The default StoreFileOps were never observed. One test now wraps fs/promises.open and each handle's
sync and close, and records the store's bytes at every call: the staged file is synced and closed
while the store still holds its old bytes, and on Unix the directory is synced and closed after the
store changed. A second test puts a directory at <store>.lock and requires the lock to fail within
3 s with the lock path named, under the default 30 s wait bound.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>