A partly deleted empty volume lost its deleting mark when the next sweep
found a surviving copy read-only. Later sweeps then skipped the vid as
under-replicated, so the empty copy kept its slot after it became
deletable again. Only a copy that gained data or was written recently
clears the mark now; a read-only or missing copy just postpones the
cleanup.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>