zebra-spaces: SFU mic fallback when mesh PC is present-but-not-connected

CLIENT_LOG telemetry showed the phone re-promoted to speaker, published
to SFU successfully, but neither the host nor the other speaker heard
them. Cause: the page's ontrack handler skipped attaching SFU mic
whenever peers.has(uuid) — even if that peer's mesh PC was in
'failed' or 'disconnected' state from an earlier role-change cycle.

Fix two paths:

1. ontrack-side: only skip SFU mic when peers.get(uuid).connectionState
   is actually 'connected'. A stale entry or a failing PC no longer
   blocks the SFU fallback; receiver hears the publisher via SFU until
   mesh actually delivers.

2. mesh-fails-side: when an existing mesh PC transitions to 'failed',
   the audio element was bound to the dying mesh stream. Reach into
   sfuStreamsByPubHex and re-attach the cached SFU stream so the
   listener hears continuous audio while the mesh reconnect runs in
   the background, instead of a silent gap.

Mesh stays the preferred path when it's actually working — only
takes over the audio binding via its own ontrack when 'connected'.

web/zebra-spaces.html

@@ -2531,10 +2531,17 @@ function handleRemoteSfuTrack(ev){
   for (const [uuid, mm] of members){
     try {
       if (mm.pubkey && hex(unb64(mm.pubkey)) === pubHex){
-        /* speakers get their peers' audio via mesh (lower latency) —
+        /* speakers get their peers' audio via mesh (lower latency)
-         * skip the duplicate SFU mic. screens + cameras still came
+         * AT THE TIMES THE MESH PC IS CONNECTED. A stale or failing
-         * through above. */
+         * mesh PC must NOT block the SFU fallback — that's how the
-        if (canSpeak(myRole) && peers.has(uuid)) return;
+         * 'phone re-promoted but nobody hears them' regression
+         * appeared: the peers map still had an entry whose state
+         * was 'failed', so we skipped SFU and the receiver got no
+         * audio at all. */
+        if (canSpeak(myRole)){
+          const meshPC = peers.get(uuid);
+          if (meshPC && meshPC.connectionState === 'connected') return;
+        }
         attachSfuTrack(uuid, ev.streams[0]);
         return;
       }
@@ -3433,6 +3440,11 @@ async function connectToPeer(uuid, weOffer){
     if (pc.connectionState === 'failed' && peers.get(uuid) === pc){
       logLine('', 'peer '+uuid+' failed — reconnecting');
       tearPeer(uuid);
+      /* Mesh PC just died; the audio element for this peer was bound to
+       * the dying mesh stream and won't recover on its own. Switch back
+       * to the cached SFU stream so the user keeps hearing them while
+       * mesh reconnect attempts run in the background. */
+      try { attachCachedSfuStreamFor(uuid); } catch(_){}
       /* let the offerer drive recovery */
       setTimeout(()=>{ if (members.has(uuid) && canSpeak(members.get(uuid).role) && canSpeak(myRole))
         connectToPeer(uuid, myUUID < uuid); }, 1500);
@@ -4010,8 +4022,8 @@ logLine('', 'ready — pick a handle, type a rendezvous code, enter the space');
 
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