Shared Dictionaries: compression that keeps up with the agentic web

What this post added

Introduces support for shared compression dictionaries, specifically delta compression, based on RFC 9842. This allows browsers to use previously cached versions of resources as dictionaries to compress subsequent requests, sending only diffs. This is crucial for managing the increased frequency of deploys driven by agentic web development and agentic crawlers. The implementation involves new HTTP headers (`Use-As-Dictionary`, `Available-Dictionary`) and content encodings (`dcb`, `dcz`). Cloudflare's initial phase provides passthrough support, ensuring correct caching behavior by varying cache keys on `Available-Dictionary` and `Accept-Encoding`.