A new-chat turn fired the chat stream (streamText) and title generation
(generateText) concurrently to the same z.ai coding endpoint. That plan
stalls one of two concurrent requests, so the chat stream black-holed for
~300s (undici headers timeout) and the turn hung forever in every browser;
the AI SDK then retried 3x. Server logs showed two concurrent POSTs to
/chat/completions per turn — one 200 in ~8s, the other "fetch failed after
301209ms". Bypassing the custom undici transport did not help, confirming
the cause is the concurrency, not the transport.
Move generateTitle from before the response pipe into onFinish, so it runs
solo AFTER the stream's provider call completes. A first turn that errors or
aborts no longer auto-titles (fallback "Untitled chat" already handles a
null title) — acceptable, and it removes the request that was stalling.
fd66ee6cce