Kotlin's Self-Referential Generics: Enforcing Type Safety at System Boundaries

At the UI/Domain boundary where compile-time types naturally blur, self-referential generics combined with sealed classes provide a standardized, type-safe way to communicate between layers. This pattern prevents type mismatches from reaching production by enforcing variance constraints at compile time while maintaining ergonomic API design. Understanding how covariance and contravariance work in this context is the difference between thoughtful architecture and cargo-culting generic patterns.