- rootFileTargets gives robots.txt, sitemap.xml and llms.txt their backend
target also in state unknown without a last answer, so the failing fetch
answers 503 with Retry-After: 60 instead of the app's 404 (L4 WR-08)
- an older backend (absent) still passes through; sitemap files and
verification files still need a site answer
- expect-seo-down.txt expects the 503s and states the staging reason
8cdf35929a