keepLastMessageOnError does not keep last message on DataStream

[Aarr0w]

Description

"ai": "^3.4.10"
Even with keepLastMessageOnError: true, the user's last message disappears when an error is thrown from a tool in streamText
the route.ts api is returning streamText result.toDataStreamResponse()

Code example

const {
    input,
    handleInputChange,
    handleSubmit,
    messages,
    setMessages,
  } = useChat({
    id,
    api,
    keepLastMessageOnError: true,
    onError(error) {
      console.log(error);
      console.log(JSON.stringify(messages.at(-1)) // does not see previous user message
    },
  });

export async function POST(req: NextRequest) {
  const { messages } = (await req.json()) as {
    messages: Message[];
  };
  const dataStream = new StreamData();

    const result =  await streamText({
    	model: gpt4o,
    	messages: convertToCoreMessages(messages),
    	system: systemPrompt,

    	tools: {
      		getWeather: {
        		description: "gets weather info",
        		parameters: z.object({}),
        		execute: async function (args: any) {
          			// using AISDKError b/c regular Error does not show up in useChat onError(), same message behavior
          			throw new AISDKError({
            			name: "simulated error",
            			message: "user message disappears",
          			});
        		},
      		},
    });
    
 return result.toDataStreamResponse({data: dataStream});
}

Additional context

No response

[ernecastro]

I'm having this issue as well. It makes really hard to handle errors and retries.

[lgrammel]

this functionality has been changed with ai sdk 5