P75: The Radion-QCD Condensate Mechanism — Why the Gravitational Coupling Switches Off at the Quark-Hadron Transition

The CCEGA framework derives G_eff(ρ) = G_N exp(−ρ/ρ_c) from 5D brane-world geometry, but the non-minimal coupling ξ = 1 (P43 §8.4) is set by naturalness and not derived. Separately, P74 documents the numerical observation ρ_c = Λ_QCD³/ℏ³c³. This paper proposes a physical mechanism connecting both open problems: the coupling of the radion field to the QCD trace anomaly through the gluon condensate ⟨G²⟩(ρ). As matter density approaches ρ_c, the gluon condensate dissolves at the quark-hadron transition, displacing the radion and reducing G_eff exponentially. Numerical tests with three independent models yield ξ_eff ≈ 1.00, 1.05, and 0.90 — all compatible with ξ = 1. The formal derivation from the DBI + QCD action remains an open problem. Falsifiable via lattice QCD (2027–2030).