Two guards for a server deployed by hand, which the West Jefferson production
box is.
An existing venv is reused, which is right for a repair or an upgrade of an
install this made, and wrong when the venv belongs to a different Python. The
wheelhouse is tagged for one minor version, so pip finds no candidate for the
compiled packages and dies partway through - after Python has been installed and
the application tree replaced. The two versions are now compared up front and
the run stops with both numbers and what to do about it.
Switching deployment method removes the other method's IIS artifact. That is
correct when this installer owns both and dangerous when it does not: a wrong
-MountAlias would call Remove-WebApplication on a live mount with no prompt and
no error, and the first sign would be the site returning 404. It now refuses
unless a version stamp shows this installer made the install, or -AdoptExisting
is passed, and the refusal lists exactly what it would have removed.
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