Diversity Contraction Across Substrates: A Boundary Law for Semantic Exhaustion

A boundary law for semantic exhaustion, importing the strong-Allee / extinction-threshold structure from ecology and extending it with two new results: the Mediation Ratchet (state-coupled mediation manufacturing a collapse trap in a floored substrate, with a closed-form critical threshold alpha* = p/g0) and resolution-relativity (the regime as a function of type-resolution epsilon). Transposed from population abundance to diversity as the state variable, with recursive model collapse, institutional reproduction, linguistic flattening, political economy, and stabilizing selection as five substrates under one operator family. Includes a four-study empirical research program and explicit falsifiers.