# Device Status LWT MAC Resolution Design

## Goal

When a device publishes its MQTT last-will status on `/MAC/publish/status`, resolve the MAC address to the stored `deviceNo` before updating device status.

## Design

- Keep `DeviceStatusHandler` responsible for parsing status payloads and invoking status updates.
- Reuse `DeviceIdentityResolver` to translate the Topic identity into an `AppDevice` and then its `deviceNo`.
- The resolver first supports an existing `deviceNo` Topic and falls back to a case-insensitive `mac_address` lookup. This preserves compatibility while handling LWT Topics that contain a MAC address.
- If no device matches the Topic identity, do not update any record; keep the existing warning log.
- Update the handler documentation to state that the Topic identity may be either a device number or a MAC address.

## Verification

Add a focused unit test using the real `DeviceIdentityResolver` with a mocked `AppDeviceMapper`. The test publishes an offline status with a MAC identity and verifies that:

1. The mapper looks up the MAC address.
2. `MqttDeviceStatusService.markOffline` receives the resolved `deviceNo`.
3. No status update uses the MAC address as a device number.

## Scope

This change only covers `/MAC/publish/status`. Other MQTT communication continues to use `deviceNo` according to the existing protocol.
