Tagging and pinning replaced the message's whole keyword set with a
copy built from the list row. When the row was stale - the mail had
been read or answered on another device since - the write cleared
`$seen` or `$answered` again, and removed tags were written as `false`,
which a JMAP keyword map may not hold.
Keyword writes now go out as `keywords/<name>` patches for just the
keywords that change, removals as `null`, through the call that
reports a refused update. The local row gets the same patch.
Linus Rath
aa0075a8e1