feat：修改log,优化关系构建逻辑，节省token，

src/chat/utils/chat_message_builder.py

@@ -551,6 +551,9 @@ def build_readable_messages(
         show_actions: 是否显示动作记录
     """
     # 创建messages的深拷贝，避免修改原始列表
+    if not messages:
+        return ""
+
     copy_messages = [msg.copy() for msg in messages]
 
     if show_actions and copy_messages: