> Py_SetProgramName() should be a relative or absolute path that can be used to set sys.executable and other values appropriately.

Key point here is *can be*, but it doesn't have to be. Given it has fallbacks all the way to "python"/"python3", we can't realistically use it as sys.executable just because it has a value.

And right now, it's used to locate the current executable (which is unnecessary on Windows), which is then assumed to be correct for sys.executable. Most embedding cases require *this* assumption to be overridden, not the previous assumption.