Added 1.21.1 mod targets

- Build Fabric, Forge and NeoForge per target listed in gradle/mod-targets.json (1.21.1, 26.3)
- Add 1.21.1 adapter source overlays under adapters/*/src/versions/1.21.1
- Add verifyModdedMatrix and per-target Java runtime verification of loader jars
- Re-inject persistent dimensions from the levels-ready hook before the watchdog starts
- Wait for queued chunks and the final save before pregen completes
- Add the 1.21.1 data version and datapack supported_formats range
- Cascade regions whose sea or shore pool loses every biome
- Use Gson calls available on the 1.21.1 runtime

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

@@ -166,6 +166,12 @@ public final class ModdedEngineBootstrap {
         ModdedStartup.prepareForStartup();
     }
 
+    public static void levelsReady(NativeModdedServer server) {
+        server.refreshWorlds();
+        bindWorldGenerators(server);
+        ModdedStartup.reinjectPersistentDimensions(server);
+    }
+
     public static void serverStarted(NativeModdedServer server) {
         // Prime the off-thread level snapshot before anything can read it; the per-tick refresh in
         // ModdedScheduler.tick has not run yet at this point.

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

@@ -14,6 +14,7 @@ public final class ModdedLifecycleCallbacks {
         return new NativeModdedCallbacks(
                 ModdedEngineBootstrap::serverAboutToStart,
                 ModdedEngineBootstrap::start,
+                ModdedEngineBootstrap::levelsReady,
                 ModdedEngineBootstrap::serverStarted,
                 ModdedEngineBootstrap::stop,
                 ModdedEngineBootstrap::stopped,

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

@@ -45,6 +45,9 @@ public final class ModdedMixinAudit {
     private static final AtomicBoolean AUDITED = new AtomicBoolean(false);
 
     static final List<ExpectedMixin> EXPECTED = List.of(
+            new ExpectedMixin(ENTITY_CONFIG, "ServerLevelsReadyMixin",
+                    NativeMixinTarget.SERVER, "volmlib$levelsReady",
+                    false, NativeMixinFlags::levelsReadyRan),
             new ExpectedMixin(ENTITY_CONFIG, "RegistryClientNamesMixin",
                     NativeMixinTarget.REGISTRY_PACKET, "volmlib$clientRegistryNames",
                     false, NativeMixinFlags::registryClientNamesRan),

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

@@ -91,7 +91,6 @@ public final class ModdedStartup {
         }
         ModdedForcedDatapack.verifyInjected();
         ModdedMixinAudit.runOnce();
-        reinjectPersistentDimensions(server);
 
         ModdedScheduler scheduler = ModdedEngineBootstrap.schedulerOrNull();
         if (scheduler == null) {

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

@@ -114,15 +114,9 @@ public final class ModdedPregenMethod implements PregeneratorMethod {
     @Override
     public void close() {
         try {
-            if (!sync) {
-                try {
-                    semaphore.tryAcquire(maxInFlight, 5, TimeUnit.SECONDS);
-                } catch (InterruptedException e) {
-                    Thread.currentThread().interrupt();
-                }
-            }
-            ModdedIrisLog.info("Iris modded pregen done: dim={} completed={} peakInFlight={} finalLimit={}",
-                    runtime.worldIdentity(), completed.get(), inFlightPeak.get(), adaptiveLimit.get());
+            awaitPendingChunks();
+            ModdedIrisLog.info("Iris modded pregen closing: dim={} completed={} pending={} peakInFlight={} finalLimit={}",
+                    runtime.worldIdentity(), completed.get(), inFlight.get(), inFlightPeak.get(), adaptiveLimit.get());
             try {
                 engine.syncGenerationHistory();
             } catch (RuntimeException e) {
@@ -180,6 +174,39 @@ public final class ModdedPregenMethod implements PregeneratorMethod {
                 || queuedFinalSave.get() != null;
     }
 
