Dart & Flutter: Full duplex connection

Flutter's SDK already has everything you need to manage complex forms — no packages required. Listenable.merge turns any combination of ValueNotifier, TextEditingController, FocusNode, and ChangeNotifier into a single reactive form controller.

Dart has no defer, no RAII, no scope guards. When multi-step async initialization fails midway, you need to unwind only what was set up — in reverse order, crash-safe. Here's a 6-line closure chain pattern that gives you transactional init, safe teardown, and cancellation support for free.