The problem is that our ‘glib-networking’ package is configured without
libproxy as a dependency; thus it does not install
‘glib-pacrunner.service’, which in turn leads to that D-Bus error.

The solution is to add libproxy to the inputs of glib-networking.
However, that creates a dependency loop because libproxy depends on
network-manager → libsoup → glib-networking.

To break the loop, we probably need to introduce
glib-networking-minimal and have network-manager depend on it
(indirectly).

Thoughts?

Ludo’.