Improve Cleanup

[ConnorNelson]

The parent-death signal setting is also
cleared upon changes to any of the following thread
credentials: effective user ID, effective group ID,
filesystem user ID, or filesystem group ID.

-- https://man7.org/linux/man-pages/man2/prctl.2.html

We need to make sure pid 1 gets killed.

[ConnorNelson]

A good temporary option is to set_parent_death_signal() after all the setuid() code in start(). However, this is almost certainly prone to race conditions if we aren't careful.