os.path.ismount() compares st_dev against the parent dir, which silently
returns False for same-fs bind mounts. The idmap binds at runtime/<n>/
idmap/<basename> are exactly that case, so:
- cmd_umount skipped the bind-umount step every stop, leaving orphan
binds in PID 1's mount namespace.
- cmd_mount's idempotency check then "didn't see" the orphan and
re-bound on top, accumulating one mount per start/stop cycle.
Findmnt nesting like
/var/lib/left4me/runtime/2/idmap/overlays_9
└─/var/lib/left4me/runtime/2/idmap/overlays_9
is the visible symptom. Reboot wipes everything so the bug is invisible
on a fresh boot — only stop/start cycles accumulate.
Replace both ismount sites with a _is_mountpoint() helper that reads
/proc/self/mountinfo (column 5 is the mount point). Keep os.path.ismount
for the overlay merged check, where it's reliable (distinct fs type).
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
dd918aca4b