OTA: quiet the audio sources during a firmware upload

An upload during an active Spotify session crawled (~10 kB/s, 197 s)
and ended in a reset (seen twice). Workaround:
- aes67_ota_on_update(cb): cb(true) right before an accepted upload
  writes flash, cb(false) if it then fails.
- The player pauses Spotify (spotify_pause -> SpircHandler::setPause, the
  app follows) and suspends HLS fetching (hls_suspend); resumed if the
  upload fails. AES67 TX keeps running (silence).
- Verified: upload during Spotify playback paused the session and
  installed in 25.8 s (normal for 2 MB), clean reboot and self-test.
  Root cause still open (noted in CLAUDE.md with the other cspot items).

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

components/aes67_ota/aes67_ota.c

@@ -23,6 +23,26 @@
 
 static const char *TAG = "ota";
 
+#define MAX_UPDATE_CBS 4
+static aes67_ota_update_cb_t s_update_cbs[MAX_UPDATE_CBS];
+static int s_update_n;
+
+esp_err_t aes67_ota_on_update(aes67_ota_update_cb_t cb)
+{
+    if (s_update_n >= MAX_UPDATE_CBS) {
+        return ESP_ERR_NO_MEM;
+    }
+    s_update_cbs[s_update_n++] = cb;
+    return ESP_OK;
+}
+
+static void notify_update(bool starting)
+{
+    for (int i = 0; i < s_update_n; i++) {
+        s_update_cbs[i](starting);
+    }
+}
+
 static bool is_pending(void)
 {
     esp_ota_img_states_t st;
@@ -114,6 +134,7 @@ static esp_err_t ota_post(httpd_req_t *req)
     esp_ota_handle_t ota = 0;
     size_t total = 0, fill = 0;
     const char *err_msg = NULL;
+    bool notified = false;
     int64_t t0 = esp_timer_get_time();
 
     while (total < req->content_len) {
@@ -137,6 +158,8 @@ static esp_err_t ota_post(httpd_req_t *req)
             }
             const esp_app_desc_t *d = (const esp_app_desc_t *)(buf + DESC_OFFSET);
             ESP_LOGI(TAG, "image %.32s %.32s", d->project_name, d->version);
+            notify_update(true);    // project quiets streaming/decoding before the flash writes
+            notified = true;
             if (esp_ota_begin(dst, OTA_WITH_SEQUENTIAL_WRITES, &ota) != ESP_OK) {
                 err_msg = "ota begin failed";
                 break;
@@ -154,15 +177,20 @@ static esp_err_t ota_post(httpd_req_t *req)
         if (ota) {
             esp_ota_abort(ota);
         }
+        if (notified) {
+            notify_update(false);
+        }
         // Rejected before the whole body was read: close instead of draining it.
         httpd_resp_set_hdr(req, "Connection", "close");
         return reject(req, err_msg);
     }
     esp_err_t err = esp_ota_end(ota);  // verifies the image (checksum/hash, chip)
     if (err != ESP_OK) {
+        notify_update(false);
         return reject(req, err == ESP_ERR_OTA_VALIDATE_FAILED ? "image verification failed" : "ota end failed");
     }
     if (esp_ota_set_boot_partition(dst) != ESP_OK) {
+        notify_update(false);
         return httpd_resp_send_err(req, HTTPD_500_INTERNAL_SERVER_ERROR, "could not set boot partition");
     }
     ESP_LOGW(TAG, "installed to %s in %.1f s, rebooting", dst->label,

components/aes67_ota/include/aes67_ota.h

@@ -2,8 +2,16 @@
 // Core component: must not depend on main/ (project code).
 #pragma once
 
+#include <stdbool.h>
+
 #include "esp_err.h"
 
 // Registers /api/ota routes. If the running image is pending verification, starts the
 // self-test: IP address + own web server answering within 60 s, else roll back.
 esp_err_t aes67_ota_init(void);
+
+// Called with true right before an accepted upload starts writing flash, and with false if that
+// upload then fails (on success the device reboots). Lets the project quiet heavy work (streaming,
+// decoding) during the flash writes. Up to 4 callbacks.
+typedef void (*aes67_ota_update_cb_t)(bool starting);
+esp_err_t aes67_ota_on_update(aes67_ota_update_cb_t cb);