Some providers only surface structured `reasoning_content` after answer
text has already streamed. The WebUI was treating those late
`reasoning_delta` frames as a fresh assistant placeholder, so the
Thinking bubble rendered below the already-visible answer.
Attach late reasoning back to the active assistant turn instead. The
bubble still renders above the message content, preserving the expected
Thinking -> answer order even when the provider protocol delivers the
reasoning post-hoc. Added a regression test for answer-first followed by
reasoning_delta/reasoning_end.
Co-authored-by: Cursor <cursoragent@cursor.com>
Xubin RenandCursor
9829cf66d2