Function update_drag_on_move 

pub fn update_drag_on_move(
    cfg: Res<'_, DragConfig>,
    moves: MessageReader<'_, '_, PointerMoved>,
    q: Query<'_, '_, (Entity, &mut DragState)>,
    starts: MessageWriter<'_, DragStartEvent>,
    deltas: MessageWriter<'_, DragMoveEvent>,
)

Walk PointerMoved events: promote Pending -> Active when distance exceeds threshold; emit DragMoveEvent while Active.