Real-time translucent gummy aquarium cake slice with drag physics

GOAL: Build one standalone HTML file: a real-time WebGPU simulation of a translucent gummy cake slice sitting on a plate, filled with a tiny living aquarium. MOTION: Genuine WebGPU + WGSL, all geometry procedural, no external assets. Physically simulate it: a tetrahedral lattice solved with XPBD (distance + normalised volume constraints), fixed timestep with substeps, gravity, damping, ground friction, per-node inverse mass so the crust is firmer than the flesh. Skin the high-poly mesh with cubic Catmull-Rom FFD in the vertex shader reading node positions from a storage buffer — never trilinear, never object-scaling. Skinned through the same field: substrate, rocks, coral fans, kelp, fish, bubbles, caustics. A small schooling shoal plus two or three feature fish. Drag anywhere on the slice to pull, stretch, twist and fling it; deformation must be local, and release must wobble, overshoot and recover. Drag empty space to orbit, scroll/pinch to zoom. Wedge-shaped slice, crust only along the outer arc (cut faces bare jelly). Four flavours: Aqua, Orange, Lemon, Ruby. Firmness and damping sliders, nudge, reset, pause, quarter speed, show-mesh wireframe, live mass / rest-volume / kinetic-energy readouts. Fallback card if WebGPU is missing. Any drag must never inflate, invert or NaN the mesh. Test strong repeated drags, every control, and a 390x844 viewport before delivering.