Merge pull request #9596 from esphome/bump-2025.7.1

2025.7.1

Doxyfile

@@ -48,7 +48,7 @@ PROJECT_NAME           = ESPHome
 # could be handy for archiving the generated documentation or if some version
 # control system is used.
 
-PROJECT_NUMBER         = 2025.7.0
+PROJECT_NUMBER         = 2025.7.1
 
 # Using the PROJECT_BRIEF tag one can provide an optional one line description
 # for a project that appears at the top of each page and should give viewer a

esphome/components/api/homeassistant_service.h

@@ -11,6 +11,15 @@ namespace esphome {
 namespace api {
 
 template<typename... X> class TemplatableStringValue : public TemplatableValue<std::string, X...> {
+ private:
+  // Helper to convert value to string - handles the case where value is already a string
+  template<typename T> static std::string value_to_string(T &&val) { return to_string(std::forward<T>(val)); }
+
+  // Overloads for string types - needed because std::to_string doesn't support them
+  static std::string value_to_string(const char *val) { return std::string(val); }  // For lambdas returning .c_str()
+  static std::string value_to_string(const std::string &val) { return val; }
+  static std::string value_to_string(std::string &&val) { return std::move(val); }
+
  public:
   TemplatableStringValue() : TemplatableValue<std::string, X...>() {}
 
@@ -19,7 +28,7 @@ template<typename... X> class TemplatableStringValue : public TemplatableValue<s
 
   template<typename F, enable_if_t<is_invocable<F, X...>::value, int> = 0>
   TemplatableStringValue(F f)
-      : TemplatableValue<std::string, X...>([f](X... x) -> std::string { return to_string(f(x...)); }) {}
+      : TemplatableValue<std::string, X...>([f](X... x) -> std::string { return value_to_string(f(x...)); }) {}
 };
 
 template<typename... Ts> class TemplatableKeyValuePair {

esphome/components/e131/e131_packet.cpp

@@ -4,6 +4,7 @@
 #include "esphome/components/network/ip_address.h"
 #include "esphome/core/log.h"
 #include "esphome/core/util.h"
+#include "esphome/core/helpers.h"
 
 #include <lwip/igmp.h>
 #include <lwip/init.h>
@@ -71,7 +72,11 @@ bool E131Component::join_igmp_groups_() {
     ip4_addr_t multicast_addr =
         network::IPAddress(239, 255, ((universe.first >> 8) & 0xff), ((universe.first >> 0) & 0xff));
 
-    auto err = igmp_joingroup(IP4_ADDR_ANY4, &multicast_addr);
+    err_t err;
+    {
+      LwIPLock lock;
+      err = igmp_joingroup(IP4_ADDR_ANY4, &multicast_addr);
+    }
 
     if (err) {
       ESP_LOGW(TAG, "IGMP join for %d universe of E1.31 failed. Multicast might not work.", universe.first);
@@ -104,6 +109,7 @@ void E131Component::leave_(int universe) {
   if (listen_method_ == E131_MULTICAST) {
     ip4_addr_t multicast_addr = network::IPAddress(239, 255, ((universe >> 8) & 0xff), ((universe >> 0) & 0xff));
 
+    LwIPLock lock;
     igmp_leavegroup(IP4_ADDR_ANY4, &multicast_addr);
   }
 

esphome/components/esp32/helpers.cpp

@@ -1,4 +1,5 @@
 #include "esphome/core/helpers.h"
+#include "esphome/core/defines.h"
 
 #ifdef USE_ESP32
 
@@ -30,6 +31,45 @@ void Mutex::unlock() { xSemaphoreGive(this->handle_); }
 IRAM_ATTR InterruptLock::InterruptLock() { portDISABLE_INTERRUPTS(); }
 IRAM_ATTR InterruptLock::~InterruptLock() { portENABLE_INTERRUPTS(); }
 
