I have a ThinkPad X1 Carbon (Gen 4) on which I'm running Debian 12 and a fairly minimal X11 setup with fvwm2 as a window manager and a few other programs, including xscreensaver, started from my .xinitrc.

Whenever I close my laptop lid, XScreenSaver gets a request to lock:

xscreensaver: 16:37:05: ClientMessage LOCK: locking

Where is this coming from, or how do I find out where it's coming from? I've already set all lid switch settings in /etc/systemd/logind.conf to ignore (and restarted the systemd-logind service), but apparently it wasn't that that was generating the request to xscreensaver.