The RQGP Interface Flux Operator and the Vacuum Inversion Threshold

We derive an exact, parameter-free interface flux operator Φ(Z, N) = Z − 1/2 Ndirectly from the Kirchhoff boundary conditions of the Refined QuantumGeometric Physics (RQGP) framework. Φ measures the net signed flux that acomposite nucleus declares at the boundary between the confined hadroniclattice (Regime 1) and the physical vacuum (Regime 2). The condition Φ = 0,equivalent to N/Z = 2, defines the Vacuum Inversion Threshold: the universalboundary at which the net proton source declaration is exactly canceled byneutron sink demand, rendering beta decay structurally inevitable. Validationagainst 80 isotopes spanning Z = 1 to Z = 118 yields consistent predictionwith zero false positives and 19 expected false negatives representing decaymechanisms outside the scope of the operator. No stable nucleus possessesΦ ≤ 0. For Φ < 0, the composite enters a regime of structural vacuumstarvation in which the proton core can no longer supply sufficient flux toservice all neutron Y-defects internally; fringe neutrons are displaced outwardto maximize their interface area with the ambient vacuum. We identify this asthe structural-mechanical origin of nuclear halo configurations. These resultsfollow without external fitting from the two locked RQGP boundary conditions.