Function install 

pub fn install()

Make Material 3 this app’s starting design system.

Two process-global pushes, both public frust seams:

1. frust::set_default_theme(baseline()) — the base a shell seeds itself with instead of its built-in Theme::neutral() fallback. Deliberately not frust::set_app_theme: a seeded default does not pin brightness, so an app installed this way still follows system dark mode.
2. frust::register_app_fonts for both bundled faces (Roboto Flex, Roboto Mono), so the type scale’s Roboto Flex stack and any mono-text component actually resolve. The faces are compiled in behind the crate’s bundled-fonts feature (default on); an app that sets default-features = false on this dependency compiles in no font bytes, install() registers neither face, and text falls back to the platform’s system faces through fontique (Roboto on Android).

Timing: must run before the first frame

A shell reads the default-theme slot and drains the font registry once, at construction, before its first rebuild. A call after that takes effect only on a later clear_app_theme-driven reseed, which may never happen — so a late call silently does nothing visible.

The supported way to get the timing right on all three platforms is frust::app!’s setup block, which runs immediately before the root component’s Component::init and therefore before any shell construction — see the crate docs for the full example.

Thread contract and repeat calls

Both underlying seams are plain Mutex-guarded process-globals callable from any thread. Calling install twice is harmless but wasteful: the second set_default_theme replaces an identical value, and the font bytes are pushed (and later re-registered, shadowing the same family names) a second time. Call it once.