Got it. It was ‘lightdm’.
…to list the services, where I found ‘lightdm’. Then
$ systemctl disable lightdm
…to disable it so it wouldn;t restart on later boots.
$ systemctl stop lightdm
…immediately stopped it, but it it didn’t drop into a console. Instead it just had a blinking, non-operational, underscore cursor. I SSH’d in to tell it reboot. Success! It rebooted into the text console.
I probably should have just rebooted instead of explicitly stopping lightdm. Now that I think about it, that blinking cursor probably was the console with an exited shell. I should have tried [alt] - [arrow] to change terminals, like you can after booting into the console.
Thanks again, igorp@