Solid work, but I haven't seen too many AGPL projects prosper over time. I'll set a reminder to check back in a year or so to look for contributor growth.
I think which license you use has less to do with number of contributors or "prosperity" than other things happening in the project.
I'm even a Signal subscriber, and just didn't think about that aspect of their shared source model.
I mentioned number of contributors as that attribute is generally predictive for longer running, healthy projects.