The notion of having a generic mediatR feature is that you get to write less code for a bunch of similar features for each domain entitiy
Mediator is one of the 23 design patterns stated inside the GOF Design Patterns book. All it does is encapsulates communication between objects, hence no coupling. It falls into the object behavior patterns category. MassTransit has a mediator implementation. Let's talk about it.
Working with HttpClient is kind of low-level stuff. Refit eases that problem for us. It creates an abstraction over HttpClient and allows us to work with an interface representing REST endpoints
Application state is subjected to change. A reducer is a pure function that takes the current state and an action been dispatched upon it. Depending on the action type it produces a new state and returns it. States are immutable.