Implement the 4-layer data model (device → encrypted backup → shared sync → federated):
- Extract shared encryption-utils from community-store (deriveSpaceKey, AES-256-GCM, rSEN format)
- Encrypt module docs at rest when space has meta.encrypted === true
- Fix relay mode persistence: relay-backup/relay-restore wire protocol + .automerge.enc blob storage
- Add backup store + REST API (PUT/GET/DELETE /api/backup/:space/:docId) with JWT auth
- Add client BackupSyncManager with delta-only push, full restore, auto-backup
- Wire backup stubs in encryptid-bridge to BackupSyncManager
- Add rspace-backups Docker volume
- Create docs/DATA-ARCHITECTURE.md design doc with threat model and data flow diagrams
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
