fix(vp8channel): client ignores frames from other participants

In single-peer mode (client), frames from unknown epochs are now
silently dropped instead of triggering a reconnect loop. This
prevents the client from mistaking another client's VP8 track
for a server restart.

Part of #67

internal/transport/vp8channel/transport.go

@@ -680,19 +680,11 @@ func (p *streamTransport) handleIncomingFrame(frame []byte) {
 	if !p.hadPeer.Swap(true) {
 		p.handleFirstPeer(peerEpoch)
 	} else if prev := p.peerEpoch.Load(); prev != peerEpoch {
-		// Peer restarted its KCP session. Reset ours so the conv state
-		// machines re-converge. CAS guards against double-reset when
-		// fragmented frames straddle the epoch boundary.
-		if p.peerEpoch.CompareAndSwap(prev, peerEpoch) {
-			p.resetKCP()
-			p.reconnectMu.Lock()
-			fn := p.reconnectFn
-			p.reconnectMu.Unlock()
-			if fn != nil {
-				fn()
-			}
-		}
-		// Drop this packet: it predates our fresh KCP session.
+		// In a multi-participant room, other clients also publish VP8
+		// tracks. Their epochs differ from our latched peer (the server).
+		// Simply ignore frames that don't match our peer — they belong to
+		// other participants we don't communicate with.
+		logger.Debugf("vp8channel: ignoring frame from unknown epoch=0x%08x (latched=0x%08x)", peerEpoch, prev)
 		return
 	}
 

internal/transport/vp8channel/transport_unit_test.go

@@ -374,8 +374,13 @@ func TestHandleIncomingFrameEpochFilteringAndReconnect(t *testing.T) {
 		t.Fatalf("stream reconnect did not reset/callback: reconnected=%v kcp=%v", reconnected, tr.kcp)
 	}
 	reconnected = false
-	tr.handleIncomingFrame(mkFrame(tr.bindingToken, 2, []byte("after-restart")))
-	if !reconnected || tr.peerEpoch.Load() != 2 || tr.kcp == nil {
-		t.Fatalf("epoch change did not reset/reconnect: reconnected=%v epoch=%d kcp=%v", reconnected, tr.peerEpoch.Load(), tr.kcp) //nolint:lll // long test description
+	// In single-peer mode, frames from a different epoch are ignored (other
+	// participants in the room). The client does NOT reconnect.
+	tr.handleIncomingFrame(mkFrame(tr.bindingToken, 2, []byte("other-participant")))
+	if reconnected {
+		t.Fatal("epoch change from another participant should not trigger reconnect")
+	}
+	if tr.peerEpoch.Load() != 1 {
+		t.Fatalf("peer epoch changed unexpectedly: got %d want 1", tr.peerEpoch.Load())
 	}
 }