Pre-Euclid Prediction of Structural Stability: A Minimal Retention Equation for Growth Saturation

We present a minimal predictive framework for late-time cosmology based on a retentive extension of structural dynamics. The model introduces a second-order equation governing the evolution of large-scale structure nodes, incorporating a retentional resistance term and a stabilization constant. The framework predicts a transition from a dynamical growth regime to a stationary structural regime characterized by growth saturation, partial decoupling between gravitational lensing and matter velocities, and the emergence of stable morphological boundaries. Key predictions include a persistent growth index plateau (gamma approximately 0.64), measurable lensing–velocity decoupling, and the existence of stable, non-diffusive void boundaries. These predictions are formulated prior to the full Euclid 2026 data release and are directly testable using upcoming observational data.