feat(esp_trace): add example to demonstrate external lib integration

examples/system/esp_trace/main/CMakeLists.txt

@@ -0,0 +1,3 @@
+idf_component_register(SRCS "app_main.c"
+                       REQUIRES ext_trace_lib
+                       INCLUDE_DIRS "")

examples/system/esp_trace/main/app_main.c

@@ -0,0 +1,76 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: CC0-1.0
+ */
+#include "sdkconfig.h"
+
+#include <stdio.h>
+#include <string.h>
+
+#include "freertos/FreeRTOS.h"
+#include "freertos/task.h"
+#include "freertos/queue.h"
+#include "esp_log.h"
+#include "esp_trace.h"
+
+static const char *TAG = "main";
+
+esp_trace_open_params_t esp_trace_get_user_params(void)
+{
+    esp_trace_open_params_t trace_params = {
+        .core_cfg = NULL,
+        .encoder_name = "ext_trace_lib",
+        .encoder_cfg = NULL,
+        .transport_name = "usb_serial_jtag",
+        .transport_cfg = NULL,
+    };
+    return trace_params;
+}
+
+static QueueHandle_t s_q;
+
+/* Producer: sends a counter value to s_q every 50 ms. Generates Q_SEND
+ * trace events and unblocks the consumer (driving TASK_IN switches). */
+static void producer(void *arg)
+{
+    uint32_t v = 0;
+    while (1) {
+        xQueueSend(s_q, &v, portMAX_DELAY);
+        v++;
+        vTaskDelay(50 / portTICK_PERIOD_MS);
+    }
+}
+
+/* Consumer: blocks on s_q indefinitely. Each receive wakes this task and
+ * fires a TASK_IN trace event when the scheduler switches us in. */
+static void consumer(void *arg)
+{
+    uint32_t v;
+    while (1) {
+        xQueueReceive(s_q, &v, portMAX_DELAY);
+    }
+}
+
+void app_main(void)
+{
+    ESP_LOGI(TAG, "Start of trace session");
+
+    // Wait some time for host to be ready
+    vTaskDelay(2000 / portTICK_PERIOD_MS);
+
+    esp_trace_start();
+
+    s_q = xQueueCreate(4, sizeof(uint32_t));
+
+    xTaskCreatePinnedToCore(producer, "producer", 2048, NULL, 5, NULL, 0);
+    xTaskCreatePinnedToCore(consumer, "consumer", 2048, NULL, 5, NULL, portNUM_PROCESSORS - 1);
+
+    // 1 second delay is enough to generate the expected number of trace events.
+    vTaskDelay(1000 / portTICK_PERIOD_MS);
+
+    esp_trace_stop();
+    esp_trace_flush();
+
+    ESP_LOGI(TAG, "End of trace session");
+}