Fix thermostat fan modes to respect fanModeSequence

[vmvarga]

Summary

• Fix the Thermostat entity to read the fan_mode_sequence attribute from the ZCL Fan Control cluster (0x0202) instead of hardcoding fan modes to [auto, on]. Devices now correctly expose Low, Medium, High, and Auto fan speeds based on the ZCL spec (Table 6-20).
• Fix the fan_mode getter to read the actual fan_mode attribute from the Fan Control cluster handler instead of guessing from the thermostat's running_state bitmap.
• Fix async_set_fan_mode to map all supported fan mode strings (low, medium, high, on, auto) to their corresponding FanMode ZCL enum values.
• Expose HVACMode.FAN_ONLY as an available HVAC mode when a Fan Control cluster is present on the endpoint, since SEQ_OF_OPERATION (derived from controlSequenceOfOperation) never includes it per ZCL spec.

Problem

The Thermostat entity hardcodes fan modes to [auto, on] and completely ignores the fan_mode_sequence attribute (attribute 0x0001) from the Fan Control cluster. Per ZCL 8 (Table 6-20), FanModeSequenceType defines which fan modes a device supports:

Value	Available Modes
0x00	Low, Medium, High
0x01	Low, High
0x02	Low, Medium, High, Auto
0x03	Low, High, Auto
0x04	On, Auto

Devices reporting e.g. fan_mode_sequence = 0x02 (Low/Medium/High/Auto) were stuck with only Auto/On in the UI.

Additionally, the thermostat never exposes HVACMode.FAN_ONLY even when the device supports SystemMode.Fan_only (0x07). The mappings HVAC_MODE_2_SYSTEM and SYSTEM_MODE_2_HVAC already handle FAN_ONLY <-> Fan_only, but hvac_modes derives its list solely from SEQ_OF_OPERATION which never includes it, since controlSequenceOfOperation only covers cooling/heating per the ZCL spec.

Changes

zha/application/platforms/climate/const.py

• Import FanMode from zigpy
• Add SEQ_FAN_MODES dict mapping fan_mode_sequence values (0x00–0x04) to fan mode string lists
• Add FAN_MODE_TO_ZCL dict mapping fan mode strings to FanMode enum values
• Add ZCL_TO_FAN_MODE reverse mapping dict

zha/application/platforms/climate/__init__.py

• fan_modes: Read fan_mode_sequence from the fan cluster handler, look up modes via SEQ_FAN_MODES, fall back to [on, auto] for unknown sequences
• fan_mode: Read actual fan_mode attribute from the fan cluster handler, map back via ZCL_TO_FAN_MODE, fall back to running_state heuristic when unavailable
• async_set_fan_mode: Use FAN_MODE_TO_ZCL mapping instead of hardcoded On/Auto branch
• hvac_modes: Append HVACMode.FAN_ONLY when a fan cluster handler is present

Backwards compatibility

• Devices with fan_mode_sequence = 0x04 still get [on, auto] (unchanged)
• Devices without a Fan Control cluster are completely unaffected
• Unknown fan_mode_sequence values fall back to [on, auto]
• No changes to HVAC_MODE_2_SYSTEM, SYSTEM_MODE_2_HVAC, or async_set_hvac_mode

Test plan

• Device with fan_mode_sequence = 0x02 exposes: Low, Medium, High, Auto
• Device with fan_mode_sequence = 0x04 (or unknown) exposes: On, Auto (backwards compatible)
• Setting fan mode to "low" sends FanMode.Low (0x01) to the device
• Setting fan mode to "high" sends FanMode.High (0x03) to the device
• Current fan mode reflects the actual fan_mode attribute from the Fan Control cluster
• Thermostat with a Fan Control cluster exposes "Fan only" as an HVAC mode
• Selecting "Fan only" writes SystemMode.Fan_only (0x07) to the thermostat
• Thermostat without a Fan Control cluster is unaffected

Affected devices

Any thermostat with a Fan Control cluster (0x0202) that reports fan_mode_sequence != 0x04, such as Tuya HVAC thermostats with cooling/heating/fan modes (e.g. _TZE204_mpbki2zm).

[puddly]

To regenerate device diagnostics files (to see what this change would affect in real devices), run the following:

python -m tools.regenerate_diagnostics

It looks like four devices (in the testing DB) change their exposed fan modes.

[codecov]

Codecov Report

❌ Patch coverage is 89.47368% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.50%. Comparing base (c51efa5) to head (75510aa).
⚠️ Report is 2 commits behind head on dev.

Files with missing lines	Patch %	Lines
zha/application/platforms/climate/__init__.py	86.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #708      +/-   ##
==========================================
- Coverage   97.51%   97.50%   -0.01%     
==========================================
  Files          62       62              
  Lines       10946    10960      +14     
==========================================
+ Hits        10674    10687      +13     
- Misses        272      273       +1     

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[vmvarga]

Should resolve #226