Derive Macro Component 

#[derive(Component)]
{
    // Attributes available to this derive:
    #[component]
    #[port]
}

Generates the ComponentNode impl (design-doc §6.3, revised per R2): traversal of #[component] fields, including Option<T> and Vec<T>; names synthesized from field names. Emits no factory registration (R5) — but R5 is reversed: the factory returns in ch29, and this derive is where its registration will land. The impl is hand-writable; the derive is convenience.