new KList<>();
+        Set<BlockPosition> visited = new HashSet<>();
+        ArrayDeque<BlockPosition> frontier = new ArrayDeque<>();
+        visited.add(origin);
+        frontier.add(origin);
+        hits.add(origin);
+        int minY = world.getMinHeight();
+        int maxY = world.getMaxHeight();
 
-        Location blockLocation = block.toBlock(world).getLocation();
-        Runnable revealTask = () -> {
-            BlockSignal.of(world, block.getX(), block.getY(), block.getZ(), 10);
+        try {
+            search:
+            while (!frontier.isEmpty()) {
+                BlockPosition at = frontier.poll();
+                for (int dx = -1; dx <= 1; dx++) {
+                    for (int dy = -1; dy <= 1; dy++) {
+                        for (int dz = -1; dz <= 1; dz++) {
+                            if (dx == 0 && dy == 0 && dz == 0) {
+                                continue;
+                            }
+                            BlockPosition next = new BlockPosition(at.getX() + dx, at.getY() + dy, at.getZ() + dz);
+                            if (next.getY() < minY || next.getY() >= maxY || !visited.add(next)) {
+                                continue;
+                            }
+                            if (key.equals(engine.getObjectPlacementKey(next.getX(), next.getY() - minY, next.getZ()))) {
+                                hits.add(next);
+                                frontier.add(next);
+                                if (hits.size() >= MAX_HITS) {
+                                    break search;
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+        } catch (Throwable e) {
+            IrisLogging.reportError(e);
+        }
+
+        revealBatch(world, hits, 0);
+    }
+
+    private static void revealBatch(World world, KList<BlockPosition> hits, int from) {
+        if (from >= hits.size()) {
+            return;
+        }
+        int to = Math.min(from + PARTICLE_BATCH_SIZE, hits.size());
+        Runnable batch = () -> {
+            for (int i = from; i < to; i++) {
+                BlockPosition p = hits.get(i);
+                BlockSignal.of(world, p.getX(), p.getY(), p.getZ(), 10);
+            }
+            BlockPosition first = hits.get(from);
             if (M.r(0.25)) {
-                world.playSound(block.toBlock(world).getLocation(), Sound.BLOCK_AMETHYST_BLOCK_CHIME, 1f, RNG.r.f(0.2f, 2f));
+                world.playSound(first.toBlock(world).getLocation(), Sound.BLOCK_AMETHYST_BLOCK_CHIME, 1f, RNG.r.f(0.2f, 2f));
             }
-            J.a(() -> {
-                while (BlockSignal.active.get() > 128) {
-                    J.sleep(5);
-                }
-
-                try {
-                    is(new BlockPosition(block.getX() + 1, block.getY(), block.getZ()));
-                    is(new BlockPosition(block.getX() - 1, block.getY(), block.getZ()));
-                    is(new BlockPosition(block.getX(), block.getY() + 1, block.getZ()));
-                    is(new BlockPosition(block.getX(), block.getY() - 1, block.getZ()));
-                    is(new BlockPosition(block.getX(), block.getY(), block.getZ() + 1));
-                    is(new BlockPosition(block.getX(), block.getY(), block.getZ() - 1));
-                    is(new BlockPosition(block.getX() + 1, block.getY(), block.getZ() + 1));
-                    is(new BlockPosition(block.getX() + 1, block.getY(), block.getZ() - 1));
-                    is(new BlockPosition(block.getX() - 1, block.getY(), block.getZ() + 1));
-                    is(new BlockPosition(block.getX() - 1, block.getY(), block.getZ() - 1));
-                    is(new BlockPosition(block.getX() + 1, block.getY() + 1, block.getZ()));
-                    is(new BlockPosition(block.getX() + 1, block.getY() - 1, block.getZ()));
-                    is(new BlockPosition(block.getX() - 1, block.getY() + 1, block.getZ()));
-                    is(new BlockPosition(block.getX() - 1, block.getY() - 1, block.getZ()));
-                    is(new BlockPosition(block.getX(), block.getY() + 1, block.getZ() - 1));
-                    is(new BlockPosition(block.getX(), block.getY() + 1, block.getZ() + 1));
-                    is(new BlockPosition(block.getX(), block.getY() - 1, block.getZ() - 1));
-                    is(new BlockPosition(block.getX(), block.getY() - 1, block.getZ() + 1));
-                    is(new BlockPosition(block.getX() - 1, block.getY() + 1, block.getZ() - 1));
-                    is(new BlockPosition(block.getX() - 1, block.getY() + 1, block.getZ() + 1));
-                    is(new BlockPosition(block.getX() - 1, block.getY() - 1, block.getZ() - 1));
-                    is(new BlockPosition(block.getX() - 1, block.getY() - 1, block.getZ() + 1));
-                    is(new BlockPosition(block.getX() + 1, block.getY() + 1, block.getZ() - 1));
-                    is(new BlockPosition(block.getX() + 1, block.getY() + 1, block.getZ() + 1));
-                    is(new BlockPosition(block.getX() + 1, block.getY() - 1, block.getZ() - 1));
-                    is(new BlockPosition(block.getX() + 1, block.getY() - 1, block.getZ() + 1));
-                } catch (Throwable e) {
-                    IrisLogging.reportError(e);
-                    e.printStackTrace();
-                }
-            });
+            revealBatch(world, hits, to);
         };
-        int delay = RNG.r.i(2, 8);
-        if (!J.runAt(blockLocation, revealTask, delay)) {
-            if (!J.isFolia()) {
-                J.s(revealTask, delay);
-            }
+        Location at = hits.get(from).toBlock(world).getLocation();
+        if (!J.runAt(at, batch, 1) && !J.isFolia()) {
+            J.s(batch, 1);
         }
     }
 
@@ -137,9 +145,7 @@ public class DustRevealer {
                         RuntimeUiMessages.DUST_FOUND_OBJECT,
                         MessageArgument.untrusted("object", a)
                 ));
-                J.a(() -> {
-                    new DustRevealer(access, world, new BlockPosition(block.getX(), block.getY(), block.getZ()), a, new KList<>());
-                });
+                J.a(() -> reveal(access, world, new BlockPosition(block.getX(), block.getY(), block.getZ()), a));
             }
         }
     }
@@ -354,24 +360,6 @@ public class DustRevealer {
         }
     }
 
-    private boolean is(BlockPosition a) {
-        if (a.getY() < world.getMinHeight() || a.getY() >= world.getMaxHeight()) {
-            return false;
-        }
-        int betterY = a.getY() - world.getMinHeight();
-        if (isValidTry(a) && engine.getObjectPlacementKey(a.getX(), betterY, a.getZ()) != null && engine.getObjectPlacementKey(a.getX(), betterY, a.getZ()).equals(key)) {
-            hits.add(a);
-            new DustRevealer(engine, world, a, key, hits);
-            return true;
-        }
-
-        return false;
-    }
-
-    private boolean isValidTry(BlockPosition b) {
-        return !hits.contains(b);
-    }
-
     private record DustLine(String text, boolean emphasis) {
     }
 }

core/src/main/java/art/arcane/iris/core/gui/PregenRenderer.java

@@ -42,7 +42,10 @@ import java.util.concurrent.locks.ReentrantLock;
 public final class PregenRenderer extends JPanel implements KeyListener {
     private static final long serialVersionUID = 2094606939770332040L;
 
-    private final KList<Runnable> order = new KList<>();
+    // Backstop: if paint() ever stalls (iconified frame, EDT hiccup), the producer must not
+    // grow this without bound — one entry per drawn chunk adds up fast on a big pregen.
+    private static final int MAX_QUEUED_DRAWS = 250_000;
+    private KList<Runnable> order = new KList<>();
     private final ReentrantLock lock = new ReentrantLock();
     private final int res = 512;
     private final BufferedImage image = new BufferedImage(res, res, BufferedImage.TYPE_INT_RGB);
@@ -71,7 +74,9 @@ public final class PregenRenderer extends JPanel implements KeyListener {
         return (Position2 c, Color color) -> {
             lock.lock();
             try {
-                order.add(() -> draw(c, color, bg));
+                if (order.size() < MAX_QUEUED_DRAWS) {
+                    order.add(() -> draw(c, color, bg));
+                }
             } finally {
                 lock.unlock();
             }
@@ -83,7 +88,11 @@ public final class PregenRenderer extends JPanel implements KeyListener {
     }
 
     public boolean isVisibleFrame() {
-        return frame != null && frame.isVisible();
+        // An iconified frame still reports isVisible() but AWT stops repainting it, which
+        // would stop the only queue drain while the producer keeps appending.
+        JFrame activeFrame = frame;
+        return activeFrame != null && activeFrame.isVisible()
+                && (activeFrame.getExtendedState() & java.awt.Frame.ICONIFIED) == 0;
     }
 
     public void close() {
@@ -99,18 +108,23 @@ public final class PregenRenderer extends JPanel implements KeyListener {
     public void paint(Graphics gx) {
         Graphics2D g = (Graphics2D) gx;
         bg = (Graphics2D) image.getGraphics();
+        // Swap the queue under the lock and drain outside it: generation threads must not
+        // block on the lock while the EDT walks a large batch, and pop()-per-entry was O(N^2).
+        KList<Runnable> batch;
         lock.lock();
         try {
-            while (order.isNotEmpty()) {
-                try {
-                    order.pop().run();
-                } catch (Throwable e) {
-                    IrisLogging.reportError(e);
-                }
-            }
+            batch = order;
+            order = new KList<>();
         } finally {
             lock.unlock();
         }
+        for (Runnable r : batch) {
+            try {
+                r.run();
+            } catch (Throwable e) {
+                IrisLogging.reportError(e);
+            }
+        }
 
         g.drawImage(image, 0, 0, getParent().getWidth(), getParent().getHeight(), (img, infoflags, x, y, width, height) -> true);
         g.setColor(Color.WHITE);

core/src/main/java/art/arcane/iris/core/gui/PregeneratorJob.java

@@ -38,7 +38,6 @@ import art.arcane.volmlib.util.function.Consumer2;
 import art.arcane.volmlib.util.mantle.runtime.Mantle;
 import art.arcane.volmlib.util.localization.MessageArgument;
 import art.arcane.volmlib.util.math.Position2;
-import art.arcane.volmlib.util.scheduling.ChronoLatch;
 import art.arcane.iris.util.common.scheduling.J;
 
 import java.awt.Color;
@@ -46,12 +45,14 @@ import java.util.List;
 import java.util.concurrent.CopyOnWriteArrayList;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
-import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Consumer;
 
 public class PregeneratorJob implements PregenListener, PregenRenderSource {
-    private static final long WORLD_SHUTDOWN_TIMEOUT_MILLIS = 15_000L;
+    // Must exceed the worker's own worst-case teardown budget (AsyncPregenMethod close:
+    // 60s permit drain + 120s flush + plate reclaim), or a routine drain trips the deadline
+    // and aborts the engine shutdown sequence mid-teardown.
+    private static final long WORLD_SHUTDOWN_TIMEOUT_MILLIS = 200_000L;
     private static final Color COLOR_EXISTS = parseColor("#4d7d5b");
     private static final Color COLOR_BLACK = parseColor("#4d7d5b");
     private static final Color COLOR_MANTLE = parseColor("#3c2773");
@@ -69,14 +70,12 @@ public class PregeneratorJob implements PregenListener, PregenRenderSource {
     private final IrisPregenerator pregenerator;
     private final Position2 min;
     private final Position2 max;
-    private final ChronoLatch cl = new ChronoLatch(TimeUnit.MINUTES.toMillis(1));
     private final Engine engine;
     private final ExecutorService service;
     private final Thread worker;
     private final PregenPhaseTracker apiPhases = new PregenPhaseTracker();
     private PregenRenderer renderer;
     private Consumer2<Position2, Color> drawFunction;
-    private int rgc = 0;
     private String[] info;
     private volatile double lastChunksPerSecond = 0D;
     private volatile long lastChunksRemaining = 0L;
@@ -87,14 +86,6 @@ public class PregeneratorJob implements PregenListener, PregenRenderSource {
     private volatile String lastMethod = IrisLanguage.plain(DesktopUiMessages.PREGEN_METHOD_PENDING);
 
     public PregeneratorJob(PregenTask task, PregeneratorMethod method, Engine engine) {
-        instance.updateAndGet(old -> {
-            if (old != null) {
-                old.pregenerator.close();
-                old.worker.interrupt();
-                old.close();
-            }
-            return this;
-        });
         this.engine = engine;
         monitor = new MemoryMonitor(50);
         saving = false;
@@ -120,6 +111,19 @@ public class PregeneratorJob implements PregenListener, PregenRenderSource {
         worker.setPriority(Thread.MIN_PRIORITY);
         worker.setDaemon(true);
         worker.setUncaughtExceptionHandler((thread, ex) -> IrisLogging.reportError(ex));
+
+        // Publish into the static only after every field is assigned (the volatile swap is
+        // what makes them visible to metrics/shutdown readers), and start the worker after
+        // publication so it also sees a complete object.
+        // CAS-or-throw: updateAndGet must be side-effect free (it can re-apply on
+        // contention), and silently killing the previous job overlapped its 60s+120s
+        // teardown with the new job's generation. Replacement goes through
+        // shutdownAndWait first, matching the modded adapter's rejection contract.
+        if (!instance.compareAndSet(null, this)) {
+            monitor.close();
+            service.shutdown();
+            throw new IllegalStateException("An Iris pregeneration job is already running; stop it first.");
+        }
         worker.start();
     }
 
@@ -138,6 +142,14 @@ public class PregeneratorJob implements PregenListener, PregenRenderSource {
             return false;
         }
 
+        if (!inst.worker.isAlive() && inst.worker.getState() != Thread.State.NEW) {
+            // The worker died without running onClose (early abort); clear the phantom job so
+            // it stops suppressing entity spawns and blocking future pregens. A NEW worker is
+            // a job mid-construction, not a dead one.
+            instance.compareAndSet(inst, null);
+            return false;
+        }
+
         J.a(() -> {
             inst.pregenerator.close();
             inst.worker.interrupt();
@@ -432,17 +444,11 @@ public class PregeneratorJob implements PregenListener, PregenRenderSource {
 
     @Override
     public void onRegionGenerated(int x, int z) {
-        shouldGc();
-        rgc++;
+        // No forced System.gc() here: a wall-clock full STW collection mid-generation stalled
+        // everything; MantleHeapPressure's 96% panic reclaim already owns heap pressure.
         broadcastRegionDelta(x, z, IrisMessage.PregenRegionDelta.STATE_DONE);
     }
 
-    private void shouldGc() {
-        if (cl.flip() && rgc > 16) {
-            System.gc();
-        }
-    }
-
     private void broadcastRegionDelta(int regionX, int regionZ, int state) {
         IrisProtocolServer protocolServer = IrisServices.getOrNull(IrisProtocolServer.class);
         if (protocolServer == null) {

core/src/main/java/art/arcane/iris/core/gui/VisionGUI.java

@@ -24,6 +24,7 @@ import art.arcane.iris.engine.framework.render.IrisRenderer;
 import art.arcane.iris.engine.framework.render.RenderType;
 import art.arcane.iris.engine.framework.Engine;
 import art.arcane.iris.engine.framework.PreservationRegistry;
+import art.arcane.iris.spi.IrisLogging;
 import art.arcane.iris.spi.IrisServices;
 import art.arcane.iris.engine.object.IrisBiome;
 import art.arcane.iris.engine.object.IrisRegion;
@@ -281,7 +282,7 @@ public class VisionGUI extends JPanel implements MouseWheelListener, KeyListener
     }
 
     public boolean updateEngine() {
-        if (engine.isClosed()) {
+        if (engine.isClosed() || engine.isClosing() || engine.getComplex() == null) {
             try {
                 Engine reacquired = GuiHost.get().findActiveEngine();
                 if (reacquired != null && !reacquired.isClosed()) {
@@ -451,12 +452,19 @@ public class VisionGUI extends JPanel implements MouseWheelListener, KeyListener
                     double mk = mscale;
                     double mkd = scale;
                     e.submit(() -> {
-                        PrecisionStopwatch ps = PrecisionStopwatch.start();
-                        BufferedImage b = renderer.render(x * mscale, z * mscale, div * mscale, div / (lowtile ? 3 : 1), currentType);
-                        rs.put(ps.getMilliseconds());
-                        working.remove(key);
-                        if (mk == mscale && mkd == scale) {
-                            positions.put(key, b);
+                        // finally: a render throw is swallowed by the discarded Future, and a
+                        // leaked key permanently blocks the admission gate (working < 9).
+                        try {
+                            PrecisionStopwatch ps = PrecisionStopwatch.start();
+                            BufferedImage b = renderer.render(x * mscale, z * mscale, div * mscale, div / (lowtile ? 3 : 1), currentType);
+                            rs.put(ps.getMilliseconds());
+                            if (mk == mscale && mkd == scale) {
+                                positions.put(key, b);
+                            }
+                        } catch (Throwable ex) {
+                            IrisLogging.debug("Vision tile render failed: " + ex.getClass().getSimpleName() + ": " + ex.getMessage());
+                        } finally {
+                            working.remove(key);
                         }
                     });
                 }
@@ -472,12 +480,17 @@ public class VisionGUI extends JPanel implements MouseWheelListener, KeyListener
         double mk = mscale;
         double mkd = scale;
         eh.submit(() -> {
-            PrecisionStopwatch ps = PrecisionStopwatch.start();
-            BufferedImage b = renderer.render(x * mscale, z * mscale, div * mscale, div / lowq, currentType);
-            rs.put(ps.getMilliseconds());
-            workingfast.remove(key);
-            if (mk == mscale && mkd == scale) {
-                fastpositions.put(key, b);
+            try {
+                PrecisionStopwatch ps = PrecisionStopwatch.start();
+                BufferedImage b = renderer.render(x * mscale, z * mscale, div * mscale, div / lowq, currentType);
+                rs.put(ps.getMilliseconds());
+                if (mk == mscale && mkd == scale) {
+                    fastpositions.put(key, b);
+                }
+            } catch (Throwable ex) {
+                IrisLogging.debug("Vision tile render failed: " + ex.getClass().getSimpleName() + ": " + ex.getMessage());
+            } finally {
+                workingfast.remove(key);
             }
         });
         return null;
@@ -507,12 +520,30 @@ public class VisionGUI extends JPanel implements MouseWheelListener, KeyListener
 
