Stage 6: server image with a console installer (0.4.0)

- server/ profile and build-iso.sh [desktop|server]; make iso-server,
  make qemu-server, run-qemu.sh --serial; login on tty and ttyS0
- das-server: SSH, chrony, NetworkManager/dhcpcd, Docker with Compose,
  nftables (closed except SSH, own table), fail2ban reading socklog,
  sshd without root passwords, Docker log rotation, tools
- das-server-install: dialog installer in Ukrainian and English, or
  unattended with --config; GPT + Btrfs subvolumes, GRUB for UEFI and BIOS,
  serial console, SSH key with optional keys-only logins
- das-install-common: mount-source and postinstall shared with Calamares
- dsv: runit service manager (list, enable, disable, start, stop,
  restart, status, logs) with bash completion, also on the desktop
- das-update split into a subpackage without GTK; the window and tray
  icon move to /usr/libexec/das/das-update-gui
- das-snapper-setup enables dbus, which snapper needs
- TODO: ISO size review with measured numbers and options

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

srcpkgs/das-tools/files/src/cmd/das-update/main.go

@@ -1,10 +1,13 @@
 // Command das-update updates Das OS with a snapper snapshot taken before
 // the update, so a broken update can be rolled back from the boot menu.
 //
-//	das-update          window that lists and installs updates
+//	das-update          the update window on a desktop, otherwise the same as --cli
 //	das-update --tray   background check, shows a tray icon when updates are available
-//	das-update --cli    the same in a terminal (servers, ssh); -y skips the question
+//	das-update --cli    update in a terminal (servers, ssh); -y skips the question
 //	das-update --apply  the privileged part, started by the window through pkexec
+//
+// The window and the tray icon are a separate program from das-tools
+// (guiPath), so this one has no GTK dependency.
 package main
 
 import (
@@ -42,27 +45,42 @@ func main() {
 	case *cli:
 		os.Exit(runCLI(*yes))
 	case *tray:
-		os.Exit(runTray())
+		// Nothing to show without the desktop part
+		if haveGUI() {
+			execGUI()
+		}
 	default:
-		os.Exit(runWindow())
+		if haveGUI() && haveDisplay() {
+			execGUI()
+		}
+		os.Exit(runCLI(*yes))
 	}
 }
 
-// Machine-readable lines that --apply prints for the window, among the
-// plain output of xbps.
-const (
-	markStep     = "@@step "
-	markSnapshot = "@@snapshot "
-	markReboot   = "@@reboot"
-	markUpToDate = "@@uptodate"
-	markError    = "@@error "
-)
+// guiPath is the window and tray icon program from das-tools.
+const guiPath = "/usr/libexec/das/das-update-gui"
+
+func haveGUI() bool {
+	_, err := os.Stat(guiPath)
+	return err == nil
+}
+
+func haveDisplay() bool {
+	return os.Getenv("DISPLAY") != "" || os.Getenv("WAYLAND_DISPLAY") != ""
+}
+
+// execGUI replaces this process with the graphical part, passing the
+// arguments on. It returns only when that fails.
+func execGUI() {
+	err := syscall.Exec(guiPath, append([]string{guiPath}, os.Args[1:]...), os.Environ())
+	fmt.Fprintln(os.Stderr, "das-update:", err)
+}
 
 type markReporter struct{ w io.Writer }
 
-func (r markReporter) Step(title string) { fmt.Fprintln(r.w, markStep+title) }
+func (r markReporter) Step(title string) { fmt.Fprintln(r.w, update.MarkStep+title) }
 func (r markReporter) Output() io.Writer { return r.w }
-func (r markReporter) Snapshot(n int)    { fmt.Fprintf(r.w, "%s%d\n", markSnapshot, n) }
+func (r markReporter) Snapshot(n int)    { fmt.Fprintf(r.w, "%s%d\n", update.MarkSnapshot, n) }
 
 func runApply() int {
 	if os.Geteuid() != 0 {
@@ -74,13 +92,13 @@ func runApply() int {
 	r := markReporter{os.Stdout}
 	res, err := update.System().Apply(context.Background(), r)
 	if err != nil {
-		fmt.Println(markError + err.Error())
+		fmt.Println(update.MarkError + err.Error())
 		return 1
 	}
 	if len(res.Updates) == 0 {
-		fmt.Println(markUpToDate)
+		fmt.Println(update.MarkUpToDate)
 	} else if res.Reboot {
-		fmt.Println(markReboot)
+		fmt.Println(update.MarkReboot)
 	}
 	return 0
 }