(Re-posting in unix per the suggestion in /sf/ask/960287611/)
The short question is, what should a shell do if it is in an orphaned process group that doesn't own the tty? But I recommend reading the long question because it's amusing.
Here is a fun and exciting way to turn your laptop into a portable space heater, using your favorite shell (unless you're one of those tcsh weirdos):
#include <unistd.h>
int main(void) {
if (fork() == 0) {
execl("/bin/bash", "/bin/bash", …