Function lumen_node_set_attr 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn lumen_node_set_attr(
    node: LumenNode,
    name: *const c_char,
    value: *const c_char,
) -> LumenStatus

Set an attribute on node. KNOWN attrs (id / class / text / disabled) route to their typed component; others land in the generic attribute map. Thread-safe.