fix(e2ee): revert to PR #904 branch, add MAT-144 diagnostics

PR #921 requires custom WebRTC build not yet available.
Added diagnostic logging: encryption_type per track, frame_cryptors count,
and DEC_FAILED re-keying cooldown (5s) to reduce log spam.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

voice.py

@@ -671,14 +671,12 @@ class VoiceSession:
 
             @self.lk_room.on("track_subscribed")
             def on_ts(t, pub, p):
-                logger.info("Track sub: %s %s kind=%s muted=%s", p.identity, pub.sid, t.kind, pub.muted)
-                # NOTE: Do NOT create rtc.AudioStream here — it competes with AgentSession's
-                # internal audio pipeline for event loop time, causing intermittent VAD failures
-                # (user_state stuck on "away"). See MAT-40. Use e2ee_state_changed for flow confirmation.
-                # MAT-144: Pre-derive HKDF in Python, pass derived key with KDF_RAW.
-                # This ensures exact HKDF match with Element Call JS for both audio AND video.
+                # MAT-144: Log encryption_type to diagnose frame cryptor creation
+                enc_type = getattr(pub, 'encryption_type', 'N/A')
+                logger.info("Track sub: %s %s kind=%s muted=%s enc_type=%s source=%s",
+                            p.identity, pub.sid, t.kind, pub.muted, enc_type,
+                            getattr(pub, 'source', 'N/A'))
                 # Store video track for on-demand vision (look_at_screen tool)
-                # Screen share = source "screen_share" or "screenshare"; camera = "camera" or default
                 if int(t.kind) == 2:  # video track (LiveKit: 1=audio, 2=video)
                     track_source = getattr(pub, 'source', None) or "unknown"
                     self._video_track = t
@@ -690,6 +688,13 @@ class VoiceSession:
                                 track_type, caller_id, len(self._caller_all_keys))
                     try:
                         kp_local = self.lk_room.e2ee_manager.key_provider
+                        # MAT-144: Log frame cryptors count for diagnostics
+                        try:
+                            fc_map = self.lk_room.e2ee_manager.frame_cryptors()
+                            logger.info("E2EE_DIAG: frame_cryptors count=%d keys=%s",
+                                        len(fc_map), list(fc_map.keys()) if fc_map else [])
+                        except Exception:
+                            logger.info("E2EE_DIAG: frame_cryptors() not available")
                         if self._caller_all_keys:
                             for idx, base_k in sorted(self._caller_all_keys.items()):
                                 _derive_and_set_key(kp_local, caller_id, base_k, idx)