fix(store-and-forward): re-seed queue-depth gauge from DB on sweep, clamp at 0 (review 2026-10-21 02/C3)

tests/ZB.MOM.WW.ScadaBridge.StoreAndForward.Tests/QueueDepthGaugeTests.cs

@@ -97,6 +97,37 @@ public class QueueDepthGaugeTests : IAsyncLifetime, IDisposable
         return observed;
     }
 
+    /// <summary>
+    /// Review 2026-10-21 02/C3: rows that arrive without passing through this node's counter
+    /// paths (LocalDb CDC on a standby) are picked up by the sweep's periodic re-seed.
+    /// </summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
+    [Fact]
+    public async Task Gauge_ReseedsFromDatabase_OnSweep()
+    {
+        Assert.Equal(0, ReadQueueDepthGauge());
+        for (var i = 0; i < 3; i++)
+        {
+            await _storage.EnqueueAsync(new StoreAndForwardMessage
+            {
+                Id = $"cdc{i}",
+                Category = StoreAndForwardCategory.ExternalSystem,
+                Target = "t",
+                PayloadJson = "{}",
+                MaxRetries = 50,
+                RetryIntervalMs = 3_600_000,
+                CreatedAt = DateTimeOffset.UtcNow,
+                LastAttemptAt = DateTimeOffset.UtcNow,
+                Status = StoreAndForwardMessageStatus.Pending,
+            });
+        }
+        Assert.Equal(0, ReadQueueDepthGauge()); // counter never saw them
+
+        await _service.RetryPendingMessagesAsync();
+
+        Assert.Equal(3, ReadQueueDepthGauge());
+    }
+
     /// <summary>Verifies that gauge, tracks buffered depth, across enqueue drain and park.</summary>
     /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]