Merge pull request 'Feat/mibook boot desktop choice' (#4) from feat/mibook-boot-desktop-choice into main

Reviewed-on: #4

docs/superpowers/specs/2026-07-27-mibook-boot-desktop-choice-design.md

@@ -0,0 +1,61 @@
+# mibook: choose terminal-only vs desktop at boot
+
+## Goal
+
+Let mibook boot to a text console by default, with KDE fully installed and
+launchable on demand. The user decides after boot whether they need the
+graphical desktop, without rebuilding the system.
+
+## Behavior
+
+- mibook boots to a text console (`multi-user.target`). SDDM and Plasma do
+  **not** start automatically.
+- KDE (SDDM + Plasma 6) remains fully installed.
+- Running `desktop` in the terminal starts the SDDM display manager, which
+  presents the graphical login screen; logging in there enters a Plasma 6
+  session.
+- No reverse command. To return to a text console, stop the display manager
+  (`sudo systemctl stop display-manager`) or reboot.
+- Other machines that enable the `kde-desktop` profile are unaffected; their
+  desktop still starts on boot.
+
+## Implementation
+
+### `modules/environments/kde-desktop/default.nix`
+
+Add an opt-out option to the existing profile:
+
+- New option `my.profiles.kde-desktop.startOnBoot`, a boolean defaulting to
+  `true`. The default preserves the current behavior for every consumer.
+- The existing `config` block (SDDM, Plasma 6, user packages) stays enabled
+  whenever the profile is enabled, regardless of `startOnBoot`.
+- When `startOnBoot = false`, additionally apply:
+  - `systemd.services.display-manager.wantedBy = lib.mkForce [ ];` so SDDM is
+    defined but not pulled in by any boot target.
+  - `systemd.defaultUnit = "multi-user.target";` so the boot target is the
+    text console.
+  - A `desktop` command provided via
+    `pkgs.writeShellScriptBin "desktop" "exec sudo systemctl start display-manager.service"`,
+    added to `environment.systemPackages`.
+
+### `machines/mibook/environments.nix`
+
+Set `kde-desktop.startOnBoot = false;` alongside the existing
+`kde-desktop.enable = true;`.
+
+## Testing / verification
+
+- `nix build '.#nixosConfigurations.mibook.config.system.build.toplevel'`
+  builds without error.
+- After `nixos-rebuild switch` on mibook: system boots to a TTY, no SDDM;
+  running `desktop` brings up the SDDM login and a working Plasma session.
+- Confirm jupiter (or any non-mibook consumer) is unchanged: its evaluated
+  `systemd.defaultUnit` / display-manager wantedBy are not altered.
+
+## Trade-offs
+
+- `desktop` relies on `sudo`; the user has sudo access, so no extra
+  configuration is required.
+- Chose "boot to terminal, launch on demand" over a GRUB boot-menu entry
+  because it is more robust across NixOS generations and needs no fragile
+  static kernel entries.

machines/mibook/environments.nix

@@ -6,6 +6,7 @@ in
 {
   my.profiles = {
     kde-desktop.enable = true;
+    kde-desktop.startOnBoot = false;
     zsh.enable = true;
     apps = {
       desktop_apps = true;

modules/environments/kde-desktop/default.nix

@@ -11,9 +11,19 @@ in
 {
   options.my.profiles.kde-desktop = with lib; {
     enable = mkEnableOption "KDE Desktop Environment";
+    startOnBoot = mkOption {
+      type = types.bool;
+      default = true;
+      description = ''
+        Whether the display manager (SDDM) starts automatically at boot.
+        When false, the system boots to a text console and KDE can be
+        launched on demand with the `desktop` command.
+      '';
+    };
   };
 
-  config = lib.mkIf cfg.enable {
+  config = lib.mkIf cfg.enable (lib.mkMerge [
+    {
       services = {
         displayManager.sddm.enable = true;
         displayManager.sddm.wayland.enable = true;
@@ -23,5 +33,15 @@ in
         # Programms can be added here...
         numix-icon-theme
       ];
-  };
+    }
+    (lib.mkIf (!cfg.startOnBoot) {
+      # Boot to a text console; SDDM stays installed but is not pulled in
+      # by any boot target. Launch KDE on demand with `desktop`.
+      systemd.services.display-manager.wantedBy = lib.mkForce [ ];
+      systemd.defaultUnit = lib.mkForce "multi-user.target";
+      environment.systemPackages = [
+        (pkgs.writeShellScriptBin "desktop" "exec sudo systemctl start display-manager.service")
+      ];
+    })
+  ]);
 }