Contained catalog capture errors

- A worldgen catalog capture that fails with any throwable, during the server-thread scan or the background encode, always completes its future and frees the next capture
- Errors are logged with their stacktrace and no longer escape server startup; only virtual machine errors are rethrown after cleanup

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

@@ -55,56 +55,68 @@ public final class ModdedWorldgenCatalogs {
 
     public static CompletableFuture<CaptureResult> capture(NativeModdedServer server) {
         Objects.requireNonNull(server, "server");
+        return capture(() -> scan(server));
+    }
+
+    static CompletableFuture<CaptureResult> capture(CaptureScan scan) {
         CompletableFuture<CaptureResult> pending = new CompletableFuture<>();
         CompletableFuture<CaptureResult> running = RUNNING.compareAndExchange(null, pending);
         if (running != null) {
             return running;
         }
-        long startedAt = System.nanoTime();
-        NativeModdedLoader loader = ModdedEngineBootstrap.loader();
-        NativeWorldgenScan scan;
-        CatalogCaptureContext context;
+        CaptureWork work;
         try {
-            scan = NativeWorldgenScan.scan(server, loader);
-            context = new CatalogCaptureContext(loader.minecraftVersion(), loader.platformName(),
-                    System.currentTimeMillis(), loader.mods());
-        } catch (RuntimeException failure) {
+            work = scan.scan();
+        } catch (Throwable failure) {
             ModdedIrisLog.error("Iris could not read the worldgen registries for the catalog", failure);
             finish(pending, null, failure);
+            rethrowIfVirtualMachineError(failure);
             return pending;
         }
-        long scanMillis = elapsedMillis(startedAt);
-        Path file = catalogFile();
-        Thread worker = new Thread(() -> encodeAndWrite(new PendingCapture(scan, context, file, startedAt, scanMillis), pending),
-                "Iris Worldgen Catalog");
+        Thread worker = new Thread(() -> complete(work, pending), "Iris Worldgen Catalog");
         worker.setDaemon(true);
         worker.start();
         return pending;
     }
 
-    private static void encodeAndWrite(PendingCapture capture, CompletableFuture<CaptureResult> pending) {
+    private static CaptureWork scan(NativeModdedServer server) {
+        long startedAt = System.nanoTime();
+        NativeModdedLoader loader = ModdedEngineBootstrap.loader();
+        NativeWorldgenScan scan = NativeWorldgenScan.scan(server, loader);
+        CatalogCaptureContext context = new CatalogCaptureContext(loader.minecraftVersion(), loader.platformName(),
+                System.currentTimeMillis(), loader.mods());
+        PendingCapture capture = new PendingCapture(scan, context, catalogFile(), startedAt, elapsedMillis(startedAt));
+        return () -> encodeAndWrite(capture);
+    }
+
+    private static void complete(CaptureWork work, CompletableFuture<CaptureResult> pending) {
         try {
-            NativeWorldgenSnapshot snapshot = capture.scan().encode();
-            WorldgenCatalog catalog = WorldgenCatalogAssembler.assemble(snapshot, capture.context());
-            WorldgenCatalogStore.write(capture.file(), catalog);
-            LATEST.set(catalog);
-            CaptureResult result = new CaptureResult(catalog, capture.file(), elapsedMillis(capture.startedAt()));
-            ModdedIrisLog.info("Iris worldgen catalog: {} namespaces, {} biomes, {} placed features, {} structures, "
-                            + "{} dimension types, {} level stems -> {} ({}ms server thread, {}ms total)",
-                    catalog.namespaces().size(), catalog.biomes().size(), catalog.placedFeatures().size(),
-                    catalog.structures().size(), catalog.dimensionTypes().size(), catalog.levelStems().size(),
-                    capture.file(), capture.scanMillis(), result.millis());
-            reportEncodeFailures(snapshot.failures());
-            finish(pending, result, null);
+            finish(pending, work.run(), null);
         } catch (IOException failure) {
-            ModdedIrisLog.error("Iris could not write the worldgen catalog to " + capture.file(), failure);
+            ModdedIrisLog.error("Iris could not write the worldgen catalog", failure);
             finish(pending, null, new UncheckedIOException(failure));
-        } catch (RuntimeException failure) {
+        } catch (Throwable failure) {
             ModdedIrisLog.error("Iris could not build the worldgen catalog", failure);
             finish(pending, null, failure);
+            rethrowIfVirtualMachineError(failure);
         }
     }
 
