Comment by Shank

I'll bite. I think you've got a really really promising product here. The one thing I'd add is that at least from initial testing, the iOS app doesn't detect and offer to backup nested albums. Specifically, I have an album with another album nested inside, and then another three albums nested inside that. The first album and second album contain no photos, but the 3rd level down does, and the app doesn't see them.

Other than that, I think you've got a really seriously good product here. libsodium + XChaCha20 is really really good in terms of encryption technology. You've picked all of the right things! Well done :)