fix(failover): switch to P1 immediately when enabling auto failover

Previously, enabling auto failover kept using the current provider until
the first failure, causing inconsistency when the current provider was
not in the failover queue. When stopping proxy, the restored config
would not match user expectations.

New behavior:
- Enable auto failover = immediately switch to queue P1
- Subsequent routing follows queue order (P1→P2→...)
- Auto-add current provider to queue if queue is empty

Changes:
- Add switch_proxy_target() for hot-switching during proxy mode
- Update provider_router to use queue order when failover enabled
- Sync tray menu Auto click with the same logic
- Update UI tooltips to reflect new semantics
- Add tests for queue-only routing scenario

src-tauri/src/tray.rs

@@ -211,6 +211,28 @@ fn handle_auto_click(app: &tauri::AppHandle, app_type: &AppType) -> Result<(), A
     if let Some(app_state) = app.try_state::<AppState>() {
         let app_type_str = app_type.as_str();
 
+        // 强一致语义：Auto 模式开启后立即切到队列 P1（P1→P2→...）
+        // 若队列为空，则尝试把“当前供应商”自动加入队列作为 P1，避免用户陷入无法开启的死锁。
+        let mut queue = app_state.db.get_failover_queue(app_type_str)?;
+        if queue.is_empty() {
+            let current_id =
+                crate::settings::get_effective_current_provider(&app_state.db, app_type)?;
+            let Some(current_id) = current_id else {
+                return Err(AppError::Message(
+                    "故障转移队列为空，且未设置当前供应商，无法启用 Auto 模式".to_string(),
+                ));
+            };
+            app_state
+                .db
+                .add_to_failover_queue(app_type_str, &current_id)?;
+            queue = app_state.db.get_failover_queue(app_type_str)?;
+        }
+
+        let p1_provider_id = queue
+            .first()
+            .map(|item| item.provider_id.clone())
+            .ok_or_else(|| AppError::Message("故障转移队列为空，无法启用 Auto 模式".to_string()))?;
+
         // 真正启用 failover：启动代理服务 + 执行接管 + 开启 auto_failover
         let proxy_service = &app_state.proxy_service;
 
@@ -238,6 +260,16 @@ fn handle_auto_click(app: &tauri::AppHandle, app_type: &AppType) -> Result<(), A
             .db
             .set_proxy_flags_sync(app_type_str, true, true)?;
 
+        // 3.1) 立即切到队列 P1（热切换：不写 Live，仅更新 DB/settings/备份）
+        if let Err(e) = futures::executor::block_on(
+            proxy_service.switch_proxy_target(app_type_str, &p1_provider_id),
+        ) {
+            log::error!("[Tray] Auto 模式切换到队列 P1 失败: {e}");
+            return Err(AppError::Message(format!(
+                "Auto 模式切换到队列 P1 失败: {e}"
+            )));
+        }
+
         // 4) 更新托盘菜单
         if let Ok(new_menu) = create_tray_menu(app, app_state.inner()) {
             if let Some(tray) = app.tray_by_id("main") {
@@ -249,7 +281,8 @@ fn handle_auto_click(app: &tauri::AppHandle, app_type: &AppType) -> Result<(), A
         let event_data = serde_json::json!({
             "appType": app_type_str,
             "proxyEnabled": true,
-            "autoFailoverEnabled": true
+            "autoFailoverEnabled": true,
+            "providerId": p1_provider_id
         });
         if let Err(e) = app.emit("proxy-flags-changed", event_data.clone()) {
             log::error!("发射 proxy-flags-changed 事件失败: {e}");