Is there a particular reason -- I could not find one in the history -- that these 2 docs should remain hidden: ?

docs/markdown/Writing Plugins/common-plugin-tasks/plugins-package-goal.md:hidden: true
docs/markdown/Writing Plugins/common-plugin-tasks/plugins-run-goal.md:hidden: true

I think they have been visible in the past, so maybe they're rotten? Check the git history for them and see when/why the hidden was added.

Looks like they have had that set since "Adds current contents of readme.com docs to repo and adds notes on how to sync."

Interesting! Both those docs are visible here: https://www.pantsbuild.org/v2.7/docs/plugins-run-goal and https://www.pantsbuild.org/v2.7/docs/plugins-package-goal. I'm guessing 2.7 might predate such a migration? Not sure. It predates my involvement in Pants by a long time...

Hmm, are the content of those current? Could be an error

They are not fully correct as I recall. I think the basic setup works but if you copy-paste it you'd have errors on imports and so on.