fix(notification-outbox): give KPI response a failure shape; log status-query faults

tests/ScadaLink.NotificationOutbox.Tests/NotificationOutboxActorQueryTests.cs

@@ -323,6 +323,8 @@ public class NotificationOutboxActorQueryTests : TestKit
 
         var response = ExpectMsg<NotificationKpiResponse>();
         Assert.Equal("corr-11", response.CorrelationId);
+        Assert.True(response.Success);
+        Assert.Null(response.ErrorMessage);
         Assert.Equal(7, response.QueueDepth);
         Assert.Equal(2, response.StuckCount);
         Assert.Equal(3, response.ParkedCount);
@@ -332,4 +334,27 @@ public class NotificationOutboxActorQueryTests : TestKit
         _repository.Received(1).ComputeKpisAsync(
             Arg.Any<DateTimeOffset>(), Arg.Any<DateTimeOffset>(), Arg.Any<CancellationToken>());
     }
+
+    [Fact]
+    public void KpiRequest_RepositoryThrows_RepliesFailureResponse()
+    {
+        _repository.ComputeKpisAsync(
+                Arg.Any<DateTimeOffset>(), Arg.Any<DateTimeOffset>(), Arg.Any<CancellationToken>())
+            .ThrowsAsync(new InvalidOperationException("kpi db down"));
+        var actor = CreateActor();
+
+        actor.Tell(new NotificationKpiRequest("corr-12"), TestActor);
+
+        // A repository fault yields a failure NotificationKpiResponse, not a Status.Failure.
+        var response = ExpectMsg<NotificationKpiResponse>();
+        Assert.Equal("corr-12", response.CorrelationId);
+        Assert.False(response.Success);
+        Assert.NotNull(response.ErrorMessage);
+        Assert.Contains("kpi db down", response.ErrorMessage);
+        Assert.Equal(0, response.QueueDepth);
+        Assert.Equal(0, response.StuckCount);
+        Assert.Equal(0, response.ParkedCount);
+        Assert.Equal(0, response.DeliveredLastInterval);
+        Assert.Null(response.OldestPendingAge);
+    }
 }