diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Drivers/DriverHostActor.cs b/src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Drivers/DriverHostActor.cs
index e62c8d2d..b287ca3c 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Drivers/DriverHostActor.cs
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Drivers/DriverHostActor.cs
@@ -2018,6 +2018,12 @@ public sealed class DriverHostActor : ReceiveActor, IWithTimers, IWithUnboundedS
             return;
         }
 
+        // Gitea #641 review — the node is already acknowledged (the SDK applies the client's ack); tell the
+        // projector too, or the next driver Clear projects (Active=false, Acked=prev=false) and un-acknowledges it.
+        // Most sources (MTConnect, FOCAS) send no Acknowledge transition back, and the projector now survives a
+        // deploy rather than resetting to its acked default.
+        _nativeAlarmProjector.MarkAcknowledged(msg.ConditionNodeId);
+
         if (!_children.TryGetValue(target.DriverInstanceId, out var entry))
         {
             _log.Debug("DriverHost {Node}: driver {Driver} not running for alarm ack of {Cond} — dropped",
diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Drivers/NativeAlarmProjector.cs b/src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Drivers/NativeAlarmProjector.cs
index fb0f8075..9e10f29b 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Drivers/NativeAlarmProjector.cs
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Drivers/NativeAlarmProjector.cs
@@ -40,6 +40,17 @@ public sealed class NativeAlarmProjector
             StatusCode: e.QualityStatusCode ?? OpcUaStatus.Good);
     }
 
+    /// <summary>
+    ///     Gitea #641 review — record a client acknowledgement the node manager applied to <paramref name="nodeId"/>
+    ///     and routed toward the driver. The projector otherwise never sees it, and a later Clear would project the
+    ///     stale unacknowledged prior. An untracked condition already defaults to acknowledged.
+    /// </summary>
+    /// <param name="nodeId">The acknowledged condition node id.</param>
+    public void MarkAcknowledged(string nodeId)
+    {
+        if (_prior.TryGetValue(nodeId, out var p)) _prior[nodeId] = (p.Active, true);
+    }
+
     /// <summary>Clears all tracked per-node state.</summary>
     public void Clear() => _prior.Clear();
 
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/Drivers/DriverHostActorNativeAlarmTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/Drivers/DriverHostActorNativeAlarmTests.cs
index 1ac1b060..36701991 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/Drivers/DriverHostActorNativeAlarmTests.cs
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/Drivers/DriverHostActorNativeAlarmTests.cs
@@ -473,6 +473,33 @@ public sealed class DriverHostActorNativeAlarmTests : RuntimeActorTestBase
         cleared.State.Acknowledged.ShouldBeFalse("nobody acknowledged it");
     }
 
+    /// <summary>
+    ///     Gitea #641 review — a CLIENT acknowledgement is applied to the node by the SDK and only ROUTED here; the
+    ///     projector must learn of it. Before #641 the projector was cleared on every deploy, so a Clear arriving
+    ///     after one defaulted Acked to true and happened to be right for a client-acked alarm; now that the
+    ///     projector survives the deploy, a projector that never heard the ack projects the Clear as UNacked and
+    ///     un-acknowledges the alarm the operator acknowledged.
+    /// </summary>
+    [Fact]
+    public void A_clear_after_a_client_acknowledge_and_a_redeploy_stays_acknowledged()
+    {
+        var db = NewInMemoryDbFactory();
+        var deploymentId = SeedV3AlarmDeployment(db, RevA, Driver: "drv-1", Tag: "temp_hi");
+        var (actor, publish, coordinator) = SpawnHostAndApplyWithCoordinator(db, deploymentId);
+
+        actor.Tell(Transition(AlarmTransitionKind.Raise));
+        publish.ExpectMsg<OpcUaPublishActor.AlarmStateUpdate>(TimeSpan.FromSeconds(5)).State.Acknowledged.ShouldBeFalse();
+
+        // The client's Acknowledge on the node, routed toward the driver (no transition comes back for it).
+        actor.Tell(new DriverHostActor.RouteNativeAlarmAck(AlarmRawPath, "seen", "op"));
+        Redeploy(db, actor, publish, coordinator);
+
+        actor.Tell(Transition(AlarmTransitionKind.Clear));
+        var cleared = publish.FishForMessage<OpcUaPublishActor.AlarmStateUpdate>(_ => true, TimeSpan.FromSeconds(5));
+        cleared.State.Active.ShouldBeFalse();
+        cleared.State.Acknowledged.ShouldBeTrue("the operator acknowledged it before it cleared");
+    }
+
     private static DriverInstanceActor.AttributeAlarmPublished Transition(AlarmTransitionKind kind) =>
         new("drv-1", new AlarmEventArgs(
             new StubAlarmHandle(), "Temp", AlarmRawPath, "OffNormalAlarm", kind.ToString(), AlarmSeverity.High, Ts,