The previous test deleted a file mid-iteration, but is_file()
caught it before stat() ran — so the new try/except never executed.
Monkeypatch Path.stat to raise FileNotFoundError on the third call
for the victim path (after is_symlink and is_file pass), simulating
the exact TOCTOU window between is_file() and stat().
A file deleted between os.walk() and path.stat() raises
FileNotFoundError, which propagated uncaught and failed the entire
discover() sweep. With enough failures this trips the circuit
breaker, silencing the poller.
Catch FileNotFoundError around the stat() call and skip the file.
The next sweep (or watchfiles) will emit the DELETE event.
