fix: reserve Qwen3-Omni NVFP4 backend fix (#7200)

Signed-off-by: kunkunblueberry <1833921874@qq.com>

tests/engine/test_stage_engine_args.py

@@ -11,6 +11,7 @@ from pathlib import Path
 
 import pytest
 from pydantic.fields import FieldInfo
+from transformers import Qwen3OmniMoeConfig
 from vllm.config import CacheConfig as VllmCacheConfig
 from vllm.config import CompilationConfig as VllmCompilationConfig
 from vllm.config import LoadConfig as VllmLoadConfig
@@ -19,6 +20,7 @@ from vllm.config import ProfilerConfig as VllmProfilerConfig
 from vllm.config import SchedulerConfig as VllmSchedulerConfig
 from vllm.engine.arg_utils import EngineArgs
 
+from tests.helpers.stage_config import get_deploy_config_path, modify_stage_config
 from vllm_omni.config.omni_config import (
     _LLM_STAGE_ENGINE_FIELDS,
     OmniStageCacheConfig,
@@ -155,6 +157,44 @@ def test_qwen3_omni_preserves_explicit_moe_backend():
     assert engine_args["moe_backend"] == "flashinfer"
 
 
+def test_qwen3_omni_preserves_explicit_auto_moe_backend():
+    engine_args = {
+        "model_arch": "Qwen3OmniMoeForConditionalGeneration",
+        "moe_backend": "auto",
+    }
+
+    stage_init_utils._maybe_set_qwen3_omni_moe_backend(engine_args)
+
+    assert engine_args["moe_backend"] == "auto"
+
+
+def test_qwen3_omni_nvfp4_ci_config_preserves_auto_moe_backend(tmp_path):
+    """The NVFP4 CI deploy opts stage 0 into vLLM's auto backend selection."""
+    hf_config = Qwen3OmniMoeConfig(enable_audio_output=True)
+    pipeline = resolve_pipeline_config("qwen3_omni_moe", hf_config)
+    assert pipeline is not None
+    nvfp4_deploy = modify_stage_config(
+        get_deploy_config_path("ci/qwen3_omni_moe.yaml"),
+        updates={"stages": {0: {"moe_backend": "auto"}}},
+    )
+    deploy = load_deploy_config(nvfp4_deploy)
+    legacy_stages = merge_pipeline_deploy(pipeline, copy.deepcopy(deploy))
+    omni_config = VllmOmniConfig.from_pipeline_config(
+        pipeline,
+        user_deploy_config=copy.deepcopy(deploy),
+        cli_overrides={"model": str(tmp_path)},
+    )
+
+    for stage_id, expected_backend in ((0, "auto"), (1, "triton")):
+        legacy_stage = next(stage for stage in legacy_stages if stage.stage_id == stage_id)
+        typed_stage = omni_config.stage_by_id(stage_id)
+        for engine_args in (
+            build_engine_args_dict(legacy_stage.to_omegaconf(), str(tmp_path)),
+            build_engine_args_dict_from_omni_stage_config(typed_stage, str(tmp_path)),
+        ):
+            assert engine_args["moe_backend"] == expected_backend
+
+
 def _engine_arg_inputs(tmp_path: Path) -> tuple[PipelineConfig, DeployConfig, str]:
     parent_model = tmp_path / "parent-model"
     stage_model = tmp_path / "stage-model"