Operation stream termination is not an error

According to the GrpcRemoteExecutor when it occurs after a !done operation response. Remove the error from the
ExperimentalRemoteGrpcExecutor and reinforce both with tests.

Update the FakeExecutionService to generate compatible error responses that appear in the ExecuteResponse, rather than the operation error field, per the REAPI spec. Made required adjustments to ExGRE Test invocations to avoid the ExecutionStatusException interpretation of DEADLINE_EXCEEDED -> FAILED_PRECONDITION in ExecuteResponse.

Closes #18785.

PiperOrigin-RevId: 546925894
Change-Id: I7a489c8bc936a83cfd94e0138437f3fe6d152da8

src/main/java/com/google/devtools/build/lib/remote/ExperimentalGrpcRemoteExecutor.java

@@ -146,10 +146,12 @@ ExecuteResponse start() throws IOException, InterruptedException {
         // retrying when received a unauthenticated error, and propagate to refreshIfUnauthenticated
         // which will then call retrier again. It will reset the retry time counter so we could
         // retry more than --remote_retry times which is not expected.
-        response =
-            retrier.execute(
-                () -> Utils.refreshIfUnauthenticated(this::execute, callCredentialsProvider),
-                executeBackoff);
+        if (lastOperation == null) {
+          response =
+              retrier.execute(
+                  () -> Utils.refreshIfUnauthenticated(this::execute, callCredentialsProvider),
+                  executeBackoff);
+        }
 
         // If no response from Execute(), use WaitExecution() in a "loop" which is implemented
         // inside the retry block.
@@ -216,6 +218,7 @@ ExecuteResponse waitExecution() throws IOException {
     }
 
     /** Process a stream of operations from Execute() or WaitExecution(). */
+    @Nullable
     ExecuteResponse handleOperationStream(Iterator<Operation> operationStream) throws IOException {
       try {
         while (operationStream.hasNext()) {
@@ -258,8 +261,8 @@ ExecuteResponse handleOperationStream(Iterator<Operation> operationStream) throw
           }
         }
 
-        // The operation completed successfully but without a result.
-        throw new IOException("Remote server error: execution terminated with no result");
+        // The operation stream completed successfully but without a result.
+        return null;
       } finally {
         close(operationStream);
       }