     @Override
     public void paint(Graphics gx) {
-        if (engine.isClosed() && !updateEngine()) {
+        // Cover the closing window too: releaseRuntime nulls the complex BEFORE closed flips,
+        // and a paint NPE in that window killed the self-driven repaint loop forever.
+        if ((engine.isClosed() || engine.isClosing() || engine.getComplex() == null) && !updateEngine()) {
             EventQueue.invokeLater(() -> {
                 try { setVisible(false); } catch (Throwable ignored) { }
             });
             return;
         }
+        try {
+            paintBody(gx);
+        } catch (Throwable e) {
+            IrisLogging.debug("Vision paint failed: " + e.getClass().getSimpleName() + ": " + e.getMessage());
+        } finally {
+            // The repaint loop is entirely self-driven from here; it must survive any render
+            // exception or the window freezes on a stale frame permanently.
+            long sleepMs = eco ? 32 : 16;
+            J.a(() -> {
+                J.sleep(sleepMs);
+                repaint();
+            });
+        }
+    }
+
+    private void paintBody(Graphics gx) {
 
         velocity = Math.abs(ox - oxp) * 0.36 + Math.abs(oz - ozp) * 0.36;
         oxp = lerp(oxp, ox, 0.36);
@@ -587,6 +618,16 @@ public class VisionGUI extends JPanel implements MouseWheelListener, KeyListener
             }
         }
 
+        // Bounded, not pruned-to-frame: the low-quality cache is the pan placeholder, but
+        // unbounded growth while panning leaked one BufferedImage per visited tile forever.
+        if (fastpositions.size() > 4096) {
+            for (BlockPosition i : fastpositions.k()) {
+                if (!gg.contains(i)) {
+                    fastpositions.remove(i);
+                }
+            }
+        }
+
         handleFollow();
         renderOverlays(g, p.getMilliseconds());
 
@@ -594,12 +635,6 @@ public class VisionGUI extends JPanel implements MouseWheelListener, KeyListener
             return;
         }
 
-        long targetMs = eco ? 32 : 16;
-        long sleepMs = Math.max(1, targetMs - (long) p.getMilliseconds());
-        J.a(() -> {
-            J.sleep(sleepMs);
-            repaint();
-        });
     }
 
     private void renderGrid(Graphics2D g, int tileSize, double offsetX, double offsetZ) {

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

@@ -768,7 +768,7 @@ public final class IrisWorldRemovalService {
         public CompletableFuture<Void> endMaintenance(ResolvedWorld resolvedWorld) {
             World world = resolvedWorld.loadedWorld();
             if (world != null) {
-                IrisToolbelt.endWorldMaintenance(world, "world-remove");
+                IrisToolbelt.endWorldMaintenance(world, "world-remove", true);
             }
             return CompletableFuture.completedFuture(null);
         }

core/src/main/java/art/arcane/iris/core/link/WorldEditLink.java

@@ -3,14 +3,17 @@ package art.arcane.iris.core.link;
 import art.arcane.iris.spi.IrisLogging;
 import art.arcane.iris.engine.data.cache.AtomicCache;
 import art.arcane.volmlib.util.data.Cuboid;
+import art.arcane.volmlib.util.scheduling.ChronoLatch;
 import org.bukkit.Bukkit;
 import org.bukkit.World;
 import org.bukkit.entity.Player;
 
 import java.lang.reflect.InvocationTargetException;
+import java.util.function.BooleanSupplier;
 
 public class WorldEditLink {
     private static final AtomicCache<Boolean> active = new AtomicCache<>();
+    private static final ChronoLatch errorThrottle = new ChronoLatch(60_000);
 
     public static Cuboid getSelection(Player p) {
         if (!hasWorldEdit())
@@ -42,16 +45,40 @@ public class WorldEditLink {
                     (int) min.getClass().getDeclaredMethod("z").invoke(max)
             );
         } catch (Throwable e) {
-            IrisLogging.error("Could not get selection");
-            e.printStackTrace();
-            IrisLogging.reportError(e);
-            active.reset();
-            active.aquire(() -> false);
+            if (errorThrottle.flip()) {
+                IrisLogging.error("Could not get selection");
+                e.printStackTrace();
+                IrisLogging.reportError(e);
+            }
+            invalidate();
         }
         return null;
     }
 
     public static boolean hasWorldEdit() {
-        return active.aquire(() -> Bukkit.getPluginManager().isPluginEnabled("WorldEdit"));
+        return hasWorldEdit(() -> Bukkit.getPluginManager().isPluginEnabled("WorldEdit"));
+    }
+
+    static boolean hasWorldEdit(BooleanSupplier detector) {
+        if (Boolean.TRUE.equals(active.getIfPresent())) {
+            return true;
+        }
+
+        boolean present;
+        try {
+            present = detector.getAsBoolean();
+        } catch (Throwable ignored) {
+            return false;
+        }
+
+        if (present) {
+            active.aquire(() -> Boolean.TRUE);
+        }
+
+        return present;
+    }
+
+    static void invalidate() {
+        active.reset();
     }
 }

core/src/main/java/art/arcane/iris/core/loader/IrisData.java

@@ -43,6 +43,7 @@ import art.arcane.iris.engine.object.IrisBlockData;
 import art.arcane.iris.engine.object.IrisDimension;
 import art.arcane.iris.engine.object.IrisEntity;
 import art.arcane.iris.engine.object.IrisExpression;
+import art.arcane.iris.engine.object.IrisObjectScale;
 import art.arcane.iris.engine.object.IrisGenerator;
 import art.arcane.iris.engine.object.IrisImage;
 import art.arcane.iris.engine.object.IrisJigsawPiece;
@@ -86,12 +87,20 @@ import java.util.List;
 import java.util.Map;
 import java.util.Objects;
 import java.util.Optional;
+import java.util.Collections;
+import java.util.IdentityHashMap;
 import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
 
 @Data
 public class IrisData implements ExclusionStrategy, TypeAdapterFactory {
     private static final Map<File, IrisData> dataLoaders = new ConcurrentHashMap<>();
+    // Loaders (cached or detached) that currently have registered engines; see hasActiveEngines.
+    // Identity-keyed on purpose: Lombok's @Data hashCode over this class's mutable loader state
+    // drifts while an engine runs, so a hashing set would silently fail removal and pin every
+    // engine-hosting IrisData (and its pack graph) for the JVM lifetime.
+    private static final Set<IrisData> ENGINE_HOLDERS =
+            Collections.synchronizedSet(Collections.newSetFromMap(new IdentityHashMap<>()));
     private final File dataFolder;
     private final int id;
     private final boolean datapackCompiler;
@@ -262,7 +271,7 @@ public class IrisData implements ExclusionStrategy, TypeAdapterFactory {
             }
 
             for (File i : PackDirectoryResolver.listVisiblePackDirectories(
-                    IrisPlatforms.get().dataFolder("packs"))) {
+                    IrisPlatforms.get().packsFolder())) {
                 IrisData dm = get(i);
                 if (dm == nearest) continue;
                 T t = dm.load(type, key, false);
@@ -338,6 +347,30 @@ public class IrisData implements ExclusionStrategy, TypeAdapterFactory {
         }
     }
 
+    /**
+     * True when any loader — including detached {@link #openRuntime(File)} instances, which
+     * never enter the dataLoaders cache — has a live engine reading the given pack folder.
+     * The dataLoaders cache cannot answer this question: engines only ever attach to
+     * openRuntime instances.
+     */
+    public static boolean hasActiveEngines(File dataFolder) {
+        Path target = dataFolder.toPath().toAbsolutePath().normalize();
+        IrisData[] holders;
+        synchronized (ENGINE_HOLDERS) {
+            holders = ENGINE_HOLDERS.toArray(new IrisData[0]);
+        }
+        for (IrisData data : holders) {
+            if (data.getEngines().isEmpty()) {
+                ENGINE_HOLDERS.remove(data);
+                continue;
+            }
+            if (data.getDataFolder().toPath().toAbsolutePath().normalize().equals(target)) {
+                return true;
+            }
+        }
+        return false;
+    }
+
     public void registerEngine(Engine engine) {
         Objects.requireNonNull(engine, "engine");
         synchronized (engines) {
@@ -348,6 +381,7 @@ public class IrisData implements ExclusionStrategy, TypeAdapterFactory {
             }
             engines.add(engine);
         }
+        ENGINE_HOLDERS.add(this);
     }
 
     public void unregisterEngine(Engine engine) {
@@ -359,9 +393,12 @@ public class IrisData implements ExclusionStrategy, TypeAdapterFactory {
             while (iterator.hasNext()) {
                 if (iterator.next() == engine) {
                     iterator.remove();
-                    return;
+                    break;
                 }
             }
+            if (engines.isEmpty()) {
+                ENGINE_HOLDERS.remove(this);
+            }
         }
     }
 
@@ -383,6 +420,7 @@ public class IrisData implements ExclusionStrategy, TypeAdapterFactory {
         synchronized (engines) {
             engines.clear();
         }
+        ENGINE_HOLDERS.remove(this);
         dataLoaders.remove(dataFolder, this);
     }
 
@@ -425,6 +463,7 @@ public class IrisData implements ExclusionStrategy, TypeAdapterFactory {
 
     public synchronized void hotloaded() {
         StructureGraphCatalog.invalidate(this);
+        IrisObjectScale.invalidate();
         closed = false;
         possibleSnippets = new KMap<>();
         builder = new GsonBuilder()
@@ -490,6 +529,7 @@ public class IrisData implements ExclusionStrategy, TypeAdapterFactory {
 
     public void dump() {
         StructureGraphCatalog.invalidate(this);
+        IrisObjectScale.invalidate();
         for (ResourceLoader<?> i : loaders.values()) {
             i.clearCache();
         }

core/src/main/java/art/arcane/iris/core/loader/ResourceLoader.java

@@ -63,8 +63,8 @@ import java.util.Objects;
 import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ExecutorService;
-import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.Executors;
+import java.util.concurrent.RejectedExecutionException;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.function.Consumer;
 import java.util.function.Predicate;
@@ -79,14 +79,8 @@ import java.util.zip.GZIPOutputStream;
 public class ResourceLoader<T extends IrisRegistrant> implements MeteredCache {
     public static final AtomicDouble tlt = new AtomicDouble(0);
     private static final int CACHE_SIZE = 100000;
-    private static final ExecutorService schemaBuildExecutor = Executors.newSingleThreadExecutor(runnable -> {
-        Thread thread = new Thread(runnable, "Iris-Schema-Builder");
-        thread.setDaemon(true);
-        thread.setPriority(Thread.MIN_PRIORITY);
-        return thread;
-    });
+    private static volatile ExecutorService schemaBuildExecutor;
     private static final Set<String> schemaBuildQueue = ConcurrentHashMap.newKeySet();
-    private static final AtomicBoolean schemaBuildExecutorRegistered = new AtomicBoolean();
     protected final AtomicCache<KList<File>> folderCache;
     protected volatile KSet<String> firstAccess;
     protected File root;
@@ -124,11 +118,32 @@ public class ResourceLoader<T extends IrisRegistrant> implements MeteredCache {
         IrisLogging.debug("Loader<" + C.GREEN + resourceTypeName + C.LIGHT_PURPLE + "> created in " + C.RED + "IDM/" + manager.getId() + C.LIGHT_PURPLE + " on " + C.GRAY + manager.getDataFolder().getPath());
         if (options.registerPreservation()) {
             IrisServices.get(PreservationRegistry.class).registerCache(this);
+        }
+    }
+
+    /**
+     * Lazily (re)creates the schema-build pool. PreservationSVC shutdownNow()s every
+     * registered executor on plugin disable; a static final pool registered once was dead for
+     * the rest of the JVM after a hot reload, breaking every studio workspace refresh. Each
+     * created pool is registered with the CURRENT cycle's preservation registry.
+     */
+    private static synchronized ExecutorService schemaBuildExecutor() {
+        ExecutorService current = schemaBuildExecutor;
+        if (current == null || current.isShutdown()) {
+            schemaBuildQueue.clear();
+            current = Executors.newSingleThreadExecutor(runnable -> {
+                Thread thread = new Thread(runnable, "Iris-Schema-Builder");
+                thread.setDaemon(true);
+                thread.setPriority(Thread.MIN_PRIORITY);
+                return thread;
+            });
+            schemaBuildExecutor = current;
             PreservationRegistry preservation = IrisServices.getOrNull(PreservationRegistry.class);
-            if (preservation != null && schemaBuildExecutorRegistered.compareAndSet(false, true)) {
-                preservation.register(schemaBuildExecutor);
+            if (preservation != null) {
+                preservation.register(current);
             }
         }
+        return current;
     }
 
     public JSONObject buildSchema() {
@@ -145,15 +160,22 @@ public class ResourceLoader<T extends IrisRegistrant> implements MeteredCache {
         File a = new File(getManager().getDataFolder(), ".iris/schema/" + getFolderName() + "-schema.json");
         String schemaPath = a.getAbsolutePath();
         if (schemaBuildQueue.add(schemaPath)) {
-            schemaBuildExecutor.execute(() -> {
-                try {
-                    IO.writeAll(a, new SchemaBuilder(objectClass, manager).construct().toString(4));
-                } catch (Throwable e) {
-                    IrisLogging.reportError(e);
-                } finally {
-                    schemaBuildQueue.remove(schemaPath);
-                }
-            });
+            try {
+                schemaBuildExecutor().execute(() -> {
+                    try {
+                        IO.writeAll(a, new SchemaBuilder(objectClass, manager).construct().toString(4));
+                    } catch (Throwable e) {
+                        IrisLogging.reportError(e);
+                    } finally {
+                        schemaBuildQueue.remove(schemaPath);
+                    }
+                });
+            } catch (RejectedExecutionException rejected) {
+                // Never let a dead pool leak the queue entry or escape into workspace
+                // generation (which would delete the user's .code-workspace on the way out).
+                schemaBuildQueue.remove(schemaPath);
+                IrisLogging.warn("Schema build skipped (executor unavailable): " + schemaPath);
+            }
         }
 
         return o;
@@ -475,7 +497,9 @@ public class ResourceLoader<T extends IrisRegistrant> implements MeteredCache {
         }
 
         KSet<String> set = firstAccess;
-        if (set != null) set.add(name);
+        // contains-first: CHM.add takes the bin monitor even when the key is present, and
+        // every generation thread hammers the same few keys through this line.
+        if (set != null && !set.contains(name)) set.add(name);
         return loadCache.get(name);
     }
 

core/src/main/java/art/arcane/iris/core/localization/DirectorCommandMessages.java

@@ -148,7 +148,7 @@ public final class DirectorCommandMessages {
     );
     public static final TextKey COMMAND_DEVELOPER_DIRECTOR_GENERATE_CHUNKS_INTO_BUFFERS_NO_WORLD_WRITES_HASH_BLOCKS_BIOMES_CAPTURES_GOLDEN = TextKey.of(
             "iris.director.commanddeveloper.director.generate_chunks_into_buffers_no_world_writes_hash_blocks_biomes_captures_golden",
-            "Generate chunks into buffers (no world writes) and hash blocks+biomes; captures a golden file or verifies against an existing one. Resets mantle in the scanned area - use on disposable test worlds."
+            "Generate chunks into buffers (no world writes) and hash blocks+biomes; captures a golden file or verifies against an existing one. Deletes the world's entire mantle - use on disposable test worlds."
     );
     public static final TextKey COMMAND_DEVELOPER_PARAM_WORLD_SCAN = TextKey.of(
             "iris.director.commanddeveloper.param.world_scan",
@@ -168,7 +168,7 @@ public final class DirectorCommandMessages {
     );
     public static final TextKey COMMAND_DEVELOPER_PARAM_DELETE_MANTLE_DATA_SCAN_AREA_FIRST_FULL_REGENERATION_FROM_SCRATCH = TextKey.of(
             "iris.director.commanddeveloper.param.delete_mantle_data_scan_area_first_full_regeneration_from_scratch",
-            "Delete mantle data in the scan area first for full regeneration from scratch"
+            "Delete the world's entire mantle folder first for full regeneration from scratch"
     );
     public static final TextKey COMMAND_DEVELOPER_PARAM_CONCURRENT_CHUNK_GENERATIONS_1_STRICTLY_SERIAL_ORDER_DEPENDENCE_TESTING = TextKey.of(
             "iris.director.commanddeveloper.param.concurrent_chunk_generations_1_strictly_serial_order_dependence_testing",

core/src/main/java/art/arcane/iris/core/nms/INMS.java

@@ -25,9 +25,37 @@ import org.bukkit.Bukkit;
 
 public class INMS {
     //@done
-    private static final INMSBinding binding = bind();
+    private static final INMSBinding binding;
+    private static final Throwable bindFailure;
+
+    // A throwing field initializer would leave this class permanently erroneous — every
+    // later touch raises NoClassDefFoundError and buries the real "unsupported Minecraft
+    // version" message. Capture the failure so callers can report the actual cause.
+    static {
+        INMSBinding bound = null;
+        Throwable failure = null;
+        try {
+            bound = bind();
+        } catch (Throwable t) {
+            failure = t;
+        }
+        binding = bound;
+        bindFailure = failure;
+    }
+
+    public static boolean isBound() {
+        return binding != null;
+    }
+
+    public static Throwable bindFailure() {
+        return bindFailure;
+    }
 
     public static INMSBinding get() {
+        if (binding == null) {
+            throw new IllegalStateException("Iris NMS binding is unavailable: "
+                    + (bindFailure == null ? "unknown failure" : bindFailure.getMessage()), bindFailure);
+        }
         return binding;
     }
 

core/src/main/java/art/arcane/iris/core/nms/INMSBinding.java

@@ -262,6 +262,13 @@ public interface INMSBinding {
         return true;
     }
 
+    /**
+     * Removes any instrumentation installed by {@link #injectBukkit()}. Must be idempotent;
+     * called on plugin disable and pre-unload so the transformer cannot outlive the plugin.
+     */
+    default void uninjectBukkit() {
+    }
+
     KMap<Material, List<BlockProperty>> getBlockProperties();
 
     private void validateDimensionTypes(WorldCreator c) {

core/src/main/java/art/arcane/iris/core/pack/IrisPack.java

@@ -154,7 +154,7 @@ public class IrisPack {
      * @return the file path
      */
     public static File packsPack(String name) {
-        return IrisPlatforms.get().dataFolderNoCreate(StudioSVC.WORKSPACE_NAME, name);
+        return IrisPlatforms.get().packsFolderNoCreate(name);
     }
 
     private static KList<File> collectFiles(File f, String fileExtension) {

core/src/main/java/art/arcane/iris/core/pack/IrisPackRepository.java

@@ -47,7 +47,7 @@ public class IrisPackRepository {
     private String repo = "overworld";
 
     @Builder.Default
-    private String branch = "stable";
+    private String branch = PackDownloader.DEFAULT_BRANCH;
 
     @Builder.Default
     private String tag = "";
@@ -96,7 +96,7 @@ public class IrisPackRepository {
             return IrisPackRepository.builder()
                     .user("IrisDimensions")
                     .repo(g)
-                    .branch("stable")
+                    .branch(PackDownloader.DEFAULT_BRANCH)
                     .build();
         }
 
