This is handled in the framing of the question: “… it doesn't ever have to handle more than one request at once (at least from the same client, so we can assum

This is handled in the framing of the question: “… it doesn't ever have to handle more than one request at once (at least from the same client, so we can assume this is a single-server per-client type of architecture).“ For sure a multithreaded async queue would be a very interesting interview, but if you started with the send system the interview is constructed around youd run out of time quickly.