花括号解析报错

LangChain 03：Message解析

# 原来的（会触发模板解析）
executor_prompt_tpl = ChatPromptTemplate.from_messages([
    ("system", executor_prompt.format(past_steps=past_steps_str, current_step=current_plan_str)),
    ("placeholder", "{messages}")
])
past_steps_str:'{"actionTitle": "...", "symbols": ["TSLA","AAPL"], ...} I have fetched ...'
导致解析错误

# ✅ 用 SystemMessage 固定文本；用 MessagesPlaceholder 承载对话消息
executor_prompt_tpl = ChatPromptTemplate.from_messages([
    SystemMessage(content=executor_prompt.format(
        past_steps=past_steps_str,
        current_step=current_plan_str
    )),
    MessagesPlaceholder("messages"),
])