So I took another break. And then I showed what I had to a friend who has a hobbyist interest, and his enthusiasm (eventually) encouraged me to resume work on the game. So over the last couple days I got player movement sorted out:
After Christmas maybe I'll spring for a Fraps registration so I can record more than thirty seconds' worth of video at a time.
You may notice there's a bug in the pellet graphics on a couple of the sides. They're billboarded sprites, and I think the shader is ignoring one axis when aligning them to the camera. So on the top and bottom sides, they seem to wink out. I need to take another look at that.