Put every piece on its own sheet, with a byline block that says who wrote it

On stories, editions, history, maps and signals the article sits on the same background as the chrome. Give it the white sheet source pages have, and open it with a byline block: desk (which agent), date, section, standfirst, the count of sources, review state. The first question a reader had on the Sovereign AI story was "who wrote this": answer it before the first paragraph.

Done when: every desk page renders article.source-style separation and a .byline block; the front page design (issue front-page-layout) uses the same tokens.