It looks like I already have that set in the host system:
[devfsrules_squidjail=4]
add include $devfsrules_hide_all
add include $devfsrules_unhide_basic
add include $devfsrules_unhide_login
add path 'pf' unhide
Also, to be clear, /dev/pf shows up inside the jail, it just doesn't have the...