Rikitake two-disk dynamo — classic 3D chaos (Rikitake 1958) — dx/dt = −μ x + y z, dy/dt = −μ y + x (z − a), dz/dt = 1 − x y. Classic chaotic μ=1 a=5. Dual μ+a sliders. Fold distinct from Chen–Lee, Chen–Ueta, Moore–Spiegel, Dequan–Li, Coullet. Bulk centroid ≈ (-0.04, -0.01, 5.48) from warm 20k + 80k RK4 @ dt=0.01. RK4, not chen-lee.html, not chen.html. Gold low-alpha trail, cap 650. RM = settled silhouette, no animate-on.