A brand-new chat's first turn streamed and finished successfully, but the
whole assistant response vanished from the UI. On finish the window adopts
the server-created chat id, which changed the <ChatThread> key and remounted
it — discarding the live useChat store (the full answer) and re-seeding from
not-yet-persisted history, so only the user message remained.
- chat-thread: pin the useChat store id to a per-mount value so adopting the
chatId prop no longer recreates the store and wipes the live turn.
- ai-chat-window: derive the thread mount key via setState-during-render and
move the live-thread marker in lockstep with the adopted id, so in-place
adoption keeps the same mounted thread while real chat switches still
remount and re-seed; gate the history loader to a freshly opened chat.
- cancel a pending adoption on New chat / explicit chat selection.
- log the raw stream error to the browser console for debugging.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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