step 5-6: compose experience

js/desktop/src/features/particles/media-particle-view.tsx

@@ -33,12 +33,18 @@ export const MediaParticleView = forwardRef<MediaParticleHandle, MediaParticleVi
   onEnded,
   onProgress,
 }, ref) {
-  const { data: url, error } = useDownloadUrl(particle.properties.object_id);
+  // Prefer the worker-produced iOS-playable variant when present so desktop
+  // and mobile read the same canonical asset. Falls back to the original.
+  const activeObjectId =
+    particle.properties.transcoded_object_id ?? particle.properties.object_id;
+  const activeMime =
+    particle.properties.transcoded_mime_type ?? particle.properties.mime_type;
+  const { data: url, error } = useDownloadUrl(activeObjectId);
   const { attachments } = useParticleAttachments(streamPath, particle.id);
 
   const videoRef = useRef<HTMLVideoElement>(null);
   const audioRef = useRef<HTMLAudioElement>(null);
-  const isAudio = particle.properties.mime_type?.startsWith("audio/");
+  const isAudio = activeMime?.startsWith("audio/");
 
   useImperativeHandle(ref, () => ({
     seek(deltaSec: number) {