Returns:
            CallbackManagerForToolRun: The callback manager for the tool run.
        """
        if run_id is None:
            run_id = uuid.uuid4()
        _handle_event(
            self.handlers,
            "on_tool_start",
            "ignore_agent",
            serialized,
            input_str,
            run_id=run_id,
            parent_run_id=self.parent_run_id,
            tags=self.tags,
            metadata=self.metadata,
            **kwargs,
        )
        return CallbackManagerForToolRun(
            run_id=run_id,
            handlers=self.handlers,
            inheritable_handlers=self.inheritable_handlers,
            parent_run_id=self.parent_run_id,
            tags=self.tags,
            inheritable_tags=self.inheritable_tags,
            metadata=self.metadata,
            inheritable_metadata=self.inheritable_metadata,
        )
[docs]    def on_retriever_start(
        self,
        serialized: Dict[str, Any],
        query: str,
        run_id: Optional[UUID] = None,
        parent_run_id: Optional[UUID] = None,
        **kwargs: Any,
    ) -> CallbackManagerForRetrieverRun:
        """Run when retriever starts running."""
        if run_id is None:
            run_id = uuid.uuid4()
        _handle_event(
            self.handlers,
            "on_retriever_start",
            "ignore_retriever",
            serialized,
            query,
            run_id=run_id,
            parent_run_id=self.parent_run_id,
            tags=self.tags,
            metadata=self.metadata,
            **kwargs,
        )
        return CallbackManagerForRetrieverRun(
            run_id=run_id,
            handlers=self.handlers,