@@ -112,7 +112,7 @@ public class IrisPackRepository {
     }
 
     public void install(VolmitSender sender, Runnable whenComplete) throws MalformedURLException {
-        File pack = IrisPlatforms.get().dataFolderNoCreate(StudioSVC.WORKSPACE_NAME, getRepo());
+        File pack = IrisPlatforms.get().packsFolderNoCreate(getRepo());
 
         if (!pack.exists()) {
             File dl = new File(IrisPlatforms.get().dataFolder("cache", "temp"), "dltk-" + UUID.randomUUID() + ".zip");

core/src/main/java/art/arcane/iris/core/pack/PackBiomeLayerValidator.java

@@ -0,0 +1,87 @@
+/*
+ * Iris is a World Generator for Minecraft Servers
+ * Copyright (c) 2026 Arcane Arts (Volmit Software)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package art.arcane.iris.core.pack;
+
+import art.arcane.volmlib.util.json.JSONArray;
+import art.arcane.volmlib.util.json.JSONObject;
+
+import java.io.File;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.List;
+
+/**
+ * Validates biome layer stacks. caveCeilingLayers reuses the height generators built from layers,
+ * so a biome with more ceiling entries than surface entries has no generator for the extras; the
+ * engine skips them, and this validator surfaces the mistake to the author at validate time.
+ */
+final class PackBiomeLayerValidator {
+    /** Both layers and caveCeilingLayers default to a single entry when absent (IrisBiome field initializers). */
+    private static final int DEFAULT_LAYER_COUNT = 1;
+
+    private PackBiomeLayerValidator() {
+    }
+
+    static List<String> validateCeilingLayerCounts(File biomesFolder) {
+        List<String> blockingErrors = new ArrayList<>();
+        if (biomesFolder == null || !biomesFolder.isDirectory()) {
+            return blockingErrors;
+        }
+
+        List<File> biomeFiles = PackValidationIo.listJsonRecursive(biomesFolder);
+        biomeFiles.sort(Comparator.comparing(File::getPath));
+        for (File biomeFile : biomeFiles) {
+            String biomeKey = PackValidationIo.deriveKey(biomesFolder, biomeFile);
+            JSONObject biome;
+            try {
+                biome = new JSONObject(Files.readString(biomeFile.toPath(), StandardCharsets.UTF_8));
+            } catch (Throwable e) {
+                // Invalid JSON is reported by the graph validators; layer counts have nothing to add.
+                continue;
+            }
+
+            Integer layers = arrayLength(biome, "layers", biomeKey, blockingErrors);
+            Integer ceiling = arrayLength(biome, "caveCeilingLayers", biomeKey, blockingErrors);
+            if (layers == null || ceiling == null) {
+                continue;
+            }
+
+            if (ceiling > layers) {
+                blockingErrors.add("Biome '" + biomeKey + "' declares " + ceiling + " caveCeilingLayers but only "
+                        + layers + " layers. caveCeilingLayers reuses the layers height generators and must not have more entries.");
+            }
+        }
+        return blockingErrors;
+    }
+
+    private static Integer arrayLength(JSONObject biome, String field, String biomeKey, List<String> blockingErrors) {
+        if (!biome.has(field) || biome.isNull(field)) {
+            return DEFAULT_LAYER_COUNT;
+        }
+
+        JSONArray array = biome.optJSONArray(field);
+        if (array == null) {
+            blockingErrors.add("Biome '" + biomeKey + "' " + field + " must be an array.");
+            return null;
+        }
+        return array.length();
+    }
+}

core/src/main/java/art/arcane/iris/core/pack/PackDimensionValidator.java

@@ -18,6 +18,7 @@
 
 package art.arcane.iris.core.pack;
 
+import art.arcane.iris.engine.object.IrisDimensionType;
 import art.arcane.volmlib.util.json.JSONArray;
 import art.arcane.volmlib.util.json.JSONObject;
 
@@ -45,6 +46,7 @@ final class PackDimensionValidator {
             }
 
             validateImportedStructurePolicy(dimensionKey, dimJson, blockingErrors, warnings);
+            validateDimensionHeights(packFolder, dimensionKey, dimJson, blockingErrors);
 
             JSONArray regionsArray = dimJson.optJSONArray("regions");
             if (regionsArray == null || regionsArray.length() == 0) {
@@ -226,4 +228,84 @@ final class PackDimensionValidator {
         }
         return resolved;
     }
+
+    /**
+     * Mirrors the IrisDimensionType constructor checks so a pack that would throw at world creation
+     * fails validation instead. Defaults must match the POJOs exactly: dimensionHeight absent means
+     * the IrisDimension field initializer (-64..320); present-but-partial means the IrisRange field
+     * initializers (min 16, max 32); logicalHeight absent means 256.
+     */
+    static void validateDimensionHeights(File packFolder, String dimensionKey, JSONObject dimJson, List<String> blockingErrors) {
+        JSONObject range = resolveDimensionHeight(packFolder, dimJson);
+        if (range == null && dimJson.has("dimensionHeight") && !dimJson.isNull("dimensionHeight")) {
+            if (!(dimJson.opt("dimensionHeight") instanceof String)) {
+                blockingErrors.add("Dimension '" + dimensionKey + "' dimensionHeight must be an object or a range snippet reference.");
+            }
+            // Unresolvable snippet references are reported by the content-key machinery.
+            return;
+        }
+
+        int minY;
+        int maxY;
+        if (range == null) {
+            minY = -64;
+            maxY = 320;
+        } else {
+            minY = (int) range.optDouble("min", 16D);
+            maxY = (int) range.optDouble("max", 32D);
+        }
+        int height = maxY - minY;
+        int logicalHeight = dimJson.optInt("logicalHeight", 256);
+
+        if (height < IrisDimensionType.MIN_HEIGHT || height > IrisDimensionType.MAX_HEIGHT) {
+            blockingErrors.add("Dimension '" + dimensionKey + "' dimensionHeight span (max - min) is " + height
+                    + "; it must be between " + IrisDimensionType.MIN_HEIGHT + " and " + IrisDimensionType.MAX_HEIGHT + ".");
+        } else if ((height & (IrisDimensionType.HEIGHT_STEP - 1)) != 0) {
+            blockingErrors.add("Dimension '" + dimensionKey + "' dimensionHeight span (max - min) is " + height
+                    + "; it must be a multiple of " + IrisDimensionType.HEIGHT_STEP + ".");
+        }
+        if (minY < IrisDimensionType.MIN_MIN_Y || minY > IrisDimensionType.MAX_MIN_Y) {
+            blockingErrors.add("Dimension '" + dimensionKey + "' dimensionHeight.min is " + minY
+                    + "; it must be between " + IrisDimensionType.MIN_MIN_Y + " and " + IrisDimensionType.MAX_MIN_Y + ".");
+        } else if ((minY & (IrisDimensionType.HEIGHT_STEP - 1)) != 0) {
+            blockingErrors.add("Dimension '" + dimensionKey + "' dimensionHeight.min is " + minY
+                    + "; it must be a multiple of " + IrisDimensionType.HEIGHT_STEP + ".");
+        }
+        if (logicalHeight < 0) {
+            blockingErrors.add("Dimension '" + dimensionKey + "' logicalHeight is " + logicalHeight + "; it cannot be negative.");
+        } else if (logicalHeight > height) {
+            blockingErrors.add("Dimension '" + dimensionKey + "' logicalHeight is " + logicalHeight
+                    + "; it cannot be greater than the dimension height of " + height + ".");
+        }
+    }
+
+    private static JSONObject resolveDimensionHeight(File packFolder, JSONObject dimJson) {
+        if (!dimJson.has("dimensionHeight") || dimJson.isNull("dimensionHeight")) {
+            return null;
+        }
+
+        JSONObject inline = dimJson.optJSONObject("dimensionHeight");
+        if (inline != null) {
+            return inline;
+        }
+
+        String reference = dimJson.optString("dimensionHeight", null);
+        if (reference == null || !reference.startsWith("snippet/")) {
+            return null;
+        }
+        // Mirror IrisData's snippet adapter: canonical snippet/range/... is used verbatim; any other
+        // snippet/... reference is re-rooted under this field's snippet folder.
+        if (!reference.startsWith("snippet/range/")) {
+            reference = "snippet/range/" + reference.substring("snippet/".length());
+        }
+        File snippet = new File(packFolder, reference + ".json");
+        if (!snippet.isFile()) {
+            return null;
+        }
+        try {
+            return new JSONObject(Files.readString(snippet.toPath(), StandardCharsets.UTF_8));
+        } catch (Throwable e) {
+            return null;
+        }
+    }
 }

core/src/main/java/art/arcane/iris/core/pack/PackDownloader.java

@@ -55,6 +55,12 @@ import java.util.zip.ZipEntry;
 import java.util.zip.ZipInputStream;
 
 public final class PackDownloader {
+    /**
+     * The branch every download path falls back to when the caller did not name one. Compile-time
+     * constant so Director {@code @Param(defaultValue = ...)} annotations can reference it.
+     */
+    public static final String DEFAULT_BRANCH = "stable";
+    private static final String HEAD_REF = "HEAD";
     private static final String DEFAULT_OVERWORLD_PACK = "overworld";
     private static final String DEFAULT_OVERWORLD_REPOSITORY = "IrisDimensions/overworld";
     private static final String DEFAULT_OVERWORLD_REF = "master";
@@ -234,6 +240,13 @@ public final class PackDownloader {
         String url = directUrl ? ref : resolveGithubArchiveUrl(repo, ref);
         sendFeedback(feedback, IrisLanguage.plain(PackDownloadMessages.DOWNLOADING, MessageArgument.untrusted("url", url)) + " ");
         File zip = WebCache.getNonCachedFile("pack-" + repo, url, ARCHIVE_LIMITS.maxArchiveBytes());
+        if ((zip == null || !zip.exists()) && !directUrl && DEFAULT_BRANCH.equals(ref)) {
+            // A repo without the shared default branch still resolves via its HEAD; one retry, never recursive.
+            String headUrl = resolveGithubArchiveUrl(repo, HEAD_REF);
+            sendFeedback(feedback, IrisLanguage.plain(PackDownloadMessages.DOWNLOADING, MessageArgument.untrusted("url", headUrl)) + " ");
+            zip = WebCache.getNonCachedFile("pack-" + repo, headUrl, ARCHIVE_LIMITS.maxArchiveBytes());
+            url = headUrl;
+        }
         File temp = WebCache.getTemp();
         File work = new File(temp, "dl-" + UUID.randomUUID());
 
@@ -436,17 +449,21 @@ public final class PackDownloader {
                     + " (required primary dimension is missing).");
         }
 
-        Optional<IrisData> loadedData = IrisData.getLoaded(new File(packsFolder, prepared.key()));
-        if (loadedData.isEmpty()) {
-            loadedData = IrisData.getLoaded(target.toFile());
-        }
-        if (loadedData.isPresent()) {
+        // A registered loader alone is not "active": startup validation registers a loader for
+        // every visible pack (permanently), which made force-updating any installed pack
+        // impossible. Live engines only ever attach to detached openRuntime loaders, so the
+        // gate must go through the engine index, not the cached loader's own engine list.
+        // Stale cached registrations are closed so the swap cannot race a loader holding the
+        // old tree.
+        if (IrisData.hasActiveEngines(target.toFile())) {
             sendFeedback(
                     feedback,
                     "Pack '" + prepared.key() + "' is active and cannot be replaced safely. Unload its worlds before retrying."
             );
             return null;
         }
+        IrisData.getLoaded(new File(packsFolder, prepared.key())).ifPresent(IrisData::close);
+        IrisData.getLoaded(target.toFile()).ifPresent(IrisData::close);
         try (AtomicDirectoryPublisher.Publication publication = AtomicDirectoryPublisher.publish(staging, target)) {
             publication.commit();
             try {
@@ -471,7 +488,7 @@ public final class PackDownloader {
         Set<Path> roots = new LinkedHashSet<>();
         roots.add(packsRoot);
         if (IrisPlatforms.isBound()) {
-            roots.add(IrisPlatforms.get().dataFolder("packs").toPath().toAbsolutePath().normalize());
+            roots.add(IrisPlatforms.get().packsFolder().toPath().toAbsolutePath().normalize());
         }
         for (Path root : roots) {
             if (!Files.isDirectory(root)) {

core/src/main/java/art/arcane/iris/core/pack/PackExportClosure.java

@@ -0,0 +1,72 @@
+/*
+ * Iris is a World Generator for Minecraft Servers
+ * Copyright (c) 2026 Arcane Arts (Volmit Software)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package art.arcane.iris.core.pack;
+
+import art.arcane.iris.engine.object.IrisObjectMarker;
+import art.arcane.iris.engine.object.IrisObjectPlacement;
+import art.arcane.volmlib.util.collection.KSet;
+
+/**
+ * Shared key collection for the pack packagers. Both the Bukkit re-serializing compiler and the
+ * modded verbatim-copy compiler must export the complete ambient-spawning graph: object placements
+ * carry markers, markers carry spawners, spawners carry entities, entities carry loot. These
+ * helpers keep the two packagers walking placements identically.
+ */
+public final class PackExportClosure {
+    private PackExportClosure() {
+    }
+
+    public static KSet<String> collectMarkerKeys(Iterable<IrisObjectPlacement> placements) {
+        KSet<String> markerKeys = new KSet<>();
+        if (placements == null) {
+            return markerKeys;
+        }
+        for (IrisObjectPlacement placement : placements) {
+            if (placement == null || placement.getMarkers() == null) {
+                continue;
+            }
+            for (IrisObjectMarker marker : placement.getMarkers()) {
+                if (marker == null || marker.getMarker() == null || marker.getMarker().isBlank()) {
+                    continue;
+                }
+                markerKeys.add(marker.getMarker());
+            }
+        }
+        return markerKeys;
+    }
+
+    public static KSet<String> collectObjectKeys(Iterable<IrisObjectPlacement> placements) {
+        KSet<String> objectKeys = new KSet<>();
+        if (placements == null) {
+            return objectKeys;
+        }
+        for (IrisObjectPlacement placement : placements) {
+            if (placement == null || placement.getPlace() == null) {
+                continue;
+            }
+            for (String key : placement.getPlace()) {
+                if (key == null || key.isBlank()) {
+                    continue;
+                }
+                objectKeys.add(key);
+            }
+        }
+        return objectKeys;
+    }
+}

core/src/main/java/art/arcane/iris/core/pack/PackGeneratorDuplicateValidator.java

@@ -0,0 +1,165 @@
+/*
+ * Iris is a World Generator for Minecraft Servers
+ * Copyright (c) 2026 Arcane Arts (Volmit Software)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package art.arcane.iris.core.pack;
+
+import art.arcane.volmlib.util.json.JSONArray;
+import art.arcane.volmlib.util.json.JSONObject;
+
+import java.io.File;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.TreeMap;
+
+/**
+ * Warns when two generator files with identical content are both referenced by biomes. IrisGenerator's
+ * equals ignores the load key and IrisComplex buckets generators into a HashSet, so only one of a
+ * content-identical pair survives; biomes linked to the losing key resolve 0/0 height bounds and
+ * contribute a flat band at fluid height.
+ *
+ * <p>The fingerprint is a conservative approximation of IrisGenerator.equals built from raw JSON
+ * (sorted keys, canonical number formatting). It can miss a collision where one file spells out a
+ * value the other leaves defaulted, and it ignores fields the POJO does not declare - acceptable
+ * for a warning aimed at the copy-the-file-and-forget-the-seed mistake.
+ */
+final class PackGeneratorDuplicateValidator {
+    private static final String GENERATOR_SNIPPET_FOLDER = "snippet/generator-layer/";
+
+    private PackGeneratorDuplicateValidator() {
+    }
+
+    static List<String> validateDuplicateGenerators(File packFolder) {
+        List<String> warnings = new ArrayList<>();
+        if (packFolder == null || !packFolder.isDirectory()) {
+            return warnings;
+        }
+        File generatorsFolder = new File(packFolder, "generators");
+        if (!generatorsFolder.isDirectory()) {
+            return warnings;
+        }
+
+        Set<String> referenced = collectReferencedGeneratorKeys(packFolder);
+        Map<String, List<String>> byFingerprint = new TreeMap<>();
+        List<File> generatorFiles = PackValidationIo.listJsonRecursive(generatorsFolder);
+        generatorFiles.sort(Comparator.comparing(File::getPath));
+        for (File generatorFile : generatorFiles) {
+            String key = PackValidationIo.deriveKey(generatorsFolder, generatorFile);
+            String fingerprint;
+            try {
+                fingerprint = fingerprint(new JSONObject(Files.readString(generatorFile.toPath(), StandardCharsets.UTF_8)));
+            } catch (Throwable e) {
+                continue;
+            }
+            byFingerprint.computeIfAbsent(fingerprint, ignored -> new ArrayList<>()).add(key);
+        }
+
+        for (List<String> group : byFingerprint.values()) {
+            List<String> referencedKeys = group.stream().filter(referenced::contains).sorted().toList();
+            if (referencedKeys.size() < 2) {
+                continue;
+            }
+            warnings.add("Generators " + String.join(", ", referencedKeys)
+                    + " have identical content and are both referenced by biomes. Iris buckets generators by value"
+                    + " (IrisGenerator equals ignores the load key), so only one survives and biomes referencing the"
+                    + " others get a zero height band. Give each generator a distinct value (for example a different"
+                    + " seed) or point every biome at a single key.");
+        }
+        return warnings;
+    }
+
+    private static Set<String> collectReferencedGeneratorKeys(File packFolder) {
+        Set<String> referenced = new HashSet<>();
+        File biomesFolder = new File(packFolder, "biomes");
+        if (!biomesFolder.isDirectory()) {
+            return referenced;
+        }
+        for (File biomeFile : PackValidationIo.listJsonRecursive(biomesFolder)) {
+            JSONObject biome;
+            try {
+                biome = new JSONObject(Files.readString(biomeFile.toPath(), StandardCharsets.UTF_8));
+            } catch (Throwable e) {
+                continue;
+            }
+            JSONArray links = biome.optJSONArray("generators");
+            if (links == null) {
+                continue;
+            }
+            for (int i = 0; i < links.length(); i++) {
+                JSONObject link = links.optJSONObject(i);
+                if (link == null) {
+                    String reference = links.optString(i, null);
+                    link = resolveGeneratorLayerSnippet(packFolder, reference);
+                    if (link == null) {
+                        continue;
+                    }
+                }
+                referenced.add(link.optString("generator", "default"));
+            }
+        }
+        return referenced;
+    }
+
+    private static JSONObject resolveGeneratorLayerSnippet(File packFolder, String reference) {
+        if (reference == null || !reference.startsWith("snippet/")) {
+            return null;
+        }
+        String resolved = reference.startsWith(GENERATOR_SNIPPET_FOLDER)
+                ? reference
+                : GENERATOR_SNIPPET_FOLDER + reference.substring("snippet/".length());
+        File snippet = new File(packFolder, resolved + ".json");
+        if (!snippet.isFile()) {
+            return null;
+        }
+        try {
+            return new JSONObject(Files.readString(snippet.toPath(), StandardCharsets.UTF_8));
+        } catch (Throwable e) {
+            return null;
+        }
+    }
+
+    private static String fingerprint(Object value) {
+        if (value instanceof JSONObject object) {
+            Map<String, String> sorted = new TreeMap<>();
+            for (String key : object.keySet()) {
+                sorted.put(key, fingerprint(object.get(key)));
+            }
+            StringBuilder builder = new StringBuilder("{");
+            sorted.forEach((key, child) -> builder.append(key).append('=').append(child).append(';'));
+            return builder.append('}').toString();
+        }
+        if (value instanceof JSONArray array) {
+            StringBuilder builder = new StringBuilder("[");
+            for (int i = 0; i < array.length(); i++) {
+                builder.append(fingerprint(array.get(i))).append(';');
+            }
+            return builder.append(']').toString();
+        }
+        if (value instanceof Number number) {
+            // Gson deserializes 1 and 1.0 into the same field value; fingerprint them alike.
+            return Double.toString(number.doubleValue());
+        }
+        return String.valueOf(value);
+    }
+}

core/src/main/java/art/arcane/iris/core/pack/PackLootValidator.java

@@ -34,10 +34,18 @@ final class PackLootValidator {
     private PackLootValidator() {
     }
 
