RoomIdentity.derive() in TetherKit: ubiquityIdentityToken (iCloud account, portable across devices) → IOKit/identifierForVendor (hardware, device-tied) → Keychain UUID (last resort). No user config needed. Both apps auto-connect on relaunch if server URL was previously saved. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>