diff --git a/tests/ZB.MOM.WW.ScadaBridge.NotificationOutbox.Tests/NotificationOutboxActorDispatchTests.cs b/tests/ZB.MOM.WW.ScadaBridge.NotificationOutbox.Tests/NotificationOutboxActorDispatchTests.cs
index b16a2698..160dcf50 100644
--- a/tests/ZB.MOM.WW.ScadaBridge.NotificationOutbox.Tests/NotificationOutboxActorDispatchTests.cs
+++ b/tests/ZB.MOM.WW.ScadaBridge.NotificationOutbox.Tests/NotificationOutboxActorDispatchTests.cs
@@ -108,6 +108,29 @@ public class NotificationOutboxActorDispatchTests : TestKit
             .Returns(new[] { config });
     }
 
+    /// <summary>
+    /// Drives a sweep to completion by re-telling <see cref="InternalMessages.DispatchTick"/>
+    /// on every poll iteration until <paramref name="assertion"/> holds. This is the durable
+    /// barrier for chained-sweep tests: the in-flight guard (<c>_dispatching</c>) is only
+    /// lowered when a sweep's <see cref="InternalMessages.DispatchComplete"/> round-trips back
+    /// to the actor — AFTER the side-effect the assertion observes — so a single one-shot tick
+    /// can race the still-raised guard and be silently dropped (the dispatcher's intended
+    /// overlap protection), permanently stalling the count. A dropped tick is never retried, so
+    /// merely widening the wait cannot recover it. Re-telling each poll is idempotent (a tick
+    /// landing while the guard is up is harmlessly dropped) and the assertion's exact-count
+    /// strength is preserved unchanged.
+    /// </summary>
+    private void DrivePollingTick(IActorRef actor, Action assertion)
+    {
+        AwaitAssert(
+            () =>
+            {
+                actor.Tell(InternalMessages.DispatchTick.Instance);
+                assertion();
+            },
+            duration: TimeSpan.FromSeconds(10));
+    }
+
     [Fact]
     public void DispatchTick_ClaimsDueNotifications_AndInvokesAdapter()
     {
@@ -254,20 +277,48 @@ public class NotificationOutboxActorDispatchTests : TestKit
         SetupSmtpRetryPolicy(maxRetries: 5, retryDelay: TimeSpan.FromMinutes(1));
         // GetDueAsync throws on every call: the dispatch pass's task could fault if the
         // failure were not handled, which would leave _dispatching stuck true forever.
+        // Count every claim via a thread-safe counter so the assertions can reason about
+        // the number of sweeps that actually ran without depending on NSubstitute's
+        // exact-count matchers (see the de-race note below).
+        var claimAttempts = 0;
         _outboxRepository.GetDueAsync(Arg.Any<DateTimeOffset>(), Arg.Any<int>(), Arg.Any<CancellationToken>())
-            .Returns<IReadOnlyList<Notification>>(_ => throw new InvalidOperationException("db down"));
+            .Returns<IReadOnlyList<Notification>>(_ =>
+            {
+                Interlocked.Increment(ref claimAttempts);
+                throw new InvalidOperationException("db down");
+            });
         var actor = CreateActor([]);
 
         // First tick: the pass faults internally but must still clear the in-flight guard.
         actor.Tell(InternalMessages.DispatchTick.Instance);
-        AwaitAssert(() => _outboxRepository.Received(1).GetDueAsync(
-            Arg.Any<DateTimeOffset>(), Arg.Any<int>(), Arg.Any<CancellationToken>()));
+        AwaitAssert(
+            () => Assert.True(Volatile.Read(ref claimAttempts) >= 1),
+            duration: TimeSpan.FromSeconds(10));
 
-        // Second tick after the first completes: if the guard had wedged, this would be
-        // dropped and GetDueAsync would still show only one call.
-        actor.Tell(InternalMessages.DispatchTick.Instance);
-        AwaitAssert(() => _outboxRepository.Received(2).GetDueAsync(
-            Arg.Any<DateTimeOffset>(), Arg.Any<int>(), Arg.Any<CancellationToken>()));
+        // The guard must clear after the faulted sweep so a fresh tick runs another sweep.
+        //
+        // De-race (S11): the in-flight guard (_dispatching) is only lowered when the
+        // faulted sweep's DispatchComplete round-trips back to the actor — which happens
+        // AFTER the GetDueAsync side-effect the barrier above observes. So a single second
+        // tick sent right after that barrier can race the guard while it is still up and
+        // be silently dropped (the dispatcher's intended overlap protection), leaving the
+        // claim count stuck at one forever — a dropped tick is never retried, so widening
+        // the timeout cannot recover it. Re-tell the tick on every poll iteration instead:
+        // a tick that lands while the guard is still up is harmlessly dropped, and the
+        // first tick that lands after the guard lowers runs a fresh sweep. The assertion
+        // is "at least two sweeps ran" rather than "exactly two": that is strictly the
+        // wedge invariant under test (a wedged guard would pin the count at one no matter
+        // how many ticks arrive), and an at-least assertion is immune to the surplus ticks
+        // the re-tell driver may land under CPU starvation.
+        AwaitAssert(
+            () =>
+            {
+                actor.Tell(InternalMessages.DispatchTick.Instance);
+                Assert.True(
+                    Volatile.Read(ref claimAttempts) >= 2,
+                    "the in-flight guard wedged: a second dispatch tick never ran a fresh sweep");
+            },
+            duration: TimeSpan.FromSeconds(10));
     }
 
