fix: prevent deadlock when relaunching after in-app update (#4069)

The updater's relaunch() (and app.restart()) triggers ExitRequested
with code RESTART_EXIT_CODE, which the handler treated as a regular
exit: it called api.prevent_exit() and spawned an async cleanup task.

However Tauri silently ignores prevent_exit() for restart requests
(see ExitRequestApi::prevent_exit docs), so the event loop keeps
shutting down regardless and fires every plugin's RunEvent::Exit hook.
Two threads then deadlock:

- the spawned cleanup task runs save_window_state on a tokio worker,
  holding the window-state plugin's internal mutex while querying
  window geometry, which dispatches to the main thread and blocks;
- the main thread, already inside the plugin's own RunEvent::Exit
  hook, blocks on that same mutex.

The app freezes forever on the restarting screen with the update
already installed; force-quit + reopen comes back on the new version
(#3998). Confirmed on macOS by sampling the frozen process: main
thread parked in tauri_plugin_window_state save_window_state mutex
lock, tokio worker parked in is_maximized -> mpsc recv.

Fix: classify exit requests (None / restart / user exit) and let
restart requests fall through untouched to Tauri's default restart
flow (RunEvent::Exit -> re-exec). On that path window state is saved
by the plugin's exit hook on the main thread, the tray icon is
cleaned up by Tauri's internal cleanup_before_exit, and proxy/live
config restore is unnecessary because the new instance takes over
immediately. The regular exit path (tray quit) is unchanged.

With the fix, a simulated updater relaunch (request_restart) re-execs
the new process in under 200ms, 3/3 runs; normal quit still performs
full cleanup.

Co-authored-by: thisTom <19346741+thisTom@users.noreply.github.com>

src-tauri/src/lib.rs

@@ -1443,14 +1443,37 @@ pub fn run() {
     app.run(|app_handle, event| {
         // 处理退出请求（所有平台）
         if let RunEvent::ExitRequested { api, code, .. } = &event {
-            // code 为 None 表示运行时自动触发（如隐藏窗口的 WebView 被回收导致无存活窗口），
-            // 此时应仅阻止退出、保持托盘后台运行；
-            // code 为 Some(_) 表示用户主动调用 app.exit() 退出（如托盘菜单"退出"），
-            // 此时执行清理后退出。
-            if code.is_none() {
-                log::info!("运行时触发退出请求（无存活窗口），阻止退出以保持托盘后台运行");
-                api.prevent_exit();
-                return;
+            match classify_exit_request(*code) {
+                // code 为 None 表示运行时自动触发（如隐藏窗口的 WebView 被回收导致无存活窗口），
+                // 此时应仅阻止退出、保持托盘后台运行。
+                ExitRequestAction::StayInTray => {
+                    log::info!("运行时触发退出请求（无存活窗口），阻止退出以保持托盘后台运行");
+                    api.prevent_exit();
+                    return;
+                }
+                // code 为 RESTART_EXIT_CODE：app.restart() / 自更新 relaunch 发起的重启。
+                // 这条路径上 prevent_exit() 会被 Tauri 忽略，事件循环必定退出，随后由
+                // Tauri 在 RunEvent::Exit 后用新二进制 re-exec（macOS 会按更新后的
+                // Info.plist 解析可执行名）。
+                //
+                // 绝不能复用下面的异步清理任务：该任务在 tokio 线程调 save_window_state，
+                // 持有 window-state 插件锁的同时向主线程查询窗口几何；而主线程此刻正在
+                // 退出事件循环，并在插件自带的 RunEvent::Exit 钩子里等待同一把锁——双方
+                // 互等造成进程永久卡死（更新已安装但应用冻结、不再重启，见 #3998）。
+                //
+                // 重启路径交还 Tauri 默认流程即可：
+                //   - 窗口状态：插件 Exit 钩子在主线程保存（同线程读取窗口几何，无死锁）
+                //   - 托盘图标：Tauri 内部 cleanup_before_exit 清理，正常走 Drop
+                //   - 代理/Live 配置：无需恢复，重启后新实例立即接管并恢复代理状态
+                //   - 100ms 落盘等待：重启前的 DB 写入均为命令驱动、此刻已完成，
+                //     与所有 Tauri 应用默认重启路径的行为一致，无需额外等待
+                ExitRequestAction::DeferToTauriRestart => {
+                    log::info!("收到重启请求 (code={code:?})，交由 Tauri 默认重启流程 re-exec");
+                    return;
+                }
+                // 其它 Some(_)：用户主动调用 app.exit() 退出（如托盘菜单"退出"），
+                // 此时执行清理后退出。
+                ExitRequestAction::CleanupAndExit => {}
             }
 
             log::info!("收到用户主动退出请求 (code={code:?})，开始清理...");
@@ -1891,6 +1914,36 @@ fn show_database_init_error_dialog(
         .blocking_show()
 }
 
+// ============================================================
+// 退出请求分类
+// ============================================================
+
+/// `RunEvent::ExitRequested` 的三类来源，处理方式必须区分。
+///
+/// 关键约束：重启请求（`code == RESTART_EXIT_CODE`）上 `prevent_exit()` 会被
+/// Tauri 静默忽略（见 `ExitRequestApi::prevent_exit` 文档），事件循环必定继续
+/// 退出并触发各插件的 `RunEvent::Exit` 钩子；任何与之并发的自定义清理任务都
+/// 可能与插件退出钩子争用同一状态而死锁。
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum ExitRequestAction {
+    /// `code` 为 `None`：运行时自动触发（如隐藏窗口的 WebView 被回收导致无存活
+    /// 窗口），阻止退出、保持托盘后台运行。
+    StayInTray,
+    /// `code` 为 `RESTART_EXIT_CODE`：`app.restart()` / 自更新 relaunch 发起的
+    /// 重启，不拦截、不做自定义清理，交还 Tauri 默认 re-exec 流程。
+    DeferToTauriRestart,
+    /// 其它 `Some(_)`：用户主动退出（托盘「退出」等），执行完整异步清理后结束进程。
+    CleanupAndExit,
+}
+
+fn classify_exit_request(code: Option<i32>) -> ExitRequestAction {
+    match code {
+        None => ExitRequestAction::StayInTray,
+        Some(tauri::RESTART_EXIT_CODE) => ExitRequestAction::DeferToTauriRestart,
+        Some(_) => ExitRequestAction::CleanupAndExit,
+    }
+}
+
 // ============================================================
 // 在应用主动退出前显式持久化窗口状态
 // ============================================================
@@ -1908,3 +1961,33 @@ pub fn save_window_state_before_exit(app_handle: &tauri::AppHandle) {
         log::info!("已在退出前保存窗口状态");
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::{classify_exit_request, ExitRequestAction};
+
+    #[test]
+    fn no_code_keeps_app_alive_in_tray() {
+        assert_eq!(classify_exit_request(None), ExitRequestAction::StayInTray);
+    }
+
+    #[test]
+    fn restart_exit_code_defers_to_tauri_default_restart() {
+        assert_eq!(
+            classify_exit_request(Some(tauri::RESTART_EXIT_CODE)),
+            ExitRequestAction::DeferToTauriRestart
+        );
+    }
+
+    #[test]
+    fn user_exit_codes_run_cleanup_then_exit() {
+        assert_eq!(
+            classify_exit_request(Some(0)),
+            ExitRequestAction::CleanupAndExit
+        );
+        assert_eq!(
+            classify_exit_request(Some(1)),
+            ExitRequestAction::CleanupAndExit
+        );
+    }
+}