… you can then do "systemctl start capsule@<somename>.service" to start the capsule. This spawns a per-user service manager, with a shortlived dynamic user. Once you do "systemctl stop capsule@<somename>.service" it goes away again. And inside that service manager all services defined and enabled in the aforementioned directory will be invoked.

You don't really have to place service files in that dir btw. You can also just start the capsule as-is, and then invoke stuff dynamically inside…