The Return of the Lemma: Launchpads, corridor obstructions, and the shape of a counterexample

We refine the frontier formulation of Gilbreath’s Conjecture by proving a new local obstruction. Although the conjecture still reduces to showing that the {0,2}-frontier never reaches position 4, we show that the most direct minimal erosion corridor from the initial frontier-8 row is impossible. In particular, any pure minimal 8 → 7 → 6 → 5 → 4 collapse would force a zero-block in positions 4–7 of the launchpad row, whereas Row 2 has twos there. Thus one natural route to failure is eliminated by proof, and any remaining counterexample must arise through a more complicated frontier dynamic. This companion note reframes the earlier local-bound reduction in terms of frontier dynamics and the {0,2} basin. For correspondence and updates: BMorgan007(at)protonmail.com