Well, was experimenting a bit with cards.conf file again.
Clearly, I begin to see my previous exposure to NixOS have put some not correct assumptions in my mind.
Mostly, that binary packages can be seen as a cache version of ports.
Well, in NixOS, a new package version does not replace an old version, it just add a new version.
I guess that make it easier to handle dependencies.
Anyway, I had only ports in my /etc/cards.conf and I had just removed the url option.
And I did a cards sync...
And then I got the idea to do sudo cards upgrade ... expecting that if new ports existed it would take them...
I did not even do a "ports -u" before... still have badly newbie ideas.
I began to see that sudo cards upgrade was removing all the packages on the system.
Thought I should do Ctrl-C to limit the damage... but I was finding it so funny that I decided to let it continue.
And it did until there were not enough packages on the system to continue removing packages.
So in the end, the gui was mostly there (some missing icons), but nothing reacted.
I tried to Ctrl-Alt-F3 to go to a real terminal.
Was able to write my login name, but the system was not asking for a password anymore.
So I rebooted by pressing the power button... and rebooted on the other Linux system... from where I am writing this.
I think I will study your Scenario E more closely now.