That finally got things working the way I want them.
What are our lessons for today, class?
Here’s the big one: I will never again install an nVidia card unless forced at gunpoint, and if that happens I will find a way to make my assailant eat the fucking gun afterwards. I had lots better uses for 3.5 days than tearing my hair out over this.
When your instincts tell you not to trust closed source, pay attention. Even if it means you don’t get instant gratification.
While X is 10,000% percent more autoconfiguring than it used to be, it still has embarrassing gaps. The requirement that I manually adjust the virtual-screen size was stupid.
UPDATE: My friend Paula Matuszek rightly comments: “You missed a lesson: When you have a problem in a complex system, the first thing to do is check each component individually, in isolation from as much else as possible. Yes, even if they were working before.”
Now I must get back to doing real work.