Would it be possible to somehow encode the list of relays into some sort of hash (not the word I am looking for, as I currently understand hashes are one way)
Wish list: coracle direct links work in most contexts, but boy are they long. This is a problem when posting them to, e.g. SMS.
The satellite.earth client has much shorter direct links. I'm guessing they use a hash, or possibly a database with random ids.
An example of a satellite.earth direct link:
https://satellite.earth/thread/note1cy5ggl77z0z5u9tup993wsl9me0tanhsudm9ueefr4glqmwcrresv6exhf
Of course, given the nature of Nostr, I can post with Coracle, and then get a direct link from satellite.earth.
Discussion
No. The only thing that exists are compression algorithms (zip) but in this case the difference would be negligible and the efforts herculean.