toAISdkFormat and stream export issues (AI SDK v5)

  const result1 = await agent1.streamVNext(finalMessages, {
    runtimeContext,
    stopWhen: stepCountIs(100),
  });

  const stream = createUIMessageStream({
    execute: async ({ writer }) => {
      for await (const part of toAISdkFormat(result1, { from: 'agent' })!) {
        writer.write(part);
      }
    },
    generateId: generateUUID,
    onFinish: async ({ messages: finished }) => {
      await saveMessages({
        messages: finished
          .filter((m) => m.role !== 'user')
          .map((m) => ({
            id: isUuidV4(m.id) ? m.id : generateUUID(),
            role: m.role,
            parts: m.parts as ChatMessagePart[],
            createdAt: new Date(),
            attachments: [],
            chatId,
          })),
      });
    },
    onError: () => 'Oops, an error occurred!',
  });

  // Set headers and return SSE stream (Express.js adaptation)
  res.writeHead(200, {
    'Content-Type': 'text/event-stream',
    'Cache-Control': 'no-cache',
    Connection: 'keep-alive',
    'Access-Control-Allow-Origin': '*',
  });

  const sseStream = stream.pipeThrough(new JsonToSseTransformStream());
  const reader = sseStream.getReader();