add client event for failed video playback (#11170)

src/analytics/metrics/types.ts

@@ -1346,6 +1346,26 @@ export type Events = {
   // user dismissed the empty-followers promo banner
   'invite:followersPromo:dismiss': {}
 
+  /**
+   * Fired when a video fails terminally during playback: unreachable (404),
+   * undecodable, or the client lacks the required codecs. Complements the
+   * Sentry-only video.playback spans with a countable, unsampled event.
+   */
+  'video:playback:failed': {
+    surface: 'feed' | 'immersiveFeed'
+    presentation: 'video' | 'gif'
+    /**
+     * Coarse failure bucket: VideoNotFoundError, HLSUnsupportedError, an
+     * hls.js error details code (e.g. bufferAppendError), or PlayerError on
+     * native.
+     */
+    errorClass: string
+    /** Truncated to 256 chars */
+    errorMessage: string
+    /** HLS playlist URL, identifies the exact video for server-side lookup */
+    playlist: string
+  }
+
   // === Video upload funnel (Frontend Spec section D) ===
   // Every event carries uploadId (client-generated UUID, ties one upload
   // session end-to-end) + engine (compression engine id, e.g.