Thank you.

New window master switch assy arrived today. Less than $14 shipped. It was the problem, apparently. Works perfectly now. For now.

This system is not intuitive to troubleshoot until you understand there are electronics in both the local switches and the master. Then it still isn't, lol.

To summerize:
Neither the local nor master switch would lower the RF window.
Motor/regulator assy was hot wired and worked perfectly. Hotwire jogging the window to center and then testing revealed that actuating either switch "down" sent the window up instead. Actuating either switch "up" did nothing.
Swapping in a local switch from another window made no difference.
This made me suspect faulty electonics in the master switch. Replacing the master switch resolved the problem.

To OP, not saying master switch electronics is the problem, but if more than window quit at the same time, but at least one works, it's a pretty good bet, if only because it's a very cheap and easy thing to try.