Foundation lib for v1.12.0 cron rewrite skill-tree backup/restore.
Zero dependencies. Uses fs.cpSync (recursive + preserveTimestamps) without
dereference (Node 22.17.x regression) and without filter (Windows symlink-
type bug).
- backupDir(srcDir, backupRoot, opts) → {backupPath, retentionDays, restore()}
- Backup-id format YYYY-MM-DDTHH-MM-SS (filesystem-safe; no colons)
- .backup-meta.json sentinel written as first action inside backupPath
- restore() writes .rollback-in-progress at backupRoot BEFORE rmSync+cpSync
so a crashed restore leaves the sentinel for the next run to detect
- detectStaleRollback(backupRoot) — boolean predicate over sentinel
- cleanupOldBackups(backupRoot, retentionDays) — 3-step age resolution:
meta.created_at → dir mtime → skip-with-warning (never delete a dir
whose age cannot be established)
12/12 tests pass: timestamp format, content round-trip, sentinel lifecycle,
retention, mtime fallback, unparseable-meta skip, missing-root no-op.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