+#ifdef CONFIG_LWIP_TCPIP_CORE_LOCKING
+#include "lwip/priv/tcpip_priv.h"
+#endif
+
+LwIPLock::LwIPLock() {
+#ifdef CONFIG_LWIP_TCPIP_CORE_LOCKING
+  // When CONFIG_LWIP_TCPIP_CORE_LOCKING is enabled, lwIP uses a global mutex to protect
+  // its internal state. Any thread can take this lock to safely access lwIP APIs.
+  //
+  // sys_thread_tcpip(LWIP_CORE_LOCK_QUERY_HOLDER) returns true if the current thread
+  // already holds the lwIP core lock. This prevents recursive locking attempts and
+  // allows nested LwIPLock instances to work correctly.
+  //
+  // If we don't already hold the lock, acquire it. This will block until the lock
+  // is available if another thread currently holds it.
+  if (!sys_thread_tcpip(LWIP_CORE_LOCK_QUERY_HOLDER)) {
+    LOCK_TCPIP_CORE();
+  }
+#endif
+}
+
+LwIPLock::~LwIPLock() {
+#ifdef CONFIG_LWIP_TCPIP_CORE_LOCKING
+  // Only release the lwIP core lock if this thread currently holds it.
+  //
+  // sys_thread_tcpip(LWIP_CORE_LOCK_QUERY_HOLDER) queries lwIP's internal lock
+  // ownership tracking. It returns true only if the current thread is registered
+  // as the lock holder.
+  //
+  // This check is essential because:
+  // 1. We may not have acquired the lock in the constructor (if we already held it)
+  // 2. The lock might have been released by other means between constructor and destructor
+  // 3. Calling UNLOCK_TCPIP_CORE() without holding the lock causes undefined behavior
+  if (sys_thread_tcpip(LWIP_CORE_LOCK_QUERY_HOLDER)) {
+    UNLOCK_TCPIP_CORE();
+  }
+#endif
+}
+
 void get_mac_address_raw(uint8_t *mac) {  // NOLINT(readability-non-const-parameter)
 #if defined(CONFIG_SOC_IEEE802154_SUPPORTED)
   // When CONFIG_SOC_IEEE802154_SUPPORTED is defined, esp_efuse_mac_get_default

esphome/components/esp8266/helpers.cpp

@@ -22,6 +22,10 @@ void Mutex::unlock() {}
 IRAM_ATTR InterruptLock::InterruptLock() { state_ = xt_rsil(15); }
 IRAM_ATTR InterruptLock::~InterruptLock() { xt_wsr_ps(state_); }
 
+// ESP8266 doesn't support lwIP core locking, so this is a no-op
+LwIPLock::LwIPLock() {}
+LwIPLock::~LwIPLock() {}
+
 void get_mac_address_raw(uint8_t *mac) {  // NOLINT(readability-non-const-parameter)
   wifi_get_macaddr(STATION_IF, mac);
 }

esphome/components/ethernet/ethernet_component.cpp

@@ -420,6 +420,7 @@ network::IPAddresses EthernetComponent::get_ip_addresses() {
 }
 
 network::IPAddress EthernetComponent::get_dns_address(uint8_t num) {
+  LwIPLock lock;
   const ip_addr_t *dns_ip = dns_getserver(num);
   return dns_ip;
 }
@@ -527,6 +528,7 @@ void EthernetComponent::start_connect_() {
   ESPHL_ERROR_CHECK(err, "DHCPC set IP info error");
 
   if (this->manual_ip_.has_value()) {
+    LwIPLock lock;
     if (this->manual_ip_->dns1.is_set()) {
       ip_addr_t d;
       d = this->manual_ip_->dns1;
@@ -559,8 +561,13 @@ bool EthernetComponent::is_connected() { return this->state_ == EthernetComponen
 void EthernetComponent::dump_connect_params_() {
   esp_netif_ip_info_t ip;
   esp_netif_get_ip_info(this->eth_netif_, &ip);
-  const ip_addr_t *dns_ip1 = dns_getserver(0);
+  const ip_addr_t *dns_ip1;
-  const ip_addr_t *dns_ip2 = dns_getserver(1);
+  const ip_addr_t *dns_ip2;
+  {
+    LwIPLock lock;
+    dns_ip1 = dns_getserver(0);
+    dns_ip2 = dns_getserver(1);
+  }
 
   ESP_LOGCONFIG(TAG,
                 "  IP Address: %s\n"

esphome/components/libretiny/helpers.cpp

@@ -26,6 +26,10 @@ void Mutex::unlock() { xSemaphoreGive(this->handle_); }
 IRAM_ATTR InterruptLock::InterruptLock() { portDISABLE_INTERRUPTS(); }
 IRAM_ATTR InterruptLock::~InterruptLock() { portENABLE_INTERRUPTS(); }
 
