i think this was a mixup on my part, something is actually wrong with the software on that laptop that isn't on this desktop.

* init/dhcpcd is broken when invoked on my wired connection somehow and i'm pretty sure it *isn't* broken when invoked by wpa_supplicant
* systemd/dhclient works fine on my ubuntu box.
* init/dhclient works fine on my devuan box.
* systemd?/whatever purism uses works fine.

either a dhcpcd setting or dhcpcd itself is increasingly looking blameworthy here