🍄 Bettong Truffle Foraging Lab (2D): Scent-Gradient Chemotaxis & Spore Dispersal

This 2D companion strips the burrowing marsupial's foraging down to the mechanism that actually drives it: a real diffusion-decay scent field radiating from buried truffles, a chemotaxing bettong that steers up the gradient with paired sensors and falls back to random search when the trail goes cold, and a digging success probability derived from the true local scent concentration rather than proximity alone. The mutualism closes the loop — every truffle eaten starts a gut-passage timer, and every defecation is a chance for spores to germinate a new truffle nearby, so truffle density, diffusion range and bettong sensitivity all visibly reshape not just one dig but the whole multi-generation foraging-and-reseeding cycle.