Distribute master OTA images to slaves over ESP-NOW.

After UART OTA the master reads the staged partition in 4 KiB blocks (200 B ESP-NOW chunks), waits for per-slave block ACKs, and fixes the final partial block. Slaves reuse ota_uart; send pacing and logging improve reliability.

Co-authored-by: Cursor <cursoragent@cursor.com>

main/ota_uart.h

@@ -2,6 +2,7 @@
 #define OTA_UART_H
 
 #include "esp_err.h"
+#include "esp_partition.h"
 #include <stdbool.h>
 #include <stddef.h>
 #include <stdint.h>
@@ -39,7 +40,19 @@ ota_feed_result_t ota_uart_feed(const uint8_t *data, size_t len);
 
 uint32_t ota_uart_bytes_written(void);
 
-/** Flush remainder, esp_ota_end, set boot partition on success. */
-esp_err_t ota_uart_finish(bool *success_out);
+/**
+ * Flush remainder and esp_ota_end. When set_boot is false, the staged image
+ * remains readable via ota_uart_get_staged_image() until ota_uart_apply_boot().
+ */
+esp_err_t ota_uart_finish(bool set_boot, bool *success_out);
+
+/** Staged partition after ota_uart_finish(false, …); valid until apply_boot or abort. */
+bool ota_uart_get_staged_image(const esp_partition_t **partition_out,
+                               uint32_t *size_out);
+
+/** Set boot partition to the last staged image (after slave distribution). */
+esp_err_t ota_uart_apply_boot(void);
+
+void ota_uart_clear_staged(void);
 
 #endif