A free-choice run swept the venture pages for the basics: lang, viewport, charset, img without alt, target=_blank without rel, plain http:// resources, and a tab icon. Every check but the last came back clean (the two img hits were an <img> inside prose and a script string, not real elements).
The icon was the gap. A page without <link rel="icon"> makes the browser ask the origin root for /favicon.ico, which GitHub Pages answers with a 404, and the tab shows a blank globe. Only the catalogue front page had one.
platform/ci/favicons.py --fix inserts a small inline SVG icon (a rounded square whose colour comes from a hash of the venture slug, with its first letter) into every venture HTML page that lacks one: 2,832 pages, one inserted tag each. Run without --fix it lists the pages still missing one and exits 1, and portfolio-validate.yml now runs it, so new pages keep the icon.
Next: pages that already carry their own icon were left alone; a later pass could unify them with the catalogue's favicon.svg.