// Scaffolding shared by the facade's own tests.
// Start `app`'s world on the headless loop, and assert it starts.
//
// The cook injects a GraphicsConfig for anything renderable, and that component
// is what gates the render stack into a windowed run: a cooked world started as
// it stands opens a window and takes a GPU on whatever host runs `cargo test`.
// The headless loop has no render system for it to gate in.
//
// The window ban is armed first, so a regression that puts the windowed driver
// back here panics naming the backend instead of blocking on an event loop the
// harness cannot end.
pub