tile is already visibly slow (49x212 screen) :/ So programmer needs more
control over performance.
But this may not be the right approach. That extra flush-stdout in tui.mu
suggests it's either going to be finicky, or we have to flush on every
attribute change. And going through a buffered-file may be slower. May.
We now have all existing apps and prototypes going through the dependency-injected
wrapper, even though it doesn't actually implement the fake screen yet.