-    static List<String> validateLootGraph(File packFolder) {
+    record LootGraphIssues(List<String> errors, List<String> warnings) {
+        LootGraphIssues {
+            errors = List.copyOf(errors);
+            warnings = List.copyOf(warnings);
+        }
+    }
+
+    static LootGraphIssues validateLootGraph(File packFolder) {
         List<String> blockingErrors = new ArrayList<>();
+        List<String> warnings = new ArrayList<>();
         if (packFolder == null || !packFolder.isDirectory()) {
-            return blockingErrors;
+            return new LootGraphIssues(blockingErrors, warnings);
         }
 
         File lootFolder = new File(packFolder, PackValidator.LOOT_FOLDER);
@@ -69,10 +77,10 @@ final class PackLootValidator {
                 }
                 String resourceType = PackStructurePlacementValidator.structureHostType(folderName);
                 String resourceKey = PackValidationIo.deriveKey(resourceFolder, resourceFile);
-                validateLootReference(resourceType, resourceKey, resource.opt("loot"), lootKeys, blockingErrors);
+                validateLootReference(resourceType, resourceKey, resource.opt("loot"), lootKeys, blockingErrors, warnings);
             }
         }
-        return blockingErrors;
+        return new LootGraphIssues(blockingErrors, warnings);
     }
 
     private static void validateLootTable(String lootKey, JSONObject table, List<String> blockingErrors) {
@@ -158,17 +166,20 @@ final class PackLootValidator {
     }
 
     private static void validateLootReference(String resourceType, String resourceKey, Object rawLoot,
-                                              Set<String> lootKeys, List<String> blockingErrors) {
+                                              Set<String> lootKeys, List<String> blockingErrors, List<String> warnings) {
         String path = resourceType + " '" + resourceKey + "'.loot";
         if (!(rawLoot instanceof JSONObject reference)) {
             blockingErrors.add(path + " must be an object.");
             return;
         }
+        boolean clearMode = false;
         if (reference.has("mode")) {
             Object rawMode = reference.opt("mode");
             if (!(rawMode instanceof String mode)
                     || !Set.of("ADD", "CLEAR", "REPLACE", "FALLBACK").contains(mode)) {
                 blockingErrors.add(path + ".mode must be ADD, CLEAR, REPLACE, or FALLBACK.");
+            } else {
+                clearMode = "CLEAR".equals(mode);
             }
         }
         if (reference.has("multiplier")) {
@@ -189,6 +200,10 @@ final class PackLootValidator {
             blockingErrors.add(path + ".tables must be an array.");
             return;
         }
+        if (clearMode && tables.length() > 0) {
+            warnings.add(path + " uses mode CLEAR and lists " + tables.length()
+                    + " table(s); CLEAR clears parent tables and contributes no tables of its own, so these entries are dead. Use REPLACE to substitute them.");
+        }
         for (int tableIndex = 0; tableIndex < tables.length(); tableIndex++) {
             Object rawTableKey = tables.opt(tableIndex);
             if (!(rawTableKey instanceof String tableKey) || tableKey.isBlank()) {

core/src/main/java/art/arcane/iris/core/pack/PackStyledRangeDefaultValidator.java

@@ -0,0 +1,154 @@
+/*
+ * Iris is a World Generator for Minecraft Servers
+ * Copyright (c) 2026 Arcane Arts (Volmit Software)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package art.arcane.iris.core.pack;
+
+import art.arcane.volmlib.util.json.JSONArray;
+import art.arcane.volmlib.util.json.JSONObject;
+
+import java.io.File;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.List;
+import java.util.Locale;
+
+/**
+ * Catches the shared IrisStyledRange class default (min 16, max 32) leaking into pack content.
+ * The POJO cannot distinguish an empty object from an explicit 16/32 after Gson runs, so the raw
+ * JSON is the only place this mistake is still visible: an objects[].densityStyle of {} places
+ * 16-32 objects per chunk, and a caveProfile.densityThreshold of {} hollows the whole cave range.
+ */
+final class PackStyledRangeDefaultValidator {
+    private static final String STYLE_RANGE_SNIPPET_FOLDER = "snippet/style-range/";
+
+    record Validation(List<String> errors, List<String> warnings) {
+        Validation {
+            errors = List.copyOf(errors);
+            warnings = List.copyOf(warnings);
+        }
+    }
+
+    private PackStyledRangeDefaultValidator() {
+    }
+
+    static Validation validate(File packFolder) {
+        List<String> errors = new ArrayList<>();
+        List<String> warnings = new ArrayList<>();
+        if (packFolder == null || !packFolder.isDirectory()) {
+            return new Validation(errors, warnings);
+        }
+
+        for (String folderName : PackValidator.STRUCTURE_HOST_FOLDERS) {
+            File resourceFolder = new File(packFolder, folderName);
+            if (!resourceFolder.isDirectory()) {
+                continue;
+            }
+            List<File> resourceFiles = PackValidationIo.listJsonRecursive(resourceFolder);
+            resourceFiles.sort(Comparator.comparing(File::getPath));
+            String type = hostType(folderName);
+            for (File resourceFile : resourceFiles) {
+                String key = PackValidationIo.deriveKey(resourceFolder, resourceFile);
+                JSONObject json;
+                try {
+                    json = new JSONObject(Files.readString(resourceFile.toPath(), StandardCharsets.UTF_8));
+                } catch (Throwable e) {
+                    continue;
+                }
+
+                validateObjectPlacements(packFolder, type, key, json, errors, warnings);
+                validateCaveProfileThreshold(packFolder, type, key, json.optJSONObject("caveProfile"), errors, warnings);
+            }
+        }
+        return new Validation(errors, warnings);
+    }
+
+    private static void validateObjectPlacements(File packFolder, String type, String key, JSONObject json,
+                                                 List<String> errors, List<String> warnings) {
+        JSONArray objects = json.optJSONArray("objects");
+        if (objects == null) {
+            return;
+        }
+        for (int i = 0; i < objects.length(); i++) {
+            JSONObject placement = objects.optJSONObject(i);
+            if (placement == null || !placement.has("densityStyle") || placement.isNull("densityStyle")) {
+                continue;
+            }
+            checkRange(packFolder, placement.opt("densityStyle"),
+                    type + " '" + key + "' objects[" + i + "].densityStyle",
+                    "16-32 objects per chunk", "remove densityStyle to use the scalar density field",
+                    errors, warnings);
+        }
+    }
+
+    private static void validateCaveProfileThreshold(File packFolder, String type, String key, JSONObject caveProfile,
+                                                     List<String> errors, List<String> warnings) {
+        if (caveProfile == null || !caveProfile.has("densityThreshold") || caveProfile.isNull("densityThreshold")) {
+            return;
+        }
+        checkRange(packFolder, caveProfile.opt("densityThreshold"),
+                type + " '" + key + "' caveProfile.densityThreshold",
+                "a carve threshold of 16-32, hollowing the entire vertical range",
+                "remove densityThreshold to keep the cave profile default",
+                errors, warnings);
+    }
+
+    private static void checkRange(File packFolder, Object raw, String path, String consequence, String removal,
+                                   List<String> errors, List<String> warnings) {
+        JSONObject range = null;
+        String via = "";
+        if (raw instanceof JSONObject inline) {
+            range = inline;
+        } else if (raw instanceof String reference && reference.startsWith("snippet/")) {
+            String resolved = reference.startsWith(STYLE_RANGE_SNIPPET_FOLDER)
+                    ? reference
+                    : STYLE_RANGE_SNIPPET_FOLDER + reference.substring("snippet/".length());
+            File snippet = new File(packFolder, resolved + ".json");
+            if (!snippet.isFile()) {
+                return; // Missing snippets are reported by the content-key machinery.
+            }
+            try {
+                range = new JSONObject(Files.readString(snippet.toPath(), StandardCharsets.UTF_8));
+                via = " (via snippet '" + resolved + "')";
+            } catch (Throwable e) {
+                return;
+            }
+        }
+        if (range == null) {
+            return;
+        }
+
+        boolean hasMin = range.has("min") && !range.isNull("min");
+        boolean hasMax = range.has("max") && !range.isNull("max");
+        if (!hasMin && !hasMax) {
+            errors.add(path + via + " omits both min and max, which resolves to the shared IrisStyledRange default of "
+                    + consequence + ". Set min and max explicitly, or " + removal + ".");
+        } else if (!hasMin || !hasMax) {
+            String missing = hasMin ? "max" : "min";
+            String defaultValue = hasMin ? "32" : "16";
+            warnings.add(path + via + " omits " + missing + ", which falls back to the shared IrisStyledRange default of "
+                    + defaultValue + ". Set it explicitly if that is not intended.");
+        }
+    }
+
+    private static String hostType(String folderName) {
+        String singular = folderName.endsWith("s") ? folderName.substring(0, folderName.length() - 1) : folderName;
+        return singular.substring(0, 1).toUpperCase(Locale.ROOT) + singular.substring(1);
+    }
+}

core/src/main/java/art/arcane/iris/core/pack/PackValidator.java

@@ -77,7 +77,9 @@ public final class PackValidator {
 
         PackDimensionValidator.validateDimensions(packFolder, dimensionFiles, blockingErrors, warnings);
         blockingErrors.addAll(PackCaveProfileValidator.validateLegacyFields(packFolder));
-        blockingErrors.addAll(PackLootValidator.validateLootGraph(packFolder));
+        PackLootValidator.LootGraphIssues lootIssues = PackLootValidator.validateLootGraph(packFolder);
+        addDistinct(blockingErrors, lootIssues.errors());
+        addDistinct(warnings, lootIssues.warnings());
         blockingErrors.addAll(PackObjectSurfaceValidator.validateRemovedWorldgenFields(packFolder));
         blockingErrors.addAll(PackObjectSurfaceValidator.validateObjectSurfaceSupport(packFolder));
         blockingErrors.addAll(PackObjectSurfaceValidator.validateUnsupportedStructureTransforms(packFolder));
@@ -96,6 +98,11 @@ public final class PackValidator {
                 new File(packFolder, "spawners"), new File(packFolder, "entities")));
         blockingErrors.addAll(PackSpawnValidator.validateCustomBiomeSpawns(
                 new File(packFolder, "biomes"), PackSpawnValidator::resolveEntitySpawnCategory));
+        blockingErrors.addAll(PackBiomeLayerValidator.validateCeilingLayerCounts(new File(packFolder, "biomes")));
+        PackStyledRangeDefaultValidator.Validation styledRanges = PackStyledRangeDefaultValidator.validate(packFolder);
+        addDistinct(blockingErrors, styledRanges.errors());
+        addDistinct(warnings, styledRanges.warnings());
+        addDistinct(warnings, PackGeneratorDuplicateValidator.validateDuplicateGenerators(packFolder));
 
         // Strict content mode promotes unresolved keys and bad block properties from advisory to blocking. Palette
         // -sourced findings are exempt and stay warnings - see ContentKeyValidator.collectContentKeyIssues.

core/src/main/java/art/arcane/iris/core/pregenerator/IrisPregenerator.java

@@ -199,14 +199,17 @@ public class IrisPregenerator {
     }
 
     public void start() {
-        init();
-        task.iterateAllChunks((_a, _b) -> totalChunks.incrementAndGet());
-        startTime.set(M.ms());
-        ticker.start();
-        checkRegions();
         PrecisionStopwatch p = PrecisionStopwatch.start();
         boolean completed = false;
+        // Everything runs inside the try: an early throw from init/checkRegions must still
+        // reach shutdown(), or the ticker/monitor threads leak and listener.onClose never
+        // fires — leaving a phantom job that suppresses spawns and blocks future pregens.
         try {
+            init();
+            task.iterateAllChunks((_a, _b) -> totalChunks.incrementAndGet());
+            startTime.set(M.ms());
+            ticker.start();
+            checkRegions();
             int[] regionBounds = task.regionBounds();
             generator.onRegionBounds(regionBounds[0], regionBounds[1], regionBounds[2], regionBounds[3]);
             task.iterateRegions((x, z) -> visitRegion(x, z, true));
@@ -371,10 +374,13 @@ public class IrisPregenerator {
 
                 generator.generateChunk(xx, zz, listener);
             });
-            generator.onRegionSubmitted(x, z);
         }
 
         if (hit) {
+            // Exactly once per visited region, on BOTH branches: a cache-completed region that
+            // never releases its sentinel wedges neighbor eviction for the whole resume
+            // frontier (allNeighborsDrained can never pass around it).
+            generator.onRegionSubmitted(x, z);
             listener.onRegionGenerated(x, z);
 
             if (saveLatch.flip()) {
@@ -391,7 +397,9 @@ public class IrisPregenerator {
             }
 
             generatedRegions.add(pos);
-            checkRegions();
+            // No checkRegions() here: re-spiraling every region after every completed region
+            // was O(regions^2) dead work on the submitter thread (result discarded, and the
+            // only side effect was CachedPregenMethod faulting plates against eviction).
         }
     }
 

core/src/main/java/art/arcane/iris/core/pregenerator/methods/AsyncPregenMethod.java

@@ -57,7 +57,11 @@ import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicLong;
 
 public class AsyncPregenMethod implements PregeneratorMethod {
+    // THREAD_COUNT records the pool's original size while boosted; BOOST_HOLDERS counts live
+    // jobs holding the boost. Pairing them per instance stops a dying job (whose close can
+    // land minutes after its replacement started) from shrinking the pool under the live job.
     private static final AtomicInteger THREAD_COUNT = new AtomicInteger();
+    private static final AtomicInteger BOOST_HOLDERS = new AtomicInteger();
     private static final int ADAPTIVE_TIMEOUT_STEP = 3;
     private static final int ADAPTIVE_RECOVERY_INTERVAL = 8;
     private static final long CLOSE_DRAIN_TIMEOUT_SECONDS = 60L;
@@ -102,6 +106,7 @@ public class AsyncPregenMethod implements PregeneratorMethod {
     private final AtomicLong failed = new AtomicLong();
     private final AtomicLong lastProgressAt = new AtomicLong(M.ms());
     private final AtomicBoolean closing = new AtomicBoolean();
+    private final AtomicBoolean holdsWorkerBoost = new AtomicBoolean();
     private final Object permitMonitor = new Object();
     private volatile Engine metricsEngine;
     private volatile Mantle cachedMantle;
@@ -738,8 +743,8 @@ public class AsyncPregenMethod implements PregeneratorMethod {
                 + ", recommendedCap=" + recommendedRuntimeConcurrencyCap
                 + ", urgent=" + urgent
                 + ", timeout=" + timeoutSeconds + "s");
-        if (workerPoolThreads > 0) {
-            increaseWorkerThreads();
+        if (workerPoolThreads > 0 && holdsWorkerBoost.compareAndSet(false, true)) {
+            acquireWorkerThreadBoost();
         }
     }
 
@@ -775,7 +780,9 @@ public class AsyncPregenMethod implements PregeneratorMethod {
 
             flushAllRemainingChunks();
             executor.shutdown();
-            resetWorkerThreads();
+            if (holdsWorkerBoost.compareAndSet(true, false)) {
+                releaseWorkerThreadBoost();
+            }
         } finally {
             if (interrupted) {
                 Thread.currentThread().interrupt();
@@ -945,7 +952,21 @@ public class AsyncPregenMethod implements PregeneratorMethod {
         return null;
     }
 
-    public static void increaseWorkerThreads() {
+    public static void acquireWorkerThreadBoost() {
+        if (BOOST_HOLDERS.getAndIncrement() > 0) {
+            return;
+        }
+        increaseWorkerThreads();
+    }
+
+    public static void releaseWorkerThreadBoost() {
+        if (BOOST_HOLDERS.decrementAndGet() > 0) {
+            return;
+        }
+        resetWorkerThreads();
+    }
+
+    private static void increaseWorkerThreads() {
         THREAD_COUNT.updateAndGet(i -> {
             if (i > 0) {
                 return i;
@@ -974,7 +995,7 @@ public class AsyncPregenMethod implements PregeneratorMethod {
         });
     }
 
-    public static void resetWorkerThreads() {
+    private static void resetWorkerThreads() {
         THREAD_COUNT.updateAndGet(i -> {
             if (i == 0) {
                 return 0;

core/src/main/java/art/arcane/iris/core/pregenerator/methods/MedievalPregenMethod.java

@@ -207,18 +207,28 @@ public class MedievalPregenMethod implements PregeneratorMethod {
         }
 
         listener.onChunkGenerating(x, z);
-        if (J.isFolia()) {
-            futures.add(PaperLib.getChunkAtAsync(world, x, z, true).thenAccept(c -> {
-                if (c != null) {
-                    lastUse.put(c, M.ms());
-                }
-                listener.onChunkGenerated(x, z);
-                listener.onChunkCleaned(x, z);
-            }));
-            return;
-        }
-
-        futures.add(scheduleChunkLoad(x, z, listener));
+        // Single choke point for failure accounting: without onChunkFailed a lossy run can
+        // never satisfy allVisitsComplete, so a finished pregen reports as aborted forever.
+        CompletableFuture<?> chunkFuture = J.isFolia()
+                ? PaperLib.getChunkAtAsync(world, x, z, true).thenAccept(c -> {
+                    if (c != null) {
+                        lastUse.put(c, M.ms());
+                    }
+                    listener.onChunkGenerated(x, z);
+                    try {
+                        listener.onChunkCleaned(x, z);
+                    } catch (Throwable e) {
+                        // Already counted as generated; a throw here must not also count the
+                        // chunk failed through the whenComplete choke point below.
+                        IrisLogging.reportError(e);
+                    }
+                })
+                : scheduleChunkLoad(x, z, listener);
+        futures.add(chunkFuture.whenComplete((r, err) -> {
+            if (err != null) {
+                listener.onChunkFailed(x, z);
+            }
+        }));
     }
 
     private CompletableFuture<?> scheduleChunkLoad(int x, int z, PregenListener listener) {
@@ -294,12 +304,15 @@ public class MedievalPregenMethod implements PregeneratorMethod {
                     IrisLogging.reportError(error);
                 }
 
