Function apply_joint_graph_changes 

pub fn apply_joint_graph_changes(
    changes: MessageReader<'_, '_, JointGraphChange>,
    joint_graph: Res<'_, JointGraph>,
    islands: Option<ResMut<'_, PhysicsIslands>>,
    body_islands: Query<'_, '_, &mut BodyIslandNode, Or<(With<Disabled>, Without<Disabled>)>>,
    commands: Commands<'_, '_>,
)

Applies JointGraphChange messages to PhysicsIslands.