perf(desktop): keep the WebView2 tree out of the tray-resident state

The desktop shell used to build the WebView at startup unconditionally, so a
minimized (autostart) instance pulled up the whole Chromium tree and sat in the
tray holding ~189 MB of committed memory while nobody was looking at it. Two
changes, neither of which touches the headless or MCP paths:

- Skip creating the WebView when starting minimized; build it on first show.
  Measured: 0 msedgewebview2 processes while resident, backend ~5 MB.
- Drop the WebView to WebView2's low memory target level
  (ICoreWebView2_19::SetMemoryUsageTargetLevel) when hiding to the tray, and
  restore it before showing again. Measured ~10-20% off committed memory,
  and unlike tearing the WebView down it keeps the page alive, so open tabs
  and terminal panes survive.

The native controller comes from wry's WebViewExtWindows trait, so no fork of
wry is involved. Runtimes without ICoreWebView2_19 are handled by the cast
failing, which is a silent no-op.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Cargo.lock

@@ -4751,6 +4751,8 @@ dependencies = [
  "tracing-subscriber",
  "tray-icon",
  "uuid",
+ "webview2-com",
+ "windows-core",
  "winres",
  "wry",
 ]

Cargo.toml

@@ -38,6 +38,10 @@ async-trait = "0.1"
 wry = "0.57.0"
 tao = "0.37.1"
 tray-icon = "0.26.1"
+# 托盘驻留时把 WebView2 降到低内存档（ICoreWebView2_19::SetMemoryUsageTargetLevel）。
+# 只用 wry 暴露的 controller() 拿原生接口，不碰 wry 内部实现。
+webview2-com = "0.39.1"
+windows-core = "0.62"
 
 [target.'cfg(windows)'.build-dependencies]
 winres = "0.1"

src/desktop.rs

@@ -147,6 +147,71 @@ fn build_tray_menu(state: &Arc<AppState>) -> Result<Menu> {
     Ok(menu)
 }
 
+/// 把 WebView2 切到低内存档 / 还原。
+///
+/// 低内存档（`COREWEBVIEW2_MEMORY_USAGE_TARGET_LEVEL_LOW`）是 WebView2 官方给"不显示时省内存"
+/// 用的接口：渲染进程会主动收缩缓存与工作集，代价是重绘变慢——所以只该在窗口隐藏时用，
+/// 重新显示前必须还原。比"把 WebView 拆了重建"好得多：页面不重载，标签页与终端现场都还在。
+///
+/// 老版本 WebView2 Runtime 没有这个接口，`cast` 会失败，此时静默跳过（不降级、不报错）。
+#[cfg(windows)]
+fn set_webview_memory_level(webview: &wry::WebView, low: bool) {
+    use webview2_com::Microsoft::Web::WebView2::Win32::{
+        ICoreWebView2_19, COREWEBVIEW2_MEMORY_USAGE_TARGET_LEVEL_LOW,
+        COREWEBVIEW2_MEMORY_USAGE_TARGET_LEVEL_NORMAL,
+    };
+    use windows_core::Interface as _;
+    use wry::WebViewExtWindows;
+
+    let Ok(core) = (unsafe { webview.controller().CoreWebView2() }) else {
+        return;
+    };
+    let Ok(core19) = core.cast::<ICoreWebView2_19>() else {
+        return;
+    };
+    let level = if low {
+        COREWEBVIEW2_MEMORY_USAGE_TARGET_LEVEL_LOW
+    } else {
+        COREWEBVIEW2_MEMORY_USAGE_TARGET_LEVEL_NORMAL
+    };
+    let _ = unsafe { core19.SetMemoryUsageTargetLevel(level) };
+}
+
+/// 主窗口 WebView 的创建。刻意不在启动时无条件调用：一个隐藏窗口同样会把整套 Chromium
+/// 拉起来（实测约 145 MB），而开机自启的常态就是"躺在托盘里没人点"。
+fn build_main_webview(window: &Window, url: &str) -> Option<wry::WebView> {
+    match WebViewBuilder::new().with_url(url).build(window) {
+        Ok(wv) => Some(wv),
+        Err(e) => {
+            tracing::error!("创建主窗口 WebView 失败: {e}");
+            None
+        }
+    }
+}
+
+/// 显示主窗口：没建过 WebView 就建，建过就还原内存档再显示。
+fn show_main_window(window: &Window, webview: &mut Option<wry::WebView>, url: &str) {
+    if webview.is_none() {
+        *webview = build_main_webview(window, url);
+    }
+    if let Some(wv) = webview.as_ref() {
+        set_webview_memory_level(wv, false);
+        let _ = wv.set_visible(true);
+    }
+    window.set_visible(true);
+    window.set_minimized(false);
+    window.set_focus();
+}
+
+/// 最小化到托盘：WebView 留着（页面不重载，标签页与终端现场都保住），但降到低内存档。
+fn hide_main_window(window: &Window, webview: &Option<wry::WebView>) {
+    if let Some(wv) = webview.as_ref() {
+        let _ = wv.set_visible(false);
+        set_webview_memory_level(wv, true);
+    }
+    window.set_visible(false);
+}
+
 pub fn run_desktop_window(
     state: Arc<AppState>,
     rt_handle: tokio::runtime::Handle,
@@ -191,9 +256,12 @@ pub fn run_desktop_window(
         .build(&event_loop)?;
 
     let url = format!("http://127.0.0.1:{port}");
-    let _webview = WebViewBuilder::new()
-        .with_url(&url)
-        .build(&window)?;
+    // 启动即最小化（开机自启的常态）时先不建 WebView，等第一次真正显示再建。
+    let mut main_webview: Option<wry::WebView> = if start_minimized {
+        None
+    } else {
+        build_main_webview(&window, &url)
+    };
 
     // 系统托盘事件转发到主事件循环
     let proxy_tray = proxy.clone();
@@ -244,7 +312,7 @@ pub fn run_desktop_window(
                         *control_flow = ControlFlow::Exit;
                     } else {
                         // 默认最小化驻留到系统托盘，保持后台不断连
-                        window.set_visible(false);
+                        hide_main_window(&window, &main_webview);
                     }
                 } else if let Some(removed) = standalone_windows.remove(&window_id) {
                     // 独立终端窗口点击 ×：完全关闭并销毁该窗口
@@ -252,9 +320,7 @@ pub fn run_desktop_window(
                 }
             }
             Event::UserEvent(DesktopUserEvent::ShowWindow) => {
-                window.set_visible(true);
-                window.set_minimized(false);
-                window.set_focus();
+                show_main_window(&window, &mut main_webview, &url);
             }
             Event::UserEvent(DesktopUserEvent::OpenStandaloneTerminal { host_id }) => {
                 // 如果该主机已有打开的独立终端窗口，直接唤醒并聚焦
@@ -308,17 +374,13 @@ pub fn run_desktop_window(
                     ..
                 } = tray_ev
                 {
-                    window.set_visible(true);
-                    window.set_minimized(false);
-                    window.set_focus();
+                    show_main_window(&window, &mut main_webview, &url);
                 }
             }
             Event::UserEvent(DesktopUserEvent::TrayMenu(menu_ev)) => {
                 let id_str = menu_ev.id.0.as_str();
                 if id_str == MENU_ID_SHOW {
-                    window.set_visible(true);
-                    window.set_minimized(false);
-                    window.set_focus();
+                    show_main_window(&window, &mut main_webview, &url);
                 } else if id_str == MENU_ID_QUIT {
                     standalone_windows.clear();
                     host_to_window.clear();