Structural Differentiation Cosmology (SDC): Minimal Observational Testability and Closure of the Framework

Structural Differentiation Cosmology (SDC) interprets cosmic evolutionas irreversible internal differentiation of a closed universe,rather than physical expansion driven by additional energy components. This version provides a minimal closure of the framework by identifyinga single decisive observational criterion under which SDC may bedistinguished from standard cosmology. No new entities or mechanismsare introduced. The framework is explicitly falsifiable and completewith respect to its core claim.