Assistant's UIMessage contains no parts after upgrade to 0.3.0 #257
Description
TanStack AI version
0.3.0
Framework/Library version
NextJS 16.1.4
Describe the bug and the steps to reproduce it
When receiving Assistant UIMessage it contains no parts even tho the SSE stream clearly shows that it returns the full stream.
Assistant UIMessage object
{ "id": "msg-1769792562080-lm3kri", "role": "assistant", "parts": [], "createdAt": "2026-01-30T17:02:42.080Z" }
Stream response:
`data: {"type":"done","id":"resp_09013e7f2283eaec00697ce43268308196a79e858d6b032d6c","model":"gpt-5.2-2025-12-11","timestamp":1769792562413,"usage":{"promptTokens":96,"completionTokens":16,"totalTokens":112},"finishReason":"stop"}
data: [DONE]`
Your Minimal, Reproducible Example - (Sandbox Highly Recommended)
Sorry none
Screenshots or Videos (Optional)
No response
Do you intend to try to help solve this bug with your own PR?
None
Terms & Code of Conduct
- I agree to follow this project's Code of Conduct
- I understand that if my bug cannot be reliable reproduced in a debuggable environment, it will probably not be fixed and this issue may even be closed.