^C to a running `joltc --nrepl-server` aborted with "thread does not
own mutex" because the accept-loop thread absorbed SIGINT in its foreign
accept() call, where Chez can't run the keyboard-interrupt handler, and
run-main-pump's tight condition-wait loop wasn't interruptible anyway.
Block SIGINT in the primordial thread before starting the server so the
accept loop inherits a blocked mask, park in a single interruptible
condition-wait via the new park-until-interrupt, and run registered
shutdown hooks (newest-first, each isolated) from the keyboard-interrupt
handler before (exit 0). The stop fn now drops .nrepl-port via the new
jolt.host/delete-file seam — clojure.java.io/delete-file doesn't exist
in Jolt and silently no-ops, so .nrepl-port was never removed.
46c9c7b4d9