+// LibreTiny doesn't support lwIP core locking, so this is a no-op
+LwIPLock::LwIPLock() {}
+LwIPLock::~LwIPLock() {}
+
 void get_mac_address_raw(uint8_t *mac) {  // NOLINT(readability-non-const-parameter)
   WiFi.macAddress(mac);
 }

esphome/components/lvgl/widgets/meter.py

@@ -264,7 +264,7 @@ class MeterType(WidgetType):
                                 color_start,
                                 color_end,
                                 v[CONF_LOCAL],
-                                size.process(v[CONF_WIDTH]),
+                                await size.process(v[CONF_WIDTH]),
                             ),
                         )
                     if t == CONF_IMAGE:

esphome/components/mqtt/mqtt_client.cpp

@@ -193,13 +193,17 @@ void MQTTClientComponent::start_dnslookup_() {
   this->dns_resolve_error_ = false;
   this->dns_resolved_ = false;
   ip_addr_t addr;
+  err_t err;
+  {
+    LwIPLock lock;
 #if USE_NETWORK_IPV6
-  err_t err = dns_gethostbyname_addrtype(this->credentials_.address.c_str(), &addr,
+    err = dns_gethostbyname_addrtype(this->credentials_.address.c_str(), &addr, MQTTClientComponent::dns_found_callback,
-                                         MQTTClientComponent::dns_found_callback, this, LWIP_DNS_ADDRTYPE_IPV6_IPV4);
+                                     this, LWIP_DNS_ADDRTYPE_IPV6_IPV4);
 #else
-  err_t err = dns_gethostbyname_addrtype(this->credentials_.address.c_str(), &addr,
+    err = dns_gethostbyname_addrtype(this->credentials_.address.c_str(), &addr, MQTTClientComponent::dns_found_callback,
-                                         MQTTClientComponent::dns_found_callback, this, LWIP_DNS_ADDRTYPE_IPV4);
+                                     this, LWIP_DNS_ADDRTYPE_IPV4);
 #endif /* USE_NETWORK_IPV6 */
+  }
   switch (err) {
     case ERR_OK: {
       // Got IP immediately

esphome/components/rp2040/helpers.cpp

@@ -44,6 +44,10 @@ void Mutex::unlock() {}
 IRAM_ATTR InterruptLock::InterruptLock() { state_ = save_and_disable_interrupts(); }
 IRAM_ATTR InterruptLock::~InterruptLock() { restore_interrupts(state_); }
 
+// RP2040 doesn't support lwIP core locking, so this is a no-op
+LwIPLock::LwIPLock() {}
+LwIPLock::~LwIPLock() {}
+
 void get_mac_address_raw(uint8_t *mac) {  // NOLINT(readability-non-const-parameter)
 #ifdef USE_WIFI
   WiFi.macAddress(mac);

esphome/components/web_server/__init__.py

@@ -74,13 +74,14 @@ def validate_local(config: ConfigType) -> ConfigType:
     return config
 
 
-def validate_ota_removed(config: ConfigType) -> ConfigType:
+def validate_ota(config: ConfigType) -> ConfigType:
-    # Only raise error if OTA is explicitly enabled (True)
+    # The OTA option only accepts False to explicitly disable OTA for web_server
-    # If it's False or not specified, we can safely ignore it
+    # IMPORTANT: Setting ota: false ONLY affects the web_server component
-    if config.get(CONF_OTA):
+    # The captive_portal component will still be able to perform OTA updates
+    if CONF_OTA in config and config[CONF_OTA] is not False:
         raise cv.Invalid(
-            f"The '{CONF_OTA}' option has been removed from 'web_server'. "
+            f"The '{CONF_OTA}' option in 'web_server' only accepts 'false' to disable OTA. "
-            f"Please use the new OTA platform structure instead:\n\n"
+            f"To enable OTA, please use the new OTA platform structure instead:\n\n"
             f"ota:\n"
             f"  - platform: web_server\n\n"
             f"See https://esphome.io/components/ota for more information."
@@ -185,7 +186,7 @@ CONFIG_SCHEMA = cv.All(
                 web_server_base.WebServerBase
             ),
             cv.Optional(CONF_INCLUDE_INTERNAL, default=False): cv.boolean,
-            cv.Optional(CONF_OTA, default=False): cv.boolean,
+            cv.Optional(CONF_OTA): cv.boolean,
             cv.Optional(CONF_LOG, default=True): cv.boolean,
             cv.Optional(CONF_LOCAL): cv.boolean,
             cv.Optional(CONF_SORTING_GROUPS): cv.ensure_list(sorting_group),
@@ -203,7 +204,7 @@ CONFIG_SCHEMA = cv.All(
     default_url,
     validate_local,
     validate_sorting_groups,
-    validate_ota_removed,
+    validate_ota,
 )
 
