fix(desktop): nur eine Instanz — zweiter Start holt das Fenster nach vorne

- tauri-plugin-single-instance als erstes Plugin registriert
- show_main_window-Helper ersetzt die dreifach duplizierte Fenster-Sequenz

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

apps/desktop/src-tauri/Cargo.lock

@@ -4034,6 +4034,22 @@ dependencies = [
  "zbus",
 ]
 
+[[package]]
+name = "tauri-plugin-single-instance"
+version = "2.4.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "db817fe9295e19b7d8357e900af31edb93703dd9fb6de524b007b47b6afc63b0"
+dependencies = [
+ "serde",
+ "serde_json",
+ "tauri",
+ "thiserror 2.0.18",
+ "tokio",
+ "tracing",
+ "windows-sys 0.60.2",
+ "zbus",
+]
+
 [[package]]
 name = "tauri-plugin-store"
 version = "2.4.3"
@@ -4246,6 +4262,7 @@ dependencies = [
  "tauri-plugin-autostart",
  "tauri-plugin-notification",
  "tauri-plugin-opener",
+ "tauri-plugin-single-instance",
  "tauri-plugin-store",
  "tauri-plugin-updater",
  "tauri-plugin-window-state",

apps/desktop/src-tauri/Cargo.toml

@@ -16,6 +16,7 @@ tauri-plugin-store = "2"
 tauri-plugin-notification = "2"
 tauri-plugin-autostart = "2"
 tauri-plugin-window-state = "2"
+tauri-plugin-single-instance = "2"
 reqwest = { version = "0.12", features = ["json"] }
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"

apps/desktop/src-tauri/src/lib.rs

@@ -694,8 +694,24 @@ fn get_client_info() -> String {
     client_info_label(env!("CARGO_PKG_VERSION"), env!("APP_COMMIT"))
 }
 
+/// Hauptfenster nach vorne holen. Ein minimiertes Fenster (z. B. per Win+D)
+/// wird zuerst wiederhergestellt.
+fn show_main_window(app: &AppHandle) {
+    if let Some(w) = app.get_webview_window("main") {
+        let _ = w.unminimize();
+        let _ = w.show();
+        let _ = w.set_focus();
+    }
+}
+
 pub fn run() {
     let app = tauri::Builder::default()
+        // Muss als erstes Plugin stehen. Verhindert den Doppelstart (z. B. beim
+        // Windows-Login) mit zwei Tray-Symbolen: Ein zweiter Start holt nur das
+        // Fenster der laufenden Instanz nach vorne und beendet sich sofort.
+        .plugin(tauri_plugin_single_instance::init(|app, _argv, _cwd| {
+            show_main_window(app);
+        }))
         .plugin(tauri_plugin_store::Builder::new().build())
         .plugin(tauri_plugin_notification::init())
         .plugin(tauri_plugin_window_state::Builder::default().build())
@@ -819,21 +835,12 @@ pub fn run() {
                 .tooltip(tray_labels(server_url.as_deref()).0)
                 .show_menu_on_left_click(false)
                 .on_menu_event(move |app, event| match event.id().as_ref() {
-                    "open" => {
-                        if let Some(w) = app.get_webview_window("main") {
-                            // Minimiertes Fenster (z. B. per Win+D) zuerst wiederherstellen
-                            let _ = w.unminimize();
-                            let _ = w.show();
-                            let _ = w.set_focus();
-                        }
-                    }
+                    "open" => show_main_window(app),
                     "change_server" => {
                         if let Some(w) = app.get_webview_window("main") {
                             let _ = w.navigate(setup_page_url(cfg!(windows)));
-                            let _ = w.unminimize();
-                            let _ = w.show();
-                            let _ = w.set_focus();
                         }
+                        show_main_window(app);
                     }
                     "update" => {
                         // `take()` verhindert Doppelklick-Downloads, der
@@ -889,11 +896,7 @@ pub fn run() {
                         ..
                     } = event
                     {
-                        if let Some(w) = tray.app_handle().get_webview_window("main") {
-                            let _ = w.unminimize();
-                            let _ = w.show();
-                            let _ = w.set_focus();
-                        }
+                        show_main_window(tray.app_handle());
                     }
                 })
                 .build(app)?;