fix(haskell): Persist stack directory

modules/home/users/crumb/haskell.nix

@@ -60,6 +60,7 @@ in {
         # We don't want to rebuild Hackage simply due to a reboot, do we?  }:)
         (lib.removePrefix "${config.home.homeDirectory}/"
           "${xdg-cache-dir}/cabal")
+        ".stack"
       ];
   };
 }