Review

Verified against Node source and both enabled tests.

Correctness — defers emission via process.nextTick

Node at lib/internal/fs/watchers.js:201-211:

StatWatcher.prototype.stop = function() {
  if (this._handle === null) return;
  defaultTriggerAsyncIdScope(this._handle.getAsyncId(),
                             process.nextTick,
                             emitStop,
                             this);
  this._handle.close();
  this._handle = null;
};

The defaultTriggerAsyncIdScope(..., process.nextTick, emitStop, this) resolves at runtime to process.nextTick(emitStop, this) within an async-id scope. PR's process.nextTick(() => this.emit("stop")) is the same observable behavior — the user-visible deferral is identical. The async-id scope only matters for AsyncLocalStorage context tracking, which Deno's polyfill doesn't currently propagate through the StatWatcher handle anyway, so there's no regression.

Test trace

test-fs-watch-stop-sync.js (L1-21):

const listener = common.mustNotCall(...);
const watch = fs.watchFile(__filename, common.mustNotCall());
watch.once('stop', listener);
watch.stop();
watch.removeListener('stop', listener);

Pre-PR: emit("stop") runs synchronously inside stop() → listener fires → mustNotCall fails ❌
Post-PR: process.nextTick(() => this.emit("stop")) defers → removeListener runs first → emission fires with no listener → ✅

test-fs-watch-stop-async.js (L1-19):

let triggered = false;
watch.once('stop', () => { triggered = true; });
watch.stop();
assert.strictEqual(triggered, false);  // immediately after stop()
setImmediate(() => assert.strictEqual(triggered, true));

Pre-PR: triggered flips to true synchronously inside stop() → first assertion fails ❌
Post-PR: triggered stays false until next tick → first assertion passes; setImmediate runs after next-tick queue drains, so triggered is true by then → ✅

Idempotency / double-stop safety

stop()'s early return is preserved:

if (this.#abortController.signal.aborted) {
  return;
}
this.#abortController.abort();
process.nextTick(() => this.emit("stop"));

Calling stop() twice still emits "stop" exactly once. ✓

this binding in the arrow

process.nextTick(() => this.emit("stop")) — arrow captures this from StatWatcher.prototype.stop's lexical scope, which is the StatWatcher instance. Correct.

Minor: Node would also pass this as a nextTick argument

Node uses process.nextTick(emitStop, this) (function + arg form) rather than an arrow closure. Functionally equivalent — the arrow form allocates one closure per stop, the function-arg form passes this as a param. Closure-allocation overhead is negligible since stop() is called once per watcher lifetime. Leave as-is.

Safety / performance

• One additional microtask per stop. Negligible.
• No leak: process.nextTick callback runs once and the closure is released after.
• No interaction with the async poll loop's try/catch — that loop catches its own AbortError separately from this emission path.

Config

• Added parallel/test-fs-watch-stop-async.js and parallel/test-fs-watch-stop-sync.js, alphabetically placed between -utimes.js and -watch.js. Clean.

LGTM.