zebra-spaces: listener video — playoutDelayHint=0, no lip-sync, instant tile switching

Fox 2026-06-05: "we should switch feeds immediately I don't want any algo
slowing that down."

The previous lip-sync algorithm set video receiver playoutDelayHint to
match audio's worklet delay (up to 4s on listeners). That made
spotlight-switching take up to 4s — the new tile's <video> element
had to wait for a keyframe to appear inside the 4s-deep receiver
buffer before showing the first frame.

Changes (listener role only):
- handleRemoteSfuTrack screen/camera/game branch: vDelay = 0 for
  listener (browser-lowest). Speaker/cohost/host unchanged.
- refreshLipSyncForUuid: early-return for myRole === 'listener'.
  No more retargeting video to match audio for listeners.
- retargetAllReceivers (called on role change): audio retargets
  per role; VIDEO retargets to 0 for listener, role-aware for
  others.

Listener video now plays at browser-default minimum delay. Tile
switches are instant — keyframe wait + native buffer pre-roll only,
typically <300ms.

Tradeoff accepted: listener mouth-leads-voice by approximately the
audio worklet's current cushion (1.3–4s adaptive). For consume-
content mode (lean-back listener) this is correct; switching shares
is far more important than per-syllable lip-sync.

Speakers/cohosts/hosts unaffected — their audio cushion is ~0.5s,
video matches it via lip-sync, mouths and voice align naturally.

web/zebra-spaces.html

@@ -2323,6 +2323,14 @@ async function refreshLipSyncForUuid(uuid){
    * use a fixed HTTP_STREAM_DELAY_SEC estimate (set by startStream).
    * Apply it directly with the same threshold/hysteresis as the
    * worklet path. */
+  /* Listener role: skip the video-receiver retarget entirely. Their
+   * tiles need to switch instantly when the user spotlights a
+   * different share — applying a 4s buffer to video defeats that.
+   * Audio stays at full cushion via the worklet; listener accepts
+   * mouth-leads-voice as the price of responsive switching.
+   * Fox 2026-06-05: "we should switch feeds immediately I don't
+   * want any algo slowing that down." */
+  if (myRole === 'listener') return;
   const override = httpLipSyncOverride.get(pubHex);
   if (typeof override === 'number'){
     if (Math.abs(override - e.lastApplied) < LIP_SYNC_THRESHOLD) return;
@@ -3933,17 +3941,20 @@ function handleRemoteSfuTrack(ev){
   if (kind === 'screen' || kind === 'camera' || kind === 'game'){
     logLine('', 'sfu ontrack: kind=' + kind + ' pub=' + pubHex +
                 ' track=' + ev.track.kind + ' mute=' + ev.track.muted + ' state=' + ev.track.readyState);
-    /* Video receivers (screen / camera / game) match the audio receiver's
-     * playoutDelayHint so the picture stays in sync with the voice. The
-     * mic jitter buffer is 4s; without a matching hint on video, mouse
-     * clicks / mouth movement / keystrokes lead the voice by ~4s. Audio
-     * is more vital than video — video adapts to audio's delay, never
-     * the other way around. */
-    try { if (ev.receiver) ev.receiver.playoutDelayHint = playoutDelayForRole(myRole); } catch(_){}
-    try { if (ev.receiver) ev.receiver.jitterBufferTarget = playoutDelayForRole(myRole) * 1000; } catch(_){}
-    /* register for the dynamic lip-sync algorithm — the next worklet
-     * 'buffered' message will recompute this video receiver's target
-     * to match the audio's total delay (native jbuf + worklet). */
+    /* Video receivers: speakers/cohosts/hosts match audio's delay for
+     * lip-sync. Listeners get playoutDelayHint=0 (browser-lowest)
+     * so spotlight tile switches are instant — fox 2026-06-05: "we
+     * should switch feeds immediately I don't want any algo slowing
+     * that down." Tradeoff: listener mouths lead voice by ~audio
+     * cushion (1.3–4s adaptive). Acceptable for content-consumption
+     * mode where switching shares is more critical than per-syllable
+     * lip-sync. */
+    const vDelay = (myRole === 'listener') ? 0 : playoutDelayForRole(myRole);
+    try { if (ev.receiver) ev.receiver.playoutDelayHint = vDelay; } catch(_){}
+    try { if (ev.receiver) ev.receiver.jitterBufferTarget = vDelay * 1000; } catch(_){}
+    /* Register for lip-sync — but the refresh loop also skips video
+     * apply for listeners, so this is a no-op for listener tiles.
+     * Kept registered in case role changes mid-session (promote). */
     if (ev.receiver) registerLipSyncVideo(pubHex, kind, ev.receiver);
   }
   /* MSID-supplant safety: the SFU re-uses the same streamID
@@ -5593,15 +5604,19 @@ function retargetAllReceivers(role){
       try { node.jbuf.port.postMessage({ cmd: 'retarget', targetSeconds: target }); } catch(_){}
     }
   }
-  /* SFU sub PC receivers — audio (the native side, downstream of which
-   * the worklet sits) AND video (which sits directly on the receiver). */
+  /* SFU sub PC receivers. Audio gets the role-aware target (matching
+   * the worklet downstream). Video for listeners gets 0 — instant tile
+   * switching. Video for non-listeners matches audio. */
+  const vTarget = role === 'listener' ? 0 : target;
   if (sfuSubPC && typeof sfuSubPC.getReceivers === 'function'){
     for (const r of sfuSubPC.getReceivers()){
-      try { r.playoutDelayHint = target; } catch(_){}
-      try { r.jitterBufferTarget = target * 1000; } catch(_){}
+      const isVideo = r.track && r.track.kind === 'video';
+      const t = isVideo ? vTarget : target;
+      try { r.playoutDelayHint = t; } catch(_){}
+      try { r.jitterBufferTarget = t * 1000; } catch(_){}
     }
   }
-  logLine('', 'retarget all receivers → '+target+'s (role='+role+')');
+  logLine('', 'retarget all receivers → aud='+target+'s vid='+vTarget+'s (role='+role+')');
 }
 
 async function onRoleChanged(prev, next){
@@ -7081,8 +7096,8 @@ logLine('', 'ready — pick a handle, type a rendezvous code, enter the space');
 
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