I'm thinking what's wrong is that my ignition lock is locked into the "on" position and, for whatever reason, will not turn back to "off." Maybe things will be better tomorrow. Maybe.
I was able to shut off the engine, finally, by pulling the fuse for the engine control and disconnecting the battery. I don't foresee any problems with starting the car again by reconnecting everything-- I was able to crank the starter at least.
But man, car trouble is the last thing I need right now.