A diagram that lives in the same file as its prose, reviewed in the same diff.
Here a ```mermaid block renders through the prose code component, which
lays a wide diagram out at 1:1 with a scroll and Fit / 1:1 / fullscreen
controls rather than shrinking it to 9px type. The estate diagrams are the
worked example: five pictures of the design-system estate, each node dated,
drawn from a named source.