vec2f64

declare function vec2f64(x: number, y: number): vec2f64
declare function vec2f64(scalar: number): vec2f64

A number in a parameter or a return position is the scalar slot. The ambient file declares a GPU scalar as a branded number whose brand is optional, so a literal and any branded scalar both fill it.

type f32 = number & { readonly [f32Tag]?: true }

A declaration you write still needs a width, and a bare number on a field or a parameter is refused; the TypeScript constructs page carries that row with the compiler's own message.