Commits d62e201 and af4c3fd add ‘system-service-type’, which is the now
the real root of the service DAG, and ‘profile-service-type’, which is
the service that populates the system profile
(aka. /run/current-system/profile.)
The latter means that services can add packages to the system profile,
which is useful in some cases.
For instance, with commit 87f4001, Wicd adds itself to the system
profile so that ‘wicd-client’ and other commands are automatically
available, without having to fiddle with the ‘packages’ field of the OS.
This should simplify things a bit.