Exit DrainPacketQueue thread when build completes.

src/Build/BackEnd/Components/Communications/NodeProviderOutOfProcBase.cs

@@ -683,6 +683,7 @@ public NodeContext(
                 // We select a thread size empirically - for debug builds the minimum possible stack size was too small.
                 // The current size is reported to not have the issue.
                 _drainPacketQueueThread = new Thread(DrainPacketQueue, 0x30000);
+                _drainPacketQueueThread.Name = "DrainPacketQueueThread";
                 _drainPacketQueueThread.IsBackground = true;
                 _drainPacketQueueThread.Start(this);
             }
@@ -850,10 +851,13 @@ private void DrainPacketQueue(object state)
                                 serverToClientStream.Write(writeStreamBuffer, i, lengthToWrite);
                             }
 
-                            if (IsExitPacket(packet))
+                            if (packet is NodeBuildComplete)
                             {
-                                context._exitPacketState = ExitPacketState.ExitPacketSent;
-                                context._packetQueueDrainDelayCancellation.Cancel();
+                                if (IsExitPacket(packet))
+                                {
+                                    context._exitPacketState = ExitPacketState.ExitPacketSent;
+                                    context._packetQueueDrainDelayCancellation.Cancel();
+                                }
 
                                 return;
                             }