fix: prevent tool description cache mutation (#3540)

main/xiaozhi-server/core/providers/tools/unified_tool_manager.py

@@ -47,9 +47,12 @@ class ToolManager:
         return all_tools
 
     def get_function_descriptions(self) -> List[Dict[str, Any]]:
-        """获取所有工具的函数描述（OpenAI格式）"""
+        """获取所有工具的函数描述（OpenAI格式）
+
+        返回缓存的浅拷贝，防止调用方就地修改污染缓存。
+        """
         if self._cached_function_descriptions is not None:
-            return self._cached_function_descriptions
+            return list(self._cached_function_descriptions)
 
         descriptions = []
         tools = self.get_all_tools()
@@ -57,7 +60,7 @@ class ToolManager:
             descriptions.append(tool_definition.description)
 
         self._cached_function_descriptions = descriptions
-        return descriptions
+        return list(descriptions)
 
     def has_tool(self, tool_name: str) -> bool:
         """检查是否存在指定工具"""