[ota] Devirtualize OTA backend calls

Each platform defines exactly one OTA backend subclass (marked final),
so using concrete types in unique_ptr eliminates virtual dispatch overhead.

- Move make_ota_backend() declaration from base header to each concrete
  backend header with concrete return type
- Add ota_backend_factory.h convenience header for consumers
- Use concrete unique_ptr types in ota_esphome, http_request, and
  web_server consumers

esphome/components/esphome/ota/ota_esphome.h

@@ -2,7 +2,7 @@
 
 #include "esphome/core/defines.h"
 #ifdef USE_OTA
-#include "esphome/components/ota/ota_backend.h"
+#include "esphome/components/ota/ota_backend_factory.h"
 #include "esphome/components/socket/socket.h"
 #include "esphome/core/helpers.h"
 #include "esphome/core/log.h"
@@ -86,7 +86,17 @@ class ESPHomeOTAComponent final : public ota::OTAComponent {
 
   socket::ListenSocket *server_{nullptr};
   std::unique_ptr<socket::Socket> client_;
-  std::unique_ptr<ota::OTABackend> backend_;
+#ifdef USE_ESP8266
+  std::unique_ptr<ota::ESP8266OTABackend> backend_;
+#elif defined(USE_ESP32)
+  std::unique_ptr<ota::IDFOTABackend> backend_;
+#elif defined(USE_RP2040)
+  std::unique_ptr<ota::ArduinoRP2040OTABackend> backend_;
+#elif defined(USE_LIBRETINY)
+  std::unique_ptr<ota::ArduinoLibreTinyOTABackend> backend_;
+#elif defined(USE_HOST)
+  std::unique_ptr<ota::HostOTABackend> backend_;
+#endif
 
   uint32_t client_connect_time_{0};
   uint16_t port_;

esphome/components/http_request/ota/ota_http_request.cpp

@@ -8,10 +8,6 @@
 
 #include "esphome/components/md5/md5.h"
 #include "esphome/components/watchdog/watchdog.h"
-#include "esphome/components/ota/ota_backend.h"
-#include "esphome/components/ota/ota_backend_esp8266.h"
-#include "esphome/components/ota/ota_backend_arduino_rp2040.h"
-#include "esphome/components/ota/ota_backend_esp_idf.h"
 
 namespace esphome {
 namespace http_request {
@@ -69,7 +65,7 @@ void OtaHttpRequestComponent::flash() {
   }
 }
 
-void OtaHttpRequestComponent::cleanup_(std::unique_ptr<ota::OTABackend> backend,
+void OtaHttpRequestComponent::cleanup_(decltype(ota::make_ota_backend()) backend,
                                        const std::shared_ptr<HttpContainer> &container) {
   if (this->update_started_) {
     ESP_LOGV(TAG, "Aborting OTA backend");

esphome/components/http_request/ota/ota_http_request.h

@@ -1,6 +1,6 @@
 #pragma once
 
-#include "esphome/components/ota/ota_backend.h"
+#include "esphome/components/ota/ota_backend_factory.h"
 #include "esphome/core/component.h"
 #include "esphome/core/defines.h"
 #include "esphome/core/helpers.h"
@@ -39,7 +39,7 @@ class OtaHttpRequestComponent final : public ota::OTAComponent, public Parented<
   void flash();
 
  protected:
-  void cleanup_(std::unique_ptr<ota::OTABackend> backend, const std::shared_ptr<HttpContainer> &container);
+  void cleanup_(decltype(ota::make_ota_backend()) backend, const std::shared_ptr<HttpContainer> &container);
   uint8_t do_ota_();
   std::string get_url_with_auth_(const std::string &url);
   bool http_get_md5_();

esphome/components/ota/ota_backend.h

@@ -130,7 +130,5 @@ OTAGlobalCallback *get_global_ota_callback();
 // - notify_state_deferred_() when in separate task (e.g., web_server OTA)
 // This ensures proper listener execution in all contexts.
 #endif
-std::unique_ptr<ota::OTABackend> make_ota_backend();
-
 }  // namespace ota
 }  // namespace esphome

esphome/components/ota/ota_backend_arduino_libretiny.cpp

@@ -12,7 +12,7 @@ namespace ota {
 
 static const char *const TAG = "ota.arduino_libretiny";
 
-std::unique_ptr<ota::OTABackend> make_ota_backend() { return make_unique<ota::ArduinoLibreTinyOTABackend>(); }
+std::unique_ptr<ArduinoLibreTinyOTABackend> make_ota_backend() { return make_unique<ArduinoLibreTinyOTABackend>(); }
 
 OTAResponseTypes ArduinoLibreTinyOTABackend::begin(size_t image_size) {
   // Handle UPDATE_SIZE_UNKNOWN (0) which is used by web server OTA

esphome/components/ota/ota_backend_arduino_libretiny.h

@@ -20,6 +20,8 @@ class ArduinoLibreTinyOTABackend final : public OTABackend {
   bool md5_set_{false};
 };
 
+std::unique_ptr<ArduinoLibreTinyOTABackend> make_ota_backend();
+
 }  // namespace ota
 }  // namespace esphome
 

esphome/components/ota/ota_backend_arduino_rp2040.cpp

@@ -14,7 +14,7 @@ namespace ota {
 
 static const char *const TAG = "ota.arduino_rp2040";
 
