# Phase 4: Retention & Cleanup

**Status:** ⬜ Not Started
**Parent plan:** [PLAN.md](./PLAN.md)
**Domain:** backend

## Objective
Implement automatic retention enforcement — prune old backups after each backup
operation and on server startup.

## Tasks

- [ ] Task 1: Add `Prune()` method to backup engine
  - Delete backups exceeding retention count (keep N most recent)
  - Return count of pruned backups
- [ ] Task 2: Call Prune after every CreateBackup (both manual and auto)
- [ ] Task 3: Call Prune on server startup
- [ ] Task 4: Clean up orphaned files (files in backup dir not in metadata)
- [ ] Task 5: Log pruning results

## Files to Modify/Create
- `internal/backup/engine.go` — add Prune method
- `cmd/server/main.go` — call prune on startup

## Acceptance Criteria
- Backups exceeding retention count are automatically deleted
- Both file and metadata are removed during pruning
- Orphaned files (no metadata) are cleaned up
- Pruning runs after each backup and on startup
- Pruning results logged

## Handoff to Next Phase
<!-- Filled in after completion -->