`; a page without it is served intact and no card is requested: the card is never appended at the end of the document. ## The page response: cache contract doubleshift never caches its answers ([No cache](https://docs.shftd2.com/how-it-works.md#no-cache)). The response of **your page** to the agent is yours. The Cloudflare Worker library applies the header rules below to every page it enriches. A page it serves without a card goes out as your origin or cache answered it, headers included, like the human page. On the other paths, apply these rules in your configuration, at least to every response that carries a card: * **Never let the human page vary by visitor.** The cached human page must not read the `User-Agent` nor call doubleshift. * **Serve the agent response with** `Cache-Control: private, no-store` or `public, max-age=0, must-revalidate`, **and no validators** (`ETag`, `Last-Modified`). Build these headers from scratch; never copy the origin's `s-maxage` or CDN-specific headers. * **Never forward a conditional request on the agent path.** Drop `If-None-Match` and `If-Modified-Since`: a `304` leaves nothing to compose. * After injecting, **drop `Content-Length` and `Content-Encoding`** if your path buffers the body. * **Check both orders**, cold and warm: see [Verify and troubleshoot](https://docs.shftd2.com/verify.md). ## Timeout budget Budget **800 ms** for the call from a CDN edge: `timeoutMs` with the Worker library, the include timeout on an ESI stack, where `onerror="continue"` renders the page without the card. On serverless platforms (Vercel, Netlify functions…), use **about 2,500 ms**: a cold start alone can exceed 800 ms. Record a timed-out call apart from a no-fill. ## Moved These sections now have their own pages. ### Options The edge library's options and defaults are in the [edge library reference](https://docs.shftd2.com/api/edge-library.md#options). ### Diagnostics The edge library's diagnostics are in the [edge library reference](https://docs.shftd2.com/api/edge-library.md#diagnostics). ### Verify The checks and the troubleshooting are in [Verify and troubleshoot](https://docs.shftd2.com/verify.md). ### Direct delivery logs What each way of sending delivery records gives you is in [Delivery logs](https://docs.shftd2.com/delivery-logs.md). This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.