-                try {
-                    generateChunkSync(x, z, listener).get(CHUNK_WAIT_TIMEOUT_SECONDS, TimeUnit.SECONDS);
-                    future.complete(null);
-                } catch (Throwable fallbackError) {
-                    future.completeExceptionally(fallbackError);
-                }
+                // Chain instead of blocking: parking this MultiBurst worker on a 60s get()
+                // pinned a shared pool thread per failing chunk.
+                generateChunkSync(x, z, listener).whenComplete((r, fallbackError) -> {
+                    if (fallbackError != null) {
+                        future.completeExceptionally(fallbackError);
+                    } else {
+                        future.complete(null);
+                    }
+                });
             }
         });
 
@@ -314,7 +327,13 @@ public class MedievalPregenMethod implements PregeneratorMethod {
         Chunk chunk = world.getChunkAt(x, z);
         lastUse.put(chunk, M.ms());
         listener.onChunkGenerated(x, z);
-        listener.onChunkCleaned(x, z);
+        try {
+            listener.onChunkCleaned(x, z);
+        } catch (Throwable e) {
+            // The chunk already counted as generated; a throw here must not also count it
+            // as failed through the whenComplete choke point.
+            IrisLogging.reportError(e);
+        }
     }
 
     @Override

core/src/main/java/art/arcane/iris/core/project/IrisCodeWorkspace.java

@@ -131,16 +131,28 @@ public class IrisCodeWorkspace {
         project.getPath().mkdirs();
         File ws = getCodeWorkspaceFile();
 
+        // Render before touching the file: a config-generation failure has nothing to do with
+        // the existing workspace file, and deleting it before a rethrowing rebuild silently
+        // destroyed the author's workspace on every boot.
+        String rendered;
         try {
-            writeIfChanged(ws, createCodeWorkspaceConfig().toString(4));
+            rendered = createCodeWorkspaceConfig().toString(4);
+        } catch (Throwable e) {
+            IrisLogging.reportError(e);
+            IrisLogging.warn("Could not generate the code workspace config for " + ws.getAbsolutePath() + "; leaving the existing workspace file untouched.");
+            return false;
+        }
+
+        try {
+            writeIfChanged(ws, rendered);
             return true;
         } catch (Throwable e) {
             IrisLogging.reportError(e);
             IrisLogging.warn("Project invalid: " + ws.getAbsolutePath() + " Re-creating. You may loose some vs-code workspace settings! But not your actual project!");
             ws.delete();
             try {
-                IO.writeAll(ws, createCodeWorkspaceConfig());
-            } catch (IOException e1) {
+                IO.writeAll(ws, rendered);
+            } catch (Throwable e1) {
                 IrisLogging.reportError(e1);
                 e1.printStackTrace();
             }

core/src/main/java/art/arcane/iris/core/project/IrisPackageCompiler.java

@@ -29,6 +29,8 @@ import art.arcane.iris.engine.object.IrisDimension;
 import art.arcane.iris.engine.object.IrisEntity;
 import art.arcane.iris.engine.object.IrisGenerator;
 import art.arcane.iris.engine.object.IrisLootTable;
+import art.arcane.iris.core.pack.PackExportClosure;
+import art.arcane.iris.engine.object.IrisMarker;
 import art.arcane.iris.engine.object.IrisObjectPlacement;
 import art.arcane.iris.engine.object.IrisRegion;
 import art.arcane.iris.engine.object.IrisSpawner;
@@ -49,6 +51,7 @@ import org.zeroturnaround.zip.ZipUtil;
 
 import java.io.File;
 import java.io.IOException;
+import java.util.Comparator;
 import java.util.LinkedHashSet;
 import java.util.Set;
 import java.util.UUID;
@@ -62,8 +65,25 @@ public class IrisPackageCompiler {
     }
 
     public File compilePackage(VolmitSender sender, boolean obfuscate, boolean minify) {
+        // Detached loader on purpose: obfuscation rewrites the placement 'place' lists on the
+        // loaded resources, which must never leak into the shared cached pack state — a second
+        // export against a mutated cache produced archives with an empty objects/ directory.
+        IrisData dm = IrisData.openRuntime(project.getPath());
+        try {
+            return compilePackage(dm, sender, obfuscate, minify);
+        } finally {
+            dm.close();
+        }
+    }
+
+    private static <T> void addIfPresent(KSet<T> set, T value) {
+        if (value != null) {
+            set.add(value);
+        }
+    }
+
+    private File compilePackage(IrisData dm, VolmitSender sender, boolean obfuscate, boolean minify) {
         String dimm = project.getName();
-        IrisData dm = IrisData.get(project.getPath());
         IrisDimension dimension = dm.getDimensionLoader().load(dimm);
         File folder = new File(IrisPlatforms.get().dataFolder(), "exports/" + dimension.getLoadKey());
         IO.delete(folder);
@@ -82,20 +102,35 @@ public class IrisPackageCompiler {
         KSet<IrisLootTable> loot = new KSet<>();
         KSet<IrisBlockData> blocks = new KSet<>();
 
+        // KSet is ConcurrentHashMap-backed: both add(null) and remove(null) throw NPE, so a
+        // failed loader lookup must be filtered at the add site, never stripped afterwards.
         for (String i : dm.getBlockLoader().getPossibleKeys()) {
-            blocks.add(dm.getBlockLoader().load(i));
+            addIfPresent(blocks, dm.getBlockLoader().load(i));
         }
 
-        dimension.getRegions().forEach((i) -> regions.add(dm.getRegionLoader().load(i)));
-        dimension.getLoot().getTables().forEach((i) -> loot.add(dm.getLootLoader().load(i)));
+        dimension.getRegions().forEach((i) -> addIfPresent(regions, dm.getRegionLoader().load(i)));
+        dimension.getLoot().getTables().forEach((i) -> addIfPresent(loot, dm.getLootLoader().load(i)));
         regions.forEach((i) -> biomes.addAll(i.getAllBiomes(() -> dm)));
-        regions.forEach((r) -> r.getLoot().getTables().forEach((i) -> loot.add(dm.getLootLoader().load(i))));
-        regions.forEach((r) -> r.getEntitySpawners().forEach((sp) -> spawners.add(dm.getSpawnerLoader().load(sp))));
-        dimension.getEntitySpawners().forEach((sp) -> spawners.add(dm.getSpawnerLoader().load(sp)));
-        biomes.forEach((i) -> i.getGenerators().forEach((j) -> generators.add(j.getCachedGenerator(() -> dm))));
-        biomes.forEach((r) -> r.getLoot().getTables().forEach((i) -> loot.add(dm.getLootLoader().load(i))));
-        biomes.forEach((r) -> r.getEntitySpawners().forEach((sp) -> spawners.add(dm.getSpawnerLoader().load(sp))));
-        collectSpawnerEntityKeys(spawners).forEach((i) -> entities.add(dm.getEntityLoader().load(i)));
+        regions.forEach((r) -> r.getLoot().getTables().forEach((i) -> addIfPresent(loot, dm.getLootLoader().load(i))));
+        regions.forEach((r) -> r.getEntitySpawners().forEach((sp) -> addIfPresent(spawners, dm.getSpawnerLoader().load(sp))));
+        dimension.getEntitySpawners().forEach((sp) -> addIfPresent(spawners, dm.getSpawnerLoader().load(sp)));
+        biomes.forEach((i) -> i.getGenerators().forEach((j) -> addIfPresent(generators, j.getCachedGenerator(() -> dm))));
+        biomes.forEach((r) -> r.getLoot().getTables().forEach((i) -> addIfPresent(loot, dm.getLootLoader().load(i))));
+        biomes.forEach((r) -> r.getEntitySpawners().forEach((sp) -> addIfPresent(spawners, dm.getSpawnerLoader().load(sp))));
+        KList<IrisObjectPlacement> allPlacements = new KList<>();
+        regions.forEach((r) -> allPlacements.addAll(r.getObjects()));
+        biomes.forEach((i) -> allPlacements.addAll(i.getObjects()));
+        KSet<IrisMarker> markers = new KSet<>();
+        for (String markerKey : PackExportClosure.collectMarkerKeys(allPlacements)) {
+            IrisMarker marker = dm.getMarkerLoader().load(markerKey);
+            if (marker == null) {
+                continue;
+            }
+            markers.add(marker);
+            marker.getSpawners().forEach((sp) -> addIfPresent(spawners, dm.getSpawnerLoader().load(sp)));
+        }
+        collectSpawnerEntityKeys(spawners).forEach((i) -> addIfPresent(entities, dm.getEntityLoader().load(i)));
+        entities.forEach((e) -> e.getLoot().getTables().forEach((i) -> addIfPresent(loot, dm.getLootLoader().load(i))));
         Set<String> structureKeys = new LinkedHashSet<>();
         collectStructureKeys(structureKeys, dimension.getStructures());
         regions.forEach((region) -> collectStructureKeys(structureKeys, region.getStructures()));
@@ -106,25 +141,23 @@ public class IrisPackageCompiler {
         StringBuilder c = new StringBuilder();
         sender.sendMessage(IrisLanguage.text(BukkitRuntimeMessages.IRIS_PROJECT_SERIALIZING_OBJECTS));
 
-        for (IrisBiome i : biomes) {
-            for (IrisObjectPlacement j : i.getObjects()) {
-                b.append(j.hashCode());
-                KList<String> newNames = new KList<>();
+        for (IrisObjectPlacement j : allPlacements) {
+            b.append(j.hashCode());
+            KList<String> newNames = new KList<>();
 
-                for (String k : j.getPlace()) {
-                    if (renameObjects.containsKey(k)) {
-                        newNames.add(renameObjects.get(k));
-                        continue;
-                    }
-
-                    String name = !obfuscate ? k : UUID.randomUUID().toString().replaceAll("-", "");
-                    b.append(name);
-                    newNames.add(name);
-                    renameObjects.put(k, name);
+            for (String k : j.getPlace()) {
+                if (renameObjects.containsKey(k)) {
+                    newNames.add(renameObjects.get(k));
+                    continue;
                 }
 
-                j.setPlace(newNames);
+                String name = !obfuscate ? k : UUID.randomUUID().toString().replaceAll("-", "");
+                b.append(name);
+                newNames.add(name);
+                renameObjects.put(k, name);
             }
+
+            j.setPlace(newNames);
         }
 
         KMap<String, KList<String>> lookupObjects = renameObjects.flip();
@@ -132,10 +165,18 @@ public class IrisPackageCompiler {
         ChronoLatch cl = new ChronoLatch(1000);
         O<Integer> ggg = new O<>();
         ggg.set(0);
-        biomes.forEach((i) -> i.getObjects().forEach((j) -> j.getPlace().forEach((k) ->
+        O<Integer> missingObjects = new O<>();
+        missingObjects.set(0);
+        allPlacements.forEach((j) -> j.getPlace().forEach((k) ->
         {
             try {
-                File f = dm.getObjectLoader().findFile(lookupObjects.get(k).get(0));
+                KList<String> sources = lookupObjects.get(k);
+                File f = sources == null || sources.isEmpty() ? null : dm.getObjectLoader().findFile(sources.get(0));
+                if (f == null) {
+                    missingObjects.set(missingObjects.get() + 1);
+                    IrisLogging.error("Missing object for placement key " + k);
+                    return;
+                }
                 IO.copyFile(f, new File(folder, "objects/" + k + ".iob"));
                 gb.append(IO.hash(f));
                 ggg.set(ggg.get() + 1);
@@ -146,9 +187,15 @@ public class IrisPackageCompiler {
                     sender.sendMessage(IrisLanguage.text(BukkitRuntimeMessages.IRIS_PROJECT_WROTE_ANOTHER_OBJECTS, MessageArgument.untrusted("g", String.valueOf(g))));
                 }
             } catch (Throwable e) {
+                missingObjects.set(missingObjects.get() + 1);
                 IrisLogging.reportError(e);
             }
-        })));
+        }));
+        if (missingObjects.get() > 0) {
+            // A package missing objects must fail loudly, not ship as a clean "compiled".
+            throw new IllegalStateException(missingObjects.get()
+                    + " object(s) could not be exported for pack '" + dimm + "'; package compile aborted.");
+        }
 
         b.append(IO.hash(gb.toString()));
         c.append(IO.hash(b.toString()));
@@ -205,6 +252,19 @@ public class IrisPackageCompiler {
                 b.append(IO.hash(a));
             }
 
+            // Sorted so package.json.hash stays stable across runs.
+            for (IrisSpawner i : spawners.stream().sorted(Comparator.comparing(IrisSpawner::getLoadKey)).toList()) {
+                a = new JSONObject(new Gson().toJson(i)).toString(minify ? 0 : 4);
+                IO.writeAll(new File(folder, "spawners/" + i.getLoadKey() + ".json"), a);
+                b.append(IO.hash(a));
+            }
+
+            for (IrisMarker i : markers.stream().sorted(Comparator.comparing(IrisMarker::getLoadKey)).toList()) {
+                a = new JSONObject(new Gson().toJson(i)).toString(minify ? 0 : 4);
+                IO.writeAll(new File(folder, "markers/" + i.getLoadKey() + ".json"), a);
+                b.append(IO.hash(a));
+            }
+
             c.append(IO.hash(b.toString()));
             String finalHash = IO.hash(c.toString());
             JSONObject meta = new JSONObject();

core/src/main/java/art/arcane/iris/core/runtime/GoldenHashEngine.java

@@ -149,7 +149,10 @@ public final class GoldenHashEngine {
 
             if (request.resetMantle()) {
                 progress.stage(IrisLanguage.plain(RuntimeProgressMessages.CHUNK_STAGE_RESETTING_MANTLE));
-                resetMantleFull();
+                if (!resetMantleFull()) {
+                    // A partial reset silently invalidates the capture; never scan over it.
+                    return false;
+                }
             }
 
             List<int[]> targets = ChunkSpiral.centerOut(request.centerChunkX(), request.centerChunkZ(), radius);
@@ -184,29 +187,24 @@ public final class GoldenHashEngine {
         }
     }
 
-    private void resetMantleFull() {
+    private boolean resetMantleFull() {
+        Mantle mantle = engine.getMantle().getMantle();
         try {
-            Mantle mantle = engine.getMantle().getMantle();
-            mantle.saveAll();
-            File folder = mantle.getDataFolder();
-            File[] files = folder.listFiles();
-            if (files != null) {
-                for (File file : files) {
-                    if (file.isFile()) {
-                        file.delete();
-                    }
-                }
-            }
+            // resetStorage invalidates the IOWorker channel cache before unlinking; deleting
+            // behind cached channels sent every post-reset plate write to an unlinked inode.
+            mantle.resetStorage();
             feedback.ok(IrisLanguage.plain(
                     RuntimeProgressMessages.GOLDEN_MANTLE_RESET,
-                    MessageArgument.untrusted("path", folder.getAbsolutePath())
+                    MessageArgument.untrusted("path", mantle.getDataFolder().getAbsolutePath())
             ));
+            return true;
         } catch (Throwable e) {
             IrisLogging.reportError(e);
             feedback.warn(IrisLanguage.plain(
                     RuntimeProgressMessages.GOLDEN_MANTLE_RESET_FAILED,
                     MessageArgument.untrusted("type", e.getClass().getSimpleName())
             ));
+            return false;
         }
     }
 
@@ -345,11 +343,18 @@ public final class GoldenHashEngine {
 
         List<String> body = orderedBody(lines);
         List<String> mismatches = new ArrayList<>();
+        // Display strings and diagnosis input are different shapes: diagnose() parses a bare
+        // "<x> <z>" key, and feeding it a localized sentence aborted the diagnosis whenever
+        // the FIRST mismatch was a chunk missing from the golden capture.
+        String firstMismatchKey = null;
         for (String line : body) {
             int second = line.indexOf(' ', line.indexOf(' ') + 1);
             String key = line.substring(0, second);
             String golden = goldenChunks.get(key);
             if (!line.equals(golden)) {
+                if (firstMismatchKey == null) {
+                    firstMismatchKey = key;
+                }
                 mismatches.add(golden == null
                         ? IrisLanguage.plain(
                                 RuntimeProgressMessages.GOLDEN_MISSING_IN_GOLDEN,
@@ -400,7 +405,7 @@ public final class GoldenHashEngine {
         IrisLogging.info("goldenhash MISMATCH: " + mismatches.size() + "/" + body.size() + " -> " + current.getAbsolutePath());
 
         progress.stage(IrisLanguage.plain(RuntimeProgressMessages.CHUNK_STAGE_DIAGNOSING));
-        diagnose(mismatches.getFirst());
+        diagnose(firstMismatchKey);
         return false;
     }
 

core/src/main/java/art/arcane/iris/core/runtime/InPlaceChunkRegenerator.java

@@ -44,6 +44,8 @@ import org.bukkit.generator.ChunkGenerator.ChunkData;
 import java.util.List;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.Semaphore;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.function.Consumer;
 
 public final class InPlaceChunkRegenerator {
     private static final int BIOME_STEP = 4;
@@ -111,36 +113,41 @@ public final class InPlaceChunkRegenerator {
 
             inFlight.acquire();
             MultiBurst.burst.lazy(() -> {
-                TerrainChunk buffer = TerrainChunk.create(world);
-                try {
-                    engine.generate(chunkX << 4, chunkZ << 4, buffer, false);
-                } catch (Throwable e) {
-                    IrisLogging.reportError(e);
-                    reporter.countApplied(false);
-                    inFlight.release();
-                    allApplied.countDown();
-                    return;
-                }
-
-                boolean scheduled = J.runRegion(world, chunkX, chunkZ, () -> {
-                    boolean ok = false;
-                    try {
-                        applyToLiveChunk(chunkX, chunkZ, buffer);
-                        ok = true;
-                    } catch (Throwable e) {
-                        IrisLogging.reportError(e);
-                    } finally {
+                // Settle exactly once no matter which path fails: an unguarded throw here
+                // (TerrainChunk.create, runRegion) parked the regen thread on the latch
+                // forever and stranded the player's boss bar. CAS is required — on Folia's
+                // owned-region path runRegion runs the apply inline before returning.
+                AtomicBoolean settled = new AtomicBoolean();
+                Consumer<Boolean> settle = ok -> {
+                    if (settled.compareAndSet(false, true)) {
                         reporter.countApplied(ok);
                         inFlight.release();
                         allApplied.countDown();
                     }
-                });
+                };
+                try {
+                    TerrainChunk buffer = TerrainChunk.create(world);
+                    engine.generate(chunkX << 4, chunkZ << 4, buffer, false);
 
