I want a web cache that runs on my network transparently caching everything that goes through it. It would be a LRU cache but with the ability to easily mark some resource as archived such that it never gets deleted. A browser extension could be used to do this marking. Unfortunately client-side js makes this very difficult or even impossible to do.

We really dropped the ball when it came to running random js from websites. The number of people who truly run only free software these days is close to zero. I used to block all js about 10 years ago but it was a losing battle and ended up being essentially an opt out from society.