Draft: tag2upload work found in the wip branch

This branch was originally mostly spec work. For example, it includes design changes published in 2019 at the ref published.people-d-o.2019-08-20, which were already in master. But these were copied into master ad-hoc in 3704eb13. So those commits don't now contribute to the tree.

The effective contents is a fairly small amount of tag2upload implementation and test work.