fix(kpi-history): backlogTotal trend records the real site-backlog aggregate instead of a hardwired zero

src/ZB.MOM.WW.ScadaBridge.AuditLog/Kpi/AuditLogKpiSampleSource.cs

@@ -3,6 +3,12 @@ using ZB.MOM.WW.ScadaBridge.Commons.Interfaces.Kpi;
 using ZB.MOM.WW.ScadaBridge.Commons.Interfaces.Repositories;
 using ZB.MOM.WW.ScadaBridge.Commons.Types.Kpi;
 
+// Task 10 (arch-review 04): the append-only repository leaves the snapshot's
+// BacklogTotal at zero; the real backlog is the cross-site health aggregate that
+// only the central node knows. An optional IAuditBacklogProvider supplies it so
+// the *history* sample stops recording a hardwired zero (the live tile already
+// filled this in). Sites/tests leave it unregistered → null → snapshot fallback.
+
 namespace ZB.MOM.WW.ScadaBridge.AuditLog.Kpi;
 
 /// <summary>
@@ -44,18 +50,30 @@ public sealed class AuditLogKpiSampleSource : IKpiSampleSource
     private const string BacklogTotalMetric = KpiMetrics.AuditLog.BacklogTotal;
 
     private readonly IAuditLogRepository _repository;
+    private readonly IAuditBacklogProvider? _backlogProvider;
 
     /// <summary>
     /// Initializes a new instance of the <see cref="AuditLogKpiSampleSource"/> class.
     /// </summary>
     /// <param name="repository">
     /// Append-only Audit Log repository — its <see cref="IAuditLogRepository.GetKpiSnapshotAsync"/>
-    /// supplies the volume, error, and backlog counts snapshotted here.
+    /// supplies the volume and error counts snapshotted here (its <c>BacklogTotal</c>
+    /// is always zero — see <paramref name="backlogProvider"/>).
     /// </param>
-    public AuditLogKpiSampleSource(IAuditLogRepository repository)
+    /// <param name="backlogProvider">
+    /// Optional cross-site backlog aggregate. When registered (central node), the
+    /// <c>backlogTotal</c> sample records its value; when absent (sites / unit tests,
+    /// where MS.DI resolves the default) the source falls back to the snapshot's own
+    /// <c>BacklogTotal</c> — i.e. zero, the pre-Task-10 behavior. Injecting the seam
+    /// keeps the append-only repo out of the in-memory health aggregator.
+    /// </param>
+    public AuditLogKpiSampleSource(
+        IAuditLogRepository repository,
+        IAuditBacklogProvider? backlogProvider = null)
     {
         ArgumentNullException.ThrowIfNull(repository);
         _repository = repository;
+        _backlogProvider = backlogProvider;
     }
 
     /// <inheritdoc/>
@@ -78,11 +96,15 @@ public sealed class AuditLogKpiSampleSource : IKpiSampleSource
             return [];
         }
 
+        // Backlog: the provider's cross-site aggregate when registered (central),
+        // otherwise the snapshot's own value (zero) as the site/test fallback.
+        var backlogTotal = _backlogProvider?.GetPendingBacklogTotal() ?? snapshot.BacklogTotal;
+
         return
         [
             Sample(TotalEventsLastHourMetric, snapshot.TotalEventsLastHour, capturedAtUtc),
             Sample(ErrorEventsLastHourMetric, snapshot.ErrorEventsLastHour, capturedAtUtc),
-            Sample(BacklogTotalMetric, snapshot.BacklogTotal, capturedAtUtc),
+            Sample(BacklogTotalMetric, backlogTotal, capturedAtUtc),
         ];
     }