In the course of working on something else I noticed something in the existing experimental package: it effectively tries to create /run/openarc twice (once in the postinst script, and then again with tmpfiles.d). Also, they disagreed on what mode it should be created in (post-install: 0755, tmpfiles.d: 0750; post-install wins).
Between cleaning up that duplication and using sysusers.d to create the openarc user, I think we can eliminate the postinst script entirely. I uploaded a change which uses RuntimeDirectory=openarc to create /run/openarc, replacing both postinst and tmpfiles. It’s built on top of Michael’s latest commit: https://salsa.debian.org/pfish/openarc/-/commit/a3b779ceda51749c88272858c30974b64ce70752
