fix: only touch the task watchdog from tasks that are subscribed to it

Only loop() is subscribed.  setConnected() runs on the WiFi event task
and reached SocketEmitter::endEmit(), whose plain esp_task_wdt_reset()
logged "esp_task_wdt_reset(707): task not found" on every boot.  The web
and socket handlers on async_tcp did the same.

/scanaps on async_tcp called esp_task_wdt_add(NULL) after the scan,
subscribing a task that nothing resets, so the board could panic 15 s
after a scan from the UI.

TaskWdt.h resets only a subscribed task and re-adds a task after a long
call only when it was watched before.

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

test/stubs/esp_task_wdt.h

@@ -0,0 +1,34 @@
+#pragma once
+// Stands in for ESP-IDF's task watchdog for one calling task.  Tests set
+// whether it is subscribed and count the resets.
+typedef int esp_err_t;
+#ifndef ESP_OK
+#define ESP_OK 0
+#endif
+#ifndef ESP_ERR_NOT_FOUND
+#define ESP_ERR_NOT_FOUND 0x105
+#endif
+
+struct FakeTaskWdt {
+  bool subscribed = false;
+  int resets = 0;
+  int adds = 0;
+};
+inline FakeTaskWdt fakeTaskWdt;
+
+inline esp_err_t esp_task_wdt_status(void *) { return fakeTaskWdt.subscribed ? ESP_OK : ESP_ERR_NOT_FOUND; }
+inline esp_err_t esp_task_wdt_reset() {
+  if(!fakeTaskWdt.subscribed) return ESP_ERR_NOT_FOUND;
+  fakeTaskWdt.resets++;
+  return ESP_OK;
+}
+inline esp_err_t esp_task_wdt_delete(void *) {
+  if(!fakeTaskWdt.subscribed) return ESP_ERR_NOT_FOUND;
+  fakeTaskWdt.subscribed = false;
+  return ESP_OK;
+}
+inline esp_err_t esp_task_wdt_add(void *) {
+  fakeTaskWdt.adds++;
+  fakeTaskWdt.subscribed = true;
+  return ESP_OK;
+}

test/test_taskwdt/test_taskwdt.cpp

@@ -0,0 +1,49 @@
+#include <unity.h>
+#include "TaskWdt.h"
+
+void setUp() { fakeTaskWdt = FakeTaskWdt(); }
+void tearDown() {}
+
+/*********************************************************************
+ * resetTaskWdt
+ ********************************************************************/
+static void test_resetTaskWdt_resets_a_subscribed_task() {
+  fakeTaskWdt.subscribed = true;
+  resetTaskWdt();
+  TEST_ASSERT_EQUAL_INT(1, fakeTaskWdt.resets);
+}
+static void test_resetTaskWdt_skips_a_task_that_is_not_subscribed() {
+  // The WiFi event task and async_tcp.
+  resetTaskWdt();
+  TEST_ASSERT_EQUAL_INT(0, fakeTaskWdt.resets);
+  TEST_ASSERT_FALSE(fakeTaskWdt.subscribed);
+}
+
+/*********************************************************************
+ * pauseTaskWdt / resumeTaskWdt
+ ********************************************************************/
+static void test_pause_resume_puts_a_watched_task_back() {
+  fakeTaskWdt.subscribed = true;
+  const bool paused = pauseTaskWdt();
+  TEST_ASSERT_TRUE(paused);
+  TEST_ASSERT_FALSE(fakeTaskWdt.subscribed);
+  resumeTaskWdt(paused);
+  TEST_ASSERT_TRUE(fakeTaskWdt.subscribed);
+}
+static void test_pause_resume_leaves_an_unwatched_task_unwatched() {
+  // /scanaps on async_tcp: adding it would panic once nothing resets it.
+  const bool paused = pauseTaskWdt();
+  TEST_ASSERT_FALSE(paused);
+  resumeTaskWdt(paused);
+  TEST_ASSERT_FALSE(fakeTaskWdt.subscribed);
+  TEST_ASSERT_EQUAL_INT(0, fakeTaskWdt.adds);
+}
+
+int main(int, char **) {
+  UNITY_BEGIN();
+  RUN_TEST(test_resetTaskWdt_resets_a_subscribed_task);
+  RUN_TEST(test_resetTaskWdt_skips_a_task_that_is_not_subscribed);
+  RUN_TEST(test_pause_resume_puts_a_watched_task_back);
+  RUN_TEST(test_pause_resume_leaves_an_unwatched_task_unwatched);
+  return UNITY_END();
+}