-std::unique_ptr<ota::OTABackend> make_ota_backend() { return make_unique<ota::ArduinoRP2040OTABackend>(); }
+std::unique_ptr<ArduinoRP2040OTABackend> make_ota_backend() { return make_unique<ArduinoRP2040OTABackend>(); }
 
 OTAResponseTypes ArduinoRP2040OTABackend::begin(size_t image_size) {
   // OTA size of 0 is not currently handled, but

esphome/components/ota/ota_backend_arduino_rp2040.h

@@ -22,6 +22,8 @@ class ArduinoRP2040OTABackend final : public OTABackend {
   bool md5_set_{false};
 };
 
+std::unique_ptr<ArduinoRP2040OTABackend> make_ota_backend();
+
 }  // namespace ota
 }  // namespace esphome
 

esphome/components/ota/ota_backend_esp8266.cpp

@@ -48,7 +48,7 @@ namespace esphome::ota {
 
 static const char *const TAG = "ota.esp8266";
 
-std::unique_ptr<ota::OTABackend> make_ota_backend() { return make_unique<ota::ESP8266OTABackend>(); }
+std::unique_ptr<ESP8266OTABackend> make_ota_backend() { return make_unique<ESP8266OTABackend>(); }
 
 OTAResponseTypes ESP8266OTABackend::begin(size_t image_size) {
   // Handle UPDATE_SIZE_UNKNOWN (0) by calculating available space

esphome/components/ota/ota_backend_esp8266.h

@@ -54,5 +54,7 @@ class ESP8266OTABackend final : public OTABackend {
   bool md5_set_{false};
 };
 
+std::unique_ptr<ESP8266OTABackend> make_ota_backend();
+
 }  // namespace esphome::ota
 #endif  // USE_ESP8266

esphome/components/ota/ota_backend_esp_idf.cpp

@@ -11,7 +11,7 @@
 namespace esphome {
 namespace ota {
 
-std::unique_ptr<ota::OTABackend> make_ota_backend() { return make_unique<ota::IDFOTABackend>(); }
+std::unique_ptr<IDFOTABackend> make_ota_backend() { return make_unique<IDFOTABackend>(); }
 
 OTAResponseTypes IDFOTABackend::begin(size_t image_size) {
 #ifdef USE_OTA_ROLLBACK

esphome/components/ota/ota_backend_esp_idf.h

@@ -27,6 +27,8 @@ class IDFOTABackend final : public OTABackend {
   bool md5_set_{false};
 };
 
+std::unique_ptr<IDFOTABackend> make_ota_backend();
+
 }  // namespace ota
 }  // namespace esphome
 #endif  // USE_ESP32

esphome/components/ota/ota_backend_factory.h

@@ -0,0 +1,15 @@
+#pragma once
+
+#include "ota_backend.h"
+
+#ifdef USE_ESP8266
+#include "ota_backend_esp8266.h"
+#elif defined(USE_ESP32)
+#include "ota_backend_esp_idf.h"
+#elif defined(USE_RP2040)
+#include "ota_backend_arduino_rp2040.h"
+#elif defined(USE_LIBRETINY)
+#include "ota_backend_arduino_libretiny.h"
+#elif defined(USE_HOST)
+#include "ota_backend_host.h"
+#endif

esphome/components/ota/ota_backend_host.cpp

@@ -8,7 +8,7 @@ namespace esphome::ota {
 // Stub implementation - OTA is not supported on host platform.
 // All methods return error codes to allow compilation of configs with OTA triggers.
 
-std::unique_ptr<ota::OTABackend> make_ota_backend() { return make_unique<ota::HostOTABackend>(); }
+std::unique_ptr<HostOTABackend> make_ota_backend() { return make_unique<HostOTABackend>(); }
 
 OTAResponseTypes HostOTABackend::begin(size_t image_size) { return OTA_RESPONSE_ERROR_UPDATE_PREPARE; }
 

esphome/components/ota/ota_backend_host.h

@@ -17,5 +17,7 @@ class HostOTABackend final : public OTABackend {
   bool supports_compression() override { return false; }
 };
 
+std::unique_ptr<HostOTABackend> make_ota_backend();
+
 }  // namespace esphome::ota
 #endif

esphome/components/web_server/ota/ota_web_server.cpp

@@ -1,7 +1,7 @@
 #include "ota_web_server.h"
 #ifdef USE_WEBSERVER_OTA
 
-#include "esphome/components/ota/ota_backend.h"
+#include "esphome/components/ota/ota_backend_factory.h"
 #include "esphome/core/application.h"
 #include "esphome/core/log.h"
 
@@ -71,7 +71,7 @@ class OTARequestHandler : public AsyncWebHandler {
   bool ota_success_{false};
 
  private:
-  std::unique_ptr<ota::OTABackend> ota_backend_{nullptr};
+  decltype(ota::make_ota_backend()) ota_backend_{nullptr};
 };
 
 void OTARequestHandler::report_ota_progress_(AsyncWebServerRequest *request) {