1. run setup.exe which we've determined somehow will spawn Au_.exe
1. then wait for the Au_.exe to finish, which we are pretty confident can only be the child spawned in line 2 because we waited for any other Au_.exe processes we might have in line 1
Whilst there's a narrow window for another Au_.exe to start executing between line 1 and 2, in practice this formulation seems to work rather reliably.