Public projects: a face anyone can see

A project's owner can make it public: its tile on the overview then loads for anyone, signed in or not. Signed out, all you can do is look.

What a signed-out viewer reads is not the board's log. The log holds every project and its whole history, and the host grants reading a collection all or nothing. So each public project has one summary document, in a collection anyone may read (virta:public): the project's name, icon, colors, description, links and version, how many tasks are open, in progress and blocked, and when it last changed. No task, body, comment, history or file is in it. One read per project is also the least a scraper can cost.

• Only a person signed in on the board makes a project public. The public setting counts when the host stamped it as written in a session; an agent's token can turn it off, never on.
• The summary is derived, never edited. Any signed-in board or agent that sees it out of date rewrites it (syncPublic), and removes the summary of a project that is no longer public. A summary written from a later point in the log is never replaced by an older one.
• What was public has been seen. Turning it off removes the summary; it can't recall what a viewer or a cache already has.

virta project publish        # bring the public summaries up to date (it also happens after any write)