[Bugfix][Qwen3-Omni] Fix synchronous Thinker pipeline parallelism (#7345)

Signed-off-by: Deep Shah <deep@socratic.co>

tests/worker/test_pp_intermediate_output.py

@@ -0,0 +1,48 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM-Omni project
+"""Non-final pipeline outputs must reach vLLM's existing PP sender unchanged."""
+
+from types import SimpleNamespace
+
+import pytest
+import torch
+from vllm.sequence import IntermediateTensors
+from vllm.v1.worker.gpu_model_runner import GPUModelRunner
+
+from vllm_omni.worker.gpu_model_runner import OmniGPUModelRunner
+
+pytestmark = [pytest.mark.core_model, pytest.mark.cpu, pytest.mark.parallel]
+
+
+def test_nonfinal_forward_bypasses_final_output_conversion(monkeypatch):
+    intermediate = IntermediateTensors({"hidden_states": torch.ones(4, 8), "residual": torch.ones(4, 8)})
+    monkeypatch.setattr(GPUModelRunner, "_model_forward", lambda *args, **kwargs: intermediate)
+
+    def final_only_converter(*args, **kwargs):
+        pytest.fail("A non-final rank must not convert intermediate tensors to OmniOutput")
+
+    runner = object.__new__(OmniGPUModelRunner)
+    runner.model = SimpleNamespace(make_omni_output=final_only_converter, have_multimodal_outputs=True)
+    runner._build_model_kwargs_extra = lambda: {}
+    result = runner._model_forward()
+    assert result is intermediate
+    hidden, multimodal = runner.extract_multimodal_outputs(result)
+    assert hidden is intermediate
+    assert multimodal == {}
+
+
+def test_final_tensor_still_uses_model_converter(monkeypatch):
+    tensor = torch.ones(4, 8)
+    monkeypatch.setattr(GPUModelRunner, "_model_forward", lambda *args, **kwargs: tensor)
+    converted = object()
+    calls = []
+
+    def convert(value, **kwargs):
+        calls.append(value)
+        return converted
+
+    runner = object.__new__(OmniGPUModelRunner)
+    runner.model = SimpleNamespace(make_omni_output=convert)
+    runner._build_model_kwargs_extra = lambda: {}
+    assert runner._model_forward() is converted
+    assert calls == [tensor]