Fix reasoning_parser crash: reconstruct StructuredOutputsConfig from dict (#2845)

Signed-off-by: Mike_Qiu <qiudayu.qdy@antgroup.com>
Co-authored-by: Mike_Qiu <qiudayu.qdy@antgroup.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: Hongsheng Liu <liuhongsheng4@huawei.com>

vllm_omni/engine/stage_init_utils.py

@@ -619,6 +619,19 @@ def build_vllm_config(
         )
 
     filtered_engine_args_dict = filter_dataclass_kwargs(OmniEngineArgs, engine_args_dict)
+
+    # _to_dict serializes dataclass fields (e.g. StructuredOutputsConfig) into
+    # plain dicts.  When OmniEngineArgs is instantiated with the dict, these
+    # fields remain dicts instead of being reconstructed as dataclass objects.
+    # Later, EngineArgs.create_engine_config() does
+    #   self.structured_outputs_config.reasoning_parser = ...
+    # which fails on a plain dict.  Reconstruct the dataclass here.
+    soc = filtered_engine_args_dict.get("structured_outputs_config")
+    if isinstance(soc, dict):
+        from vllm.config import StructuredOutputsConfig
+
+        filtered_engine_args_dict["structured_outputs_config"] = StructuredOutputsConfig(**soc)
+
     omni_engine_args = OmniEngineArgs(**filtered_engine_args_dict)
 
     # Multi-stage pipelines (qwen3_tts code2wav, etc.) set max_model_len