Fix Matter fan turn_on writing invalid PercentSetting=255 (#180541)

Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>

homeassistant/components/matter/fan.py

@@ -242,7 +242,7 @@ class MatterFan(MatterEntity, FanEntity):
         # keep track of the last known mode for turn_on commands without preset
         if self._attr_preset_mode is not None:
             self._last_known_preset_mode = self._attr_preset_mode
-        if current_percent:
+        if current_percent and current_percent != 255:
             self._last_known_percentage = current_percent
 
     @callback

tests/components/matter/test_fan.py

@@ -2,6 +2,7 @@
 
 from unittest.mock import MagicMock, call
 
+from chip.clusters import Objects as clusters
 from matter_server.client.models.node import MatterNode
 import pytest
 from syrupy.assertion import SnapshotAssertion
@@ -133,8 +134,10 @@ async def test_fan_turn_on_with_percentage(
         attribute_path="1/514/2",
         value=50,
     )
-    # test again where preset_mode is omitted in the service call
-    # which should select the last active percentage
+    # test again where percentage is omitted in the service call
+    # PercentCurrent is 255 (auto) on this fixture, which is not a valid
+    # value to write back, so it should fall back to the last known preset
+    # mode instead of blindly replaying the sentinel value.
     matter_client.write_attribute.reset_mock()
     await hass.services.async_call(
         FAN_DOMAIN,
@@ -145,8 +148,8 @@ async def test_fan_turn_on_with_percentage(
     assert matter_client.write_attribute.call_count == 1
     assert matter_client.write_attribute.call_args == call(
         node_id=matter_node.node_id,
-        attribute_path="1/514/2",
-        value=255,
+        attribute_path="1/514/0",
+        value=clusters.FanControl.Enums.FanModeEnum.kAuto,
     )