zebra-spaces: mesh.recv telemetry — surface mesh PC audio decoder stats

Fox 2026-06-07 follow-up to ticket 0001: with the caa0548 fix live,
SFU sub PC receivers still show level=0 + jbuf=? on blanka-chrome.
That's EXPECTED when mesh has taken the swap (SFU receiver becomes
orphaned by design), but without a corresponding stat from the mesh
PC's own receiver we can't distinguish "mesh decoder is alive and
producing samples; SFU orphan is fine" from "mesh decoder is also
silent — both paths dead, listener hears nothing".

Add per-peer mesh.recv lines to the telemetry tick, tagged with the
short uuid prefix:

  mesh.recv u=8afc pkt=23900 lost=8 bytes=339884 jitter=0.0080
            level=0.025 jbuf=0.48s lp=0.1s

Same fields as aud.recv (the SFU sub PC line) so direct comparison
is easy. We skip peers whose connectionState !== 'connected' so a
failed mesh PC doesn't poison the line. Failure on one peer's
getStats is swallowed independently — multi-peer rooms remain
readable even if one mesh PC's stats reporter throws.

Reveals (per ticket 0001 next narrowing):
  - mesh decoder level + jbuf — proves or rules out the mesh decoder
    being orphaned at the worklet swap point
  - per-peer breakdown when mesh=N > 1, so we can tell which peer's
    mesh path is healthy and which is stalled
  - same lastPacketReceived 'lp' so a mesh RTP stall is visible at
    a glance

web/zebra-spaces.html

@@ -5877,6 +5877,41 @@ async function dumpTelemetry(){
       });
     } catch(e){ parts.push('stats.err=' + e.message); }
   }
+  /* mesh receiver stats — one line per peer's mesh PC inbound audio.
+   * Lets us tell whether the worklet is being fed by a live mesh
+   * decoder vs an orphaned one. For ticket 0001 we needed to answer:
+   * when handleRemoteSfuTrack hands off to mesh and the SFU receiver
+   * reports level=0+jbuf=? (expected — orphaned), is the MESH receiver
+   * actually decoding (level>0+jbuf>0) or also silent? fox 2026-06-07.
+   *
+   * Each peer's PC has one audio inbound-rtp; tag with the short uuid
+   * so a multi-peer room is readable. Failure on one peer's getStats
+   * doesn't stop the others. */
+  for (const [uuid, pc] of peers){
+    if (!pc || typeof pc.getStats !== 'function') continue;
+    if (pc.connectionState !== 'connected') continue;   /* skip non-live PCs */
+    try {
+      const stats = await pc.getStats(null);
+      const nowMs = Date.now();
+      stats.forEach(r => {
+        if (r.type !== 'inbound-rtp' || r.kind !== 'audio') return;
+        const lp = r.lastPacketReceivedTimestamp
+          ? ((nowMs - r.lastPacketReceivedTimestamp) / 1000).toFixed(1) + 's'
+          : '?';
+        const jbuf = (r.jitterBufferEmittedCount > 0)
+          ? (r.jitterBufferDelay / r.jitterBufferEmittedCount).toFixed(2) + 's'
+          : '?';
+        parts.push('mesh.recv u=' + uuid.slice(0,4) +
+                   ' pkt=' + (r.packetsReceived|0) +
+                   ' lost=' + (r.packetsLost|0) +
+                   ' bytes=' + (r.bytesReceived|0) +
+                   ' jitter=' + (r.jitter || 0).toFixed(4) +
+                   ' level=' + (r.audioLevel || 0).toFixed(3) +
+                   ' jbuf=' + jbuf +
+                   ' lp=' + lp);
+      });
+    } catch(_){}
+  }
   /* publisher-side stats — what we are actually emitting on the wire.
    * One line per kind so screen-audio shows up independently of
    * screen-video (earlier collapse hid scr.send.aud entirely under
@@ -8148,8 +8183,8 @@ logLine('', 'ready — pick a handle, type a rendezvous code, enter the space');
 
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