-                if (!scheduled) {
-                    IrisLogging.warn("Regen could not schedule chunk apply at " + chunkX + "," + chunkZ + " in " + world.getName() + ".");
-                    reporter.countApplied(false);
-                    inFlight.release();
-                    allApplied.countDown();
+                    boolean scheduled = J.runRegion(world, chunkX, chunkZ, () -> {
+                        boolean ok = false;
+                        try {
+                            applyToLiveChunk(chunkX, chunkZ, buffer);
+                            ok = true;
+                        } catch (Throwable e) {
+                            IrisLogging.reportError(e);
+                        } finally {
+                            settle.accept(ok);
+                        }
+                    });
+
+                    if (!scheduled) {
+                        IrisLogging.warn("Regen could not schedule chunk apply at " + chunkX + "," + chunkZ + " in " + world.getName() + ".");
+                        settle.accept(false);
+                    }
+                } catch (Throwable e) {
+                    IrisLogging.reportError(e);
+                    settle.accept(false);
                 }
             });
         }

core/src/main/java/art/arcane/iris/core/runtime/StudioOpenCoordinator.java

@@ -609,7 +609,7 @@ public final class StudioOpenCoordinator {
                 });
         return operation.whenComplete((result, throwable) -> {
             if (world != null) {
-                IrisToolbelt.endWorldMaintenance(world, "studio-close");
+                IrisToolbelt.endWorldMaintenance(world, "studio-close", true);
             }
         });
     }

core/src/main/java/art/arcane/iris/core/safeguard/IrisSafeguard.java

@@ -6,7 +6,6 @@ import art.arcane.iris.core.safeguard.task.Tasks;
 import art.arcane.iris.core.safeguard.task.ValueWithDiagnostics;
 import art.arcane.iris.spi.IrisLogging;
 import art.arcane.iris.util.common.format.C;
-import art.arcane.iris.util.common.scheduling.J;
 
 import java.util.ArrayList;
 import java.util.Collections;
@@ -15,7 +14,6 @@ import java.util.List;
 import java.util.Map;
 
 public final class IrisSafeguard {
-    private static volatile boolean forceShutdown = false;
     private static Map<Task, ValueWithDiagnostics<Mode>> results = Collections.emptyMap();
     private static Map<String, String> context = Collections.emptyMap();
     private static Map<String, List<String>> attachment = Collections.emptyMap();
@@ -100,10 +98,6 @@ public final class IrisSafeguard {
         }
     }
 
-    public static boolean isForceShutdown() {
-        return forceShutdown;
-    }
-
     private static void warning() {
         IrisLogging.warn(C.GOLD + "Iris is running in Warning Mode");
         IrisLogging.warn(C.GRAY + "Some startup checks need attention. Review the messages above for tuning suggestions.");
@@ -115,9 +109,9 @@ public final class IrisSafeguard {
         IrisLogging.error(C.DARK_RED + "Iris is running in Danger Mode");
         IrisLogging.error("");
         IrisLogging.error(C.DARK_GRAY + "--==<" + C.RED + " IMPORTANT " + C.DARK_GRAY + ">==--");
-        IrisLogging.error("Critical startup checks failed. Iris will continue startup in 10 seconds.");
-        IrisLogging.error("Review and resolve the errors above as soon as possible.");
-        J.sleep(10000L);
+        IrisLogging.error("Critical startup checks failed. Review and resolve the errors above as soon as possible.");
+        // No startup sleep: blocking the boot thread protected nothing — world creation and
+        // player admission are already gated by IrisStartupValidation.
         IrisLogging.info("");
     }
 }

core/src/main/java/art/arcane/iris/core/safeguard/task/Tasks.java

@@ -7,6 +7,7 @@ import art.arcane.iris.core.IrisWorldStorage;
 import art.arcane.iris.core.nms.INMS;
 import art.arcane.iris.core.nms.v1X.NMSBinding1X;
 import art.arcane.iris.core.safeguard.Mode;
+import art.arcane.iris.core.splash.IrisSplashComposer;
 import art.arcane.iris.engine.object.IrisDimension;
 import art.arcane.iris.util.common.misc.getHardware;
 import art.arcane.iris.util.project.agent.Agent;
@@ -99,13 +100,21 @@ public final class Tasks {
             supportedVersions = BuildConstants.MINECRAFT_VERSION;
         }
 
+        if (!INMS.isBound()) {
+            String cause = INMS.bindFailure() == null ? "Unknown NMS bind failure" : INMS.bindFailure().getMessage();
+            return withDiagnostics(Mode.UNSTABLE,
+                    Diagnostic.Logger.ERROR.create("Server Version"),
+                    Diagnostic.Logger.ERROR.create("- " + cause),
+                    Diagnostic.Logger.ERROR.create("- Iris only supports " + supportedVersions));
+        }
+
         if (!(INMS.get() instanceof NMSBinding1X)) {
             return withDiagnostics(Mode.STABLE);
         }
 
         return withDiagnostics(Mode.UNSTABLE,
-                Diagnostic.Logger.ERROR.create("Server Version"),
-                Diagnostic.Logger.ERROR.create("- Iris only supports " + supportedVersions));
+                Diagnostic.Logger.ERROR.create("NMS Disabled"),
+                Diagnostic.Logger.ERROR.create("- NMS support is disabled (general.disableNMS); Iris world creation is unavailable."));
     });
 
     private static final Task INJECTION = Task.of("injection", () -> {
@@ -149,7 +158,13 @@ public final class Tasks {
     });
 
     private static final Task JAVA = Task.of("java", () -> {
-        int version = javaVersion();
+        int version = IrisSplashComposer.javaVersion();
+        if (version < 0) {
+            return withDiagnostics(Mode.WARNING,
+                    Diagnostic.Logger.WARN.create("Java Runtime"),
+                    Diagnostic.Logger.WARN.create("- Java version could not be determined (java.version="
+                            + System.getProperty("java.version") + ")."));
+        }
         if (version == 25) {
             return withDiagnostics(Mode.STABLE);
         }
@@ -211,16 +226,4 @@ public final class Tasks {
         return new ValueWithDiagnostics<>(mode, diagnostics);
     }
 
-    private static int javaVersion() {
-        String version = System.getProperty("java.version");
-        if (version.startsWith("1.")) {
-            version = version.substring(2, 3);
-        } else {
-            int dot = version.indexOf(".");
-            if (dot != -1) {
-                version = version.substring(0, dot);
-            }
-        }
-        return Integer.parseInt(version);
-    }
 }

core/src/main/java/art/arcane/iris/core/service/ExternalDataSVC.java

@@ -67,7 +67,8 @@ public class ExternalDataSVC implements IrisService {
     @Override
     public void onEnable() {
         IrisLogging.info("Loading ExternalDataProvider...");
-        Bukkit.getPluginManager().registerEvents(this, BukkitPlatform.plugin());
+        // enable() registers every enabled service as a listener; self-registration here
+        // doubled every handler invocation.
 
         for (ProviderDefinition definition : BUILT_IN_PROVIDERS) {
             activateConfiguredProvider(definition);

core/src/main/java/art/arcane/iris/core/service/LogFilterSVC.java

@@ -1,6 +1,5 @@
 package art.arcane.iris.core.service;
 
-import art.arcane.volmlib.util.collection.KList;
 import art.arcane.iris.util.common.plugin.IrisService;
 import org.apache.logging.log4j.Level;
 import org.apache.logging.log4j.LogManager;
@@ -10,17 +9,26 @@ import org.apache.logging.log4j.core.LogEvent;
 import org.apache.logging.log4j.core.Logger;
 import org.apache.logging.log4j.message.Message;
 
+import java.util.List;
+
 public class LogFilterSVC implements IrisService, Filter {
 
     private static final String HEIGHTMAP_MISMATCH = "Ignoring heightmap data for chunk";
     private static final String RAID_PERSISTENCE = "Could not save data net.minecraft.world.entity.raid.PersistentRaid";
     private static final String DUPLICATE_ENTITY_UUID = "UUID of added entity already exists";
 
-    private static final KList<String> FILTERS = new KList<>();
+    // Immutable: check() runs on arbitrary logger threads, and the root logger is JVM-global,
+    // so a mutable static here was both a CME hazard and grew by three entries per enable.
+    private static final List<String> FILTERS = List.of(HEIGHTMAP_MISMATCH, RAID_PERSISTENCE, DUPLICATE_ENTITY_UUID);
+
+    private boolean installed = false;
 
     public void onEnable() {
-        FILTERS.add(HEIGHTMAP_MISMATCH, RAID_PERSISTENCE, DUPLICATE_ENTITY_UUID);
+        if (installed) {
+            return;
+        }
         ((Logger) LogManager.getRootLogger()).addFilter(this);
+        installed = true;
     }
 
     public void initialize() {
@@ -33,6 +41,11 @@ public class LogFilterSVC implements IrisService, Filter {
     }
 
     public void onDisable() {
+        if (!installed) {
+            return;
+        }
+        ((Logger) LogManager.getRootLogger()).get().removeFilter(this);
+        installed = false;
     }
 
     public boolean isStarted() {
@@ -116,8 +129,14 @@ public class LogFilterSVC implements IrisService, Filter {
     }
 
     private Result check(String string) {
-        if (FILTERS.stream().anyMatch(string::contains))
-            return Result.DENY;
+        if (string == null) {
+            return Result.NEUTRAL;
+        }
+        for (String filter : FILTERS) {
+            if (string.contains(filter)) {
+                return Result.DENY;
+            }
+        }
         return Result.NEUTRAL;
     }
 }

core/src/main/java/art/arcane/iris/core/service/ObjectSVC.java

@@ -24,15 +24,17 @@ import lombok.Getter;
 import org.bukkit.block.Block;
 import org.bukkit.block.data.BlockData;
 
-import java.util.ArrayDeque;
 import java.util.Deque;
+import java.util.concurrent.ConcurrentLinkedDeque;
 import java.util.Iterator;
 import java.util.Map;
 
 public class ObjectSVC implements IrisService {
 
     @Getter
-    private final Deque<Map<Block, BlockData>> undos = new ArrayDeque<>();
+    // Concurrent + global-thread pipeline: pastes publish via J.runGlobal while the undo
+    // command arrives on an async pool thread; a plain ArrayDeque was mutated from both.
+    private final Deque<Map<Block, BlockData>> undos = new ConcurrentLinkedDeque<>();
 
 
     @Override
@@ -50,7 +52,9 @@ public class ObjectSVC implements IrisService {
     }
 
     public void revertChanges(int amount) {
-        loopChange(amount);
+        if (!J.runGlobal(() -> loopChange(amount))) {
+            loopChange(amount);
+        }
     }
 
     private void loopChange(int amount) {
@@ -68,22 +72,26 @@ public class ObjectSVC implements IrisService {
      * @param blocks The blocks to remove
      */
     private void revert(Map<Block, BlockData> blocks) {
-        Iterator<Map.Entry<Block, BlockData>> it = blocks.entrySet().iterator();
+        if (blocks == null || blocks.isEmpty()) {
+            return;
+        }
+
         J.s(() -> {
+            Iterator<Map.Entry<Block, BlockData>> it = blocks.entrySet().iterator();
             int amount = 0;
             while (it.hasNext()) {
                 Map.Entry<Block, BlockData> entry = it.next();
-                BlockData data = entry.getValue();
-                entry.getKey().setBlockData(data, false);
-
+                entry.getKey().setBlockData(entry.getValue(), false);
                 it.remove();
 
-                amount++;
-
-                if (amount > 200) {
-                    J.s(() -> revert(blocks), 1);
+                if (++amount >= 200) {
+                    break;
                 }
             }
+
+            if (!blocks.isEmpty()) {
+                J.s(() -> revert(blocks), 1);
+            }
         });
     }
 }

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

@@ -219,7 +219,10 @@ public class StudioSVC implements IrisService {
             validatePublishedPack(target);
 
             IrisData installedData;
-            boolean activeRuntime = previousData != null && !previousData.getEngines().isEmpty();
+            // Live engines only ever attach to detached openRuntime loaders, never to the
+            // dataLoaders-cached previousData — so the old previousData.getEngines() test was
+            // always empty and a running world's pack could be swapped with no restart.
+            boolean activeRuntime = IrisData.hasActiveEngines(target.toFile());
             if (previousData == null) {
                 createdData = IrisData.get(target.toFile());
                 installedData = createdData;
@@ -780,7 +783,7 @@ public class StudioSVC implements IrisService {
                         return generator.closeAsync().thenApply(ignored -> true);
                     })
                     .whenComplete((unloaded, throwable) -> {
-                        IrisToolbelt.endWorldMaintenance(world, "studio-disable");
+                        IrisToolbelt.endWorldMaintenance(world, "studio-disable", true);
                         if (throwable != null) {
                             IrisLogging.reportError("Failed to unload studio world \"" + world.getName()
                                     + "\" during disable cleanup; startup deletion remains queued.", throwable);
@@ -790,7 +793,7 @@ public class StudioSVC implements IrisService {
                         }
                     });
         } catch (Throwable e) {
-            IrisToolbelt.endWorldMaintenance(world, "studio-disable");
+            IrisToolbelt.endWorldMaintenance(world, "studio-disable", true);
             IrisLogging.reportError("Failed to unload studio world \"" + world.getName() + "\" during shutdown cleanup.", e);
         }
     }

core/src/main/java/art/arcane/iris/core/service/TreeSVC.java

@@ -64,7 +64,10 @@ import java.util.concurrent.ThreadLocalRandom;
 import java.util.function.Predicate;
 
 public class TreeSVC implements IrisService {
-    private boolean block = false;
+    // Re-entrancy guard for the synthetic StructureGrowEvent this service fires from inside
+    // its own handler. callEvent dispatches inline on the calling thread, so a ThreadLocal
+    // is exact; a shared boolean let one region's growth suppress another's on Folia.
+    private static final ThreadLocal<Boolean> REENTRANT = ThreadLocal.withInitial(() -> false);
 
     @Override
     public void onEnable() {
@@ -88,7 +91,7 @@ public class TreeSVC implements IrisService {
      */
     @EventHandler(priority = EventPriority.HIGHEST)
     public void on(StructureGrowEvent event) {
-        if (block || event.isCancelled()) {
+        if (REENTRANT.get() || event.isCancelled()) {
             return;
         }
         IrisLogging.debug(this.getClass().getName() + " received a structure grow event");
@@ -161,11 +164,13 @@ public class TreeSVC implements IrisService {
             public void set(int x, int y, int z, PlatformBlockState s) {
                 BlockData d = (BlockData) s.nativeHandle();
                 Block b = event.getWorld().getBlockAt(x, y, z);
+                // Listeners get the post-growth tree, per the StructureGrowEvent contract;
+                // a fresh snapshot here handed every plugin an all-air "tree".
                 BlockState state = b.getState();
                 if (d instanceof IrisCustomData data)
                     state.setBlockData(data.getBase());
                 else state.setBlockData(d);
-                blockStateList.add(b.getState());
+                blockStateList.add(state);
                 dataCache.put(new Location(event.getWorld(), x, y, z), d);
             }
 
@@ -245,9 +250,12 @@ public class TreeSVC implements IrisService {
         Runnable growTask = () -> {
 
             StructureGrowEvent iGrow = new StructureGrowEvent(event.getLocation(), event.getSpecies(), event.isFromBonemeal(), event.getPlayer(), blockStateList);
-            block = true;
-            Bukkit.getServer().getPluginManager().callEvent(iGrow);
-            block = false;
+            REENTRANT.set(true);
+            try {
+                Bukkit.getServer().getPluginManager().callEvent(iGrow);
+            } finally {
+                REENTRANT.set(false);
+            }
 
             if (!iGrow.isCancelled()) {
                 for (BlockState state : iGrow.getBlocks()) {
@@ -338,6 +346,11 @@ public class TreeSVC implements IrisService {
     public Cuboid getSaplings(Location at, Predicate<BlockData> valid, World world) {
         KList<BlockPosition> blockPositions = new KList<>();
         grow(at.getWorld(), new BlockPosition(at.getBlockX(), at.getBlockY(), at.getBlockZ()), valid, blockPositions);
+        if (blockPositions.isEmpty()) {
+            // No matching saplings (e.g. a giant-mushroom grow event): a 1x1 plane at the
+            // event location, never the MIN/MAX sentinel cuboid below.
+            return new Cuboid(at, at);
+        }
         BlockPosition a = new BlockPosition(Integer.MIN_VALUE, Integer.MIN_VALUE, Integer.MIN_VALUE);
         BlockPosition b = new BlockPosition(Integer.MAX_VALUE, Integer.MAX_VALUE, Integer.MAX_VALUE);
 

core/src/main/java/art/arcane/iris/core/splash/IrisSplashComposer.java

@@ -24,7 +24,7 @@ public final class IrisSplashComposer {
                 prefix + style.label(" By: ") + style.value("Volmit Software (Arcane Arts)"),
                 prefix + style.label(" Web: ") + style.value("VolmitSoftware.com"),
                 prefix + style.label(" Server: ") + style.value(serverLine),
-                prefix + style.label(" Java: ") + style.value(String.valueOf(javaVersion())) + style.label(" | Date: ") + style.value(startupDate()),
+                prefix + style.label(" Java: ") + style.value(javaVersion() < 0 ? "unknown" : String.valueOf(javaVersion())) + style.label(" | Date: ") + style.value(startupDate()),
                 prefix + style.label(" Commit: ") + style.value(BuildConstants.COMMIT) + style.label("/") + style.value(BuildConstants.ENVIRONMENT),
                 "",
                 "",
@@ -54,17 +54,22 @@ public final class IrisSplashComposer {
         return lines;
     }
 
