snapshot create --prune purged the older snapshots holding a volume's
files when the volume, mounted below a configured path, was not
mounted: its empty mount point read as deleted files.
The scan now records in the local index each directory at or below a
configured path that holds an entry and is on a different device from
its parent directory, looked up once the walk has listed it, as listing
mounts an automounted volume. Under --prune, when an earlier snapshot
of that name recorded such a directory and this run does not, the run
skips the prune, keeps every older snapshot and exits non-zero, naming
the directory. For a volume retired on purpose, snapshot purge removes
the older snapshots.
Model: opus-5-5
