fix(runtime): unref the game-state watcher so it can't pin the event loop

extensions/mega-compact.ts

@@ -87,10 +87,20 @@ export default function (pi: ExtensionAPI) {
   // The PGlite indexes (vectorIndex / memoryIndex) are lazily opened module
   // singletons. closeVectorIndex()/closeMemoryIndex() existed but had no
   // non-test callers, so a session left both open: PGlite is WASM Postgres and
-  // its handles keep node's event loop alive, so `pi -p` produced its answer
-  // and then hung until killed rather than exiting. dispose() only released the
-  // fs.watch handle and the perf interval, neither of which was the culprit
-  // (the interval is unref'd).
+  // leaving it open makes process exit nondeterministic — measured on a
+  // teardown that opens both indexes, closing exits in ~3s while leaving them
+  // open either stalls ~13s or never exits at all. That is why `pi -p` produced
+  // its answer and then hung until killed.
+  //
+  // NOTE: an earlier revision of this comment claimed the fs.watch handle "was
+  // not the culprit". That was wrong. A node diagnostic report
+  // (--report-on-signal) taken at hang time shows the game-state watcher as an
+  // active AND referenced fs_event handle, which pins the event loop on its
+  // own — independently of PGlite, and on any path that never reaches
+  // session_shutdown. It is now unref'd at creation
+  // (ensureGameStateWatcherImpl), so it can no longer hold the process open;
+  // dispose() still closes it here for prompt fd release. The perf interval
+  // genuinely is not a culprit — it is unref'd.
   //
   // Both closes are idempotent and safe when the index was never opened, and
   // the next initVectorIndex()/initMemoryIndex() re-opens lazily.

extensions/mega-runtime/game-state.ts

@@ -14,6 +14,8 @@ import { disposePerf, type PerfContext } from "./perf.js";
 
 export interface GameWatcherLike {
 	close(): void;
+	/** fs.FSWatcher has it; test doubles need not. */
+	unref?(): unknown;
 }
 
 export interface GameStateContext {
@@ -142,6 +144,13 @@ export function ensureGameStateWatcherImpl(self: GameStateContext, view: GameSta
 				}
 			},
 		);
+		// The watcher is a cache-eviction convenience, never a reason to stay
+		// alive: an active+referenced fs_event handle holds node's event loop
+		// open, so a runtime that was never dispose()d (every extension test, and
+		// any `pi -p` run that skips session_shutdown) hangs the process after all
+		// work is done. unref'd like the perf interval — while pi runs there are
+		// always other referenced handles, so the watcher still fires normally.
+		self.gameStateWatcher.unref?.();
 		self.gameStateWatchDir = self.currentStateDir;
 	} catch {
 		/* non-fatal: missing dir / platform issue — next snapshot re-queries */