deployment_timestamp was int(time.time()) per-request, giving every
page load a new ?v=... query string on custom.css. Cloudflare treats
each unique URL as a new resource, so the CSS was fetched from the VM
on every page load — 64 KB over the wire per navigation.
Token now tied to static/css/custom.css mtime. The URL only changes
when the CSS actually changes, so Cloudflare can hold the file for
its full 4h TTL. Degraded-mode fallback preserves today's behaviour
if the file isn't on disk.
3 new CacheBustTokenTests; all 68 tests pass.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
