Certified critical-line bound 0.673591770245738332299780842385

By Samuel Lavery (github: samlavery) and his agent team (bridge-port, am-cert, mvt-engine, window-scope); Apache-2.0. Uses ajp88's W9A2 window and nine-point weights (ajp88-w9a2-window-nine-point, Apache-2.0, credited in the file; weights at full resolution) with our certification engine: a 16-unit tangent grid, Yuhang Shi's anchor-variance term via a per-cell curvature table (PCellVarW, his notice kept), range-end tangent anchors (PCellDKH), certificate thinning and point pruning. This certifies the same weights at margin 1.72e-5 instead of 2.92e-5 (11,857 leaves). The floor is the exact supremum of the leaf margins, H_W is enclosed to 1e-32, and long numerals use cafeai's zfNat64 source packing (reproduced unmodified with attribution).