# get the UID of the OpenBSD VM
VBoxManage list vms
# now start that with no raw IO
VBoxSDL -norawr0 -vm UID
For me, problem solved!
I do computer stuff. When I solve a problem and it's not obvious, I document it here - it's a reference for myself, and hopefully, it can save other people out there days of problem solving, googling and assorted hair-tearing.
# get the UID of the OpenBSD VM
VBoxManage list vms
# now start that with no raw IO
VBoxSDL -norawr0 -vm UID
# create the bridge interface
ifconfig bridge0 create
# add the network interfaces that are part of the bridge
# these interfaces were already configured to be UP
brconfig bridge0 add vr1
brconfig bridge0 add vr2
# most important: bring the bridge interface up too
# it took me a while to figure this out
ifconfig bridge0 up