I just noticed after checking the arch git from receiving a sudo update, that /run/sudo was never really created and was removed after installing the package [0]
because apparently systemd-tmpfiles is better for arch devs! /run/sudo (or /var/run/sudo everywhere else) is the timestamp directory for sudo [1]

root@ zen taco # cat /usr/lib/tmpfiles.d/sudo.conf
# Create an empty sudo time stamp directory on OSes using systemd.
# Sudo will create the directory itself but this can cause problems
# on systems that have SELinux enabled since the directories will be
# created with the user's security context.
d /run/sudo 0711 root root # undercase 'd' means 'create directory' [2]. 0711 means with full permission for root, execute only for group [3]
D /run/sudo/ts 0700 root root  

pacopts applytmp when? :)
[0] https://git.archlinux.org/svntogit/packages.git/commit/trunk?h=packages/sudo&id=d807e2416814f8004d79157da8c48879cabb5337
[1] https://www.sudo.ws/man/1.8.14/sudoers.man.html
[2] http://man7.org/linux/man-pages/man5/tmpfiles.d.5.html
[3] https://docstore.mik.ua/orelly/networking/puis/ch05_02.htm# PUIS-CHP-5-TAB-9