vllm - 💡(How to fix) Fix [Bug]:Qwen3.5 with reasoning-parser returns non-standard tool call format when enable_thinking=true

</details>


### 🐛 Describe the bug


## 🐛 Bug Description

When using Qwen3.5-27B with `--reasoning-parser qwen3` and `--tool-call-parser qwen3_coder` (or `hermes`), enabling thinking mode (`enable_thinking=true`) causes tool calls to be returned in non-standard XML format within the `content` field, instead of the standard OpenAI-compatible `tool_calls` array.

When `enable_thinking=false`, tool calls are correctly parsed and returned in the `tool_calls` field.



## 🚀 Launch Command

```bash
export VLLM_LOGGING_CONFIG_PATH=/home/up_docker/src/logging_config.json
export PYTORCH_NPU_ALLOC_CONF="expandable_segments:True"
export OMP_NUM_THREADS=1
export LD_PRELOAD=/usr/lib64/libjemalloc.so.2:$LD_PRELOAD
export TASK_QUEUE_ENABLE=1

vllm serve /data/Qwen3.5-27B \
  --served-model-name Qwen3.5-27B \
  --host 0.0.0.0 \
  --port 8101 \
  --data-parallel-size 1 \
  --tensor-parallel-size 4 \
  --gpu-memory-utilization 0.9 \
  --compilation-config '{"cudagraph_mode":"FULL_DECODE_ONLY"}' \
  --async-scheduling \
  --additional-config '{"enable_cpu_binding":true}' \
  --speculative_config '{"method": "qwen3_5_mtp", "num_speculative_tokens": 3, "enforce_eager": true}' \
  --enable-auto-tool-choice \
  --tool-call-parser qwen3_coder \
  --enable-chunked-prefill \
  --enable-prefix-caching \
  --reasoning-parser qwen3 \
  --max-num-batched-tokens 16384

{
    "model": "Qwen3.5-27B",
    "temperature": 0.1,
    "top_p": 0.1,
    "stream": false,
    "chat_template_kwargs": {"enable_thinking": true},
    "response_format": {
        "type": "json_schema",
        "json_schema": {
            "name": "navigator_output",
            "strict": true,
            "schema": {
                "$schema": "https://json-schema.org/draft/2020-12/schema",
                "type": "object",
                "properties": {
                    "current_state": {
                        "type": "object",
                        "properties": {
                            "evaluation_previous_goal": {"type": "string"},
                            "memory": {"type": "string"},
                            "next_goal": {"type": "string"}
                        },
                        "required": ["evaluation_previous_goal", "memory", "next_goal"]
                    },
                    "action": {
                        "type": "array",
                        "items": {"type": "object"}
                    }
                },
                "required": ["current_state", "action"]
            }
        }
    },
    "messages": [
        {"role": "user", "content": "请帮我填写日志"}
    ],
    "tools": [
        {
            "type": "function",
            "function": {
                "name": "AgentOutput",
                "description": "Agent output structure",
                "parameters": {
                    "type": "object",
                    "properties": {
                        "current_state": {
                            "type": "object",
                            "properties": {
                                "evaluation_previous_goal": {"type": "string"},
                                "memory": {"type": "string"},
                                "next_goal": {"type": "string"}
                            }
                        },
                        "action": {
                            "type": "array",
                            "items": {"type": "object"}
                        }
                    },
                    "required": ["current_state", "action"]
                }
            }
        }
    ]
}

{
    "id": "chatcmpl-8e0d6f4d5cbaf6ab",
    "object": "chat.completion",
    "created": 1778048205,
    "model": "Qwen3.5-27B",
    "choices": [
        {
            "index": 0,
            "message": {
                "role": "assistant",
                "content": "\n\n<tool_call>\n<function=AgentOutput>\n<parameter=current_state>\n{\"evaluation_previous_goal\": \"Success - 浏览器已启动...\", \"memory\": \"用户需要填写三个时间段...\", \"next_goal\": \"点击'+ 新增'按钮...\"}\n</parameter>\n<parameter=action>\n[{\"click_element\": {\"intent\": \"点击新增按钮添加日志\", \"index\": 4}}]\n</parameter>\n</function>\n</tool_call>",
                "tool_calls": [],
                "reasoning": "当前页面已经显示了我的日志页面..."
            },
            "finish_reason": "stop"
        }
    ]
}

{
    "choices": [
        {
            "message": {
                "role": "assistant",
                "content": null,
                "tool_calls": [
                    {
                        "id": "call_xxx",
                        "type": "function",
                        "function": {
                            "name": "AgentOutput",
                            "arguments": "{\"current_state\": {...}, \"action\": [...]}"
                        }
                    }
                ],
                "reasoning": "当前页面已经显示了我的日志页面..."
            }
        }
    ]
}