summer build always emitted party.Describe and []party.Info, so an
application whose framework requirement predates v0.6.0 stopped compiling
once the CLI was updated. The build now checks the party package go list
resolves in the application (a static look for Describe and Info, not a
version compare, since a local checkout reports the previous tag until
it is tagged) and, when they are missing, writes main.go and
plugins.gen.go exactly as before, with a warning to move the framework
to v0.6.0. An unresolvable party package keeps the current sources.
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