[nine_k]

I'd say that packaging an app for NixOS should include rewriting all such impure steps, and making the fonts packaged along with the app is one such step.

If the fonts can't be packaged for licensing reasons, even as a separate package, then well, you indeed can guarantee that you'd be able to install the app next time. If it's not what you seriously need, then likely the value proposition of Nix is not for you.

[colinramsay]

I agree. That doesn't negate the fact that it took me a while to understand what the issue was, see if I could get around it, work out how to disable the font downloading in Flutter, etc, etc. I may have been trying to force a round peg into a square hole but NixOS didn't do much to help me see the shape of the pegs and holes in the first place.