Viktor hit 'Too big request header' (fasthttp 431 from error-pages) on a
routed host during a brief 503 window, and sees it periodically across
ingresses: Authentik forward-auth accumulates one authentik_proxy_*
cookie per protected service on .viktorbarzin.me, so established
browsers carry multi-10KB Cookie headers — over error-pages' 5120-byte
default read buffer, which doubles as its max header size. Any error-
middleware dispatch then 431'd instead of rendering the styled page.
Same root cause class as the 2026-06-01 large_client_header_buffers
fixes on bot-block-proxy and auth-proxy-config; error-pages was the
remaining small-buffer backend on the shared chain.
aa1fccb883