I'm imagining 2 processes:
1. Process monitor shows a fullscreen black window. Launches xscreensaver --lock or something as a child process
2. Xscreensaver shows the lock screen over the top of the process monitor, with a password prompt
When the correct password is entered, xscreensaver signals to its parent process. Then both processes close gracefully.
If xscreensaver crashes without signalling, the process manager silently restarts xscreensaver.
None of that requires any changes to X. You'd just want to be sure xscreensaver is displayed on top of the process manager's black window.
https://www.jwz.org/xscreensaver/toolkits.html
I'm imagining 2 processes:
1. Process monitor shows a fullscreen black window. Launches xscreensaver --lock or something as a child process
2. Xscreensaver shows the lock screen over the top of the process monitor, with a password prompt
When the correct password is entered, xscreensaver signals to its parent process. Then both processes close gracefully.
If xscreensaver crashes without signalling, the process manager silently restarts xscreensaver.
None of that requires any changes to X. You'd just want to be sure xscreensaver is displayed on top of the process manager's black window.