fix(query): anchor=latest follows the newest sample of any level, not just the 1m rows [CI]

backend/src/MoShiro.Backend.Application/Ports/StorePorts.cs

@@ -213,6 +213,9 @@ public interface IMetricStore
     /// <summary>这条序列在某一层里最早的窗口起点；没有数据返回 null。</summary>
     ValueTask<long?> EarliestAsync(MetricLevel level, NodeId agentId, string series, CancellationToken ct);
 
+    /// <summary>这条序列在某一层里最晚的窗口起点；没有数据返回 null。</summary>
+    ValueTask<long?> LatestAsync(MetricLevel level, NodeId agentId, string series, CancellationToken ct);
+
     ValueTask<IReadOnlyList<MetricRow>> ReadAgentsAsync(MetricLevel level, IReadOnlyCollection<NodeId> agentIds, string series, long fromMs, long toMs, CancellationToken ct);
 
     ValueTask<int> DeleteOlderThanAsync(MetricLevel level, long cutoffMs, CancellationToken ct);

backend/src/MoShiro.Backend.Application/Query/RowLoader.cs

@@ -45,8 +45,19 @@ public sealed class RowLoader
             return at + 1000;
         }
 
-        IReadOnlyList<MetricRow> rows = await _metrics.ReadAsync(MetricLevel.M1, agent, series, nowMs - (7 * Steps.Day), nowMs + 60_000, ct);
-        return rows.Count == 0 ? null : rows.Max(r => r.WindowStart) + 60_000;
+        // 热层空了（Backend 刚重启、热层还没攒起来）就看持久层：各层里最晚的窗口取最大。只看 1 分钟层会落后——它比 5 分钟层更新得慢时，
+        // 窗口就被定在好几个小时以前，页面显示的全是旧数据。
+        long? latest = null;
+        foreach (MetricLevel level in new[] { MetricLevel.S10, MetricLevel.M1, MetricLevel.M5 })
+        {
+            if (await _metrics.LatestAsync(level, agent, series, ct) is { } start)
+            {
+                long end = Math.Min(start + level.WidthMs(), nowMs);
+                latest = latest is null ? end : Math.Max(latest.Value, end);
+            }
+        }
+
+        return latest;
     }
 
     /// <summary>

backend/src/MoShiro.Backend.Storage.Sqlite/SqliteMetricStore.cs

@@ -90,6 +90,11 @@ public sealed class SqliteMetricStore : IMetricStore
             c => c.Query($"SELECT MIN(window_start) FROM {level.TableName()} WHERE agent_id = @a AND series = @s", r => r.NullableLong(0), ("@a", agentId.Value), ("@s", series)).FirstOrDefault(),
             ct);
 
+    public ValueTask<long?> LatestAsync(MetricLevel level, NodeId agentId, string series, CancellationToken ct) =>
+        _db.ReadAsync(
+            c => c.Query($"SELECT MAX(window_start) FROM {level.TableName()} WHERE agent_id = @a AND series = @s", r => r.NullableLong(0), ("@a", agentId.Value), ("@s", series)).FirstOrDefault(),
+            ct);
+
     public ValueTask<IReadOnlyList<MetricRow>> ReadAgentsAsync(MetricLevel level, IReadOnlyCollection<NodeId> agentIds, string series, long fromMs, long toMs, CancellationToken ct) =>
         _db.ReadAsync<IReadOnlyList<MetricRow>>(
             c =>