Review round 2 on PR #195: the marker writes had no test, so reverting them to by-path writes, or the refusal to log-only, stayed green. The link is planted from inside the fake model call, between the walk's Lstat and the marker write, for both markers and both an outside and an in-brain relative target; red on all four flips. The marker-entry skip is now checked for .failed too. Also pins cleanRel's acceptance of a backslash as a filename byte in brainfs itself, and stops the buildAndWrite control claiming writes it does not count. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>