[Refactor] Remove legacy stage_args YAML loader (#6200)

Signed-off-by: zwhzzz0821 <2831474076@qq.com>
Co-authored-by: Hongsheng Liu <liuhongsheng4@huawei.com>

tests/entrypoints/test_async_omni_diffusion_config.py

@@ -492,6 +492,24 @@ def test_resolve_stage_configs_injects_additional_config_into_diffusion_stage(mo
     assert stage_configs[1].engine_args.additional_config == {"torchair_graph_config": {"enabled": True}}
 
 
+@pytest.mark.parametrize(
+    ("legacy_arg", "value"),
+    [
+        ("stage_configs_path", "legacy.yaml"),
+        ("stage_configs", [{"stage_id": 0}]),
+    ],
+)
+def test_resolve_stage_configs_rejects_legacy_config_arguments(legacy_arg, value):
+    engine = AsyncOmniEngine.__new__(AsyncOmniEngine)
+
+    with pytest.raises(ValueError, match=rf"`{legacy_arg}`.*`deploy_config`"):
+        engine._resolve_stage_configs(
+            "dummy-model",
+            {legacy_arg: value},
+            trust_remote_code=False,
+        )
+
+
 def test_default_stage_config_includes_quantization_config():
     """Ensure structured quantization_config survives default diffusion-stage creation."""
     quantization_config = {