Hey Ludo, Maxim, Sorry about the double-email. I messed up the first patch by mistake. The fix actually ends up being quite simple! I didn't know about `valid-derivers`, so thanks to Ludo for that.
This patch should fix the issue by restricting substitutions on the server side instead of the client side. The bug in the daemon may remain, but this should at least ensure correct functionality. Besides, it seems that we are in agreement that substitutability isn't something that should really be enforced by the client anyway. Best, Morgan
