ψ–Λ Cosmology: A Retentive Framework for the Persistence of Form Beyond Expansion

ψ–Λ Cosmology proposes that the Universe sustains structure not merely through expansion but through retention — the persistence of internal difference (Δψ) even as dynamical motion fades. By introducing the retentive term Λψ, the model extends ΛCDM into a post-dynamical regime where correlation outlasts motion and energy endures as form rather than flux. The framework defines a formal Lagrangian of retention, establishes equilibrium at Δψ₀ = (β / 2α) Ξ, and predicts measurable phenomena: correlation-time plateaus, stilled heat (E_ret ≠ 0 as Tψ → 0), and topological invariants surviving cosmic dilution. ψ–Λ complements ΛCDM rather than replacing it, introducing a vocabulary of persistence and continuity suited for late-time cosmology and deep-space observation. All parameters are open, reproducible, and testable via the provided CLI simulation and Zenodo reproducibility pack.