Support for responses API background mode

[hi019]

It would be great if the SDK supported the background mode API.
Related issues:

• Vercel or CloudFlare timeout issue #59 (comment)
• openai responses background parameter vercel/ai#6723

[seratch]

Thanks for writing in. There are some technical challenges on supporting background mode in agents, but we're aware of the need.

[hi019]

Got it. Thanks!

[seratch]

For long-running tasks, we now encourage using sandbox agents and its future enhancements. For this reason, we won't add background mode support per Responses API call.