A Covariant Effective Model for Coherence-Capacity Cosmology: Equations, Degeneracies, and Observational Tests

This paper replaces an earlier heuristic cosmology with a covariant effective-model interface. Coherence capacity in Modal Triplet Theory is an admissibility margin; by itself it does not determine a spacetime metric, expansion, acceleration, a causal horizon, a cosmological singularity, or an arrow of time. A Jordan-frame scalar-tensor action is declared in which a scalar capacity variable is proposed as the large-scale image of MTT capacity data. The metric equation, scalar equation, homogeneous Friedmann equations, and exact acceleration condition are derived. A reconstruction-degeneracy theorem shows that freely chosen coupling functions can reproduce broad classes of expansion histories, so agreement with measured expansion is not a prediction until MTT selects those functions and their initial data independently. Capacity-zero level sets are separated from Lorentzian horizons, positive capacity is separated from past completeness, and time orientation is separated from irreversible entropy production. The result is a conditional effective realization and an explicit observational test contract, not a derivation of cosmology from the present MTT axioms.