[ubuntu] Preventing an application from starting at boot

This should be a trivial matter, but it's got me beat. Some time ago my system (ruing on a laptop) powered off when the battery power ran out. And since then, whenever I've needed to reboot, I've had shotwell starting up - this must have been a program ruing when the system first stopped.

I don't want it; it's aoying. The trouble is, I can't find for the life of me where the configuration or settings file is which tells my system to start shotwell. I'm ruing KDE, but it's not listed in the KDE autostart directory. Nor is it in /etc/rc.local, /etc/xdg/autostart, or any of the files related to my shell, zsh. I've performed iumerable "grep -R shotwell ." on different directories, and found nothing. My Session Management has "Restore previous session" ticked, but even if I kill shotwell, if keeps bouncing back on a reboot.

Something, somewhere must be starting shotwell automatically... but where? And what? And how do I find it?

Thanks,
-A.