fix(windows): offer WebView2 runtime download when it is missing

CHANGELOG.md

@@ -15,6 +15,7 @@
 - Added: `app-it-static` companion plugin (`plugins/app-it-static/`) — a macOS sibling of `app-it` for **finished or buildable** apps. Builds once, then serves the built output (`dist/`/`build/`/`out/`/…) from a tiny zero-dependency static server (~15 MB) or directly via `file://` (~0 MB) — **no dev server**, instead of the 300–700 MB a dev server holds. Reuses `app-it`'s native Swift WebKit window, icon pipeline, and one-folder Dock install (the five shared templates are byte-identical and CI guards them against drift). The served output is a snapshot; `desktop:rebuild` refreshes it. Inspired by r/ClaudeAI launch feedback (see README → Community nudge) and recorded in [ADR 0006](docs/decisions/0006-static-companion-snapshot-model.md).
 - Added: Windows beta scaffold (`plugins/app-it-windows/`) — a sibling plugin mirroring the macOS contract with Windows primitives (WPF + WebView2 host, PowerShell lifecycle scripts, multi-resolution `.ico`, Start Menu `.lnk`). Build + lint gated by a required `windows-latest` CI job; **untested on real hardware, looking for a maintainer.** See [docs/WINDOWS.md](docs/WINDOWS.md).
 - Fixed (Windows beta): the generated launcher's **taskbar right-click menu showed `app-it-host`** instead of the app name (#9). The shell reads that label from the executable's embedded `FileDescription`, which the former build-once-then-rename flow left at the project default. `desktop-build.ps1` now publishes the WebView2 host **per app**, with identity split from the file name: `-p:AssemblyName=<slug>` gives a stable, always-valid file name (so the per-app build cache lookup is exact), while `-p:AssemblyTitle`/`-p:Product`=`<App Name>` set the embedded `FileDescription` + `ProductName` the taskbar actually reads (the `.csproj` sets neither, so there's nothing to override, and the free-form app name never has to be a valid file name). Per-app exes are cached under `assets\build\wrapper-windows\<slug>\` (mtime-aware), so the trade vs the old single shared publish is one `dotnet publish` per app on first build. Validated on real Windows 11 hardware. (Note: the Windows shell caches taskbar identity per executable, so an existing app shows the new name only after its cache turns over; a clean install shows it immediately.)
+- Fixed (Windows beta): when the WebView2 runtime is missing (Windows LTSC/Server and some clean installs ship without it), the host caught the failure with a generic, developer-facing error. It now catches `WebView2RuntimeNotFoundException` specifically and offers to open Microsoft's download page (Yes/No) so an end user can fix it themselves; the catch-all handler also now names the download URL. Validated on real Windows 11 hardware.
 
 ## 0.1.0 - 2026-05-30
 

plugins/app-it-windows/skills/app-it-windows/templates/wrapper-windows/MainWindow.xaml.cs

@@ -31,6 +31,13 @@ public partial class MainWindow : Window
     private bool _quitting;
     private bool _trayHintShown;
 
+    // Microsoft's canonical WebView2 download page (the "Evergreen Standalone"
+    // installer). Windows LTSC/Server and some clean installs ship without the
+    // runtime; this is where an end user gets it. Locale-neutral — Microsoft
+    // redirects to the user's region.
+    private const string WebView2DownloadUrl =
+        "https://developer.microsoft.com/microsoft-edge/webview2/";
+
     public MainWindow(HostConfig config)
     {
         _config = config;
@@ -84,12 +91,29 @@ private async void OnLoaded(object sender, RoutedEventArgs e)
 
             Web.CoreWebView2.Navigate(_config.Url!);
         }
+        catch (WebView2RuntimeNotFoundException)
+        {
+            // The Evergreen runtime is genuinely absent (common on Windows
+            // LTSC / Server, which ship without Edge). This is the one failure
+            // an end user can fix themselves, so offer to open the download
+            // page instead of leaving them at a dead window. Caught separately
+            // from the generic handler below so we only point at the installer
+            // when that is actually the problem.
+            var open = MessageBox.Show(
+                $"{_config.Title} needs the Microsoft Edge WebView2 runtime, " +
+                "which isn't installed on this PC.\n\n" +
+                "Click Yes to open the Microsoft download page. Install the " +
+                "\"Evergreen Standalone\" runtime, then relaunch.",
+                _config.Title, MessageBoxButton.YesNo, MessageBoxImage.Warning);
+            if (open == MessageBoxResult.Yes) OpenInDefaultBrowser(WebView2DownloadUrl);
+        }
         catch (Exception ex)
         {
             MessageBox.Show(
                 "WebView2 failed to start.\n\n" + ex.Message + "\n\n" +
-                "The WebView2 Evergreen runtime may be missing on this machine — " +
-                "see docs/WINDOWS.md for the maintainer checklist.",
+                "If the Microsoft Edge WebView2 runtime is missing, install it from\n" +
+                WebView2DownloadUrl + "\nthen relaunch. See docs/WINDOWS.md for the " +
+                "maintainer checklist.",
                 _config.Title, MessageBoxButton.OK, MessageBoxImage.Error);
         }
     }