box Node {
    weak parent
    weak sibling
}

static box Main {
    main() {
        local n1 = new Node()
        local n2 = new Node()
        n1.parent = weak n2
        n1.sibling = n1.parent  // ✅ WeakRef → WeakRef
        print("OK: weak field transfer")
        return 0
    }
}