plugin:install pinned only modules chosen in the same plan, so a second
plugin package in a module the application already required was
installed at the newest release, moving the plugin already there, and
with --source the repository was cloned a second time. PlanInstall now
seeds every module of summer.yaml: a plugin in one installs at the
installed version with no go get or clone (only its summer.yaml entry),
and is refused with a plugin:update hint when that version has no
release of it or is not a release. A git URL whose repository is already
a submodule, or whose module the application has, is refused.
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