The old static homepage had a skip link at the top of the document — the one that lets a keyboard user jump past the nav straight into the page. WCAG calls it Bypass Blocks. It was one anchor tag.
The homepage got rewritten into a React route. The link did not come with it. Grepping the codebase afterward found no skip link anywhere, on any page, which means it had been gone since the rewrite landed and nothing caught it.
Nothing would have. There is no automated check here for "a feature that used to exist still exists." Tests cover behavior someone wrote a test for. The skip link had no test because it had never needed one — it was static HTML in a file that got deleted.
It is back now, as a shared component wired into both nav contexts, using the sr-only / focus-visible pattern so it stays invisible until focused. The lesson I took is smaller than the fix: when a rewrite deletes a file, read the file it deletes.