 
@@ -288,7 +289,11 @@ async def to_code(config):
         cg.add(var.set_css_url(config[CONF_CSS_URL]))
         cg.add(var.set_js_url(config[CONF_JS_URL]))
     # OTA is now handled by the web_server OTA platform
-    # The CONF_OTA option is kept only for backwards compatibility validation
+    # The CONF_OTA option is kept to allow explicitly disabling OTA for web_server
+    # IMPORTANT: This ONLY affects the web_server component, NOT captive_portal
+    # Captive portal will still be able to perform OTA updates even when this is set
+    if config.get(CONF_OTA) is False:
+        cg.add_define("USE_WEBSERVER_OTA_DISABLED")
     cg.add(var.set_expose_log(config[CONF_LOG]))
     if config[CONF_ENABLE_PRIVATE_NETWORK_ACCESS]:
         cg.add_define("USE_WEBSERVER_PRIVATE_NETWORK_ACCESS")

esphome/components/web_server/ota/ota_web_server.cpp

@@ -5,6 +5,10 @@
 #include "esphome/core/application.h"
 #include "esphome/core/log.h"
 
+#ifdef USE_CAPTIVE_PORTAL
+#include "esphome/components/captive_portal/captive_portal.h"
+#endif
+
 #ifdef USE_ARDUINO
 #ifdef USE_ESP8266
 #include <Updater.h>
@@ -25,7 +29,22 @@ class OTARequestHandler : public AsyncWebHandler {
   void handleUpload(AsyncWebServerRequest *request, const String &filename, size_t index, uint8_t *data, size_t len,
                     bool final) override;
   bool canHandle(AsyncWebServerRequest *request) const override {
-    return request->url() == "/update" && request->method() == HTTP_POST;
+    // Check if this is an OTA update request
+    bool is_ota_request = request->url() == "/update" && request->method() == HTTP_POST;
+
+#if defined(USE_WEBSERVER_OTA_DISABLED) && defined(USE_CAPTIVE_PORTAL)
+    // IMPORTANT: USE_WEBSERVER_OTA_DISABLED only disables OTA for the web_server component
+    // Captive portal can still perform OTA updates - check if request is from active captive portal
+    // Note: global_captive_portal is the standard way components communicate in ESPHome
+    return is_ota_request && captive_portal::global_captive_portal != nullptr &&
+           captive_portal::global_captive_portal->is_active();
+#elif defined(USE_WEBSERVER_OTA_DISABLED)
+    // OTA disabled for web_server and no captive portal compiled in
+    return false;
+#else
+    // OTA enabled for web_server
+    return is_ota_request;
+#endif
   }
 
   // NOLINTNEXTLINE(readability-identifier-naming)
@@ -152,7 +171,7 @@ void OTARequestHandler::handleUpload(AsyncWebServerRequest *request, const Strin
 
   // Finalize
   if (final) {
-    ESP_LOGD(TAG, "OTA final chunk: index=%u, len=%u, total_read=%u, contentLength=%u", index, len,
+    ESP_LOGD(TAG, "OTA final chunk: index=%zu, len=%zu, total_read=%u, contentLength=%zu", index, len,
              this->ota_read_length_, request->contentLength());
 
     // For Arduino framework, the Update library tracks expected size from firmware header

esphome/components/web_server/web_server.cpp

@@ -268,10 +268,10 @@ std::string WebServer::get_config_json() {
   return json::build_json([this](JsonObject root) {
     root["title"] = App.get_friendly_name().empty() ? App.get_name() : App.get_friendly_name();
     root["comment"] = App.get_comment();
-#ifdef USE_WEBSERVER_OTA
+#if defined(USE_WEBSERVER_OTA_DISABLED) || !defined(USE_WEBSERVER_OTA)
-    root["ota"] = true;  // web_server OTA platform is configured
+    root["ota"] = false;  // Note: USE_WEBSERVER_OTA_DISABLED only affects web_server, not captive_portal
 #else
-    root["ota"] = false;
+    root["ota"] = true;
 #endif
     root["log"] = this->expose_log_;
     root["lang"] = "en";

