So far the server only ever answers. Sometimes it has news of its own.
WebSocket
A connection that stays open, so either side can send at any moment. It starts as an ordinary HTTP request, and then both sides agree to switch. Plain HTTP can't do this, because there the server only ever answers.
Agents reach for this whenever they hear "real time", and it's a lot to run: connections to hold open, reconnection, and proxies that drop them. Asking again every ten seconds, or a one-way stream, is often all you need, so ask which one it chose and why.
“We only need the server to send progress one way, so use server-sent events and not a WebSocket. Reconnect after a dropped connection without losing progress, and show me that working by restarting the server during a job.”