Interactive jelly tiger shark soft-body toy with physics

GOAL: Build "Shark Jelly" — Material Studies No. MOTION: 044: an interactive WebGPU soft-body study of a tiger shark cast in two layers of jelly, lying on its belly on a pale studio sweep. Same engine as the jelly series (WGSL, no libraries): signed-distance shape → surface-nets render mesh + snapped hex lattice (5 tets/cell) for XPBD with co-rotational shape matching, volume constraints, floor friction, soft grab with twist; shadow map, top-down contact AO, back-face thickness, refraction, Beer–Lambert absorption, thin-part glow, PBR Neutral tone map. Shape: elliptical section swept along the spine — blunt, broad, almost square snout, deep chest, slim caudal peduncle, belly pressed flat. All fins from one recipe (flat triangle, convex leading edge, falcate trailing edge carved by the circle through its ends, thinning to the tip, smooth-unioned): tall first dorsal, small second dorsal, long pectorals, pelvics, anal fin, heterocercal tail with a long notched upper lobe and a short lower one that props the tail on the table. Two layers: clear jelly over a milky belly whose top is the countershading line, dropping to the mouth corners. Shader markings in rest space: wavering, forking, broken tiger bars acting as a pigment film (spots toward the head), five gill slits, underslung mouth with labial furrows and a row of milky teeth, spiracles, nostrils, ampullae pores, lateral line; eyes with green-gold iris and slit pupil; trapped bubbles. Interaction: "Swish tail" drives the body by muscle strain — each tet's rest shape is lengthened/shortened along the body by a travelling wave of curvature × lateral offset (volume-preserving), so the tail really beats and a firm shark creeps forward. "Drop bait": jelly beads that swell into being over the head, fall, bounce, collide with the deformed body and can be tossed. Palettes Steel / Amber / Gummy; readouts mass, volume %, fork length, live tail bend in degrees; firmness & damping sliders, ¼ speed, mesh overlay, pause, reset; editorial UI in English.