Thanks! I've lurked forever but apparently my search skills have failed me this time.
Speaking of, unfortunately
# rcctl disable xenodm did not fix the problem. This had no effect on logs/rc.conf.local or output, so there is nothing new to post for that.
To permute things, I also tried removing
machdep.allowaperture=2 from rc.conf.local. I cross referenced this change with a warning in X0rg.0.log which says "Check that you have set 'machdep.allowaperture=1' in /etc/sysctl.conf and reboot your machine." This was probably there to begin with, but I went ahead and created a /etc/sysctl.conf file with the line
machdep.allowaperture=1 and rebooted. This didn't fix the problem, but it did remove the warning from X0rg.0.log. I also tried iterating through allowaperature=2 and 3, as per
xf86(4).