Bodies list their contact points from the last step with getContacts: the
other body, a world point and normal, and the normal force. Core
Interactions keeps each body's contacts and derives contact events from
the same lists, so getContacts agrees with contactbegin/contactend and
clears on reset.

Materials gain torsionalFriction and rollingFriction, and drives gain
frictionLoss and armature. MuJoCo simulates them; Rapier, USD export, and
MuJoCo distance and unconstrained joints reject them.

Co-authored-by: Claude Opus 5.5 (1M context) <noreply@anthropic.com>