Skip primary-only setup when running as secondary instance

main.go

 package main
 
 import (
+	"context"
+	"log"
+	"os"
+
 	"SystemUpdater/backend/eepm"
 	_ "SystemUpdater/lib/gtks/logging"
 	"SystemUpdater/lib/i18n"
@@ -8,8 +12,6 @@ import (
 	"SystemUpdater/service"
 	"SystemUpdater/store"
 	"SystemUpdater/ui"
-	"log"
-	"os"
 
 	"github.com/diamondburned/gotk4-adwaita/pkg/adw"
 	"github.com/diamondburned/gotk4/pkg/gio/v2"
@@ -19,6 +21,42 @@ import (
 func main() {
 	i18n.Init()
 
+	app := adw.NewApplication("ru.ximperlinux.SystemUpdater", gio.ApplicationHandlesCommandLine)
+
+	// The command-line handler runs in the primary instance. The local
+	// (secondary) instance only forwards the command line via D-Bus and
+	// waits for the primary to mark it Done().
+	app.ConnectCommandLine(func(cmdLine *gio.ApplicationCommandLine) int {
+		args := cmdLine.Arguments()
+
+		background := false
+		for _, arg := range args {
+			if arg == "--background" {
+				background = true
+			}
+		}
+
+		if !background {
+			app.Activate()
+		}
+
+		cmdLine.Done()
+		return 0
+	})
+
+	if err := app.Register(context.Background()); err != nil {
+		log.Fatalf("Failed to register application: %v", err)
+	}
+
+	if app.IsRemote() {
+		// Secondary instance: nothing to do locally — app.Run() will
+		// forward the command line to the primary and exit as soon as
+		// the primary calls cmdLine.Done().
+		os.Exit(app.Run(os.Args))
+	}
+
+	// ---- primary-only setup below ----
+
 	st := store.NewStore()
 	defer st.Close()
 
@@ -45,8 +83,6 @@ func main() {
 	}
 	defer eepmClient.Close()
 
-	app := adw.NewApplication("ru.ximperlinux.SystemUpdater", gio.ApplicationHandlesCommandLine)
-
 	notificationSvc := service.NewNotificationService(&app.Application.Application)
 	historySvc := service.NewHistoryService(st, historyFile)
 	updateSvc := service.NewUpdateService(st, eepmClient, historySvc)
@@ -71,23 +107,6 @@ func main() {
 		window.Window.Present()
 	})
 
-	app.ConnectCommandLine(func(cmdLine *gio.ApplicationCommandLine) int {
-		args := cmdLine.Arguments()
-
-		background := false
-		for _, arg := range args {
-			if arg == "--background" {
-				background = true
-			}
-		}
-
-		if !background {
-			app.Activate()
-		}
-
-		return 0
-	})
-
 	defer func() {
 		schedulerSvc.Stop()
 		log.Println("Application shutdown complete")