The menu builder marks two links by node ID, and the blackout block is one site's node

Problem/Motivation

Two numbers decide what a menu answers with. A link whose route points at node 15 is marked services_link in the response, and a link pointing at node 25 is marked prices_link. Those are node IDs of one site: on every other site the two markers land on whatever content happens to have those IDs, or on nothing at all. A response key that is right on one site and silently wrong everywhere else is worse than a missing one, because nothing about it looks broken.

The same shape appears in the static data endpoint: the notice a site shows while it is on reduced service is read by building a paragraph that points at node 12.

Proposed resolution

• A link is marked because the site says which link that is, not because of a number: the roles a site fills already answer questions of exactly this shape, and the special pages of a site are named there today.
• The same for the block the notice comes from: the site names the object, as it already names its contacts, its footer and its awards.
• An unfilled role means an absent key, not a guessed one.
• Coverage that a site which named nothing gets neither marker and no error.

Remaining tasks

Everything.