systemd --user managers after systemd upgrade

[Mike Gilbert <floppym@xxxxxxxxxx>]

I recently added systemd v256 to Gentoo's ebuild repo. While testing
the upgrade process from v255, I have run into an issue.

After the upgrade, my KDE Plasma session stopped working, and I was
unable to execute a reboot from the GUI.

Looking at the journal, I see several messages like this one:

Jun 29 14:21:30 naomi systemd[2387904]:
/usr/lib/systemd/systemd-executor (deleted): error while loading
shared libraries: libsystemd-core-255.so: cannot open shared object
file: No such file or directory

It appears to be executing a deleted binary
(/usr/lib/systemd/systemd-executor), likely via /proc/1/fd/..., and
then fails when loading a deleted shared library
(libsystemd-core-255.so).

The new versions of these files do exist on the filesystem. Also, I
was able to reboot the system by switching to a text console and
pressing ctrl-alt-delete.

Any idea what happened here? I'm not sure if this is a systemd bug, or
if I missed something in my packaging script (ebuild).