Taming the 3D Cosserat hair physics

Getting the physical tip lag right was a massive battle against stiffness and chaotic particles. I spent hours dialing in a discrete 3D Cosserat elastic rod simulation for the brush bristles, implemented in a 287-line CosseratBristleCluster.ts file. Early iterations were either too rigid or produced bizarre, sperm-like particle trails that broke the meditative vibe. By tuning the bending stiffness and stepping the physics at 0.016s intervals, we finally achieved a natural viscoelastic lag that responds organically to trackpad pressure and momentum.