The Point of Memory and the Saturated Grid: A Retention-Based Architecture for the Late-Time Universe

This preprint introduces a retention-based framework for the late-time universe in which cosmic structure transitions from a fluid-dynamic regime to a retained architectural phase. The paper defines the Point of Memory Mψ, characterized by the simultaneous appearance of z^{}≈1.7, γ≈0.64, and invariant topological identity dχcell/dz≈0. The framework introduces a new observable, Ψresid=ΦWL-ΦRSD, interpreted as Metric Memory: residual curvature preserved after dynamical growth has saturated. Based on this observable, the paper develops: a taxonomy of Retention Shells and Chimera Regions; formal registry cards and Chimera IDs; Architectural Cells and the Saturated Grid / Frozen Web; a minimal retention term Λψ; a derived retained-phase attractor in which γeff→0.64. The paper proposes an observational program for future data from Euclid Consortium and Dark Energy Spectroscopic Instrument, including tests based on weak lensing, redshift-space distortions, persistent homology, and non-diffusive void boundaries. All mathematical expressions are written in plain text form to preserve compatibility with repository rendering and copy-paste export.