Adventures in printing:
The proprietary blob plugin for HPLIP is ported to FreeBSD by literally saying "this Linux library is actually for FreeBSD" and adding a tiny implementation of a couple glibc functions, amazing! But HPLIP is not necessary for my printer, foo2zjs is an open source driver that supports it.
PostScript is not PostScript, apparently. (Actually my printer wants PDF, it seems — setting generic PDF on the client side when network printing over CUPS worked.)
And if CUPS doesn't see the printer when using the open source drivers, it IS a permissions issue, make sure to restart devd to activate the rule that's included with the cups package. (The fact that HPLIP sees the printer is… odd. Was it running HPLIP stuff as root?)