StreamProcessor starts the trace and mints the request id before the
agent is built, so pre-fetch retrieval and compression are inside it and
side-channel LLM calls share the id. complete_stream activates it in the
SSE pump thread, binds the message and conversation, and writes it once
however the stream ends: paused, failed, abandoned or superseded (dropped).
user_logs rows now carry request_id and message_id.
arc53-machine
bae842d151