Add integration test for deprecated ClimateTraits compat layer

tests/integration/fixtures/external_components/legacy_climate_component/__init__.py

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+"""Legacy climate component — tests deprecated ClimateTraits setters backward compat."""

tests/integration/fixtures/external_components/legacy_climate_component/climate/__init__.py

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+"""Legacy climate platform that uses deprecated ClimateTraits setters."""
+
+import esphome.codegen as cg
+from esphome.components import climate
+import esphome.config_validation as cv
+
+legacy_climate_ns = cg.esphome_ns.namespace("legacy_climate_test")
+LegacyClimate = legacy_climate_ns.class_("LegacyClimate", climate.Climate, cg.Component)
+
+CONFIG_SCHEMA = climate.climate_schema(LegacyClimate).extend(cv.COMPONENT_SCHEMA)
+
+
+async def to_code(config):
+    var = await climate.new_climate(config)
+    await cg.register_component(var, config)

tests/integration/fixtures/external_components/legacy_climate_component/climate/legacy_climate.h

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+#pragma once
+
+#include "esphome/components/climate/climate.h"
+#include "esphome/core/component.h"
+
+namespace esphome {
+namespace legacy_climate_test {
+
+/// Test climate that uses the DEPRECATED ClimateTraits setters for custom modes.
+/// This validates backward compatibility for external components that haven't migrated.
+class LegacyClimate : public climate::Climate, public Component {
+ public:
+  void setup() override {
+    this->mode = climate::CLIMATE_MODE_OFF;
+    this->target_temperature = 22.0f;
+    this->current_temperature = 20.0f;
+    this->publish_state();
+  }
+
+  float get_setup_priority() const override { return setup_priority::LATE; }
+
+ protected:
+  climate::ClimateTraits traits() override {
+    auto traits = climate::ClimateTraits();
+    traits.add_feature_flags(climate::CLIMATE_SUPPORTS_CURRENT_TEMPERATURE);
+    traits.set_supported_modes({climate::CLIMATE_MODE_OFF, climate::CLIMATE_MODE_HEAT, climate::CLIMATE_MODE_COOL});
+    traits.set_visual_min_temperature(16.0f);
+    traits.set_visual_max_temperature(30.0f);
+    traits.set_visual_temperature_step(0.5f);
+
+    // DEPRECATED API: setting custom modes directly on ClimateTraits.
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
+    traits.set_supported_custom_fan_modes({"Turbo", "Silent", "Auto"});
+    traits.set_supported_custom_presets({"Eco Mode", "Night Mode"});
+#pragma GCC diagnostic pop
+
+    return traits;
+  }
+
+  void control(const climate::ClimateCall &call) override {
+    if (call.get_mode().has_value()) {
+      this->mode = *call.get_mode();
+    }
+    if (call.get_target_temperature().has_value()) {
+      this->target_temperature = *call.get_target_temperature();
+    }
+    if (call.get_custom_fan_mode() != nullptr) {
+      this->set_custom_fan_mode_(call.get_custom_fan_mode());
+    }
+    if (call.get_custom_preset() != nullptr) {
+      this->set_custom_preset_(call.get_custom_preset());
+    }
+    this->publish_state();
+  }
+};
+
+}  // namespace legacy_climate_test
+}  // namespace esphome