fix：第一轮跑

lib/features/web/presentation/mall_web_host.dart

@@ -0,0 +1,131 @@
+import 'dart:async';
+
+import 'package:flutter/material.dart';
+import 'package:url_launcher/url_launcher.dart';
+import 'package:webview_flutter/webview_flutter.dart';
+
+import '../application/mall_web_host_controller.dart';
+
+/// 常驻在 Tab Shell 上层的商城 H5 宿主。
+class MallWebHost extends StatefulWidget {
+  const MallWebHost({super.key, required this.onExit});
+  final VoidCallback onExit;
+
+  @override
+  State<MallWebHost> createState() => _MallWebHostState();
+}
+
+class _MallWebHostState extends State<MallWebHost> {
+  final _host = MallWebHostController.instance;
+  WebViewController? _controller;
+  String? _loadedUrl;
+  String? _error;
+  int _progress = 0;
+
+  @override
+  void initState() {
+    super.initState();
+    _host.state.addListener(_sync);
+    _host.attachBackHandler(_goBack);
+    _sync();
+  }
+
+  @override
+  void dispose() {
+    _host.state.removeListener(_sync);
+    _host.detachBackHandler();
+    super.dispose();
+  }
+
+  void _sync() {
+    final url = _host.state.value.url;
+    if (url != null && url != _loadedUrl) _load(url);
+    if (mounted) setState(() {});
+  }
+
+  void _load(String rawUrl) {
+    final uri = Uri.tryParse(rawUrl);
+    if (uri == null || (uri.scheme != 'https' && uri.scheme != 'http')) {
+      _error = '商城链接不可用';
+      return;
+    }
+    _error = null;
+    _progress = 0;
+    _loadedUrl = rawUrl;
+    _controller ??= WebViewController()
+      ..setJavaScriptMode(JavaScriptMode.unrestricted)
+      ..addJavaScriptChannel(
+        'JinzhiBridge',
+        onMessageReceived: (message) {
+          if (message.message == 'close') widget.onExit();
+        },
+      )
+      ..setNavigationDelegate(
+        NavigationDelegate(
+          onProgress: (value) {
+            if (mounted) setState(() => _progress = value);
+          },
+          onWebResourceError: (error) {
+            if (error.isForMainFrame == false) return;
+            if (mounted) setState(() => _error = error.description);
+          },
+          onNavigationRequest: (request) async {
+            final target = Uri.tryParse(request.url);
+            if (target == null ||
+                target.scheme == 'http' ||
+                target.scheme == 'https') {
+              return NavigationDecision.navigate;
+            }
+            if (await canLaunchUrl(target)) {
+              await launchUrl(target, mode: LaunchMode.externalApplication);
+            }
+            return NavigationDecision.prevent;
+          },
+        ),
+      );
+    unawaited(_controller!.loadRequest(uri));
+  }
+
+  Future<void> _goBack() async {
+    final controller = _controller;
+    if (controller != null && await controller.canGoBack()) {
+      await controller.goBack();
+    }
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final current = _host.state.value;
+    if (current.url == null) return const SizedBox.shrink();
+    return ColoredBox(
+      color: Theme.of(context).scaffoldBackgroundColor,
+      child: Stack(
+        children: [
+          if (_controller != null)
+            Positioned.fill(child: WebViewWidget(controller: _controller!)),
+          if (_error != null)
+            Center(
+              child: Column(
+                mainAxisSize: MainAxisSize.min,
+                children: [
+                  const Icon(Icons.wifi_off_rounded, size: 32),
+                  const SizedBox(height: 12),
+                  const Text('商城加载失败'),
+                  const SizedBox(height: 8),
+                  TextButton(
+                    onPressed: () => _load(_loadedUrl ?? ''),
+                    child: const Text('重新加载'),
+                  ),
+                ],
+              ),
+            ),
+          if (_error == null && _progress < 100)
+            const Align(
+              alignment: Alignment.topCenter,
+              child: LinearProgressIndicator(minHeight: 2),
+            ),
+        ],
+      ),
+    );
+  }
+}