I serve one GT connection over a length-framed socket.

Requests and module events share my mailbox, which is the point: a reply is a frame carrying the id GT sent, an event is a frame with none, and GT tells them apart on arrival. One socket carries both directions, so there is no second connection for GT to lose.

I evaluate in a spawned task rather than inline: an eval may take as long as user code takes, and events queued behind a Process.sleep/1 would arrive late. Replies carry their id, so they may return in any order.