- RetentionPolicy (last/daily/weekly/monthly) and PruneService: forget
snapshots the policy drops, delete packs nothing uses and repack mostly
unused ones by copying encrypted blobs as-is; new packs are indexed
before old ones are removed
- a location lock keeps prune and backups apart; append-only locations
are never pruned (cleanup via the location's lifecycle rules)
- weekly prune from the background job; occ backup:prune [--dry-run],
backup:retention, backup:target:append-only
- tests: forget+prune frees space and the remaining snapshot restores
identically, repack of mixed packs, dry-run preview, retention buckets
