The branch that normalizes plain JSON error lines from streaming upstreams (lines without the SSE data: prefix) called Chats.upsert_message_to_chat_by_id_and_message_id without await. The coroutine was never executed, so the error was never written to the chat and Python emitted a "coroutine was never awaited" RuntimeWarning instead. The frontend still received the error event, but after a reload the message showed no trace of the failure.
The parallel error-persist branch further down the same handler already awaits the call; this aligns the two.
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