Hello again,

just a hint for the resolute ones among us, as I think this hasn't been
mentioned on this list yet: Adding the following lines to e.g. the file
/etc/apt/preferences.d/avoid-systemd should make ultimately sure, that
libsystemd0 will not be accidentally pulled in by some felted package:

Package: libsystemd0
Pin: release o=Debian
Pin-Priority: -1

Unfortunately apt does not handle this transparently, when failing to
install some distant systemd dependant, but reports an unfixable
dependency problem – pointing only at the very next dependency in the
chain down to libsystemd0.

The complete explained list of possible apt pin-priority categories
from <0 to >1000 you can find in the apt_preferences(5) manpage.

Florian