esphome/components/web_server/web_server_v1.cpp

@@ -192,7 +192,9 @@ void WebServer::handle_index_request(AsyncWebServerRequest *request) {
 
   stream->print(F("</tbody></table><p>See <a href=\"https://esphome.io/web-api/index.html\">ESPHome Web API</a> for "
                   "REST API documentation.</p>"));
-#ifdef USE_WEBSERVER_OTA
+#if defined(USE_WEBSERVER_OTA) && !defined(USE_WEBSERVER_OTA_DISABLED)
+  // Show OTA form only if web_server OTA is not explicitly disabled
+  // Note: USE_WEBSERVER_OTA_DISABLED only affects web_server, not captive_portal
   stream->print(F("<h2>OTA Update</h2><form method=\"POST\" action=\"/update\" enctype=\"multipart/form-data\"><input "
                   "type=\"file\" name=\"update\"><input type=\"submit\" value=\"Update\"></form>"));
 #endif

esphome/components/wifi/wifi_component_esp32_arduino.cpp

@@ -20,10 +20,6 @@
 #include "lwip/dns.h"
 #include "lwip/err.h"
 
-#ifdef CONFIG_LWIP_TCPIP_CORE_LOCKING
-#include "lwip/priv/tcpip_priv.h"
-#endif
-
 #include "esphome/core/application.h"
 #include "esphome/core/hal.h"
 #include "esphome/core/helpers.h"
@@ -295,25 +291,16 @@ bool WiFiComponent::wifi_sta_ip_config_(optional<ManualIP> manual_ip) {
   }
 
   if (!manual_ip.has_value()) {
-// sntp_servermode_dhcp lwip/sntp.c (Required to lock TCPIP core functionality!)
+    // sntp_servermode_dhcp lwip/sntp.c (Required to lock TCPIP core functionality!)
-// https://github.com/esphome/issues/issues/6591
+    // https://github.com/esphome/issues/issues/6591
-// https://github.com/espressif/arduino-esp32/issues/10526
+    // https://github.com/espressif/arduino-esp32/issues/10526
-#ifdef CONFIG_LWIP_TCPIP_CORE_LOCKING
+    {
-    if (!sys_thread_tcpip(LWIP_CORE_LOCK_QUERY_HOLDER)) {
+      LwIPLock lock;
-      LOCK_TCPIP_CORE();
-    }
-#endif
-
       // lwIP starts the SNTP client if it gets an SNTP server from DHCP. We don't need the time, and more importantly,
       // the built-in SNTP client has a memory leak in certain situations. Disable this feature.
       // https://github.com/esphome/issues/issues/2299
       sntp_servermode_dhcp(false);
-
-#ifdef CONFIG_LWIP_TCPIP_CORE_LOCKING
-    if (sys_thread_tcpip(LWIP_CORE_LOCK_QUERY_HOLDER)) {
-      UNLOCK_TCPIP_CORE();
     }
-#endif
 
     // No manual IP is set; use DHCP client
     if (dhcp_status != ESP_NETIF_DHCP_STARTED) {

esphome/const.py

@@ -4,7 +4,7 @@ from enum import Enum
 
 from esphome.enum import StrEnum
 
-__version__ = "2025.7.0"
+__version__ = "2025.7.1"
 
 ALLOWED_NAME_CHARS = "abcdefghijklmnopqrstuvwxyz0123456789-_"
 VALID_SUBSTITUTIONS_CHARACTERS = (

esphome/core/helpers.h

@@ -683,6 +683,23 @@ class InterruptLock {
 #endif
 };
 
+/** Helper class to lock the lwIP TCPIP core when making lwIP API calls from non-TCPIP threads.
+ *
+ * This is needed on multi-threaded platforms (ESP32) when CONFIG_LWIP_TCPIP_CORE_LOCKING is enabled.
+ * It ensures thread-safe access to lwIP APIs.
+ *
+ * @note This follows the same pattern as InterruptLock - platform-specific implementations in helpers.cpp
+ */
+class LwIPLock {
+ public:
+  LwIPLock();
+  ~LwIPLock();
+
+  // Delete copy constructor and copy assignment operator to prevent accidental copying
+  LwIPLock(const LwIPLock &) = delete;
+  LwIPLock &operator=(const LwIPLock &) = delete;
+};
+
 /** Helper class to request `loop()` to be called as fast as possible.
  *
  * Usually the ESPHome main loop runs at 60 Hz, sleeping in between invocations of `loop()` if necessary. When a higher

esphome/util.py

@@ -147,6 +147,13 @@ class RedirectText:
                     continue
 
                 self._write_color_replace(line)
+                # Check for flash size error and provide helpful guidance
+                if (
+                    "Error: The program size" in line
+                    and "is greater than maximum allowed" in line
+                    and (help_msg := get_esp32_arduino_flash_error_help())
+                ):
+                    self._write_color_replace(help_msg)
         else:
             self._write_color_replace(s)
 
