// why am I so n00b?

All of my Debian desktop installs running KDE received an update a month or two ago which rendered the “Apper” package management application broken, failing with the following error:

Unable to open database read-only: Database action 'prepare dependency insert 
statement' failed: table dependencies has no column named items_installed

The solution is to delete the Listaller cache DB:

rm -r /var/lib/listaller/db/

The cache will be recreated automatically with the expected structure on the next run of Apper (or other PackageKit type thing).