cache — a behavioral revalidation lint

  Plenty of origins serve an ETag that can never match: compression or a
  template nonce varies per response, so every If-None-Match comes back 200
  with a full body. The headers look perfect and nothing warns — your cache
  revalidates forever and never once succeeds.

    curl 'aadhar.sh/cache?url=https://example.com/app.css'

  ── what it does ────────────────────────────────────────────────────────────
  No header grading. It fetches the target twice to see whether the validator
  survives two identical requests, then replays it with If-None-Match and
  reports what the origin actually did. For HTML it also asks for a second
  representation and checks the Vary header against the answer — the
  shared-cache trap this site hit in production (#195).

  cost    3-4 subrequests, headers only; bodies are cancelled unread
  shares  Lens's 30/min per-address budget

  &url= probe a resource