This one's in frontend_keypress(), which is supposed to close the
window on the first keypress after the session inside it terminates
(that is, if your close-on-exit settings haven't made it close already
at that point).
It looks to me as if that behaviour doesn't currently _work_, and
hasn't worked for quite a while (certainly it was broken as of 0.70,
well before I started on this weekend's refactoring), because when the
session terminates we delete inst->ldisc and that's what would
otherwise be calling frontend_keypress. I should probably decide what
to do about that at some point. But for the moment, I'm satisfied to
simply not break this functionality any worse by making it not a
process-global exit :-)
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