[api] Use StringRef for HomeassistantServiceMap.value to eliminate heap allocations

esphome/components/api/api.proto

@@ -763,7 +763,7 @@ message SubscribeHomeassistantServicesRequest {
 
 message HomeassistantServiceMap {
   string key = 1;
-  string value = 2 [(no_zero_copy) = true];
+  string value = 2;
 }
 
 message HomeassistantActionRequest {
@@ -779,7 +779,7 @@ message HomeassistantActionRequest {
   bool is_event = 5;
   uint32 call_id = 6 [(field_ifdef) = "USE_API_HOMEASSISTANT_ACTION_RESPONSES"];
   bool wants_response = 7 [(field_ifdef) = "USE_API_HOMEASSISTANT_ACTION_RESPONSES_JSON"];
-  string response_template = 8 [(no_zero_copy) = true, (field_ifdef) = "USE_API_HOMEASSISTANT_ACTION_RESPONSES_JSON"];
+  string response_template = 8 [(field_ifdef) = "USE_API_HOMEASSISTANT_ACTION_RESPONSES_JSON"];
 }
 
 // Message sent by Home Assistant to ESPHome with service call response data

esphome/components/api/api_pb2.h

@@ -1053,7 +1053,7 @@ class SubscribeHomeassistantServicesRequest final : public ProtoMessage {
 class HomeassistantServiceMap final : public ProtoMessage {
  public:
   StringRef key{};
-  std::string value{};
+  StringRef value{};
   void encode(ProtoWriteBuffer buffer) const override;
   void calculate_size(ProtoSize &size) const override;
 #ifdef HAS_PROTO_MESSAGE_DUMP
@@ -1081,7 +1081,7 @@ class HomeassistantActionRequest final : public ProtoMessage {
   bool wants_response{false};
 #endif
 #ifdef USE_API_HOMEASSISTANT_ACTION_RESPONSES_JSON
-  std::string response_template{};
+  StringRef response_template{};
 #endif
   void encode(ProtoWriteBuffer buffer) const override;
   void calculate_size(ProtoSize &size) const override;

esphome/components/api/custom_api_device.h

@@ -265,7 +265,7 @@ class CustomAPIDevice {
     for (auto &it : data) {
       auto &kv = resp.data.emplace_back();
       kv.key = StringRef(it.first);
-      kv.value = it.second;  // value is std::string (no_zero_copy), assign directly
+      kv.value = StringRef(it.second);  // data map lives until send completes
     }
     global_api_server->send_homeassistant_action(resp);
   }
@@ -308,7 +308,7 @@ class CustomAPIDevice {
     for (auto &it : data) {
       auto &kv = resp.data.emplace_back();
       kv.key = StringRef(it.first);
-      kv.value = it.second;  // value is std::string (no_zero_copy), assign directly
+      kv.value = StringRef(it.second);  // data map lives until send completes
     }
     global_api_server->send_homeassistant_action(resp);
   }

esphome/components/api/homeassistant_service.h

@@ -149,11 +149,21 @@ template<typename... Ts> class HomeAssistantServiceCallAction : public Action<Ts
     std::string service_value = this->service_.value(x...);
     resp.service = StringRef(service_value);
     resp.is_event = this->flags_.is_event;
-    this->populate_service_map(resp.data, this->data_, x...);
-    this->populate_service_map(resp.data_template, this->data_template_, x...);
-    this->populate_service_map(resp.variables, this->variables_, x...);
+
+    // Local storage for lambda-evaluated strings - lives until after send
+    FixedVector<std::string> data_storage;
+    FixedVector<std::string> data_template_storage;
+    FixedVector<std::string> variables_storage;
+
+    this->populate_service_map(resp.data, this->data_, data_storage, x...);
+    this->populate_service_map(resp.data_template, this->data_template_, data_template_storage, x...);
+    this->populate_service_map(resp.variables, this->variables_, variables_storage, x...);
 
 #ifdef USE_API_HOMEASSISTANT_ACTION_RESPONSES
+#ifdef USE_API_HOMEASSISTANT_ACTION_RESPONSES_JSON
+    // IMPORTANT: Declare at outer scope so it lives until send_homeassistant_action returns.
+    std::string response_template_value;
+#endif
     if (this->flags_.wants_status) {
       // Generate a unique call ID for this service call
       static uint32_t call_id_counter = 1;
@@ -164,8 +174,7 @@ template<typename... Ts> class HomeAssistantServiceCallAction : public Action<Ts
         resp.wants_response = true;
         // Set response template if provided
         if (this->flags_.has_response_template) {
-          std::string response_template_value = this->response_template_.value(x...);
-          resp.response_template = response_template_value;
+          resp.response_template = StringRef(response_template_value = this->response_template_.value(x...));
         }
       }
 #endif
@@ -205,12 +214,23 @@ template<typename... Ts> class HomeAssistantServiceCallAction : public Action<Ts
   }
 
   template<typename VectorType, typename SourceType>
-  static void populate_service_map(VectorType &dest, SourceType &source, Ts... x) {
+  static void populate_service_map(VectorType &dest, SourceType &source, FixedVector<std::string> &value_storage,
+                                   Ts... x) {
     dest.init(source.size());
+    value_storage.init(source.size());  // Max possible, single allocation
+
     for (auto &it : source) {
       auto &kv = dest.emplace_back();
       kv.key = StringRef(it.key);
-      kv.value = it.value.value(x...);
+
+      if (it.value.is_static_string()) {
+        // Static string from YAML - zero allocation
+        kv.value = StringRef(it.value.get_static_string());
+      } else {
+        // Lambda evaluation - store result, reference it
+        value_storage.push_back(it.value.value(x...));
+        kv.value = StringRef(value_storage.back());
+      }
     }
   }
 

esphome/components/homeassistant/number/homeassistant_number.cpp

@@ -91,11 +91,14 @@ void HomeassistantNumber::control(float value) {
   resp.data.init(2);
   auto &entity_id = resp.data.emplace_back();
   entity_id.key = ENTITY_ID_KEY;
-  entity_id.value = this->entity_id_;
+  entity_id.value = StringRef(this->entity_id_);
 
   auto &entity_value = resp.data.emplace_back();
   entity_value.key = VALUE_KEY;
-  entity_value.value = to_string(value);
+  // Stack buffer - no heap allocation; %g produces shortest representation
+  char value_buf[16];
+  snprintf(value_buf, sizeof(value_buf), "%g", value);
+  entity_value.value = StringRef(value_buf);
 
   api::global_api_server->send_homeassistant_action(resp);
 }

esphome/components/homeassistant/switch/homeassistant_switch.cpp

@@ -55,7 +55,7 @@ void HomeassistantSwitch::write_state(bool state) {
   resp.data.init(1);
   auto &entity_id_kv = resp.data.emplace_back();
   entity_id_kv.key = ENTITY_ID_KEY;
-  entity_id_kv.value = this->entity_id_;
+  entity_id_kv.value = StringRef(this->entity_id_);
 
   api::global_api_server->send_homeassistant_action(resp);
 }

esphome/core/automation.h

@@ -159,6 +159,12 @@ template<typename T, typename... X> class TemplatableValue {
     return this->value(x...);
   }
 
+  /// Check if this holds a static string (const char* stored without allocation)
+  bool is_static_string() const { return this->type_ == STATIC_STRING; }
+
+  /// Get the static string pointer (only valid if is_static_string() returns true)
+  const char *get_static_string() const { return this->static_str_; }
+
  protected:
   enum : uint8_t {
     NONE,