After a few hours futzing around, I got things working.
While this is super-lamo, it’s doing a bunch of things right under the hood. There’s a world that chooses maps (from a list of one). There’s a map that draws those walls. The NPC gets an update (and just takes a random step). The PC accepts key-presses and quits cleanly. The walls block movement. I can take screenshots of play.
More importantly, I didn’t fall down a rabbit-hole of planning. Some things are placeholder at the moment, but the structure lets me expand out where I need to, when I need to.