The cache works on a resource level, what caches traditionally do, and allow you to work in context of the relevant HTTP RFC's to serve content from a cache (e.g. some file system available to the proxy), instead of making the request using the inner Service. Your typical cache basically.

Low prio item, available for others to pick up.

Feel free to be inspired by https://github.com/cloudflare/pingora/tree/main/pingora-cache, but don't copy code from it as-is, given this is licensed code, and not sure how we would need to comply with it if we would take code from it. It anyway is a different kind of way to structure proxies, so no direct mapping would be possible anyway. Just to say, a lot of the things you have to be careful about you can probably find there.