@@ -309,3 +316,34 @@ def get_serial_ports() -> list[SerialPort]:
 
     result.sort(key=lambda x: x.path)
     return result
+
+
+def get_esp32_arduino_flash_error_help() -> str | None:
+    """Returns helpful message when ESP32 with Arduino runs out of flash space."""
+    from esphome.core import CORE
+
+    if not (CORE.is_esp32 and CORE.using_arduino):
+        return None
+
+    from esphome.log import AnsiFore, color
+
+    return (
+        "\n"
+        + color(
+            AnsiFore.YELLOW,
+            "💡 TIP: Your ESP32 with Arduino framework has run out of flash space.\n",
+        )
+        + "\n"
+        + "To fix this, switch to the ESP-IDF framework which is more memory efficient:\n"
+        + "\n"
+        + "1. In your YAML configuration, modify the framework section:\n"
+        + "\n"
+        + "   esp32:\n"
+        + "     framework:\n"
+        + "       type: esp-idf\n"
+        + "\n"
+        + "2. Clean build files and compile again\n"
+        + "\n"
+        + "Note: ESP-IDF uses less flash space and provides better performance.\n"
+        + "Some Arduino-specific libraries may need alternatives.\n\n"
+    )

tests/component_tests/web_server/test_ota_migration.py

@@ -8,31 +8,31 @@ from esphome.types import ConfigType
 
 def test_web_server_ota_true_fails_validation() -> None:
     """Test that web_server with ota: true fails validation with helpful message."""
-    from esphome.components.web_server import validate_ota_removed
+    from esphome.components.web_server import validate_ota
 
     # Config with ota: true should fail
     config: ConfigType = {"ota": True}
 
     with pytest.raises(cv.Invalid) as exc_info:
-        validate_ota_removed(config)
+        validate_ota(config)
 
     # Check error message contains migration instructions
     error_msg = str(exc_info.value)
-    assert "has been removed from 'web_server'" in error_msg
+    assert "only accepts 'false' to disable OTA" in error_msg
     assert "platform: web_server" in error_msg
     assert "ota:" in error_msg
 
 
 def test_web_server_ota_false_passes_validation() -> None:
     """Test that web_server with ota: false passes validation."""
-    from esphome.components.web_server import validate_ota_removed
+    from esphome.components.web_server import validate_ota
 
     # Config with ota: false should pass
     config: ConfigType = {"ota": False}
-    result = validate_ota_removed(config)
+    result = validate_ota(config)
     assert result == config
 
     # Config without ota should also pass
     config: ConfigType = {}
-    result = validate_ota_removed(config)
+    result = validate_ota(config)
     assert result == config

tests/components/lvgl/lvgl-package.yaml

@@ -928,6 +928,12 @@ lvgl:
                           angle_range: 360
                           rotation: !lambda return 2700;
                           indicators:
+                            - tick_style:
+                                start_value: 0
+                                end_value: 60
+                                color_start: 0x0000bd
+                                color_end: 0xbd0000
+                                width: !lambda return 1;
                             - line:
                                 opa: 50%
                                 id: minute_hand

