Generalize curveMidLevel/curveFromMidLevel to curveLevelAt/curveFromLevelAt at
arbitrary phi; knotVtx and its drag inverse now read the phi a knot's truncated
x actually implies, not always 0.5.
Trigger's fade pair folds into the AHD (and goes live); the release anchors right;
Preserve rings its synthetic tail out instead of cutting it. Payload v10.