[Bugfix] Fix make_request_output TypeError on multimodal generation-stage outputs (#4579)

Signed-off-by: QianCyrus <happyloser233@gmail.com>
Co-authored-by: Hongsheng Liu <liuhongsheng4@huawei.com>

tests/engine/test_output_processor.py

@@ -4,6 +4,7 @@
 
 from unittest.mock import MagicMock
 
+import numpy as np
 import pytest
 import torch
 from vllm.outputs import PoolingRequestOutput
@@ -250,6 +251,25 @@ def test_no_detokenizer_make_request_output():
     assert AUDIO in result.outputs[0].multimodal_output
 
 
+def test_no_detokenizer_make_request_output_with_routed_experts():
+    """make_request_output accepts the routed_experts arg that the multimodal
+    output channel (_process_mm_only_outputs) passes positionally, and attaches
+    it to the completion output.
+
+    Regression: the call site passes 6 positional args
+    (..., kv_transfer_params, routed_experts) but the override previously took
+    only 5, raising TypeError on every generation-stage output.
+    """
+    s = _make_no_detok_state(RequestOutputKind.CUMULATIVE)
+    s.add_multimodal_tensor(torch.randn(10), mm_type=AUDIO)
+    routed_experts = np.zeros((2, 3), dtype=np.int32)
+    # Mirror the exact call shape of _process_mm_only_outputs.
+    result = s.make_request_output([], None, FinishReason.STOP, None, None, routed_experts)
+    assert result is not None
+    assert not isinstance(result, PoolingRequestOutput)
+    assert result.outputs[0].routed_experts is routed_experts
+
+
 def test_no_detokenizer_stream_interval_skipped():
     """stream_interval > 1 does not crash when detokenizer is None."""
     kwargs = {**_NO_DETOK_STATE_KWARGS, "stream_interval": 5}