lockBackupDirectory now passes proper-lockfile an onCompromised that records
why the lock was lost, where the default threw from a timer and ended the
process. The backup checks its lock before each original and before it
writes failures.json, and fails with "lost the lock on DIR: REASON", which
quak backup prints through run as one line before exiting 1. Releasing a
lost lock leaves backup.lock alone, as it may be another backup's. The lock
of each directory is kept by path so that a backup run with lockHeld, as
quak backup runs it, finds the lock its caller took.
Model: opus-5-5
sneak
1b1bcc1f3e