[logger] Move write_msg_() to inline platform headers

Create per-platform logger_*.h headers with inline write_msg_()
for ESP32, ESP8266, RP2040, and LibreTiny. These are all one-liners
that benefit from inlining into write_to_console_(), eliminating
function call overhead on every log message.

Host and Zephyr implementations remain in .cpp files as they are
more complex (timestamp formatting, printk + uart loop).

esphome/components/logger/logger.h

@@ -233,7 +233,11 @@ class Logger final : public Component {
   void cdc_loop_();
 #endif
   void process_messages_();
+#if defined(USE_HOST) || defined(USE_ZEPHYR)
   void write_msg_(const char *msg, uint16_t len);
+#else
+  inline void write_msg_(const char *msg, uint16_t len);  // Defined in platform-specific logger_*.h
+#endif
 
   // Format a log message with printf-style arguments and write it to a buffer with header, footer, and null terminator
   // thread_name: name of the calling thread/task, or nullptr for main task (callers already know which task they're on)
@@ -366,7 +370,7 @@ class Logger final : public Component {
   bool non_main_task_recursion_guard_{false};  // Shared guard for all non-main tasks on LibreTiny
 #endif
 #else
-  bool global_recursion_guard_{false};  // Simple global recursion guard for single-task platforms
+  bool global_recursion_guard_{false};                    // Simple global recursion guard for single-task platforms
 #endif
 
   // Large buffer placed last to keep frequently-accessed member offsets small
@@ -498,3 +502,15 @@ class LoggerMessageTrigger final : public Trigger<uint8_t, const char *, const c
 };
 
 }  // namespace esphome::logger
+
+// Platform-specific inline implementations of write_msg_()
+// Must be included after the Logger class definition is complete
+#if defined(USE_ESP32)
+#include "logger_esp32.h"
+#elif defined(USE_ESP8266)
+#include "logger_esp8266.h"
+#elif defined(USE_RP2040)
+#include "logger_rp2040.h"
+#elif defined(USE_LIBRETINY)
+#include "logger_libretiny.h"
+#endif

esphome/components/logger/logger_esp32.cpp

@@ -123,23 +123,6 @@ void Logger::pre_setup() {
 #endif
 }
 
-void HOT Logger::write_msg_(const char *msg, uint16_t len) {
-#if defined(USE_LOGGER_UART_SELECTION_USB_CDC) || defined(USE_LOGGER_UART_SELECTION_USB_SERIAL_JTAG)
-  // USB CDC/JTAG - single write including newline (already in buffer)
-  // Use fwrite to stdout which goes through VFS to USB console
-  //
-  // Note: These defines indicate the user's YAML configuration choice (hardware_uart: USB_CDC/USB_SERIAL_JTAG).
-  // They are ONLY defined when the user explicitly selects USB as the logger output in their config.
-  // This is compile-time selection, not runtime detection - if USB is configured, it's always used.
-  // There is no fallback to regular UART if "USB isn't connected" - that's the user's responsibility
-  // to configure correctly for their hardware. This approach eliminates runtime overhead.
-  fwrite(msg, 1, len, stdout);
-#else
-  // Regular UART - single write including newline (already in buffer)
-  uart_write_bytes(this->uart_num_, msg, len);
-#endif
-}
-
 const LogString *Logger::get_uart_selection_() {
   switch (this->uart_) {
     case UART_SELECTION_UART0:

esphome/components/logger/logger_esp32.h

@@ -0,0 +1,28 @@
+#pragma once
+
+#ifdef USE_ESP32
+#include "esphome/core/helpers.h"
+#include <driver/uart.h>
+
+namespace esphome::logger {
+
+inline void HOT Logger::write_msg_(const char *msg, uint16_t len) {
+#if defined(USE_LOGGER_UART_SELECTION_USB_CDC) || defined(USE_LOGGER_UART_SELECTION_USB_SERIAL_JTAG)
+  // USB CDC/JTAG - single write including newline (already in buffer)
+  // Use fwrite to stdout which goes through VFS to USB console
+  //
+  // Note: These defines indicate the user's YAML configuration choice (hardware_uart: USB_CDC/USB_SERIAL_JTAG).
+  // They are ONLY defined when the user explicitly selects USB as the logger output in their config.
+  // This is compile-time selection, not runtime detection - if USB is configured, it's always used.
+  // There is no fallback to regular UART if "USB isn't connected" - that's the user's responsibility
+  // to configure correctly for their hardware. This approach eliminates runtime overhead.
+  fwrite(msg, 1, len, stdout);
+#else
+  // Regular UART - single write including newline (already in buffer)
+  uart_write_bytes(this->uart_num_, msg, len);
+#endif
+}
+
+}  // namespace esphome::logger
+
+#endif

esphome/components/logger/logger_esp8266.cpp

@@ -28,11 +28,6 @@ void Logger::pre_setup() {
   ESP_LOGI(TAG, "Log initialized");
 }
 
-void HOT Logger::write_msg_(const char *msg, uint16_t len) {
-  // Single write with newline already in buffer (added by caller)
-  this->hw_serial_->write(msg, len);
-}
-
 const LogString *Logger::get_uart_selection_() {
 #if defined(USE_ESP8266_LOGGER_SERIAL)
   if (this->uart_ == UART_SELECTION_UART0_SWAP) {

esphome/components/logger/logger_esp8266.h

@@ -0,0 +1,13 @@
+#pragma once
+
+#ifdef USE_ESP8266
+#include "esphome/core/helpers.h"
+
+namespace esphome::logger {
+
+// Single write with newline already in buffer (added by caller)
+inline void HOT Logger::write_msg_(const char *msg, uint16_t len) { this->hw_serial_->write(msg, len); }
+
+}  // namespace esphome::logger
+
+#endif

esphome/components/logger/logger_libretiny.cpp

@@ -49,8 +49,6 @@ void Logger::pre_setup() {
   ESP_LOGI(TAG, "Log initialized");
 }
 
-void HOT Logger::write_msg_(const char *msg, uint16_t len) { this->hw_serial_->write(msg, len); }
-
 const LogString *Logger::get_uart_selection_() {
   switch (this->uart_) {
     case UART_SELECTION_DEFAULT:

esphome/components/logger/logger_libretiny.h

@@ -0,0 +1,13 @@
+#pragma once
+
+#ifdef USE_LIBRETINY
+#include "esphome/core/helpers.h"
+
+namespace esphome::logger {
+
+// Single write with newline already in buffer (added by caller)
+inline void HOT Logger::write_msg_(const char *msg, uint16_t len) { this->hw_serial_->write(msg, len); }
+
+}  // namespace esphome::logger
+
+#endif

esphome/components/logger/logger_rp2040.cpp

@@ -34,11 +34,6 @@ void Logger::pre_setup() {
 #endif
 }
 
-void HOT Logger::write_msg_(const char *msg, uint16_t len) {
-  // Single write with newline already in buffer (added by caller)
-  this->hw_serial_->write(msg, len);
-}
-
 const LogString *Logger::get_uart_selection_() {
   switch (this->uart_) {
     case UART_SELECTION_UART0:

esphome/components/logger/logger_rp2040.h

@@ -0,0 +1,13 @@
+#pragma once
+
+#ifdef USE_RP2040
+#include "esphome/core/helpers.h"
+
+namespace esphome::logger {
+
+// Single write with newline already in buffer (added by caller)
+inline void HOT Logger::write_msg_(const char *msg, uint16_t len) { this->hw_serial_->write(msg, len); }
+
+}  // namespace esphome::logger
+
+#endif