brain_edit did its own I/O by path around notes.Edit: - the pre-edit snapshot used os.ReadFile, which hung on a FIFO note held open by a writer; - the rollback (when the provenance stamp fails) used os.WriteFile; - the edit lock "<note>.lock" was opened with O_CREATE by path, so a planted dangling .lock symlink made a successful edit create a file at the link's target, in the brain or outside it. Snapshot is brainfs ReadRegular, rollback WriteRegular, and the lock is opened and removed through new brainfs OpenLock/RemoveLock: clean path, real parent directories, an existing lock must be regular, and the opened handle must be the file at the path (SameFile). Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>