fix(react): use the latest transport in useChat instead of a stale one#16546
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…tale one (#16806) Backport of #16546 to `release-v6.0`. `useChat()` creates its `Chat` instance once in a `useRef`, so a `transport` passed to `useChat()` was frozen at its first-render value and became stale after React state changes; the fix extends the existing latest-values ref pattern (already used for callbacks on v6) to also cover the transport, handing `Chat` a stable proxy transport whose `sendMessages`/`reconnectToStream` always delegate to the latest transport (falling back to a lazily created `DefaultChatTransport`). The `use-chat.ts` rewrite from `callbacksRef` to `latestRef` applied cleanly and matches main exactly, except that v6's `shouldRecreateChat` guard is kept as-is (the nullish-id guard from #16484 is backported independently in its own PR); conflict resolution was limited to the import block (v6 does not import `fireEvent` in the test file) and re-indenting the new `stale transport` test describe block to v6's flat test file structure (main wraps tests in an outer `describe('use-chat')`). Verified the ported regression test fails on v6 without the fix and passes with it. Part of the v6.0 backport tracking issue #16767. Co-authored-by: Nick Oates <nick.oates@vercel.com>
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Background
useChat()creates itsChatinstance once and stores it in auseRef(), so as a result, atransportpassed touseChat()was captured and then frozen at its value in the first render. If react state later changes, thetransportbecomes stale.A very similar problem was addressed in #8985 but with callbacks.
Summary
Rather than passing the transport directly to
Chat, this passes a proxy object that always reads the latest transport (or falls back to a default one).This uses the same solution as in #8985 for callbacks.
Manual Verification
Added a route to the ai-e2e-next example at
/chat/stale-transport-demo. It reproduces the bug without the changes made, and then is fixed with these changes.Checklist
pnpm changesetin the project root)Related Issues
Fixes #7819
Closes #12330
Closes #13464
Closes #15380
Closes #16326