messages: List[BaseMessage],
        stop: Optional[List[str]] = None,
        run_manager: Optional[CallbackManagerForLLMRun] = None,
        **kwargs: Any,
    ) -> ChatResult:
        llm_input = self._to_chat_prompt(messages)
        llm_result = self.llm._generate(
            prompts=[llm_input], stop=stop, run_manager=run_manager, **kwargs
        )
        return self._to_chat_result(llm_result)
    async def _agenerate(
        self,
        messages: List[BaseMessage],
        stop: Optional[List[str]] = None,
        run_manager: Optional[AsyncCallbackManagerForLLMRun] = None,
        **kwargs: Any,
    ) -> ChatResult:
        llm_input = self._to_chat_prompt(messages)
        llm_result = await self.llm._agenerate(
            prompts=[llm_input], stop=stop, run_manager=run_manager, **kwargs
        )
        return self._to_chat_result(llm_result)
    def _to_chat_prompt(
        self,
        messages: List[BaseMessage],
    ) -> str:
        """Convert a list of messages into a prompt format expected by wrapped LLM."""
        if not messages:
            raise ValueError("at least one HumanMessage must be provided")
        if not isinstance(messages[0], SystemMessage):
            messages = [self.system_message] + messages
        if not isinstance(messages[1], HumanMessage):
            raise ValueError(
                "messages list must start with a SystemMessage or UserMessage"
            )
        if not isinstance(messages[-1], HumanMessage):
            raise ValueError("last message must be a HumanMessage")
        prompt_parts = []