A brand-new chat (activeChatId === null) had no way to learn the id of the row
the server created: the SSE stream never returned it, so the client adopted the
NEWEST chat in the per-user list (chats.items[0]). With two tabs open, a second
tab creating a chat at ~the same time made its row the newest, so the first tab
adopted the wrong id — its later turns persisted into the other chat and the
agent rebuilt history from it (commands leaked between chats), while the live UI
still showed the original conversation. (#137)
The server now attaches the authoritative chatId to the streamed assistant
message via the AI SDK messageMetadata on the 'start' part, so it reaches the
client on the first chunk. The client reads message.metadata.chatId in useChat's
onFinish and adopts that id in place (no remount, so the live turn and the
thread's chatIdRef follow the real id and the next turn targets the right chat).
The chats.items[0] guess and the adoptNewChat ref are removed.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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