I’m bad at math. Last night, trying to roll my own collision system that handled deflection off the inside of a curved surface did not go well.
Then today it took a few more hours to get the hang of LOVE2D’s built-in physics system, but I have succeeded! Can’t show in a screenshot that my spaceship now bounces properly off the boundaries of the world, unfortunately.
Next step is to make my game actually a game by adding enemies, ways to blow them up, and ways to die. After that I can pay some heed to aesthetics.