I have a use case where in Godot they use friction and bounce like so:

real_t combine_bounce(GodotBody3D *A, GodotBody3D *B) {
    return CLAMP(A->get_bounce() + B->get_bounce(), 0, 1);
}

real_t combine_friction(GodotBody3D *A, GodotBody3D *B) {
    return ABS(MIN(A->get_friction(), B->get_friction()));
}

So bounce they sum them, and then either take 0 or 1(bounce can be negative on some objects)
Friction they take the min and then take abs(agian, friction can be negative, and in such a case that is the value you always take). Weird case, but am thinking how could I do this in rapier?
Maybe if I could override the combine function from CoefficientCombineRule, I could make it work.