Merge branch 'feat/sys_event_in_freertos' into 'master'

feat(system_init): Introduce pre-scheduler and pre-app main handler registrations

Closes IDF-16133

See merge request espressif/esp-idf!52296

components/esp_system/include/esp_private/esp_sys_event_app_init.h

@@ -0,0 +1,47 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#pragma once
+
+#include "esp_cpu.h"
+#include "esp_private/esp_sys_event.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @brief Register a handler to run on core 0 immediately before the scheduler starts
+ */
+#define ESP_PRE_SCHEDULER_HANDLER_REGISTER(fn, priority) \
+    static esp_err_t fn(void *user_arg, void *ctx); \
+    _ESP_SYS_EVENT_REGISTER(PRE_SCHEDULER, priority, __esp_pre_scheduler_##fn) \
+    { \
+        if (esp_cpu_get_core_id() != 0) { \
+            return ESP_OK; \
+        } \
+        return fn(user_arg, ctx); \
+    } \
+    static esp_err_t fn(void *user_arg, void *ctx)
+
+/**
+ * @brief Register a handler to run on every core immediately before its scheduler starts
+ */
+#define ESP_PRE_SCHEDULER_HANDLER_REGISTER_PER_CPU(fn, priority) \
+    _ESP_SYS_EVENT_REGISTER(PRE_SCHEDULER, priority, fn)
+
+/**
+ * @brief Register a handler to run in the main task immediately before app_main
+ *
+ * Handlers run in ascending priority order after all CPUs have completed
+ * FreeRTOS initialization. The scheduler and heap allocator are available.
+ */
+#define ESP_PRE_APP_MAIN_HANDLER_REGISTER(fn, priority) \
+    _ESP_SYS_EVENT_REGISTER(PRE_APP_MAIN, priority, fn)
+
+#ifdef __cplusplus
+}
+#endif