I think the flow architecture (i.e. Redux) is sufficiently descriptive for how to organize a project, at least compared to REST. There is one giant state object

I think the flow architecture (i.e. Redux) is sufficiently descriptive for how to organize a project, at least compared to REST. There is one giant state object which is essentially a struct/trivially serializable to JSON. This state can only be changed via actions/events which are themselves only structs, not full objects. Reducer function(s) transform the old state into a new state using these events (in practice people use multiple reducer functions which are chained together). This isn't even message passing really since you do have global state, it's just that this global state is changed via messages/events.