feat: implement status monitoring, fault detection, and comms watchdog

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Readme.md

@@ -11,7 +11,7 @@ This project implements a bridge between Zigbee (Home Assistant) and UART-based
 - UART communication at 9600 baud 8N1 for MideaUART protocol
 - Zigbee ZCL Thermostat cluster implementation
 - Bidirectional communication between Zigbee and UART layers
-- Status monitoring and error handling
+- Status monitoring with periodic AC polling, fault detection, and a communication watchdog
 - Configurable timing controls (50ms command spacing)
 
 ## Directory Structure
@@ -22,6 +22,7 @@ src/
   midea_protocol.c/h   - MideaUART protocol encoding/decoding
   zigbee_zcl.c/h       - Zigbee ZCL Thermostat cluster
   integration_layer.c/h- Integration between Zigbee and UART layers
+  status_monitor.c/h   - AC status polling, fault detection, and comms watchdog
   main.c               - Application entry point
 
 test/
@@ -29,6 +30,7 @@ test/
   midea_protocol_test.c       - Unit tests for MideaUART protocol
   zigbee_zcl_test.c           - Unit tests for Zigbee ZCL
   integration_layer_test.c    - Unit tests for integration layer
+  status_monitor_test.c       - Unit tests for status monitoring
 
 docs/
   protocol.md                 - MideaUART protocol details
@@ -62,6 +64,23 @@ make upload
 make test
 ```
 
+## Status Monitoring
+
+The `status_monitor` module (see `src/status_monitor.c/h`) provides:
+
+- Periodic AC status polling: sends a MideaUART status-request frame over the UART
+  driver, receives the response, and decodes it into a `midea_status_t`.
+- ZCL mapping: decoded status is mapped to ZCL Thermostat attributes
+  (`local_temperature`, `system_mode`) for Home Assistant reporting.
+- Fault detection: any non-zero `error_code` or `alarm_mask` from the AC raises a
+  fault flag (`status_monitor_has_fault`) and records the fault code.
+- Communication watchdog: tracks the time of the last successful poll and trips a
+  timeout when the poll interval (plus per-attempt timeout) is exceeded or when
+  `max_retries` consecutive attempts fail.
+
+Configuration (`status_monitor_config_t`) exposes `poll_interval_ms` (default
+5000ms), `timeout_ms` (default 1000ms), and `max_retries` (default 3).
+
 ## Implementation Progress
 
 See `docs/plans/2026-07-05-ballu-ac-esp32c6-controller-implementation.md` for detailed implementation plan and progress tracking.