[Diffusion] Fix DLO DP concurrent request execution (#5864)

Signed-off-by: lishunyang12 <lishunyang12@163.com>

tests/diffusion/test_ipc_async.py

@@ -137,6 +137,18 @@ class TestPackDiffusionOutputShmWithD2hStream:
             d2h_stream=d2h,
         )
 
+    @pytest.mark.parametrize("wrapped_in_rpc_envelope", [False, True])
+    def test_dp_tagged_output_path_with_stream(self, mocker, wrapped_in_rpc_envelope):
+        mock_pack_fields = mocker.patch(
+            "vllm_omni.diffusion.ipc._pack_diffusion_fields",
+        )
+        d2h = mocker.MagicMock()
+        result = DiffusionOutput()
+        tagged = {"dp_rank": 1, "output": result}
+        value = {"type": "diffusion_rpc_result", "result": tagged} if wrapped_in_rpc_envelope else tagged
+        pack_diffusion_output_shm(value, d2h_stream=d2h)
+        mock_pack_fields.assert_called_once_with(result, d2h_stream=d2h)
+
     def test_runner_output_path_with_stream(self, mocker):
         mock_pack_fields = mocker.patch(
             "vllm_omni.diffusion.ipc._pack_diffusion_fields",