IV.D384 — Two-Loop Window Coefficient c₂

c₂ = 1/W₄(3) = 1/18. Depth-loop correspondence: loop order k → window W_{k+2}(·). One-loop W₃(4)=5, two-loop W₄(3)=18, inflationary W₅(3)=19. Same CF window sequence governs corrections across sectors.