Sometimes, giving up is the right move
The injuries are long healed now. Having considered the question soberly, I decided that, in this case, giving up was the right move. Not everyone is cut out for bike-riding on a regular basis; if there's a knack for avoiding accidents, I probably don't have it. One injury accident in just a month and a half of regular riding is not a very encouraging track record (by comparison, I've driven cars for 30 years with only one accident, and that was caused by the other guy running a red light). The next time, if there was one, could easily be a lot worse.
I know well that Americans are notorious for fretting over risks which have, in fact, only a tiny probability of materializing. I'm not the kind of person who spends time worrying that the airline flight I'm on will be the one in ten million that gets hijacked, or obsessing over some disease I'm actually at negligible risk for. But I concluded that the risk of another serious bicycle accident was not negligible.
This week I finally put the bike up for sale. It found a buyer almost immediately. At least I got a good price for it. So that chapter is closed. Sometimes, giving up is the right move.