The Quantum Entanglement Spacetime Theory (QuEST) predicts a coupling between visible and dark sectors, interpreted as a parity-breaking interaction emerging from the structure of spacetime itself. While the original operator-level prediction yields a nonzero coupling strength, completed observational constraints from CMB birefringence and Weak Equivalence Principle experiments suggest that such a coupling must be highly suppressed in dense environments. This paper introduces an emergent suppression mechanism, termed \emph{Topological Shielding}, which arises from a geometric mismatch between the scaling of entropy and volume in the underlying MERA tensor structure. The result is a density-dependent phase transition that activates or deactivates the coupling based on local entanglement flow. The theory predicts a specific critical density below which the coupling becomes observable and above which it is shielded. Five definitive empirical tests are proposed, each offering a falsifiable criterion for detecting or excluding this predicted quantum–geometric transition of the vacuum.