Web: a screenshot or video export no longer changes the address

lib/screenshot/offscreen_capture.dart

@@ -77,14 +77,24 @@ Widget wrapForOffscreenCapture(
         return MaterialApp(
           theme: Theme.of(context),
           debugShowCheckedModeBanner: false,
-          home: child,
-          builder: (context, child) {
+          // No `home`: with one, the app builds its own navigator, and an
+          // app's navigator reports its route to the browser. Every capture
+          // then rewrote the address of the page to `/`, and a reload after
+          // a screenshot opened the library instead of the strategy. The
+          // navigator below gives the captured view the route and overlay it
+          // expects and reports nothing.
+          builder: (context, _) {
             // The captured view paints its own backdrop, or none for a
             // transparent screenshot, so the shell paints nothing under it.
             return Portal(
               child: ShadAppBuilder(
                 backgroundColor: Colors.transparent,
-                child: child!,
+                child: Navigator(
+                  onGenerateRoute: (settings) => MaterialPageRoute<void>(
+                    settings: settings,
+                    builder: (context) => child,
+                  ),
+                ),
               ),
             );
           },

test/offscreen_capture_route_test.dart

@@ -0,0 +1,43 @@
+import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:icarus/screenshot/offscreen_capture.dart';
+
+void main() {
+  testWidgets('a capture does not tell the browser the page moved',
+      (tester) async {
+    // On web the address is where a reload reopens the editor. The capture
+    // shell used to be an app with its own navigator, which reported `/` as
+    // the page's route: after a screenshot, a reload opened the library.
+    final reported = <String>[];
+    tester.binding.defaultBinaryMessenger.setMockMethodCallHandler(
+      SystemChannels.navigation,
+      (call) async {
+        if (call.method == 'routeInformationUpdated') {
+          reported.add((call.arguments as Map)['uri'] as String);
+        }
+        return null;
+      },
+    );
+    addTearDown(
+      () => tester.binding.defaultBinaryMessenger
+          .setMockMethodCallHandler(SystemChannels.navigation, null),
+    );
+
+    late BuildContext captured;
+    await tester.pumpWidget(wrapForOffscreenCapture(
+      Builder(builder: (context) {
+        captured = context;
+        return const Text('captured view');
+      }),
+    ));
+    await tester.pump();
+
+    expect(find.text('captured view'), findsOneWidget);
+    expect(reported, isEmpty);
+    // What the captured view still gets from the shell.
+    expect(Navigator.maybeOf(captured), isNotNull);
+    expect(Overlay.maybeOf(captured), isNotNull);
+    expect(ModalRoute.of(captured), isNotNull);
+  });
+}