OK, for what it's worth, it's done. They suction-cup this plate with a hole on top of it, then syringe-inject the goop in there, put a piece of tape on it and let it cure a while. It took about a half hour. The result is that the crack is almost impossible to see unless the sun hits it just right so that it reflects from the inside to your eyes. So it's not magic. It is guaranteed, and they'll take the $60 off a windshield replacement if it fails.
It did not spread at all on the way there. I did take it easy, but some shitty roads around here are hard to avoid. I think I'm set, even if it isn't completely as it was. Replacing a windshield has its own set of risks. They are often more weakly affixed to the car, and windshields are structural components in modern cars. I'm good, but still pissed it happened after so many years without that kind of hassle.
Thanks all.
Edit: Oh, that's interesting. I can't green-flag more than one post. Only the last one stays green. I guess it's just as well, since that fluorescent green all over the page might burn your retinas.