ψ-Architecture Research Series, Vol. IV — Article 3: ψ-Retention Cosmology: A Unified Structural Resolution of the Late-Time Tension Constellation

This article constitutes Article 3 of Volume IV in the ψ-Architecture Research Series and presents a unified structural interpretation of the late-time cosmological tension constellation. The ψ-Retention (Λψ) framework explains the observed suppression of structure growth not as a consequence of new dynamics or modified gravity, but as the emergence of a geometric saturation regime in which growth approaches a fixed-point plateau. The paper demonstrates how a single retentive operator accounts simultaneously for the S₈ tension, the weak ISW signal, the low-ℓ CMB power deficit, the Planck A_L anomaly, and scale-independent suppression in void lensing—while preserving metric consistency and introducing no new degrees of freedom. The framework yields a closed and falsifiable prediction set for Euclid DR1 (2026), including a late-time plateau in fσ₈(z), a constant anomalous growth index, null gravitational slip, and scale-invariant clustering and lensing suppression. ψ-Retention Cosmology is presented as a minimal, structurally consistent axis for late-time cosmology, emphasizing epistemic restraint, predictive clarity, and compatibility with standard perturbative frameworks.