fix(client): 补提交 stats-overhaul 漏掉的 account_api/kernel_process WIP

同 device_usage:account_api.dart(deviceUsage/usage 方法)、kernel_process.dart
及对应测试一直未提交,本地有→analyze/test 过,但不在 git→Windows 构建报
「deviceUsage isn't defined」。补齐使提交树自洽可构建。
孤儿组件 device_stat_row/metric_card 已无人引用,不提交。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

client/lib/bridge/kernel_process.dart

@@ -195,6 +195,22 @@ class ClashApiClient {
     return data.cast<String, int>();
   }
 
+  // ── 工具：从 /proxies 响应提取 URLTest/Fallback 组名 ──────────
+  static List<String> extractUrltestGroups(Map<String, dynamic> proxiesResponse) {
+    final proxies = proxiesResponse['proxies'];
+    if (proxies is! Map) return const [];
+    final groups = <String>[];
+    for (final entry in proxies.entries) {
+      final p = entry.value;
+      if (p is! Map) continue;
+      final type = (p['type'] as String?) ?? '';
+      if (type == 'URLTest' || type == 'Fallback') {
+        if (entry.key is String) groups.add(entry.key as String);
+      }
+    }
+    return groups;
+  }
+
   // ── 工具：从 /proxies 响应提取 URLTest 延迟列表 ──────────────
   // 扫描所有类型为 URLTest 的出口组，提取成员节点的最新 history delay。
   static List<UrltestResult> extractUrltestResults(
@@ -312,6 +328,12 @@ class DesktopKernelProcess implements KernelProcess {
   // 最新 URLTest 延迟列表（每次 stats 轮询时更新）
   List<UrltestResult> _lastUrltestResults = const [];
 
+  // URLTest/Fallback 组名（从 /proxies 提取），供主动触发延迟探测。
+  List<String> _urltestGroups = const [];
+  // 轮询计数：每 _urlTestEvery 拍主动触发一次 group/delay（补偿 urltest 惰性探测）。
+  int _pollTick = 0;
+  static const int _urlTestEvery = 12;
+
   final _statusCtrl = StreamController<VpnStatus>.broadcast();
   final _logCtrl = StreamController<String>.broadcast();
   final _statsCtrl = StreamController<VpnStatsEvent>.broadcast();
@@ -525,6 +547,7 @@ class DesktopKernelProcess implements KernelProcess {
         final connFuture = _clashApi!.getConnections();
         final proxiesFuture = _clashApi!.getProxies().then((p) {
           _lastUrltestResults = ClashApiClient.extractUrltestResults(p);
+          _urltestGroups = ClashApiClient.extractUrltestGroups(p);
         }).catchError((_) {
           // 读取失败静默跳过，保留上次缓存值
         });
@@ -532,6 +555,16 @@ class DesktopKernelProcess implements KernelProcess {
         final data = await connFuture;
         await proxiesFuture; // 等 URLTest 解析完再组帧
 
+        // 周期主动触发 group/delay 探测：sing-box urltest 默认惰性探测，
+        // 仅读 /proxies 缓存会长时间拿不到 history → 延迟空白。每 _urlTestEvery
+        // 拍主动打一次，fire-and-forget（不阻塞主统计帧），下一拍即读到新 history。
+        if ((_pollTick++ % _urlTestEvery) == 0) {
+          for (final g in _urltestGroups) {
+            unawaited(_clashApi!.getGroupDelay(g).catchError(
+                (_) => <String, int>{}));
+          }
+        }
+
         final downTotal =
             (data['downloadTotal'] as num?)?.toInt() ?? _prevDownTotal;
         final upTotal =