langchain/agents/agent.py/AgentExecutor/validate_return_direct_tool
class AgentExecutor:    def validate_return_direct_tool(cls, values: Dict) -> Dict:
        """Validate that tools are compatible with agent."""
        agent = values["agent"]
        tools = values["tools"]
        if isinstance(agent, BaseMultiActionAgent):
            for tool in tools:
                if tool.return_direct:
                    raise ValueError(
                        "Tools that have `return_direct=True` are not allowed "
                        "in multi-action agents"
                    )
        return values