ψ-Retention Cosmology: A Structural Framework for Late-Time Stability Beyond Dynamical Suppression

This article is part of the ψ-Architecture Research Series, Volume IV. It presents ψ-Retention Cosmology (Λψ), a structural framework in which late-time cosmic evolution is governed not by dynamical decay but by the emergence of geometric stability thresholds. The theory introduces a minimal retentive term, preserves metric consistency (η = 1), and explains the S₈ suppression, the anomalous growth index, the weak ISW signal, the Planck A_L anomaly, and the scale-invariant void-lensing deficit through a single structural mechanism. The paper includes the Retentive Growth Theorem, the Λψ Lagrangian, Euclid DR1 predictions, explicit falsification criteria, and a unified set of structural invariants.