A detailed walkthrough of refactoring a Flutter app's network and state management layers. The network layer wraps Dio/Vexana behind a generic interface (IProductNetworkManager) with sealed NetworkResult types, a singleton with environment setup/reset, centralized constants, json_serializable models, and abstract service interfaces for testability. The state management layer introduces a three-tier model: a global ApplicationCubit in a GetIt DI container for app-wide state, page-level Cubits with immutable Equatable state and BlocSelector for surgical rebuilds, and ValueNotifier for widget-local UI toggles. Key patterns include fold() over try/catch for network results, BlocListener for navigation side effects, and BlocSelector per field to minimize rebuilds.
