zapstore/spec/work/WORK-030-amber-session-restore-backup.md

WORK-030 — Amber Session Restore vs Device-Key Backup

Feature: FEAT-006-device-key.md Status: Complete

Tasks

• 1. Skip Amber device-key backup decrypt on session restore
  • Files: lib/main.dart
  • attemptAutoSignIn is not an interactive first sign-in; do not call maybeOfferDeviceBackup when restoring a saved Amber pubkey.
• 2. Amber backup payload uses deviceKey only
  • Files: lib/services/device_backup_service.dart, spec/features/FEAT-006-device-key.md
  • Ignore older privateKeyHex payloads; no dual-read.
• 3. Tests for restore skip and deviceKey payload
  • Files: test/services/device_backup_service_test.dart
• 4. Self-review against INVARIANTS.md

Test Coverage

Scenario	Expected	Status
Interactive Amber sign-in, no backup	Creates backup	[x]
Interactive Amber sign-in, matching backup	No restore prompt	[x]
Interactive Amber sign-in, differing backup	Offers restore	[x]
Session restore (auto sign-in)	No Amber backup decrypt	[x]
Backup JSON uses deviceKey	Round-trips; privateKeyHex ignored	[x]

Decisions

2026-07-25 — Session restore is not interactive sign-in

Context: Opening the app while Amber is remembered ran onSignInSuccess → maybeOfferDeviceBackup → Amber nip44Decrypt of the device-key backup every cold start. Users saw repeated PrivateHexKey decrypt activity in Amber.

Decision: Remove backup checks from onSignInSuccess. Interactive Amber sign-in goes through signInWithAmber, which signs in then awaits maybeOfferDeviceBackup. Session restore uses attemptAutoSignIn only.

Rationale: A flag around auto-restore raced with Riverpod listener delivery (emulator showed [I/backup] Amber backup already matches… on cold start). Explicit call sites avoid that race without artificial delays.

2026-07-25 — Backup field renamed to deviceKey

Context: Payload previously used privateKeyHex, which amplified scary Amber Activity wording around decrypting a private key.

Decision: Encrypt/decrypt JSON {"deviceKey": "<64 hex>"} only. Do not accept legacy privateKeyHex backups.

Rationale: Directed product change. Users with only an old-format backup can paste nsec or create a new backup after interactive sign-in.

Spec Issues

None — FEAT-006 updated for deviceKey per product direction.

Progress Notes

2026-07-25: Implemented restore skip + deviceKey payload. 2026-07-25: Emulator showed flag-based skip still decrypted on cold start; switched to interactive-only signInWithAmber.