+    private void awaitPendingChunks() {
+        if (sync || runtime.isServerThread()) {
+            return;
+        }
+        long deadline = System.nanoTime() + TimeUnit.SECONDS.toNanos(timeoutSeconds)
+                + TimeUnit.MILLISECONDS.toNanos(FINAL_SAVE_TIMEOUT_MILLIS);
+        boolean interrupted = false;
+        try {
+            while (inFlight.get() > 0) {
+                if (finalSaveOnServerThread.get() || !runtime.isRunning()) {
+                    return;
+                }
+                if (System.nanoTime() >= deadline) {
+                    throw new IllegalStateException("Iris pregen chunk callbacks did not finish for "
+                            + runtime.worldIdentity() + ": " + inFlight.get() + " pending");
+                }
+                try {
+                    synchronized (permitMonitor) {
+                        if (inFlight.get() > 0) {
+                            permitMonitor.wait(FINAL_SAVE_POLL_MILLIS);
+                        }
+                    }
+                } catch (InterruptedException ignored) {
+                    interrupted = true;
+                }
+            }
+        } finally {
+            if (interrupted) {
+                Thread.currentThread().interrupt();
+            }
+        }
+    }
+
     private void saveLevel(boolean wait) {
         if (wait) {
             saveFinalLevel();
@@ -237,30 +264,36 @@ public final class ModdedPregenMethod implements PregeneratorMethod {
 
     private void awaitFinalSave(FinalSaveRequest request) {
         long deadline = System.nanoTime() + TimeUnit.MILLISECONDS.toNanos(FINAL_SAVE_TIMEOUT_MILLIS);
-        while (true) {
-            if (deferFinalSaveIfRequested()) {
-                return;
+        boolean interrupted = false;
+        try {
+            while (true) {
+                if (deferFinalSaveIfRequested()) {
+                    return;
+                }
+                long remainingNanos = deadline - System.nanoTime();
+                if (remainingNanos <= 0L) {
+                    ModdedIrisLog.warn("Iris pregen level save did not complete in time for {}", runtime.worldIdentity());
+                    return;
+                }
+                long waitMillis = Math.max(1L, Math.min(FINAL_SAVE_POLL_MILLIS,
+                        TimeUnit.NANOSECONDS.toMillis(remainingNanos)));
+                try {
+                    request.completion().get(waitMillis, TimeUnit.MILLISECONDS);
+                    return;
+                } catch (InterruptedException ignored) {
+                    interrupted = true;
+                } catch (TimeoutException e) {
+                    continue;
+                } catch (ExecutionException e) {
+                    Throwable cause = e.getCause() == null ? e : e.getCause();
+                    ModdedIrisLog.error("Iris pregen level save failed for {}", runtime.worldIdentity(), cause);
+                    throw new IllegalStateException("Iris pregen level save failed for "
+                            + runtime.worldIdentity(), cause);
+                }
             }
-            long remainingNanos = deadline - System.nanoTime();
-            if (remainingNanos <= 0L) {
-                ModdedIrisLog.warn("Iris pregen level save did not complete in time for {}", runtime.worldIdentity());
-                return;
-            }
-            long waitMillis = Math.max(1L, Math.min(FINAL_SAVE_POLL_MILLIS,
-                    TimeUnit.NANOSECONDS.toMillis(remainingNanos)));
-            try {
-                request.completion().get(waitMillis, TimeUnit.MILLISECONDS);
-                return;
-            } catch (InterruptedException e) {
+        } finally {
+            if (interrupted) {
                 Thread.currentThread().interrupt();
-                return;
-            } catch (TimeoutException e) {
-                continue;
-            } catch (ExecutionException e) {
-                Throwable cause = e.getCause() == null ? e : e.getCause();
-                ModdedIrisLog.error("Iris pregen level save failed for {}", runtime.worldIdentity(), cause);
-                throw new IllegalStateException("Iris pregen level save failed for "
-                        + runtime.worldIdentity(), cause);
             }
         }
     }