Behaviour change (split out of the test commit per review).
In AI SDK v6 the useChat `onFinish` callback does NOT fire when the stream
errors. A brand-new chat whose very first turn fails would therefore never run
the post-turn path: the chat list was not invalidated and the client never
adopted the server-created chat id — so the failed chat only appeared in
history after a manual refresh (the server already creates the row and stores
the error message). Running the same `onTurnFinished()` handler on `onError`
makes the failed chat show up immediately. The error itself is still surfaced
to the user via the existing `error` state.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
1e650262a4