I haven't done anything other than binary releases in some time, although it's possible I may have fat fingered a terminal at some point. I infrequently check these boxes other than biannual release updates and mtier patches.
The checksums and timestamps of /bsd and /sbin/pfctl match another working 5.8 box, and uname -a gives: OpenBSD hostname 5.8 GENERIC.MP#0 amd64 The box is my home router and I'm very far away for the next few weeks, so will leave it as-is since it's working for now. If no one has seen this before, I'll give it another go with a fresh binary install when I'm able to get access to the box again. Thanks all!
