Function find_builtin_decl 

pub fn find_builtin_decl(
    engine_state: &EngineState,
    name: &str,
) -> Option<DeclId>

Find the first declaration with CommandType::Builtin whose name matches name, scanning from the most-recently registered declaration backwards.

This mirrors the static %name parser behavior: % always resolves to a built-in, even when a custom declaration shadows the same name in the current scope.