it looks like it’s actually windows that changed:
in cmd, “start /wait emeditor” doesn’t wait in Win10 build 1909 but if I run the same command in my VM with Win10 build 1709 it works and waits as expected.

curiously “start /wait notepad” works properly even on Win10 build 1909

perhaps it has something to do with the new ConPTY stuff introduced in Win10 1803