It was the solenoid. Fuse blown, such a rookie mistake not looking for it in the first place! But the ultimate reason for shorting out remains a mystery. I'll need to keep this in mind. Additionally, there were some leaky return lines and thus some air in the system. But this is now fixed. So, that's that. Thanks for the advice! So nice to that you guys were right on track from the beginning.
I'll keep rolling, a bit wiser
(Also note to self and others: if the pump works the injectors squirt, a little moist around the nut is probably just residual fuel leaking out.)