Spectral Non-Concentration Implies Global Regularity for 3D Navier–Stokes on T³

We establish a spectral framework for global regularity of the 3D incompressible Navier–Stokes equations on the torus T³. The central object is the shell-helical GCD interaction operator H_N[u(t)], whose minimum eigenvalue governs spectral stability of the Leray–Hopf flow. The main result (Theorem 4.1) proves that the Spectral Non-Concentration (SND) condition implies inft≥0 λ_min(H_N[u(t)]) > −1/2, precluding spectral blowup for all time. The proof reduces to a single application of Weyl's perturbation inequality given the frozen gap δ₀ = 0.20 (established unconditionally in Paper 1) and operator continuity. The remaining open step — the SND Simplex Stability Lemma — is precisely stated as the target for Paper 3. This is the second paper in a series on spectral non-concentration criteria for Navier–Stokes regularity