Function get_arch 

pub fn get_arch() -> &'static str

Return the host CPU architecture as the value of std::env::consts::ARCH ("aarch64", "x86_64", …). Compiled into the binary, so it reflects the build target the user is running — exactly the build the Download button should offer them. The browser can’t see this reliably (WKWebView masks Apple Silicon as Intel), so the renderer asks Rust and normalises the answer through normaliseArch in lib/platform.ts.