tests/integration/fixtures/api_string_lambda.yaml

@@ -0,0 +1,64 @@
+esphome:
+  name: api-string-lambda-test
+host:
+
+api:
+  actions:
+    # Service that tests string lambda functionality
+    - action: test_string_lambda
+      variables:
+        input_string: string
+      then:
+        # Log the input to verify service was called
+        - logger.log:
+            format: "Service called with string: %s"
+            args: [input_string.c_str()]
+
+        # This is the key test - using a lambda that returns x.c_str()
+        # where x is already a string. This would fail to compile in 2025.7.0b5
+        # with "no matching function for call to 'to_string(std::string)'"
+        # This is the exact case from issue #9539
+        - homeassistant.tag_scanned: !lambda 'return input_string.c_str();'
+
+        # Also test with homeassistant.event to verify our fix works with data fields
+        - homeassistant.event:
+            event: esphome.test_string_lambda
+            data:
+              value: !lambda 'return input_string.c_str();'
+
+    # Service that tests int lambda functionality
+    - action: test_int_lambda
+      variables:
+        input_number: int
+      then:
+        # Log the input to verify service was called
+        - logger.log:
+            format: "Service called with int: %d"
+            args: [input_number]
+
+        # Test that int lambdas still work correctly with to_string
+        # The TemplatableStringValue should automatically convert int to string
+        - homeassistant.event:
+            event: esphome.test_int_lambda
+            data:
+              value: !lambda 'return input_number;'
+
+    # Service that tests float lambda functionality
+    - action: test_float_lambda
+      variables:
+        input_float: float
+      then:
+        # Log the input to verify service was called
+        - logger.log:
+            format: "Service called with float: %.2f"
+            args: [input_float]
+
+        # Test that float lambdas still work correctly with to_string
+        # The TemplatableStringValue should automatically convert float to string
+        - homeassistant.event:
+            event: esphome.test_float_lambda
+            data:
+              value: !lambda 'return input_float;'
+
+logger:
+  level: DEBUG

tests/integration/test_api_string_lambda.py

@@ -0,0 +1,85 @@
+"""Integration test for TemplatableStringValue with string lambdas."""
+
+from __future__ import annotations
+
+import asyncio
+import re
+
+import pytest
+
+from .types import APIClientConnectedFactory, RunCompiledFunction
+
+
+@pytest.mark.asyncio
+async def test_api_string_lambda(
+    yaml_config: str,
+    run_compiled: RunCompiledFunction,
+    api_client_connected: APIClientConnectedFactory,
+) -> None:
+    """Test TemplatableStringValue works with lambdas that return different types."""
+    loop = asyncio.get_running_loop()
+
+    # Track log messages for all three service calls
+    string_called_future = loop.create_future()
+    int_called_future = loop.create_future()
+    float_called_future = loop.create_future()
+
+    # Patterns to match in logs - confirms the lambdas compiled and executed
+    string_pattern = re.compile(r"Service called with string: STRING_FROM_LAMBDA")
+    int_pattern = re.compile(r"Service called with int: 42")
+    float_pattern = re.compile(r"Service called with float: 3\.14")
+
+    def check_output(line: str) -> None:
+        """Check log output for expected messages."""
+        if not string_called_future.done() and string_pattern.search(line):
+            string_called_future.set_result(True)
+        if not int_called_future.done() and int_pattern.search(line):
+            int_called_future.set_result(True)
+        if not float_called_future.done() and float_pattern.search(line):
+            float_called_future.set_result(True)
+
+    # Run with log monitoring
+    async with (
+        run_compiled(yaml_config, line_callback=check_output),
+        api_client_connected() as client,
+    ):
+        # Verify device info
+        device_info = await client.device_info()
+        assert device_info is not None
+        assert device_info.name == "api-string-lambda-test"
+
+        # List services to find our test services
+        _, services = await client.list_entities_services()
+
+        # Find all test services
+        string_service = next(
+            (s for s in services if s.name == "test_string_lambda"), None
+        )
+        assert string_service is not None, "test_string_lambda service not found"
+
+        int_service = next((s for s in services if s.name == "test_int_lambda"), None)
+        assert int_service is not None, "test_int_lambda service not found"
+
+        float_service = next(
+            (s for s in services if s.name == "test_float_lambda"), None
+        )
+        assert float_service is not None, "test_float_lambda service not found"
+
+        # Execute all three services to test different lambda return types
+        client.execute_service(string_service, {"input_string": "STRING_FROM_LAMBDA"})
+        client.execute_service(int_service, {"input_number": 42})
+        client.execute_service(float_service, {"input_float": 3.14})
+
+        # Wait for all service log messages
+        # This confirms the lambdas compiled successfully and executed
+        try:
+            await asyncio.wait_for(
+                asyncio.gather(
+                    string_called_future, int_called_future, float_called_future
+                ),
+                timeout=5.0,
+            )
+        except TimeoutError:
+            pytest.fail(
+                "One or more service log messages not received - lambda may have failed to compile or execute"
+            )