V.T278 — (5/6) Uniquely Forced from Threshold Ladder Topology

Canonical ladder has exactly 6 thresholds. Exactly 1 (L_B, baryogenesis) is resonant via omega-crossing singularity. Remaining 5 involve single-sector crossings. Therefore 5/6 = |non-resonant|/|total| is uniquely forced. Also governs Y_p = (8/27)*(5/6) = 20/81.