Signal is working on a Rust library but I don't really know what state it's in. Last time I checked it was WIP alpha but that was a long time ago.
Discussion
Signal does captchas now. So not very usable for automated scripts.
How? I've never got one. Isn't it because you're sending too many messages? And maybe bypass them with AI or an army of Indian solvers?
I use VPN a lot and I post in groups with a lot of people.
But the problem is that it is unpredictable and I cannot rely on a system that can request a CAPTCHA at any time and not deliver my automated message.