fix(workspace-fs): wait for released watchers during shutdown

packages/workspace-fs/src/watch-cancellation.test.ts

@@ -148,3 +148,46 @@ test("watcher readiness refreshes edits made during the background scan", async
 	expect(entries.map((entry) => entry.name)).toContain("during-scan.txt");
 	await stream.return?.();
 });
+
+for (const phase of ["attaching", "attached"] as const) {
+	test(`close waits for the last aborted listener's ${phase} native watch`, async () => {
+		const rootPath = await root();
+		const controller = new AbortController();
+		const entered = deferred<void>();
+		const gate = deferred<void>();
+		let detached = false;
+		const manager = new FsWatcherManager({
+			backend: {
+				name: "test",
+				async subscribe() {
+					entered.resolve();
+					if (phase === "attaching") await gate.promise;
+					return {
+						async unsubscribe() {
+							await gate.promise;
+							detached = true;
+						},
+					};
+				},
+			},
+		});
+		managers.push(manager);
+		const subscription = manager
+			.subscribe(
+				{ absolutePath: rootPath, signal: controller.signal },
+				() => {},
+			)
+			.catch((error) => {
+				if (!(error instanceof Error && error.name === "AbortError"))
+					throw error;
+			});
+		await entered.promise;
+		if (phase === "attached") await subscription;
+		controller.abort();
+		const closedAfterDetach = manager.close().then(() => detached);
+		await new Promise<void>((resolve) => setImmediate(resolve));
+		gate.resolve();
+		expect(await closedAfterDetach).toBe(true);
+		await subscription;
+	});
+}

packages/workspace-fs/src/watch.ts

@@ -277,6 +277,8 @@ export class FsWatcherManager {
 	private readonly ignore: string[];
 	private readonly listGitIgnoredDirs?: FsWatcherManagerOptions["listGitIgnoredDirs"];
 	private readonly findNestedRoots: typeof findNestedRepoRoots;
+	// Last-listener cleanup leaves the path maps immediately so it can be rewatched.
+	private readonly releasing = new Set<Promise<unknown>>();
 	private readonly pending = new Map<
 		string,
 		{
@@ -381,11 +383,12 @@ export class FsWatcherManager {
 			if (pending && this.pending.get(absolutePath) === pending) {
 				this.pending.delete(absolutePath);
 				pending.controller.abort();
+				await this.trackRelease(Promise.allSettled([pending.promise]));
 			}
 			const current = this.watchers.get(absolutePath);
 			if (current?.listeners === listeners) {
 				this.watchers.delete(absolutePath);
-				await this.disposeWatcherState(current);
+				await this.trackRelease(this.disposeWatcherState(current));
 			}
 		};
 		const onAbort = () => {
@@ -402,14 +405,26 @@ export class FsWatcherManager {
 		}
 	}
 
+	private async trackRelease(work: Promise<unknown>): Promise<void> {
+		this.releasing.add(work);
+		try {
+			await work;
+		} finally {
+			this.releasing.delete(work);
+		}
+	}
+
 	async close(): Promise<void> {
 		const pending = [...this.pending.values()];
 		this.pending.clear();
 		for (const entry of pending) entry.controller.abort();
 		await Promise.allSettled(pending.map((entry) => entry.promise));
 		const states = Array.from(this.watchers.values());
 		this.watchers.clear();
-		await Promise.all(states.map((state) => this.disposeWatcherState(state)));
+		await Promise.all([
+			...this.releasing,
+			...states.map((state) => this.disposeWatcherState(state)),
+		]);
 	}
 
 	private async disposeWatcherState(state: WatcherState): Promise<void> {