- gRPC sync sends username+password in metadata on every RPC, verified by unary interceptor. No login RPC or token management. - Password stored in Android EncryptedSharedPreferences (Keystore) - Web UI retains bearer token flow for browser sessions - FIDO2/U2F scoped to web UI only, not gRPC sync path Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>