Macro web_app 

macro_rules! web_app {
    ($state_ty:ty, $build:expr $(,)?) => { ... };
    ($state_ty:ty, $state_init:expr, $build:expr $(,)?) => { ... };
}

The browser counterpart of android_app!/ios_app!: binds a Component’s state and build closure to the browser shell’s wasm-bindgen entry point. Takes the identical two-argument (state type + build expression, state built via Default) / three-argument (state type + explicit state-init expression + build expression) shape android_app! does, and app! drives it through the three-argument form exactly the way it drives android_app!/ios_app! (see @emit_mobile below) — most apps reach this through app!/web_app! rather than hand-writing the explicit state_init form.

Expands to two #[cfg(target_arch = "wasm32")] functions — so, like ios_app!, the invocation itself is unconditional and self-gating: calling web_app! off wasm32 expands to nothing. __frust_web_start is #[wasm_bindgen(start)] — wasm-bindgen’s own module-init entry point, run once when the browser instantiates the compiled .wasm — and its body is a single call into __frust_web_run, kept deliberately separate: feeding wasm_bindgen’s attribute macro a body built straight out of $state_init/$build (closures that can carry a macro-substituted $($setup)? block nested inside another closure — see app!’s @emit_mobile arm) trips its own re-parse of the function into a spurious syntax error on that nested-block shape; a plain, macro-fragment-free call is all it ever sees. __frust_web_run carries the real work, in order:

1. [__web_bootstrap]: installs the panic hook and console log sink.
2. [__web_init_state]: brings up the frust_reactive::ReactiveRuntime and runs $state_init under its root owner — the point at which a setup = { .. } block bundled into $state_init by app! (see @emit_mobile) runs, identically ordered to every other platform.
3. Hands the initialized state and $build to frust_shell_web::run_app (via the hidden [__frust_shell_web] re-export) — the browser shell’s own entry point, which owns the canvas-bound event loop and the requestAnimationFrame frame pipeline (see [__frust_shell_web]’s doc comment for the contract).