Doesn't pinboard.in support full-text archiving? If so, it's probably still limited to public content. Conceivably a bookmark extension could save a full-page screenshot and all of the text, even if the page requires auth, isn't resolvable from the internet, etc.

I suffer from the same affliction for the most part, but I do end up capturing sets of bookmarks related to research or projects that I share with colleagues. It also sometimes happens that I start a new browser profile for learning a tech and save all my bookmarks from that with the code. That has helped when it's a case of "how did I do this one thing I know I did in throwaway project X?"