vfs: RealFSProvider.watchFile ignores the listener and unwatchFile leaks it #66223

Version

main

Platform

All

Subsystem

vfs

What steps will reproduce the bug?

import { mkdtempSync, watchFile, writeFileSync, unwatchFile } from "fs";
import { create, RealFSProvider } from "node:vfs";

const d = mkdtempSync("/tmp/v-");
const f = create(new RealFSProvider(d)).mount() + "/f";
const cb = () => console.log("fired");

watchFile(f, { interval:50 }, cb);

setTimeout(() => writeFileSync(f, "x"), 50);
setTimeout(() => {
  unwatchFile(f, cb);
  console.log("done, should exit");
}, 200);

How often does it reproduce? Is there a required condition?

Always

What is the expected behavior? Why is that the expected behavior?

fired
fired
done, should exit

fired prints within ~50–100ms of the write (the { interval: 50 } poll detects the stat change), then unwatchFile(f, cb) at 200ms removes the callback and the process exits cleanly with code 0.

What do you see instead?

done, should exit
<process hangs>

fired never prints - even though the change happens at 50ms and the watcher polls every 50ms for 150ms before unwatch. cb was never registered at all. The hang after done, should exit is the leaked stub keeping the loop alive.

Additional information

No response