The fetcher sends the request ID chi's RequestID middleware put in the context as X-Request-Id, next to User-Agent and Accept, and the "upstream fetched", "image converted" and "image served" lines carry it as request_id, as the request log line does. A fetch shared by several requests runs with the first request's context values, so it carries that request's ID; README says so where it describes the shared fetch. Model: opus-5-5