You could possibly use a piece of state for that?
struct DocumentState {
var isPersistingDocuments: Bool
}
Before you start to async save these documents you can update this piece of state. In the documentReducer you can at least observe that now.
if other reducers need access to this state as well, you can use a derived state. Something like Brandon explained here: Best practice for sharing data between many features? - #4 by mbrandonw
I am not sure if that is the most efficient of approaches... But it's the easiest to wrap your head around if all reducers need to know the same information (Brandons post).