diff --git a/windows/WebViewFetchWindow.cs b/windows/WebViewFetchWindow.cs
index 3a2751c..15734cf 100644
--- a/windows/WebViewFetchWindow.cs
+++ b/windows/WebViewFetchWindow.cs
@@ -2,42 +2,103 @@ using Microsoft.Web.WebView2.Core;
 using Microsoft.Web.WebView2.Wpf;
 using System;
 using System.IO;
+using System.Threading;
 using System.Threading.Tasks;
 using System.Windows;
 
 namespace ClaudeCheckerWindows;
 
 // Invisible 1×1 window that hosts a WebView2 for authenticated API calls.
-// Uses the same user data folder as LoginWindow so the session is shared.
+// Uses the same user data folder as LoginWindow so the session (including
+// cf_clearance) is always shared and fresh — equivalent to macOS's WKWebsiteDataStore.
+//
+// Two usage modes:
+//   • Persistent (App.BackgroundBrowser): created once at startup, navigates to
+//     claude.ai once, then scripts run directly on the live page every refresh.
+//     No re-navigation = no memory accumulation.
+//   • One-shot (LoginWindow): created, used, closed — same as before.
 internal sealed class WebViewFetchWindow : Window
 {
     private readonly WebView2 _wv = new();
+    private bool _initialized;
+    private bool _readyForScript; // true after first navigation to claude.ai completes
+
+    private static readonly string UserDataFolder =
+        Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData),
+            "ClaudeChecker", "WebView2");
 
     public WebViewFetchWindow()
     {
-        Width          = 1;
-        Height         = 1;
-        Left           = -9999;
-        Top            = -9999;
-        ShowInTaskbar  = false;
-        WindowStyle    = WindowStyle.None;
+        Width              = 1;
+        Height             = 1;
+        Left               = -9999;
+        Top                = -9999;
+        ShowInTaskbar      = false;
+        WindowStyle        = WindowStyle.None;
         AllowsTransparency = true;
-        Opacity        = 0;
-        Content        = _wv;
+        Opacity            = 0;
+        Content            = _wv;
     }
 
+    // ── Persistent-mode init ──────────────────────────────────────────────────
+
+    // Call once at startup. Navigates to claude.ai so the session/cookies are
+    // established and cf_clearance is fresh. Subsequent RunScriptAsync calls
+    // skip navigation and just execute JS on the live page.
+    public async Task InitAsync()
+    {
+        await EnsureInitAsync();
+
+        var navDone = new TaskCompletionSource<bool>(TaskCreationOptions.RunContinuationsAsynchronously);
+        EventHandler<CoreWebView2NavigationCompletedEventArgs>? h = null;
+        h = (_, e) => { _wv.CoreWebView2.NavigationCompleted -= h; navDone.TrySetResult(e.IsSuccess); };
+        _wv.CoreWebView2.NavigationCompleted += h;
+        _wv.CoreWebView2.Navigate("https://claude.ai");
+
+        // Wait up to 15 s for initial navigation
+        await Task.WhenAny(navDone.Task, Task.Delay(15000));
+        _readyForScript = navDone.Task.IsCompletedSuccessfully && navDone.Task.Result;
+    }
+
+    // Run a JS script on the already-loaded claude.ai page.
+    // The script must call window.chrome.webview.postMessage(result).
+    public async Task<string?> RunScriptAsync(string script, int timeoutMs = 10000)
+    {
+        if (!_readyForScript) return null;
+
+        var tcs = new TaskCompletionSource<string?>(TaskCreationOptions.RunContinuationsAsynchronously);
+        EventHandler<CoreWebView2WebMessageReceivedEventArgs>? msgHandler = null;
+        msgHandler = (_, args) =>
+        {
+            _wv.CoreWebView2.WebMessageReceived -= msgHandler;
+            tcs.TrySetResult(args.WebMessageAsJson);
+        };
+        _wv.CoreWebView2.WebMessageReceived += msgHandler;
+
+        try { await _wv.CoreWebView2.ExecuteScriptAsync(script); }
+        catch
+        {
+            _wv.CoreWebView2.WebMessageReceived -= msgHandler;
+            return null;
+        }
+
+        _ = Task.Delay(timeoutMs).ContinueWith(_ =>
+        {
+            _wv.CoreWebView2.WebMessageReceived -= msgHandler;
+            tcs.TrySetResult(null);
+        });
+
+        return await tcs.Task;
+    }
+
+    // ── One-shot mode (LoginWindow) ───────────────────────────────────────────
+
     public async Task<string?> FetchAsync(string navigateUrl, string script, int timeoutMs = 20000)
     {
-        var env = await CoreWebView2Environment.CreateAsync(userDataFolder:
-            Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData),
-                "ClaudeChecker", "WebView2"));
-
-        await _wv.EnsureCoreWebView2Async(env);
+        await EnsureInitAsync();
 
         var tcs = new TaskCompletionSource<string?>(TaskCreationOptions.RunContinuationsAsynchronously);
 
-        // Use WebMessageReceived so the script can post back asynchronously without
-        // relying on Promise-awaiting support in the WebView2 runtime version.
         EventHandler<CoreWebView2WebMessageReceivedEventArgs>? msgHandler = null;
         msgHandler = (_, args) =>
         {
@@ -65,4 +126,18 @@ internal sealed class WebViewFetchWindow : Window
 
         return await tcs.Task;
     }
+
+    // ── Shared init ───────────────────────────────────────────────────────────
+
+    private int _initGuard;
+
+    private async Task EnsureInitAsync()
+    {
+        if (_initialized) return;
+        if (Interlocked.Exchange(ref _initGuard, 1) != 0) return;
+
+        var env = await CoreWebView2Environment.CreateAsync(userDataFolder: UserDataFolder);
+        await _wv.EnsureCoreWebView2Async(env);
+        _initialized = true;
+    }
 }