Investigate why persist services erroneously display on closure diff #67
Description
Building my system closure with nh os build . displays a diff of the current build vs. what's running on the system. This is useful to seeing changes between the config, however my persist services tend to erroneously display as "Added" or "Removed" despite not having been modified at all. It's a very strange bug that I've had ever since I migrated to using systemd services way back in #22. I haven't been too bothered by it, but its still a very weird issue that I honestly don't quite understand.
I'd understand if it showed up as "Changed", since possible derivation path changes would propagate here, but for it to show up in "Added"/"Removed" is just plain wrong.
It's easy to reproduce this issue by updating the nixpkgs revision, but even smaller changes to my config can occasionally display these. I'm uncertain as to why it happens, but I'd like to eliminate it.