+    /**
+     * Total parser: java.version values like "25-ea" or "26-internal" have no dot but a
+     * non-numeric suffix, and a cosmetic banner must never be able to abort startup.
+     *
+     * @return the feature version, or -1 when it cannot be determined
+     */
     public static int javaVersion() {
-        String version = System.getProperty("java.version");
+        String version = System.getProperty("java.version", "");
         if (version.startsWith("1.")) {
-            version = version.substring(2, 3);
-        } else {
-            int dot = version.indexOf('.');
-            if (dot != -1) {
-                version = version.substring(0, dot);
-            }
+            version = version.length() > 2 ? version.substring(2, 3) : "";
         }
-        return Integer.parseInt(version);
+        int end = 0;
+        while (end < version.length() && Character.isDigit(version.charAt(end))) {
+            end++;
+        }
+        return end == 0 ? -1 : Integer.parseInt(version, 0, end, 10);
     }
 
     public static String releaseTrain(String version) {

core/src/main/java/art/arcane/iris/core/tools/IrisConverter.java

@@ -90,6 +90,9 @@ public class IrisConverter {
                     HudSlotClaim barClaim = reportProgress
                             ? BukkitPlatform.hudSlots().open(sender.player(), new HudSlotRequest("iris:job", HudPriority.PROGRESS, 1200L, List.of(HudSurface.ACTION_BAR, HudSurface.BOSS_BAR)))
                             : null;
+                    // try/finally over the whole decode: a throw must never leak the
+                    // self-rescheduling progress task or the HUD claims.
+                    try {
                     if (mv > 2_000_000) {
                         largeObject = true;
                         IrisLogging.info(C.GRAY + "Converting.. " + schem.getName() + " -> " + schem.getName().replace(".schem", ".iob"));
@@ -149,13 +152,15 @@ public class IrisConverter {
                         }
                     }
 
-                    if (i != -1) J.car(i);
-                    if (titleClaim != null) {
-                        titleClaim.release();
-                    }
-                    if (barClaim != null) {
-                        barClaim.release();
-                        BukkitPlatform.hudLanes().hide(sender.player(), "iris:job");
+                    } finally {
+                        if (i != -1) J.car(i);
+                        if (titleClaim != null) {
+                            titleClaim.release();
+                        }
+                        if (barClaim != null) {
+                            barClaim.release();
+                            BukkitPlatform.hudLanes().hide(sender.player(), "iris:job");
+                        }
                     }
                     try {
                         object.shrinkwrap();

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

@@ -207,6 +207,7 @@ public class IrisCreator {
 
         World world = null;
         boolean bukkitRegistered = false;
+        PlatformChunkGenerator stagedGenerator = null;
         try {
             reportStudioProgress(0.08D, "resolve_dimension");
             reportStudioProgress(0.16D, "prepare_world_pack");
@@ -252,6 +253,7 @@ public class IrisCreator {
             if (access == null) {
                 throw new IrisException("Access is null. Something bad happened.");
             }
+            stagedGenerator = access;
             HudSlotClaim createClaim = !benchmark && studioProgressConsumer == null && sender.isPlayer()
                     ? openLoaderClaim("iris:world-create")
                     : null;
@@ -332,7 +334,7 @@ public class IrisCreator {
             }
             return world;
         } catch (Throwable failure) {
-            rollbackWorldCreation(worldKey, world, dimensionRoot, bukkitRegistered, failure);
+            rollbackWorldCreation(worldKey, world, stagedGenerator, dimensionRoot, bukkitRegistered, failure);
             if (failure instanceof IrisException irisException) {
                 throw irisException;
             }
@@ -655,12 +657,23 @@ public class IrisCreator {
     private void rollbackWorldCreation(
             NamespacedKey worldKey,
             World createdWorld,
+            PlatformChunkGenerator stagedGenerator,
             File dimensionRoot,
             boolean bukkitRegistered,
             Throwable failure
     ) {
         World activeWorld = createdWorld == null ? WorldIdentity.resolve(worldKey).orElse(null) : createdWorld;
         boolean safeToDelete = activeWorld != null || !containsTimeout(failure);
+        if (activeWorld == null && stagedGenerator != null) {
+            // The world never materialized, so no unload path will ever close the staged
+            // generator; without this it stays registered on WorldInitEvent and attaches a
+            // second engine when a same-name world is created later.
+            try {
+                stagedGenerator.closeAsync().get(ROLLBACK_PHASE_TIMEOUT_SECONDS, TimeUnit.SECONDS);
+            } catch (Throwable rollbackFailure) {
+                failure.addSuppressed(unwrapFailure(rollbackFailure));
+            }
+        }
         if (activeWorld != null) {
             IrisToolbelt.beginWorldMaintenance(activeWorld, "world-create-rollback", true);
             try {
@@ -682,6 +695,11 @@ public class IrisCreator {
                 if (safeToDelete && generator != null) {
                     generator.closeAsync().get(ROLLBACK_PHASE_TIMEOUT_SECONDS, TimeUnit.SECONDS);
                 }
+                // A staged generator the world never bound (e.g. the creation failed after a
+                // retry re-staged a fresh one) has no unload path either.
+                if (stagedGenerator != null && stagedGenerator != generator) {
+                    stagedGenerator.closeAsync().get(ROLLBACK_PHASE_TIMEOUT_SECONDS, TimeUnit.SECONDS);
+                }
             } catch (Throwable rollbackFailure) {
                 Throwable cause = unwrapFailure(rollbackFailure);
                 failure.addSuppressed(cause);
@@ -690,7 +708,7 @@ public class IrisCreator {
                     ServerConfigurator.restart("World creation rollback timed out for \"" + name + "\".");
                 }
             } finally {
-                IrisToolbelt.endWorldMaintenance(activeWorld, "world-create-rollback");
+                IrisToolbelt.endWorldMaintenance(activeWorld, "world-create-rollback", true);
             }
         }
 

core/src/main/java/art/arcane/iris/core/tools/IrisReflectiveAPI.java

@@ -27,15 +27,18 @@ public class IrisReflectiveAPI {
         WorldMaintenance.retainMantleDataForSlice(classname);
     }
 
+    // These delegate to IrisToolbelt so the caller's WORLD Y is rebased into mantle space
+    // (0..worldHeight). Raw pass-through silently no-opped below Y=0 and read the wrong
+    // cell everywhere else, diverging from IrisToolbelt and IrisModdedAPI semantics.
     public static void setMantleData(World world, int x, int y, int z, Object data) {
-        IrisToolbelt.access(world).getEngine().getMantle().getMantle().set(x, y, z, data);
+        IrisToolbelt.setMantleData(world, x, y, z, data);
     }
 
     public static void deleteMantleData(World world, int x, int y, int z, Class c) {
-        IrisToolbelt.access(world).getEngine().getMantle().getMantle().remove(x, y, z, c);
+        IrisToolbelt.deleteMantleData(world, x, y, z, c);
     }
 
     public static Object getMantleData(World world, int x, int y, int z, Class c) {
-        return IrisToolbelt.access(world).getEngine().getMantle().getMantle().get(x, y, z, c);
+        return IrisToolbelt.getMantleData(world, x, y, z, c);
     }
 }

core/src/main/java/art/arcane/iris/core/tools/IrisToolbelt.java

@@ -90,7 +90,7 @@ public class IrisToolbelt {
             return null;
         }
 
-        File packsFolder = IrisPlatforms.get().dataFolder("packs");
+        File packsFolder = IrisPlatforms.get().packsFolder();
         File pack = PackDirectoryResolver.resolveExisting(packsFolder, reference.pack());
         if (pack == null) {
             File found = findCaseInsensitivePack(packsFolder, reference.pack());
@@ -302,6 +302,13 @@ public class IrisToolbelt {
      * @return the pregenerator job (already started)
      */
     public static PregeneratorJob pregenerate(PregenTask task, PregeneratorMethod method, Engine engine, boolean cached) {
+        // Match the modded adapter's contract: a running job is a rejection, never a silent
+        // kill whose teardown (60s drain + 120s flush) overlaps the new job's generation.
+        // Callers that genuinely want replacement must stop the old job first
+        // (PregeneratorJob.shutdownAndWait).
+        if (PregeneratorJob.getInstance() != null) {
+            throw new IllegalStateException("An Iris pregeneration job is already running; stop it first with /iris pregen stop.");
+        }
         applyPregenPerformanceProfile(engine);
         boolean useCachedWrapper = false;
         if (cached && engine != null) {
@@ -588,17 +595,25 @@ public class IrisToolbelt {
     }
 
     public static void endWorldMaintenance(World world, String reason) {
+        endWorldMaintenance(world, reason, false);
+    }
+
+    public static void endWorldMaintenance(World world, String reason, boolean bypassMantleStages) {
         if (world == null) {
             return;
         }
 
-        endWorldMaintenance(WorldIdentity.serialize(world), reason);
+        endWorldMaintenance(WorldIdentity.serialize(world), reason, bypassMantleStages);
     }
 
     public static void endWorldMaintenance(String worldName, String reason) {
         WorldMaintenance.endWorldMaintenance(worldName, reason);
     }
 
+    public static void endWorldMaintenance(String worldName, String reason, boolean bypassMantleStages) {
+        WorldMaintenance.endWorldMaintenance(worldName, reason, bypassMantleStages);
+    }
+
     public static boolean isWorldMaintenanceActive(World world) {
         return world != null && isWorldMaintenanceActive(WorldIdentity.serialize(world));
     }
@@ -639,6 +654,14 @@ public class IrisToolbelt {
         e.getEngine().getMantle().getMantle().remove(x, y - world.getMinHeight(), z, of);
     }
 
+    public static <T> void setMantleData(World world, int x, int y, int z, T data) {
+        PlatformChunkGenerator e = access(world);
+        if (e == null || data == null) {
+            return;
+        }
+        e.getEngine().getMantle().getMantle().set(x, y - world.getMinHeight(), z, data);
+    }
+
     public static boolean removeWorld(World world) throws IOException {
         return IrisCreator.removeFromBukkitYml(IrisWorldStorage.logicalName(world));
     }

core/src/main/java/art/arcane/iris/core/tools/WorldMaintenance.java

@@ -1,17 +1,16 @@
 package art.arcane.iris.core.tools;
 
 import art.arcane.iris.core.IrisSettings;
+import art.arcane.iris.engine.mantle.MantleSliceRetention;
 import art.arcane.iris.spi.IrisLogging;
 
 import java.util.Map;
-import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.atomic.AtomicInteger;
 
 public final class WorldMaintenance {
     private static final Map<String, AtomicInteger> worldMaintenanceDepth = new ConcurrentHashMap<>();
     private static final Map<String, AtomicInteger> worldMaintenanceMantleBypassDepth = new ConcurrentHashMap<>();
-    private static final Set<String> retainedMantleSlices = ConcurrentHashMap.newKeySet();
 
     private WorldMaintenance() {
     }
@@ -37,6 +36,10 @@ public final class WorldMaintenance {
     }
 
     public static void endWorldMaintenance(String worldName, String reason) {
+        endWorldMaintenance(worldName, reason, false);
+    }
+
+    public static void endWorldMaintenance(String worldName, String reason, boolean bypassMantleStages) {
         if (worldName == null) {
             return;
         }
@@ -52,13 +55,17 @@ public final class WorldMaintenance {
             depth = 0;
         }
 
-        AtomicInteger bypassCounter = worldMaintenanceMantleBypassDepth.get(worldName);
+        // Only a bypass-begin's paired end releases bypass credit: a plain end overlapping a
+        // bypassing operation stole its credit and re-enabled mantle stages under it.
         int bypassDepth = 0;
-        if (bypassCounter != null) {
-            bypassDepth = bypassCounter.decrementAndGet();
-            if (bypassDepth <= 0) {
-                worldMaintenanceMantleBypassDepth.remove(worldName, bypassCounter);
-                bypassDepth = 0;
+        if (bypassMantleStages) {
+            AtomicInteger bypassCounter = worldMaintenanceMantleBypassDepth.get(worldName);
+            if (bypassCounter != null) {
+                bypassDepth = bypassCounter.decrementAndGet();
+                if (bypassDepth <= 0) {
+                    worldMaintenanceMantleBypassDepth.remove(worldName, bypassCounter);
+                    bypassDepth = 0;
+                }
             }
         }
 
@@ -88,14 +95,10 @@ public final class WorldMaintenance {
     }
 
     public static void retainMantleDataForSlice(String className) {
-        if (className == null) {
-            return;
-        }
-
-        retainedMantleSlices.add(className);
+        MantleSliceRetention.retain(className);
     }
 
     public static boolean isRetainingMantleDataForSlice(String className) {
-        return className != null && retainedMantleSlices.contains(className);
+        return MantleSliceRetention.isRetained(className);
     }
 }

core/src/main/java/art/arcane/iris/engine/EngineBackgroundTasks.java

@@ -18,10 +18,14 @@
 
 package art.arcane.iris.engine;
 
+import art.arcane.iris.spi.IrisLogging;
 import art.arcane.iris.util.common.scheduling.J;
 
 import java.util.ArrayList;
+import java.util.Collections;
+import java.util.IdentityHashMap;
 import java.util.List;
+import java.util.Set;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.Future;
@@ -46,8 +50,10 @@ final class EngineBackgroundTasks {
 
     boolean scheduleTrackedTask(Runnable task) {
         synchronized (backgroundTaskLock) {
-            backgroundTasks.removeIf(tracked -> tracked.completion.isDone()
-                    && !tracked.completion.isCompletedExceptionally());
+            // A finished task is not outstanding work, however it finished. Retaining failed
+            // entries made the NEXT transition's drain re-report a long-settled failure and
+            // blocked close() from ever marking the engine closed.
+            backgroundTasks.removeIf(tracked -> tracked.completion.isDone());
             if (!backgroundTaskAdmission) {
                 return false;
             }
@@ -60,6 +66,10 @@ final class EngineBackgroundTasks {
                     return null;
                 } catch (Throwable exception) {
                     tracked.completion.completeExceptionally(exception);
+                    // J.a(Callable) routes through a future nobody reads; report here or the
+                    // failure is invisible.
+                    IrisLogging.reportError(exception);
+                    IrisLogging.error("Iris background task failed.");
                     throw propagate(exception);
                 }
             });
@@ -79,6 +89,15 @@ final class EngineBackgroundTasks {
         }
         long deadline = System.nanoTime() + TimeUnit.MILLISECONDS.toNanos(BACKGROUND_TASK_TIMEOUT_MILLIS);
         Throwable failure = null;
+        // Settled-set snapshot taken ONCE at drain entry: a per-iteration isDone() sample
+        // would also suppress tasks that failed while the drain was blocked on an earlier
+        // task, letting a real in-flight failure pass the transition unreported.
+        Set<TrackedBackgroundTask> settledAtEntry = Collections.newSetFromMap(new IdentityHashMap<>());
+        for (TrackedBackgroundTask task : tasks) {
+            if (task.completion.isDone()) {
+                settledAtEntry.add(task);
+            }
+        }
         for (TrackedBackgroundTask task : tasks) {
             long remaining = deadline - System.nanoTime();
             if (remaining <= 0L) {
@@ -86,6 +105,7 @@ final class EngineBackgroundTasks {
                 failure = appendFailure(failure, new TimeoutException("Timed out waiting for Iris background tasks during " + reason + "."));
                 continue;
             }
+            boolean alreadyDone = settledAtEntry.contains(task);
             try {
                 task.completion.get(remaining, TimeUnit.NANOSECONDS);
             } catch (InterruptedException e) {
@@ -94,7 +114,13 @@ final class EngineBackgroundTasks {
                 failure = appendFailure(failure, e);
             } catch (ExecutionException | TimeoutException e) {
                 cancelBackgroundTask(task, reason);
-                failure = appendFailure(failure, e);
+                // A task that had settled before this drain began was already reported when it
+                // failed; only genuinely in-flight failures may poison this transition.
+                if (!alreadyDone) {
+                    failure = appendFailure(failure, e);
+                } else {
+                    IrisLogging.debug("Ignoring pre-settled background task failure during " + reason + ".");
+                }
             }
         }
         boolean complete;

core/src/main/java/art/arcane/iris/engine/EngineShutdownSequence.java

@@ -33,6 +33,8 @@ import art.arcane.iris.spi.IrisServices;
  * having succeeded so a partially released engine never reports itself as closed.
  */
 final class EngineShutdownSequence {
+    private static final long CLOSE_RETRY_DRAIN_TIMEOUT_MILLIS = 5000L;
+
     private final IrisEngine engine;
     private boolean runtimeReleased;
     private boolean targetReleased;
@@ -55,11 +57,50 @@ final class EngineShutdownSequence {
             engine.getClosing().set(true);
             engine.backgroundTasks.closeBackgroundTaskAdmission();
             EngineTickRegistry.unregisterTicking(engine);
-            engine.getPlatformHooks().shutdownPregenerator(engine);
+            // Best-effort like every other step: a pregen join timeout must not escape the
+            // synchronized block before anything is saved or released. On failure, save what
+            // can be saved and leave the close incomplete-but-retryable (a live pregen writer
+            // may still hold the mantle, so the releases are skipped).
+            Throwable pregenFailure = runCleanup(null, () -> engine.getPlatformHooks().shutdownPregenerator(engine));
+            if (pregenFailure != null) {
+                engine.lifecycleState = LifecycleState.FAILED;
+                failure = pregenFailure;
+                failure = runCleanup(failure, engine::savePrefetchOnce);
+                failure = runCleanup(failure, engine::saveEngineData);
+                failure = runCleanup(failure, () -> engine.getMantle().saveAllNow());
+                reportIncompleteClose(failure);
+                return;
+            }
+            Throwable drainFailure = null;
             try {
                 engine.getGenerationSessions().sealAndAwait("close", IrisEngine.SESSION_DRAIN_TIMEOUT_MILLIS, true);
             } catch (GenerationSessionException e) {
-                throw new IllegalStateException("Failed to drain Iris generation for close.", e);
+                drainFailure = e;
+            }
+            if (drainFailure != null) {
+                // A drain timeout must not abandon teardown: the world manager is the lease
+                // producer, so stop it first, then re-drain briefly.
+                IrisLogging.warn("Iris generation did not drain for close on " + engine.getWorld().name()
+                        + "; stopping the world manager and retrying.");
+                Throwable managerFailure = engine.runtime == null
+                        ? null
+                        : runCleanup(null, engine.runtime.worldManager()::close);
+                try {
+                    engine.getGenerationSessions().sealAndAwait("close-retry", CLOSE_RETRY_DRAIN_TIMEOUT_MILLIS, true);
+                    drainFailure = null;
+                } catch (GenerationSessionException e) {
+                    drainFailure = appendFailure(drainFailure, e);
+                }
+                drainFailure = appendFailure(drainFailure, managerFailure);
+            }
+            if (drainFailure != null) {
+                // A live lease may be mid-write, so the mantle must not be closed at it — but
+                // dirty plates can still be flushed (saveAll is synchronized) so terrain since
+                // the last periodic save is not lost. The close stays incomplete and retryable.
+                engine.lifecycleState = LifecycleState.FAILED;
+                failure = runCleanup(drainFailure, () -> engine.getMantle().saveAllNow());
+                reportIncompleteClose(failure);
+                return;
             }
 
             BackgroundTaskDrain backgroundDrain = engine.backgroundTasks.drainBackgroundTasks("close");
@@ -108,13 +149,17 @@ final class EngineShutdownSequence {
             }
         }
         if (failure != null) {
-            IrisLogging.error("Iris engine shutdown remains incomplete after cleanup failures for " + engine.getWorld().name() + ".");
-            IrisLogging.reportError(failure);
-            failure.printStackTrace();
-            throw new IllegalStateException("Iris engine shutdown remains incomplete after cleanup failures.", failure);
+            reportIncompleteClose(failure);
         }
     }
 
