feat: add single instance enforcement with TCP socket lock

Add single instance check using TCP listener on 127.0.0.1:53190 to prevent multiple application instances. Move AppState initialization into setup closure to include single_instance_lock field. Remove window close prevention and focus restoration handlers. Make main window non-resizable and non-maximizable.

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

@@ -1,6 +1,6 @@
 mod tunnel_manager;
 
-use std::{fs, path::PathBuf, sync::Mutex};
+use std::{fs, net::TcpListener, path::PathBuf, sync::Mutex};
 
 use base64::{engine::general_purpose::STANDARD, Engine as _};
 use rand_core::OsRng;
@@ -15,9 +15,11 @@ use x25519_dalek::{PublicKey, StaticSecret};
 
 const PROFILE_NAME: &str = "NexaVPN";
 const MAIN_WINDOW_LABEL: &str = "main";
+const SINGLE_INSTANCE_ADDR: &str = "127.0.0.1:53190";
 
 struct AppState {
     session: Mutex<Option<SessionState>>,
+    single_instance_lock: TcpListener,
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
@@ -362,12 +364,6 @@ fn ensure_app_dir(app: &AppHandle) -> Result<PathBuf, String> {
     Ok(dir)
 }
 
-fn restore_window(window: &Window) {
-    let _ = window.show();
-    let _ = window.unminimize();
-    let _ = window.set_focus();
-}
-
 fn restore_webview_window(window: &WebviewWindow) {
     let _ = window.show();
     let _ = window.unminimize();
@@ -382,6 +378,9 @@ fn hide_main_window(window: &Window) {
 pub fn run() {
     tauri::Builder::default()
         .setup(|app| {
+            let single_instance_lock = TcpListener::bind(SINGLE_INSTANCE_ADDR)
+                .map_err(|_| format!("{} is already running.", app.package_info().name))?;
+
             let open_item = MenuItemBuilder::with_id("open", "Open NexaVPN").build(app)?;
             let quit_item = MenuItemBuilder::with_id("quit", "Quit NexaVPN").build(app)?;
             let menu = MenuBuilder::new(app).items(&[&open_item, &quit_item]).build()?;
@@ -418,24 +417,20 @@ pub fn run() {
                 })
                 .build(app)?;
 
+            app.manage(AppState {
+                session: Mutex::new(None),
+                single_instance_lock,
+            });
+
             Ok(())
         })
-        .manage(AppState {
-            session: Mutex::new(None),
-        })
         .on_window_event(|window, event| match event {
-            WindowEvent::CloseRequested { api, .. } => {
-                api.prevent_close();
-                hide_main_window(window);
-            }
+            WindowEvent::CloseRequested { .. } => {}
             WindowEvent::Resized(_) => {
                 if window.is_minimized().unwrap_or(false) {
                     hide_main_window(window);
                 }
             }
-            WindowEvent::Focused(true) => {
-                restore_window(window);
-            }
             _ => {}
         })
         .invoke_handler(tauri::generate_handler![load_state, clear_session, enroll_device, sync_profile, connect_tunnel, disconnect_tunnel, tunnel_status])

desktop-client/src-tauri/tauri.conf.json

@@ -15,7 +15,8 @@
         "title": "NexaVPN",
         "width": 1120,
         "height": 760,
-        "resizable": true
+        "resizable": false,
+        "maximizable": false
       }
     ],
     "security": {