Ensure older session does not clobeer newer session. (#1974)

pkg/rtc/participant_signal.go

@@ -58,8 +58,7 @@ func (p *ParticipantImpl) SendJoinResponse(joinResponse *livekit.JoinResponse) e
 		return err
 	}
 
-	// update state after to sending message, so that no participant updates could slip through before JoinResponse is
-	// sent
+	// update state after sending message, so that no participant updates could slip through before JoinResponse is sent
 	p.updateLock.Lock()
 	if p.State() == livekit.ParticipantInfo_JOINING {
 		p.updateState(livekit.ParticipantInfo_JOINED)

pkg/rtc/room.go

@@ -1069,6 +1069,15 @@ func (r *Room) pushAndDequeueUpdates(pi *livekit.ParticipantInfo, isImmediate bo
 				return nil
 			}
 		}
+	} else {
+		ep := r.GetParticipant(identity)
+		if ep != nil {
+			epi := ep.ToProto()
+			if epi.JoinedAt > pi.JoinedAt {
+				// older session update, newer session has already become active, so nothing to do
+				return nil
+			}
+		}
 	}
 
 	if shouldSend {