The unit normal vector in world space, pointing from shape A to shape B. During a pre-contact callback this may be modified, and the solver uses the new value this step. It must stay unit length. If the callback leaves the manifold invalid, whether a non-unit normal, a non-finite value, or a point count outside [0, 2], the whole edit is discarded and the manifold is restored for that step.

public Vector2 normal { readonly get; set; }