nixos: add emacs-auto wrapper + desktop files

nixos/bootstrap.nix

@@ -4,7 +4,7 @@
     ./essential.nix
   ];
   environment.systemPackages = with pkgs; [
-    emacs
+    emacs-auto
   ];
   programs.zsh.enable = true;
   networking.firewall.enable = false;

nixos/emacs-overlay.nix

@@ -0,0 +1,132 @@
+final: prev:
+{
+  # Keep pkgs.emacs as a real Emacs package (used by other derivations / emacsPackages),
+  # but provide an "auto" wrapper for interactive use that selects the right GUI backend.
+  emacs = prev."emacs30-pgtk".override {
+    withNativeCompilation = true;
+    withTreeSitter = true;
+  };
+
+  emacs-wayland = final.emacs;
+
+  emacs-x11 = prev.emacs30.override {
+    withNativeCompilation = true;
+    withTreeSitter = true;
+  };
+
+  # Runtime launcher that chooses:
+  # - Wayland session: pgtk build with GDK_BACKEND=wayland (avoids XWayland)
+  # - X11 session: X11 build with GDK_BACKEND=x11
+  # - No display: falls back to -nw
+  #
+  # Override with EMACS_AUTO_BACKEND=wayland|x11|tty.
+  emacs-auto = final.stdenvNoCC.mkDerivation {
+    pname = "emacs-auto";
+    version = final.emacs.version or "unknown";
+    dontUnpack = true;
+    nativeBuildInputs = [ final.makeWrapper ];
+
+    installPhase =
+      let
+        emacsWayland = final.emacs-wayland;
+        emacsX11 = final.emacs-x11;
+      in
+      ''
+        mkdir -p "$out/bin" "$out/share/applications" "$out/share/icons" "$out/share/pixmaps"
+
+        # Ensure desktop integrations (icons) exist even though we don't install the raw emacs packages.
+        if [ -d "${emacsWayland}/share/icons" ]; then
+          ln -s "${emacsWayland}/share/icons/hicolor" "$out/share/icons/hicolor"
+        fi
+        if [ -d "${emacsWayland}/share/pixmaps" ]; then
+          ln -s "${emacsWayland}/share/pixmaps/"* "$out/share/pixmaps/" || true
+        fi
+
+        # Convenience explicit launchers.
+        makeWrapper ${emacsWayland}/bin/emacs "$out/bin/emacs-wayland" \
+          --set GDK_BACKEND wayland
+        makeWrapper ${emacsX11}/bin/emacs "$out/bin/emacs-x11" \
+          --set GDK_BACKEND x11
+
+        # Main launcher.
+        cat > "$out/bin/emacs" <<'EOF_EMACS_WRAPPER'
+#!${final.runtimeShell}
+set -eu
+
+backend="''${EMACS_AUTO_BACKEND:-}"
+tty=0
+for a in "$@"; do
+  case "$a" in
+    -nw|--nw|--tty|--terminal|--no-window-system) tty=1 ;;
+  esac
+done
+
+if [ "$backend" = "wayland" ] || [ "$backend" = "pgtk" ]; then
+  exec "@out@/bin/emacs-wayland" "$@"
+fi
+if [ "$backend" = "x11" ]; then
+  exec "@out@/bin/emacs-x11" "$@"
+fi
+if [ "$backend" = "tty" ]; then
+  exec "@emacsX11@/bin/emacs" -nw "$@"
+fi
+
+if [ "$tty" -eq 1 ]; then
+  # Respect the user's explicit -nw, but still run a consistent binary.
+  exec "@emacsX11@/bin/emacs" "$@"
+fi
+
+# Prefer Wayland if it looks like a Wayland session.
+if [ -n "''${WAYLAND_DISPLAY:-}" ] || [ "''${XDG_SESSION_TYPE:-}" = "wayland" ] || [ -n "''${HYPRLAND_INSTANCE_SIGNATURE:-}" ]; then
+  exec "@out@/bin/emacs-wayland" "$@"
+fi
+
+# Otherwise, if X is available, use the X11 build.
+if [ -n "''${DISPLAY:-}" ] || [ "''${XDG_SESSION_TYPE:-}" = "x11" ]; then
+  exec "@out@/bin/emacs-x11" "$@"
+fi
+
+# Headless fallback.
+exec "@emacsX11@/bin/emacs" -nw "$@"
+EOF_EMACS_WRAPPER
+
+        substituteInPlace "$out/bin/emacs" \
+          --subst-var out \
+          --replace-fail "@emacsX11@" "${emacsX11}"
+        chmod +x "$out/bin/emacs"
+
+        # emacsclient is compatible across builds as long as versions match; use one.
+        ln -s ${emacsX11}/bin/emacsclient "$out/bin/emacsclient"
+
+        cat > "$out/share/applications/emacs.desktop" <<'EOF'
+[Desktop Entry]
+Name=Emacs
+GenericName=Text Editor
+Comment=Edit text
+Exec=emacs %F
+TryExec=emacs
+Icon=emacs
+Type=Application
+Terminal=false
+Categories=Development;TextEditor;
+MimeType=text/plain;
+StartupWMClass=Emacs
+EOF
+
+        cat > "$out/share/applications/emacsclient.desktop" <<'EOF'
+[Desktop Entry]
+Name=Emacs (Client)
+GenericName=Text Editor
+Comment=Edit text using a running Emacs server
+Exec=emacsclient -c -a emacs %F
+TryExec=emacsclient
+Icon=emacs
+Type=Application
+Terminal=false
+Categories=Development;TextEditor;
+MimeType=text/plain;
+StartupWMClass=Emacs
+EOF
+      '';
+  };
+}

nixos/essential.nix

@@ -14,7 +14,7 @@
     direnv
     dpkg
     efibootmgr
-    emacs
+    emacs-auto
     fd
     ffmpeg
     file

nixos/nix.nix

@@ -55,6 +55,7 @@
     nixpkgs.overlays = [
       # (import ./nvidia-container-toolkit-overlay.nix)
       (import ./runc-overlay.nix)
+      (import ./emacs-overlay.nix)
       (import ./overlay.nix)
       # Use codex and claude-code from dedicated flakes with cachix
       (final: prev: {

nixos/overlay.nix

@@ -248,11 +248,6 @@ in
     };
   });
 
-  emacs = prev."emacs30-pgtk".override {
-    withNativeCompilation = true;
-    withTreeSitter = true;
-  };
-
   python-with-my-packages = let
     my-python-packages = python-packages:
     with python-packages; [