fix: 修复 JSON 解析导致的 tool_name 丢失问题

## 问题
商品搜索时工具名丢失，导致 404 错误：
```
HTTP Request: POST http://product_mcp:8004/tools/ "HTTP/1.1 404 Not Found"
```

URL 应该是 `/tools/search_products` 但实际是 `/tools/`（工具名丢失）

## 根本原因
当 LLM 返回带 ```json``` 代码块格式的 JSON 时：

```
```json
{
  "action": "call_tool",
  "tool_name": "search_products",
  "arguments": {"keyword": "ring"}
}
```
```

解析逻辑处理后：
1. 移除 ```` → 得到 `json\n{\n...`
2. 移除 `json` → 得到 `\n{\n...`
3. 内容以换行符开头，不是 `{`
4. 被误判为非 JSON 格式（`tool_name\n{args}`）
5. 按换行符分割，第一行为空 → `tool_name = ""`

## 解决方案
**第 189 行**：添加 `content.strip()` 去除前后空白

```python
if content.startswith("```"):
    content = content.split("```")[1]
    if content.startswith("json"):
        content = content[4:]
    # Remove leading/trailing whitespace after removing code block markers
    content = content.strip()  # ← 新增
```

## 额外改进
**第 217-224 行**：添加工具调用日志

```python
logger.info(
    "Product agent calling tool",
    tool_name=tool_name,
    arguments=arguments,
    conversation_id=state["conversation_id"]
)
```

便于调试工具调用问题。

## 测试验证

修复前：
```
tool_name = ""  (空字符串)
URL: /tools/     (缺少工具名)
```

修复后：
```
tool_name = "search_products"  (正确)
URL: /tools/search_products     (完整路径)
```

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

agent/agents/product.py

@@ -185,6 +185,8 @@ async def product_agent(state: AgentState) -> AgentState:
             content = content.split("```")[1]
             if content.startswith("json"):
                 content = content[4:]
+            # Remove leading/trailing whitespace after removing code block markers
+            content = content.strip()
 
         # Handle non-JSON format: "tool_name\n{args}"
         if '\n' in content and not content.startswith('{'):
@@ -214,9 +216,17 @@ async def product_agent(state: AgentState) -> AgentState:
 
         if action == "call_tool":
             arguments = result.get("arguments", {})
+            tool_name = result.get("tool_name", "")
+
+            logger.info(
+                "Product agent calling tool",
+                tool_name=tool_name,
+                arguments=arguments,
+                conversation_id=state["conversation_id"]
+            )
 
             # Inject context for product search (Mall API)
-            if result["tool_name"] == "search_products":
+            if tool_name == "search_products":
                 arguments["user_token"] = state.get("user_token")
                 arguments["user_id"] = state["user_id"]
                 arguments["account_id"] = state["account_id"]
@@ -230,12 +240,12 @@ async def product_agent(state: AgentState) -> AgentState:
                     )
 
             # Inject context for recommendation
-            if result["tool_name"] == "recommend_products":
+            if tool_name == "recommend_products":
                 arguments["user_id"] = state["user_id"]
                 arguments["account_id"] = state["account_id"]
 
             # Inject context for quote
-            if result["tool_name"] == "get_quote":
+            if tool_name == "get_quote":
                 arguments["account_id"] = state["account_id"]
 
             # Use entity if available
@@ -247,7 +257,7 @@ async def product_agent(state: AgentState) -> AgentState:
 
             state = add_tool_call(
                 state,
-                tool_name=result["tool_name"],
+                tool_name=tool_name,
                 arguments=arguments,
                 server="product"
             )