fix: print each log line whole

The Arduino core's log_printf() has its UART lock commented out and
writes with ets_printf(), so lines logged at the same time from
async_tcp and loop() came out interleaved character by character. It
also formats short lines into one static buffer shared by every task.

Wrap log_printf at link time and hold a mutex around the core's
log_printfv(). It never blocks before the scheduler runs, in an ISR or
in a critical section, and waits at most 50ms before printing anyway.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

platformio.ini

@@ -37,6 +37,8 @@ build_flags =
 	-DCONFIG_ESP_COREDUMP_CHECKSUM_CRC32=1
 	-DCONFIG_ESP_TASK_WDT_PANIC=1
 	-DCONFIG_ESP_COREDUMP_DECODE_INFO=1
+	; Route log_printf through src/LogLock.cpp so lines from both cores don't interleave.
+	-Wl,--wrap=log_printf
 monitor_speed = 115200
 monitor_filters = 
 	time

src/LogLock.cpp

@@ -0,0 +1,36 @@
+// Prints each log line whole.
+//
+// The Arduino core's log_printf() writes with ets_printf() and has its UART
+// lock commented out, so lines logged at the same time from async_tcp (core 0)
+// and loop() (core 1) come out interleaved character by character.  It also
+// formats short lines into one static buffer shared by every task.
+//
+// platformio.ini links with -Wl,--wrap=log_printf so every ESP_LOGx/log_x call
+// lands here and takes this lock around the core's log_printfv().
+#include <Arduino.h>
+#include <stdarg.h>
+#include "freertos/FreeRTOS.h"
+#include "freertos/semphr.h"
+#include "freertos/task.h"
+
+// Defined in the core's esp32-hal-uart.c but not declared in a header.
+extern "C" int log_printfv(const char *format, va_list arg);
+
+// Created during static initialisation, before anything can race for it.  A
+// constructor that logs before this runs simply goes unlocked.
+static SemaphoreHandle_t logMutex = xSemaphoreCreateRecursiveMutex();
+// Never wait longer than this for the lock; the line is printed anyway, so a
+// task stuck mid-log can only garble output, not hang another task.
+#define LOG_LOCK_WAIT_MS 50
+
+extern "C" int __wrap_log_printf(const char *format, ...) {
+  // No blocking before the scheduler runs, in an ISR or in a critical section.
+  const bool canLock = logMutex && xTaskGetSchedulerState() == taskSCHEDULER_RUNNING && xPortCanYield();
+  const bool locked = canLock && xSemaphoreTakeRecursive(logMutex, pdMS_TO_TICKS(LOG_LOCK_WAIT_MS)) == pdTRUE;
+  va_list arg;
+  va_start(arg, format);
+  int len = log_printfv(format, arg);
+  va_end(arg);
+  if(locked) xSemaphoreGiveRecursive(logMutex);
+  return len;
+}