Ah, you don't mean enforce a novice making a mistake, you mean ensure from a design purity perspective?

I don't think its true that you need requests to flow both ways. For example, if a downstream API needs more context from an upstream one, one solution is to pass that data down as a parameter. You don't need to allow the downstream services to independently loop back to gather more info.

Again, it depends on the business case. Software is simply too fluid to be able to architect any sort of complex system that guarantees an acyclic data flow forever.