feat(audit): M5.2 per-node stuck-count KPIs (T6) — repo per-node aggregation, actor message pair, CentralUI tiles

src/ZB.MOM.WW.ScadaBridge.ConfigurationDatabase/Repositories/NotificationOutboxRepository.cs

@@ -300,6 +300,63 @@ VALUES
                 : null)).ToList();
     }
 
+    /// <inheritdoc />
+    public async Task<IReadOnlyList<NodeNotificationKpiSnapshot>> ComputePerNodeKpisAsync(
+        DateTimeOffset stuckCutoff, DateTimeOffset deliveredSince, CancellationToken cancellationToken = default)
+    {
+        var now = DateTimeOffset.UtcNow;
+
+        // Exclude rows with NULL SourceNode (legacy / unstamped) — per-node KPIs
+        // are only meaningful when the node identity is known.
+        var queueDepth = await CountByNodeAsync(
+            n => (n.Status == NotificationStatus.Pending || n.Status == NotificationStatus.Retrying)
+                && n.SourceNode != null,
+            cancellationToken);
+
+        var stuck = await CountByNodeAsync(
+            n => (n.Status == NotificationStatus.Pending || n.Status == NotificationStatus.Retrying)
+                && n.CreatedAt < stuckCutoff
+                && n.SourceNode != null,
+            cancellationToken);
+
+        var parked = await CountByNodeAsync(
+            n => n.Status == NotificationStatus.Parked && n.SourceNode != null,
+            cancellationToken);
+
+        var delivered = await CountByNodeAsync(
+            n => n.Status == NotificationStatus.Delivered
+                && n.DeliveredAt != null && n.DeliveredAt >= deliveredSince
+                && n.SourceNode != null,
+            cancellationToken);
+
+        // Oldest non-terminal CreatedAt per node — same in-memory reduction
+        // pattern as ComputePerSiteKpisAsync (DateTimeOffset converter makes
+        // a SQL Min awkward).
+        var oldest = (await _context.Notifications
+                .Where(n => (n.Status == NotificationStatus.Pending
+                    || n.Status == NotificationStatus.Retrying)
+                    && n.SourceNode != null)
+                .Select(n => new { n.SourceNode, n.CreatedAt })
+                .ToListAsync(cancellationToken))
+            .GroupBy(x => x.SourceNode!)
+            .ToDictionary(g => g.Key, g => g.Min(x => x.CreatedAt));
+
+        var nodeNames = queueDepth.Keys
+            .Concat(stuck.Keys).Concat(parked.Keys).Concat(delivered.Keys)
+            .Distinct()
+            .OrderBy(n => n, StringComparer.Ordinal);
+
+        return nodeNames.Select(node => new NodeNotificationKpiSnapshot(
+            SourceNode: node,
+            QueueDepth: queueDepth.GetValueOrDefault(node),
+            StuckCount: stuck.GetValueOrDefault(node),
+            ParkedCount: parked.GetValueOrDefault(node),
+            DeliveredLastInterval: delivered.GetValueOrDefault(node),
+            OldestPendingAge: oldest.TryGetValue(node, out var createdAt)
+                ? now - createdAt
+                : null)).ToList();
+    }
+
     /// <summary>Counts notification rows matching <paramref name="predicate"/>, grouped by source site.</summary>
     private async Task<Dictionary<string, int>> CountBySiteAsync(
         System.Linq.Expressions.Expression<Func<Notification, bool>> predicate,
@@ -312,6 +369,22 @@ VALUES
             .ToDictionaryAsync(x => x.Site, x => x.Count, cancellationToken);
     }
 
+    /// <summary>
+    /// Counts notification rows matching <paramref name="predicate"/>, grouped by source node.
+    /// Only rows with a non-null <c>SourceNode</c> should be included; the predicate is
+    /// responsible for enforcing that guard.
+    /// </summary>
+    private async Task<Dictionary<string, int>> CountByNodeAsync(
+        System.Linq.Expressions.Expression<Func<Notification, bool>> predicate,
+        CancellationToken cancellationToken)
+    {
+        return await _context.Notifications
+            .Where(predicate)
+            .GroupBy(n => n.SourceNode!)
+            .Select(g => new { Node = g.Key, Count = g.Count() })
+            .ToDictionaryAsync(x => x.Node, x => x.Count, cancellationToken);
+    }
+
     /// <inheritdoc />
     public async Task<int> SaveChangesAsync(CancellationToken cancellationToken = default)
         => await _context.SaveChangesAsync(cancellationToken);