feat(identity): recover desktop identity from a signed-in phone

[tellaho]

Category: new-feature
User Impact: People who lose a desktop identity can securely restore it from a signed-in Buzz phone or an encrypted backup without creating a replacement identity.

Problem: A fresh or identity-lost desktop could not recover its existing full Buzz identity from an already-authorized phone, and the backup recovery path obscured the available choices. Solution: Add a SAS-confirmed reverse NIP-AB transfer, durable desktop import, a dedicated mobile recovery entry point, and clearer desktop recovery dialogs with tested loading, drag-and-drop, and failure states.

File changes

crates/buzz-core/src/pairing/session.rs
Adds the reverse encrypted payload and source-completion state transitions used for phone-to-desktop recovery.

desktop/src-tauri/src/commands/identity.rs
Exposes the existing guarded identity commit path for recovery imports.

desktop/src-tauri/src/commands/pairing.rs
Adds recovery-mode pairing, durable nsec import, start serialization, stale-task protection, and explicit rejection of unsupported recovery payloads.

desktop/src-tauri/src/lib.rs
Registers the recovery pairing command.

desktop/src/app/App.tsx
Refreshes the recovered identity before continuing onboarding.

desktop/src/features/onboarding/machineOnboarding.ts
Adds recovery transitions to the onboarding state machine.

desktop/src/features/onboarding/ui/BackupPasswordTimeline.tsx
Adds the visual backup-to-password-to-unlock progression.

desktop/src/features/onboarding/ui/IdentityRecoveryPairing.tsx
Implements QR generation, copy fallback, SAS confirmation, cancellation, expiry, and completion UI.

desktop/src/features/onboarding/ui/MachineOnboardingFlow.tsx
Connects private-key, phone, and backup recovery paths to the onboarding flow.

desktop/src/features/onboarding/ui/NostrKeyImportForm.tsx
Polishes recovery dialogs, backup drag-and-drop, loading stability, and security copy.

desktop/src/shared/api/tauri.ts
Keeps the existing pairing API surface focused on standard desktop-to-mobile pairing.

desktop/src/shared/api/tauriPairing.ts
Adds the recovery pairing invoke without growing the ratcheted shared API file.

desktop/src/testing/e2eBridge.ts
Mocks recovery pairing commands and lifecycle events for browser tests.

desktop/tests/e2e/identity-lost.spec.ts
Covers lost-identity entry, QR/copy recovery, SAS, cancellation, expiry, success, errors, backup import, drag-and-drop, and screenshots.

desktop/tests/e2e/onboarding.spec.ts
Verifies recovered identities continue through harness setup without replacement-key side effects.

mobile/lib/features/pairing/pairing_page.dart
Adds recovery-only scanning and explicit identity-handoff warnings.

mobile/lib/features/pairing/pairing_provider.dart
Recognizes recovery codes, returns the signed-in nsec after mutual SAS approval, and waits for desktop completion.

mobile/lib/features/settings/settings_page.dart
Accepts the recovery route builder at the app composition boundary to preserve feature isolation.

mobile/lib/features/settings/settings_page/connection_section.dart
Adds the signed-in “Send identity to desktop” settings action.

mobile/test/features/pairing/pairing_page_test.dart
Covers recovery-only validation and handoff messaging.

mobile/test/features/pairing/pairing_provider_test.dart
Covers reverse payload encryption, confirmation ordering, success, failure, timeout, and cleanup.

Reproduction steps

1. Launch Buzz Desktop with identity-lost state and choose Recover from your phone.
2. Confirm the QR and persistent Copy pairing code fallback appear without layout shift.
3. On a signed-in phone, open Settings → Send identity to desktop, scan or paste the recovery code, and compare the six-digit SAS on both devices.
4. Confirm on both sides and verify Desktop restores the identity and continues to harness setup.
5. Repeat from identity-lost state with Recover from a backup file; verify picker and drag-and-drop both advance to password entry and restore the encrypted backup.
6. Exercise cancellation, mismatched/unsupported codes, expired sessions, and an invalid backup; verify each returns actionable, non-stuck UI.

Screenshots

Private-key and backup recovery entry

Phone recovery QR and copy-code fallback

Verification

• cargo test -p buzz-core pairing — 71 passed
• just mobile-test — 1,169 passed
• pnpm build:e2e && pnpm exec playwright test identity-lost.spec.ts --project=smoke — 15 passed
• Full pre-push gates — desktop checks, desktop unit tests, Rust tests, Tauri checks, and mobile tests passed