Riverpod

Riverpod was written by Provider's own author, and its purpose is to fix four problems Provider has:

• Compile-time safety — providers are global variables, so there is no "not found in the tree" failure
• Reading without a context — state is reachable from outside the widget tree
• No type-based lookup — you can have as many providers of the same type as you like
• Composition — one provider can read another with ref.watch, and the dependency is tracked automatically

On the widget side you use a ConsumerWidget, whose build receives an extra WidgetRef ref parameter.

You pick a provider type by the shape of the work:

• `Provider` — an unchanging value or a service such as a repository
• `StateProvider` — a simple mutable value (a filter, the selected tab)
• `FutureProvider` — a one-off async load; it yields an AsyncValue
• `StreamProvider` — a continuous stream
• `NotifierProvider` / `AsyncNotifierProvider` — complex state with business logic

AsyncValue is particularly useful: it unifies loading, data and error into one type and, via when(), forces you to handle all three — which is how the forgotten-error-state problem disappears.