     [Fact]
@@ -410,8 +461,21 @@ public class NotificationOutboxActorDispatchTests : TestKit
         // so we don't mutate the shared _outboxRepository field that other tests in
         // this class configure differently.
         var outboxRepository = Substitute.For<INotificationOutboxRepository>();
+        // De-race (S11): hand out a fresh due notification for the FIRST THREE claims, then
+        // an empty batch forever. This caps the deliverable work — and therefore the
+        // UpdateAsync count — at exactly three, no matter how many dispatch ticks the
+        // driver below fires. Without this ceiling the exact-count barrier is doubly
+        // brittle: a single one-shot tick that races the in-flight guard is silently
+        // dropped (stalling the count below three), while a tick-per-poll driver lets
+        // queued ticks pile up under CPU starvation and overshoot three. Capping the
+        // claimable batch lets the driver re-tell ticks idempotently — surplus sweeps
+        // claim nothing and never call UpdateAsync — so Received(3) is a stable target
+        // that, once reached, cannot be exceeded.
+        var dueClaims = 0;
         outboxRepository.GetDueAsync(Arg.Any<DateTimeOffset>(), Arg.Any<int>(), Arg.Any<CancellationToken>())
-            .Returns(_ => new[] { MakeNotification() });
+            .Returns(_ => Interlocked.Increment(ref dueClaims) <= 3
+                ? new[] { MakeNotification() }
+                : Array.Empty<Notification>());
 
         // Counting factory: increments each time the DI container resolves an
         // INotificationDeliveryAdapter. Pre-fix this would have ticked once per
@@ -433,22 +497,20 @@ public class NotificationOutboxActorDispatchTests : TestKit
             new NoOpCentralAuditWriter(),
             NullLogger<NotificationOutboxActor>.Instance)));
 
-        // Fire three sweeps end-to-end. Each waits on the previous via the
-        // in-flight guard, so the UpdateAsync count climbs monotonically.
-        actor.Tell(InternalMessages.DispatchTick.Instance);
-        AwaitAssert(() => outboxRepository.Received(1).UpdateAsync(
+        // Drive dispatch sweeps until all three claimable notifications have been
+        // delivered (Received(3).UpdateAsync). DrivePollingTick re-tells the tick on
+        // every poll iteration; the GetDueAsync cap above makes that idempotent (a
+        // surplus sweep claims an empty batch and calls UpdateAsync zero times), so
+        // the count climbs to exactly three and then holds there — Received(3) is a
+        // stable ceiling rather than a fragile one-shot target. This proves multiple
+        // dispatch sweeps ran across the actor's lifetime, which is the precondition
+        // for the resolve-adapters-once assertion that follows.
+        DrivePollingTick(actor, () => outboxRepository.Received(3).UpdateAsync(
             Arg.Any<Notification>(), Arg.Any<CancellationToken>()));
 
-        actor.Tell(InternalMessages.DispatchTick.Instance);
-        AwaitAssert(() => outboxRepository.Received(2).UpdateAsync(
-            Arg.Any<Notification>(), Arg.Any<CancellationToken>()));
-
-        actor.Tell(InternalMessages.DispatchTick.Instance);
-        AwaitAssert(() => outboxRepository.Received(3).UpdateAsync(
-            Arg.Any<Notification>(), Arg.Any<CancellationToken>()));
-
-        // The adapter resolution must have happened EXACTLY ONCE despite three
-        // dispatch sweeps. Pre-fix this would have been 3 (or more).
+        // The adapter resolution must have happened EXACTLY ONCE despite the multiple
+        // dispatch sweeps just driven. Pre-fix this would have been once per sweep.
+        // This is the real invariant under test (NotificationOutbox-006).
         Assert.Equal(1, resolutionCount);
     }