core: remember last pick status in no real stream

core/src/main/java/io/grpc/internal/DelayedClientTransport.java

@@ -286,6 +286,9 @@ final void reprocess(@Nullable SubchannelPicker picker) {
 
     for (final PendingStream stream : toProcess) {
       PickResult pickResult = picker.pickSubchannel(stream.args);
+      if (!pickResult.hasResult()) {
+        stream.lastPickStatus = pickResult.getStatus();
+      }
       CallOptions callOptions = stream.args.getCallOptions();
       // User code provided authority takes precedence over the LB provided one.
       if (callOptions.getAuthority() == null && pickResult.getAuthorityOverride() != null) {

core/src/main/java/io/grpc/internal/DelayedStream.java

@@ -63,6 +63,7 @@ class DelayedStream implements ClientStream {
   private long streamSetTimeNanos;
   // No need to synchronize; start() synchronization provides a happens-before
   private List<Runnable> preStartPendingCalls = new ArrayList<>();
+  protected Status lastPickStatus;
 
   @Override
   public void setMaxInboundMessageSize(final int maxSize) {
@@ -109,6 +110,7 @@ public void appendTimeoutInsight(InsightBuilder insight) {
       } else {
         insight.appendKeyValue("buffered_nanos", System.nanoTime() - startTimeNanos);
         insight.append("waiting_for_connection");
+        insight.append(lastPickStatus);
       }
     }
   }

core/src/test/java/io/grpc/internal/DelayedClientTransportTest.java

@@ -756,7 +756,7 @@ public void pendingStream_appendTimeoutInsight_waitForReady() {
     InsightBuilder insight = new InsightBuilder();
     stream.appendTimeoutInsight(insight);
     assertThat(insight.toString())
-        .matches("\\[wait_for_ready, buffered_nanos=[0-9]+\\, waiting_for_connection]");
+        .matches("\\[wait_for_ready, buffered_nanos=[0-9]+\\, waiting_for_connection, null]");
   }
 
   private static TransportProvider newTransportProvider(final ClientTransport transport) {

core/src/test/java/io/grpc/internal/DelayedStreamTest.java

@@ -450,7 +450,8 @@ public void appendTimeoutInsight_realStreamNotSet() {
     InsightBuilder insight = new InsightBuilder();
     stream.start(listener);
     stream.appendTimeoutInsight(insight);
-    assertThat(insight.toString()).matches("\\[buffered_nanos=[0-9]+\\, waiting_for_connection]");
+    assertThat(insight.toString())
+        .matches("\\[buffered_nanos=[0-9]+\\, waiting_for_connection, null]");
   }
 
   @Test