Get a quest

Polls the outcome of a turn started by POST /api/chat or an async generation route. status done and stopped are terminal; pending and running are not. A finished turn that failed has type: "error" and, where classified, an errorCode; a stopped turn is also a failure even without type: "error", and its reply is an explanation rather than an answer. A 404 covers a quest that does not exist, one whose session was deleted, and one the caller cannot see, so polling after deleting the session returns 404. Safe (GET) requests are exempt from the per-day API-key quota: a poll consumes no daily slot, and only the per-minute burst limit applies.