+    private static CaptureResult encodeAndWrite(PendingCapture capture) throws IOException {
+        NativeWorldgenSnapshot snapshot = capture.scan().encode();
+        WorldgenCatalog catalog = WorldgenCatalogAssembler.assemble(snapshot, capture.context());
+        WorldgenCatalogStore.write(capture.file(), catalog);
+        LATEST.set(catalog);
+        CaptureResult result = new CaptureResult(catalog, capture.file(), elapsedMillis(capture.startedAt()));
+        ModdedIrisLog.info("Iris worldgen catalog: {} namespaces, {} biomes, {} placed features, {} structures, "
+                        + "{} dimension types, {} level stems -> {} ({}ms server thread, {}ms total)",
+                catalog.namespaces().size(), catalog.biomes().size(), catalog.placedFeatures().size(),
+                catalog.structures().size(), catalog.dimensionTypes().size(), catalog.levelStems().size(),
+                capture.file(), capture.scanMillis(), result.millis());
+        reportEncodeFailures(snapshot.failures());
+        return result;
+    }
+
     private static void reportEncodeFailures(EncodeFailures failures) {
         if (failures.count() == 0) {
             return;
@@ -118,7 +130,7 @@ public final class ModdedWorldgenCatalogs {
         ModdedIrisLog.warn("Iris worldgen catalog left {} entries without JSON; first: {}", failures.count(), first);
     }
 
-    private static void finish(CompletableFuture<CaptureResult> pending, CaptureResult result, RuntimeException failure) {
+    private static void finish(CompletableFuture<CaptureResult> pending, CaptureResult result, Throwable failure) {
         RUNNING.compareAndSet(pending, null);
         if (failure != null) {
             pending.completeExceptionally(failure);
@@ -127,6 +139,12 @@ public final class ModdedWorldgenCatalogs {
         pending.complete(result);
     }
 
+    private static void rethrowIfVirtualMachineError(Throwable failure) {
+        if (failure instanceof VirtualMachineError virtualMachineError) {
+            throw virtualMachineError;
+        }
+    }
+
     private static long elapsedMillis(long startedAt) {
         return TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - startedAt);
     }
@@ -134,6 +152,16 @@ public final class ModdedWorldgenCatalogs {
     public record CaptureResult(WorldgenCatalog catalog, Path file, long millis) {
     }
 
+    @FunctionalInterface
+    interface CaptureScan {
+        CaptureWork scan();
+    }
+
+    @FunctionalInterface
+    interface CaptureWork {
+        CaptureResult run() throws IOException;
+    }
+
     private record PendingCapture(NativeWorldgenScan scan, CatalogCaptureContext context, Path file, long startedAt, long scanMillis) {
     }
 }

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

@@ -0,0 +1,84 @@
+/*
+ * Iris is a World Generator for Minecraft Servers
+ * Copyright (c) 2026 Arcane Arts (Volmit Software)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package art.arcane.iris.modded.catalog;
+
+import art.arcane.iris.modded.catalog.ModdedWorldgenCatalogs.CaptureResult;
+import org.junit.Test;
+
+import java.io.IOException;
+import java.io.UncheckedIOException;
+import java.nio.file.Path;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
+
+import static org.junit.Assert.assertSame;
+import static org.junit.Assert.assertThrows;
+import static org.junit.Assert.assertTrue;
+
+public class ModdedWorldgenCatalogsTest {
+    private static final CaptureResult RESULT = new CaptureResult(null, Path.of("worldgen-catalog.json"), 1L);
+
+    @Test
+    public void scanErrorCompletesTheCaptureAndFreesTheNextOne() throws Exception {
+        CompletableFuture<CaptureResult> failed = ModdedWorldgenCatalogs.capture(() -> {
+            throw new LinkageError("registry class missing");
+        });
+
+        ExecutionException failure = assertThrows(ExecutionException.class, () -> failed.get(5, TimeUnit.SECONDS));
+        assertTrue(failure.getCause() instanceof LinkageError);
+        assertSame(RESULT, succeed());
+    }
+
+    @Test
+    public void workerErrorCompletesTheCaptureAndFreesTheNextOne() throws Exception {
+        CompletableFuture<CaptureResult> failed = ModdedWorldgenCatalogs.capture(() -> () -> {
+            throw new AssertionError("encode exploded");
+        });
+
+        ExecutionException failure = assertThrows(ExecutionException.class, () -> failed.get(5, TimeUnit.SECONDS));
+        assertTrue(failure.getCause() instanceof AssertionError);
+        assertSame(RESULT, succeed());
+    }
+
+    @Test
+    public void workerWriteFailureCompletesWithTheIoCause() throws Exception {
+        CompletableFuture<CaptureResult> failed = ModdedWorldgenCatalogs.capture(() -> () -> {
+            throw new IOException("disk full");
+        });
+
+        ExecutionException failure = assertThrows(ExecutionException.class, () -> failed.get(5, TimeUnit.SECONDS));
+        assertTrue(failure.getCause() instanceof UncheckedIOException);
+        assertSame(RESULT, succeed());
+    }
+
+    @Test
+    public void virtualMachineErrorDuringTheScanIsRethrownAfterFreeingTheCapture() throws Exception {
+        assertThrows(OutOfMemoryError.class, () -> ModdedWorldgenCatalogs.capture(() -> {
+            throw new OutOfMemoryError("scan heap");
+        }));
+
+        assertSame(RESULT, succeed());
+    }
+
+    private static CaptureResult succeed() throws InterruptedException, ExecutionException, TimeoutException {
+        return ModdedWorldgenCatalogs.capture(() -> () -> RESULT).get(5, TimeUnit.SECONDS);
+    }
+}