Forced van der Pol — dx/dt=y, dy/dt=μ(1−x²)y−x+A·cos(z), dz/dt=ω. Classic chaotic μ=1.0 A=1.0 ω=0.45 (ω fixed). Dual μ+A sliders. Display embed (x,y,sin z). Distinct from ueda.html, colpitts.html, chua.html, lorenz.html, duffing (not shipped). Bulk centroid ≈ (−0.0066, 0.0006, 0.0008). RK4 van der Pol fold. Gold low-alpha trail, cap 650. RM = settled silhouette, no animate-on.