Function catalog_root 

pub fn catalog_root() -> Option<PathBuf>

The root a capture would set text from, without reading a font: the roots [bundled_font_system] tries, checked for a manifest this build pins. A run whose answer is None would render every frame in the host’s faces, which is not the product, so a capture asks this before it draws anything.

A program that starts another build’s binary and has it draw — a test running the app beside it, which was built beside a different build directory — names this as OVERRIDE_ENV in the child, so the child sets text in the catalog this process verified rather than the one its own build path names.