Adds a working /server-fn-chat route that wires useChat to a TanStack
Start server function via the stream() connection adapter:

  useChat({
    connection: stream((messages) =>
      chatFn({ data: { messages: messages as UIMessage[] } }),
    ),
  })

The new chatFn handler in lib/server-fns.ts returns
toServerSentEventsResponse(chat({ ... })) — the stream() adapter awaits
the server function and parses the SSE response into chunks.

Sits alongside the existing index.tsx pattern (fetchServerSentEvents
to a route handler) so users can compare the two invocation styles.

…server-functions-pBsj5

# Conflicts:
#	examples/ts-react-chat/src/components/Header.tsx
#	examples/ts-react-chat/src/lib/server-fns.ts
#	packages/typescript/ai-client/src/connection-adapters.ts

…abortSignal

Address review findings on the server-function stream() adapter PR:

- Synthesized RUN_FINISHED/RUN_ERROR events in normalizeConnectionAdapter
  no longer use `as unknown as StreamChunk`. Track threadId/runId from
  upstream chunks during iteration and reuse them; fall back to synthesized
  IDs only when no upstream chunk carried them. Use the EventType enum and
  typed RunFinishedEvent/RunErrorEvent so missing required fields are caught
  by the compiler instead of papered over.
- Stop swallowing JSON.parse failures in parseSSEChunks and fetchHttpStream.
  A malformed mid-stream chunk is a protocol error; let it throw so it
  surfaces as RUN_ERROR via the connect-wrapper's catch path instead of
  silently dropping data behind a console.warn the user never sees.
- Widen stream() and rpcStream() factory signatures with an optional
  abortSignal third arg and pass it through. Backwards-compatible — callers
  that ignore the third parameter are unaffected. Lets long-running server
  functions cancel in-flight work when useChat aborts.

Tests updated to assert SyntaxError propagation rather than silent dropping
on malformed JSON, and to expect the new third call argument on factory
mocks.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

…railing buffer

Refine the SSE parser so the throw-on-parse-failure behavior doesn't regress
on legitimate SSE traffic:

- parseSSEChunks now skips SSE comment lines (`:`) and non-data fields
  (`event:`, `id:`, `retry:`) which proxies and CDNs commonly inject as
  keepalives. Previously these would have flowed into JSON.parse and
  thrown, killing otherwise-healthy streams behind any infrastructure
  that injects SSE control lines.
- readStreamLines no longer yields the unterminated trailing buffer at
  stream end. A non-empty buffer means the connection was cut mid-line,
  so the content is partial by definition — yielding it would feed
  truncated JSON to the parser and surface a misleading RUN_ERROR for
  what is really a transport-layer issue. Warn and discard instead.

Bare-line JSON (legacy/raw mode) is still accepted to preserve the
existing public behavior covered by the `should handle SSE format
without data: prefix` test.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

…t UIMessage[] in chat()

Drops the `as any` / `as Array<UIMessage>` casts previously needed when wiring
useChat through a TanStack Start server function into chat(). The stream()
factory now declares Array<UIMessage> (with a runtime assert matching the
ChatClient invariant), and chat()'s messages option accepts UIMessage[]
directly alongside ConstrainedModelMessage[] — the runtime already normalised
both via convertMessagesToModelMessages.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Pulls the @tanstack/ai changes back out — the chat() messages-option
widening to accept UIMessage[] is a separate concern from the stream()
server-function feature this PR is about. Restores the example's `as any`
cast with a comment, drops the @tanstack/ai minor bump from the changeset,
and reverts chat/index.ts to its pre-PR state. Also bumps the example
adapter to gpt-5.2.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>