Group commit generation history

- Semantic journal and saved-biome appends write without forcing; a shared flusher forces touched files within 2s outside every store lock
- GenerationHistory.sync forces pending history at world save, engine shutdown, pregen completion and before activation promotion
- A failed deferred force poisons the store the same way an uncertain append did
- Cache the active epoch pack root instead of regex-validating it on every stage open
- Tests pin append-without-force, sync barriers, failure poisoning and the save, shutdown and pregen hooks

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

@@ -116,6 +116,11 @@ public final class ModdedPregenMethod implements PregeneratorMethod {
             }
             ModdedIrisLog.info("Iris modded pregen done: dim={} completed={} peakInFlight={} finalLimit={}",
                     runtime.worldIdentity(), completed.get(), inFlightPeak.get(), adaptiveLimit.get());
+            try {
+                engine.syncGenerationHistory();
+            } catch (RuntimeException e) {
+                ModdedIrisLog.error("Iris modded pregen could not force generation history to stable storage", e);
+            }
             if (deferFinalSaveIfRequested()) {
                 return;
             }