+    private void reportIncompleteClose(Throwable failure) {
+        IrisLogging.error("Iris engine shutdown remains incomplete after cleanup failures for " + engine.getWorld().name() + ".");
+        IrisLogging.reportError(failure);
+        failure.printStackTrace();
+        throw new IllegalStateException("Iris engine shutdown remains incomplete after cleanup failures.", failure);
+    }
+
     void cleanupFailedConstruction(Throwable original) {
         engine.getClosing().set(true);
         engine.backgroundTasks.closeBackgroundTaskAdmission();

core/src/main/java/art/arcane/iris/engine/IrisComplex.java

@@ -118,7 +118,11 @@ public class IrisComplex implements DataProvider {
     private IrisRegion focusRegion;
     private Map<IrisInterpolator, IdentityHashMap<IrisBiome, GeneratorBounds>> generatorBounds;
     private Set<IrisBiome> generatorBiomes;
-    private final Map<IrisBiome, ChildSelectionPlan> childSelectionPlans = Collections.synchronizedMap(new IdentityHashMap<>());
+    // Copy-on-write: reads happen per column on every burst thread; the synchronizedMap
+    // monitor was taken on every HIT. Writes are once per biome and bounded, so a fresh map
+    // per insert is cheap. Identity keying is load-bearing (IrisBiome is mutable/value-hashed).
+    private volatile IdentityHashMap<IrisBiome, ChildSelectionPlan> childSelectionPlans = new IdentityHashMap<>();
+    private final Object childSelectionPlanLock = new Object();
 
     public IrisComplex(Engine engine) {
         this(engine, false);
@@ -169,7 +173,7 @@ public class IrisComplex implements DataProvider {
         generatorBounds = buildGeneratorBounds(engine);
         KList<IrisShapedGeneratorStyle> overlayNoise = engine.getDimension().getOverlayNoise();
         overlayStream = overlayNoise.isEmpty()
-                ? ProceduralStream.ofDouble((x, z) -> 0.0D).waste("Overlay Stream")
+                ? ProceduralStream.ofDouble((x, z) -> 0.0D)
                 : ProceduralStream.ofDouble((x, z) -> {
             double value = 0D;
 
@@ -178,22 +182,22 @@ public class IrisComplex implements DataProvider {
             }
 
             return value;
-        }).waste("Overlay Stream");
+        });
         rockStream = engine.getDimension().getRockPalette().getLayerGenerator(rng.nextParallelRNG(45), data).stream()
-                .select(engine.getDimension().getRockPalette().getBlockData(data)).waste("Rock Stream");
+                .select(engine.getDimension().getRockPalette().getBlockData(data));
         fluidStream = engine.getDimension().getFluidPalette().getLayerGenerator(rng.nextParallelRNG(78), data).stream()
-                .select(engine.getDimension().getFluidPalette().getBlockData(data)).waste("Fluid Stream");
+                .select(engine.getDimension().getFluidPalette().getBlockData(data));
         regionStyleStream = engine.getDimension().getRegionStyle().create(rng.nextParallelRNG(883), getData()).stream()
-                .zoom(engine.getDimension().getRegionZoom()).waste("Region Style");
-        regionIdentityStream = regionStyleStream.fit(Integer.MIN_VALUE, Integer.MAX_VALUE).waste("Region Identity Stream");
+                .zoom(engine.getDimension().getRegionZoom());
+        regionIdentityStream = regionStyleStream.fit(Integer.MIN_VALUE, Integer.MAX_VALUE);
         regionStream = focusRegion != null ?
                 ProceduralStream.of((x, z) -> focusRegion,
                         Interpolated.of(a -> 0D, a -> focusRegion))
                 : regionStyleStream
                 .selectRarity(data.getRegionLoader().loadAll(engine.getDimension().getRegions()))
-                .cache2D("regionStream", engine, cacheSize).waste("Region Stream");
+                .cache2D("regionStream", engine, cacheSize);
         regionIDStream = regionIdentityStream.convertCached((i) -> new UUID(Double.doubleToLongBits(i),
-                String.valueOf(i * 38445).hashCode() * 3245556666L)).waste("Region ID Stream");
+                String.valueOf(i * 38445).hashCode() * 3245556666L));
         caveBiomeStream = regionStream.contextInjecting(engine, (c, x, z) -> c.getRegion().get(x, z))
                 .convert((r)
                         -> engine.getDimension().getCaveBiomeStyle().create(rng.nextParallelRNG(InferredType.CAVE.ordinal()), getData()).stream()
@@ -201,7 +205,7 @@ public class IrisComplex implements DataProvider {
                         .zoom(r.getCaveBiomeZoom())
                         .selectRarity(loadInferredBiomes(r.getCaveBiomes(), InferredType.CAVE))
                         .onNull(emptyBiome)
-                ).convertAware2D(ProceduralStream::get).cache2D("caveBiomeStream", engine, cacheSize).waste("Cave Biome Stream");
+                ).convertAware2D(ProceduralStream::get).cache2D("caveBiomeStream", engine, cacheSize);
         inferredStreams.put(InferredType.CAVE, caveBiomeStream);
         landBiomeStream = regionStream.contextInjecting(engine, (c, x, z) -> c.getRegion().get(x, z))
                 .convert((r)
@@ -211,7 +215,7 @@ public class IrisComplex implements DataProvider {
                         .zoom(r.getLandBiomeZoom())
                         .selectRarity(loadInferredBiomes(r.getLandBiomes(), InferredType.LAND))
                 ).convertAware2D(ProceduralStream::get)
-                .cache2D("landBiomeStream", engine, cacheSize).waste("Land Biome Stream");
+                .cache2D("landBiomeStream", engine, cacheSize);
         inferredStreams.put(InferredType.LAND, landBiomeStream);
         seaBiomeStream = regionStream.contextInjecting(engine, (c, x, z) -> c.getRegion().get(x, z))
                 .convert((r)
@@ -221,7 +225,7 @@ public class IrisComplex implements DataProvider {
                         .zoom(r.getSeaBiomeZoom())
                         .selectRarity(loadInferredBiomes(r.getSeaBiomes(), InferredType.SEA))
                 ).convertAware2D(ProceduralStream::get)
-                .cache2D("seaBiomeStream", engine, cacheSize).waste("Sea Biome Stream");
+                .cache2D("seaBiomeStream", engine, cacheSize);
         inferredStreams.put(InferredType.SEA, seaBiomeStream);
         shoreBiomeStream = regionStream.contextInjecting(engine, (c, x, z) -> c.getRegion().get(x, z))
                 .convert((r)
@@ -229,60 +233,60 @@ public class IrisComplex implements DataProvider {
                         .zoom(engine.getDimension().getBiomeZoom())
                         .zoom(r.getShoreBiomeZoom())
                         .selectRarity(loadInferredBiomes(r.getShoreBiomes(), InferredType.SHORE))
-                ).convertAware2D(ProceduralStream::get).cache2D("shoreBiomeStream", engine, cacheSize).waste("Shore Biome Stream");
+                ).convertAware2D(ProceduralStream::get).cache2D("shoreBiomeStream", engine, cacheSize);
         inferredStreams.put(InferredType.SHORE, shoreBiomeStream);
         bridgeStream = focusBiome != null ? ProceduralStream.of((x, z) -> focusBiome.getInferredType(),
                 Interpolated.of(a -> 0D, a -> focusBiome.getInferredType())) :
                 engine.getDimension().getContinentalStyle().create(rng.nextParallelRNG(234234565), getData())
                         .bake().scale(1D / engine.getDimension().getContinentZoom()).bake().stream()
                         .convert((v) -> v >= engine.getDimension().getLandChance() ? InferredType.SEA : InferredType.LAND)
-                        .cache2D("bridgeStream", engine, cacheSize).waste("Bridge Stream");
+                        .cache2D("bridgeStream", engine, cacheSize);
         baseBiomeStream = focusBiome != null ? ProceduralStream.of((x, z) -> focusBiome,
                 Interpolated.of(a -> 0D, a -> focusBiome)) :
                 bridgeStream.convertAware2D((t, x, z) -> inferredStreams.get(t).get(x, z))
                         .convertAware2D(this::implode)
-                        .cache2D("baseBiomeStream", engine, cacheSize).waste("Base Biome Stream");
+                        .cache2D("baseBiomeStream", engine, cacheSize);
         heightStream = ProceduralStream.of((x, z) -> {
             IrisBiome b = focusBiome != null ? focusBiome : baseBiomeStream.get(x, z);
             return getHeight(engine, b, x, z, engine.getSeedManager().getHeight());
-        }, Interpolated.DOUBLE).cache2DDouble("heightStream", engine, cacheSize).waste("Height Stream");
+        }, Interpolated.DOUBLE).cache2DDouble("heightStream", engine, cacheSize);
         roundedHeighteightStream = heightStream.contextInjecting(engine, (c, x, z) -> c.getHeight().getDouble(x, z))
-                .round().waste("Rounded Height Stream");
+                .round();
         slopeStream = heightStream.contextInjecting(engine, (c, x, z) -> c.getHeight().getDouble(x, z))
-                .slope(3).cache2DDouble("slopeStream", engine, cacheSize).waste("Slope Stream");
+                .slope(3).cache2DDouble("slopeStream", engine, cacheSize);
         trueBiomeStream = focusBiome != null ? ProceduralStream.of((x, y) -> focusBiome, Interpolated.of(a -> 0D,
                         b -> focusBiome))
                 .cache2D("trueBiomeStream-focus", engine, cacheSize) : heightStream
                 .convertAware2D((h, x, z) ->
                         fixBiomeType(h, baseBiomeStream.get(x, z),
                                 regionStream.contextInjecting(engine, (c, xx, zz) -> c.getRegion().get(xx, zz)).get(x, z), x, z, fluidHeight))
-                .cache2D("trueBiomeStream", engine, cacheSize).waste("True Biome Stream");
+                .cache2D("trueBiomeStream", engine, cacheSize);
         trueBiomeDerivativeStream = trueBiomeStream.contextInjecting(engine, (c, x, z) -> c.getBiome().get(x, z))
-                .convert((b) -> IrisPlatforms.get().registries().biome(b.getDerivativeKey())).cache2D("trueBiomeDerivativeStream", engine, cacheSize).waste("True Biome Derivative Stream");
+                .convert((b) -> IrisPlatforms.get().registries().biome(b.getDerivativeKey())).cache2D("trueBiomeDerivativeStream", engine, cacheSize);
         heightFluidStream = heightStream.contextInjecting(engine, (c, x, z) -> c.getHeight().getDouble(x, z))
-                .max(fluidHeight).cache2DDouble("heightFluidStream", engine, cacheSize).waste("Height Fluid Stream");
-        maxHeightStream = ProceduralStream.ofDouble((x, z) -> height).waste("Max Height Stream");
+                .max(fluidHeight).cache2DDouble("heightFluidStream", engine, cacheSize);
+        maxHeightStream = ProceduralStream.ofDouble((x, z) -> height);
         terrainSurfaceDecoration = trueBiomeStream.contextInjecting(engine, (c, x, z) -> c.getBiome().get(x, z))
-                .convertAware2D((b, xx, zz) -> decorateFor(b, xx, zz, IrisDecorationPart.NONE)).cache2D("terrainSurfaceDecoration", engine, cacheSize).waste("Surface Decoration Stream");
+                .convertAware2D((b, xx, zz) -> decorateFor(b, xx, zz, IrisDecorationPart.NONE)).cache2D("terrainSurfaceDecoration", engine, cacheSize);
         terrainCeilingDecoration = trueBiomeStream.contextInjecting(engine, (c, x, z) -> c.getBiome().get(x, z))
-                .convertAware2D((b, xx, zz) -> decorateFor(b, xx, zz, IrisDecorationPart.CEILING)).cache2D("terrainCeilingDecoration", engine, cacheSize).waste("Ceiling Decoration Stream");
+                .convertAware2D((b, xx, zz) -> decorateFor(b, xx, zz, IrisDecorationPart.CEILING)).cache2D("terrainCeilingDecoration", engine, cacheSize);
         terrainCaveSurfaceDecoration = caveBiomeStream.contextInjecting(engine, (c, x, z) -> c.getCave().get(x, z))
-                .convertAware2D((b, xx, zz) -> decorateFor(b, xx, zz, IrisDecorationPart.NONE)).cache2D("terrainCaveSurfaceDecoration", engine, cacheSize).waste("Cave Surface Stream");
+                .convertAware2D((b, xx, zz) -> decorateFor(b, xx, zz, IrisDecorationPart.NONE)).cache2D("terrainCaveSurfaceDecoration", engine, cacheSize);
         terrainCaveCeilingDecoration = caveBiomeStream.contextInjecting(engine, (c, x, z) -> c.getCave().get(x, z))
-                .convertAware2D((b, xx, zz) -> decorateFor(b, xx, zz, IrisDecorationPart.CEILING)).cache2D("terrainCaveCeilingDecoration", engine, cacheSize).waste("Cave Ceiling Stream");
+                .convertAware2D((b, xx, zz) -> decorateFor(b, xx, zz, IrisDecorationPart.CEILING)).cache2D("terrainCaveCeilingDecoration", engine, cacheSize);
         shoreSurfaceDecoration = trueBiomeStream.contextInjecting(engine, (c, x, z) -> c.getBiome().get(x, z))
-                .convertAware2D((b, xx, zz) -> decorateFor(b, xx, zz, IrisDecorationPart.SHORE_LINE)).cache2D("shoreSurfaceDecoration", engine, cacheSize).waste("Shore Surface Stream");
+                .convertAware2D((b, xx, zz) -> decorateFor(b, xx, zz, IrisDecorationPart.SHORE_LINE)).cache2D("shoreSurfaceDecoration", engine, cacheSize);
         seaSurfaceDecoration = trueBiomeStream.contextInjecting(engine, (c, x, z) -> c.getBiome().get(x, z))
-                .convertAware2D((b, xx, zz) -> decorateFor(b, xx, zz, IrisDecorationPart.SEA_SURFACE)).cache2D("seaSurfaceDecoration", engine, cacheSize).waste("Sea Surface Stream");
+                .convertAware2D((b, xx, zz) -> decorateFor(b, xx, zz, IrisDecorationPart.SEA_SURFACE)).cache2D("seaSurfaceDecoration", engine, cacheSize);
         seaFloorDecoration = trueBiomeStream.contextInjecting(engine, (c, x, z) -> c.getBiome().get(x, z))
-                .convertAware2D((b, xx, zz) -> decorateFor(b, xx, zz, IrisDecorationPart.SEA_FLOOR)).cache2D("seaFloorDecoration", engine, cacheSize).waste("Sea Floor Stream");
+                .convertAware2D((b, xx, zz) -> decorateFor(b, xx, zz, IrisDecorationPart.SEA_FLOOR)).cache2D("seaFloorDecoration", engine, cacheSize);
         baseBiomeIDStream = trueBiomeStream.contextInjecting(engine, (c, x, z) -> c.getBiome().get(x, z))
                 .convertAware2D((b, x, z) -> {
                     UUID d = regionIDStream.get(x, z);
                     return new UUID(b.getLoadKey().hashCode() * 818223L,
                             d.hashCode());
                 })
-                .cache2D("", engine, cacheSize).waste("Biome ID Stream");
+                .cache2D("", engine, cacheSize);
         //@done
     }
 
@@ -598,7 +602,7 @@ public class IrisComplex implements DataProvider {
             return cachedPlan;
         }
 
-        synchronized (childSelectionPlans) {
+        synchronized (childSelectionPlanLock) {
             ChildSelectionPlan synchronizedPlan = childSelectionPlans.get(biome);
             if (synchronizedPlan != null) {
                 return synchronizedPlan;
@@ -614,7 +618,9 @@ public class IrisComplex implements DataProvider {
             options.add(biome);
 
             ChildSelectionPlan createdPlan = ChildSelectionPlan.create(options);
-            childSelectionPlans.put(biome, createdPlan);
+            IdentityHashMap<IrisBiome, ChildSelectionPlan> next = new IdentityHashMap<>(childSelectionPlans);
+            next.put(biome, createdPlan);
+            childSelectionPlans = next;
             return createdPlan;
         }
     }

core/src/main/java/art/arcane/iris/engine/IrisEngineMantle.java

@@ -389,12 +389,21 @@ public class IrisEngineMantle implements EngineMantle {
                     return worker.read(name, (regionName, in) ->
                             TectonicPlate.read(worldHeight, in, regionName.startsWith("pv."), adapter, hooks));
                 } finally {
-                    if (TectonicPlate.hasError() && IrisSettings.get().getGeneral().isDumpMantleOnError()) {
-                        File dump = IrisPlatforms.get().dataFile("dump", name + ".bin");
-                        worker.dumpDecoded(name, dump.toPath());
-                    } else {
-                        IrisLogging.debug("Read Tectonic Plate " + C.DARK_GREEN + name + C.RED + " in " + Form.duration(stopwatch.getMilliseconds(), 2));
+                    // hasError() is a consuming ThreadLocal read: evaluate exactly once. The
+                    // dump must never throw out of this finally — that would replace the
+                    // successfully parsed plate with the dump failure, and the caller would
+                    // overwrite 1024 good chunks with a fresh empty plate.
+                    boolean errored = TectonicPlate.hasError();
+                    if (errored && IrisSettings.get().getGeneral().isDumpMantleOnError()) {
+                        try {
+                            File dump = IrisPlatforms.get().dataFile("dump", name + ".bin");
+                            worker.dumpDecoded(name, dump.toPath());
+                        } catch (Throwable dumpFailure) {
+                            IrisLogging.warn("Failed to dump mantle region " + name + " for diagnostics");
+                            IrisLogging.reportError(dumpFailure);
+                        }
                     }
+                    IrisLogging.debug("Read Tectonic Plate " + C.DARK_GREEN + name + C.RED + " in " + Form.duration(stopwatch.getMilliseconds(), 2));
                 }
             }
 

core/src/main/java/art/arcane/iris/engine/WorldEntitySpawner.java

@@ -519,18 +519,7 @@ final class WorldEntitySpawner {
     }
 
     private KList<IrisEntitySpawn> spawnRandomly(List<IrisEntitySpawn> types) {
-        KList<IrisEntitySpawn> rarityTypes = new KList<>();
-        int totalRarity = 0;
-
-        for (IrisEntitySpawn i : types) {
-            totalRarity += IRare.get(i);
-        }
-
-        for (IrisEntitySpawn i : types) {
-            rarityTypes.addMultiple(i, totalRarity / IRare.get(i));
-        }
-
-        return rarityTypes;
+        return IRare.expandWeighted(types);
     }
 
     @Data