A turn/interrupt reply only acknowledges the request; turn/completed is the
authoritative signal that a turn stopped. When the 429 deadline interrupted
the root or a descendant, a bare reply was taken as confirmation, so the
turn could be settled as reusable while Codex was still running it.

Wait up to 10 seconds after the interrupt for the turn to end. A root that
does not end in time moves to the unconfirmed bound and is reported broken;
a descendant that does not end in time is abandoned and its thread marked
errored.