Signal's devs, for better or worse, are very opinionated. If you don't do it moxie's way then you're doing it wrong. I was once shut down on HN by the Signal posse because I said that I'd like to have a Signal client library that I could use to write my own custom lightweight client. Apparently I'm not worthy and clearly incapable of writing secure code. Meanwhile I have to use that crappy, gigantic official electron app that cost them at least one serious security vulnerability in the past (JS injection, if memory serves).

If you want to make a nerdy niche chat client that's probably a good mindset, but if you hope to appeal to the masses you'll have to put some water in your wine eventually. I managed to convince a couple of my groups to migrate away from WhatsApp lately, but unfortunately always towards Telegram. Signal is just not there yet if you want a drop-in replacement.

> I'd like to have a Signal client library that I could use to write my own custom lightweight client.

You already have that. Signal-cli is based on a standalone Java library distributed as part of the Signal codebase. Of course it is an unofficial client and the Signal team would really prefer you not use it, but if the Signal-cli team can develop something from that library, you probably could too.

I didn’t know that existed. Is there some way to use that to create a backup solution?

Did a quick skim and dont see why not. There's examples to receive the message. It's up to you what you want to do with it afterward.

This right here is the definition of a technicality -- so much so, that (on second thought) I wonder if this was meant to be tongue in cheek. If so, bravo.