[GPT-OSS] Structure_Tag support for gpt-oss tool-call in cot (#25515)

Signed-off-by: Hanchenli <lihanc2002@gmail.com>
Signed-off-by: Hanchenli <61769611+Hanchenli@users.noreply.github.com>
Signed-off-by: Wei Wei <wwei6@meta.com>
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>
Co-authored-by: Wei Wei <wwei6@meta.com>
Co-authored-by: Wei Wei <weiweinpu@gmail.com>
Co-authored-by: Cyrus Leung <tlleungac@connect.ust.hk>

vllm/v1/structured_output/__init__.py

@@ -73,6 +73,10 @@ class StructuredOutputManager:
                 )
                 self.reasoner = reasoner_cls(tokenizer=self.tokenizer)
 
+        self.enable_in_reasoning = (
+            self.vllm_config.structured_outputs_config.enable_in_reasoning
+        )
+
     def grammar_init(self, request: Request) -> None:
         if request.structured_output_request is None:
             return
@@ -274,7 +278,13 @@ class StructuredOutputManager:
         return bitmask_tensor.numpy()
 
     def should_fill_bitmask(self, request: Request) -> bool:
+        # NOTE (Hanchen) if enable_in_reasoning is True, it means that
+        # the model needs to be constrained in reasoning. So we should always
+        # enable the bitmask filling.
+
         if self.reasoner is not None:
+            if self.enable_in_reasoning:
+                return True
             assert request.structured_output_request is not None
             if request.structured_output_request.reasoning_ended is None:
                 request.structured_output_request.reasoning_ended = (
@@ -297,6 +307,10 @@ class StructuredOutputManager:
         if self.reasoner is None:
             return True
 
+        # if the model needs structured in reasoning, we should advance
+        if self.enable_in_reasoning:
+            return True
+
         structured_req = request.structured_output_request
         if structured_req.reasoning_ended:
             return True