ψ-Acoustic Retention: The Survival of Difference Beyond Sound

This article develops ψ-Acoustic Retention, a theoretical extension of the ψ-Architecture in which acoustic structure persists beyond the disappearance of the physical sound wave. The framework defines the ψ-acoustic shadow S_{\psi}^{(\mathrm{acou})} as the structural remainder of Δψ that remains non-zero when amplitude A(t)\to 0. Building on the retentive Lagrangian, the work introduces an acoustic Retentive Floor, formulates a Penrose-style interpretation where silence functions as a boundary analogous to metric extinction, and demonstrates how large architectural spaces — cathedrals, tunnels, deep transit halls — generate ψ-retentive pockets detectable through long-lived residual correlations. This article establishes ψ-acoustic shadows as measurable invariants and expands the ψ-corpus into the acoustic domain.