Sooner or later, I had to cut the slot for the blade, and I wasn’t looking forward to it. There is a method of cheating at this in a Lee Valley newsletter article [ed: link updated in 2021], but the only appropriate saw I have for doing this is my dovetail saw, which wasn’t gonna work.
So that meant cutting it “freehand.” And I’m really supposed to be able to do this sooner or later, anyway, because it’s the same as sawing a tenon cheek. Unfortunately, I haven’t been very good at that.
I decided that it would probably be a good idea to practice. So I marked out a bunch of lines on some scrap and sawed away:

The first tries were not encouraging. In fact, at first, I screwed up about seven times versus one instance where it wasn’t that bad. Eventually, though, I managed to relax and let the saw do the work instead of holding with a death grip. I did three good ones in a row. It seemed time.
It took what seemed to be an eternity, but once I had established the kerf (approaching from both sides), it was a cakewalk.

I managed to split the marking line. I hope that this means better tenons in the future.
Next up is cutting the mortise for the back and the holes for the saw screws and nuts. It’s starting to occur to me that this saw handle is now far better than the beat-up saw blade that it’s going to go on.