CDN-236: The Near-Linear Gate

CDN-236 converts the CDN-235 amplification-window bound into a coherence-order gate. Using A_env = lambda^(1/2 + kappa/2), where kappa=0 is diffusive accumulation and kappa=1 is linear coherence accumulation, lambda=20 requires kappa=0.851 for zero residual matter at the CDN-230 separation threshold. Moderate order kappa=0.50 leaves R/bar=2.386, strong order kappa=0.75 still leaves R/bar=0.820, and linear kappa=1 overshoots by 1.459 M_bar. Near-linear cluster closure remains conditional; residual matter stays explicit until kappa is derived or measured.