feat(emacs): Set {EDITOR,VISUAL} to Emacs

- Includes a tiny wrapper script which connects to the Emacs daemon if it's
  running, or simply runs `emacs` otherwise.

users/crumb/programs/emacs.nix

@@ -56,12 +56,24 @@ let
       done
     '';
   };
+
+  emacsclient-or-emacs = pkgs.writeShellScriptBin "emacsclient-or-emacs" ''
+    emacsclient --alternate-editor=${emacsWrapper}/bin/emacs "$@"
+  '';
 in {
   sydnix.impermanence.cache.directories = [
     # Impermanence expects the path to be relative to ~.
     (lib.removePrefix config.home.homeDirectory straightBaseDir)
   ];
 
+  # Set emacsclient as the default editor for the time being.
+  home.sessionVariables =
+    let e = "${emacsclient-or-emacs}/bin/emacsclient-or-emacs";
+    in {
+      "EDITOR" = e;
+      "VISUAL" = e;
+    };
+
   home.file =
     let default =
           lib.removePrefix "${config.home.homeDirectory}/"
@@ -74,6 +86,7 @@ in {
 
   home.packages = [
     emacsWrapper
+    emacsclient-or-emacs
   ] ++ fontPackages;
 
   # There's probably a better place to put this, but the current setup demands
@@ -85,5 +98,6 @@ in {
     enable = true;
     # Generate a desktop entry for emacsclient.
     client.enable = true;
+    package = emacsWrapper;
   };
 }