feat(extension): expose host version and WebView page events

ui/flutter/test/app/webview_event_session_test.dart

@@ -0,0 +1,34 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter_inappwebview/flutter_inappwebview.dart';
+import 'package:gopeed/app/rpc/webview_rpc_service.dart';
+
+class _Profile extends Fake implements WebViewProfile {}
+
+void main() {
+  TestWidgetsFlutterBinding.ensureInitialized();
+  test('closed emits reason once and closes listener stream', () async {
+    final page = WebViewRpcPageSession(
+      pageId: 'test',
+      profile: _Profile(),
+      headless: true,
+      debug: false,
+      title: '',
+      width: 1,
+      height: 1,
+      userAgent: '',
+    );
+    // Consume the expected ready failure when an unopened page is disposed.
+    final pending = page.execute('1', []);
+    final failure = expectLater(pending, throwsA(isA<WebViewRpcException>()));
+    final events = page.events.toList();
+    await page.dispose(reason: 'user');
+    await page.dispose(reason: 'api');
+    await failure;
+    expect(await events, [
+      {
+        'event': 'closed',
+        'data': {'reason': 'user'},
+      },
+    ]);
+  });
+}