feat(worker): route alarm acks through the operator-authenticated AckMsg writer

AlarmCommandHandler -> AlarmDispatcher -> IAlarmAckWriter: the dispatcher resolves the ack item through the consumer and the writer authenticates the operator and writes the comment. The executor builds AlarmAckOperator from operator_user/domain/password, maps AlarmAckOutcome to the reply (Applied/Unconfirmed Ok, AlarmNotFound/NotAckable InvalidRequest, AuthenticationFailed/WriteRejected MxaccessFailure) and reports escaping exceptions by type and HRESULT only, so operator_password cannot leak. Removes the inert managed/WNAL alarm-client ack path.

Claude-Session: https://claude.ai/code/session_016J6isfcgqy4SB2RK3ZvFvT

src/ZB.MOM.WW.MxGateway.Worker.Tests/MxAccess/AlarmCommandExecutorTests.cs

@@ -116,7 +116,7 @@ public sealed class AlarmCommandExecutorTests
     [Fact]
     public void AcknowledgeAlarm_WithHandler_RoutesNativeStatusIntoHresultAndPayload()
     {
-        FakeAlarmHandler handler = new FakeAlarmHandler { AcknowledgeReturn = 0 };
+        FakeAlarmHandler handler = new FakeAlarmHandler();
         MxAccessCommandExecutor executor = NewExecutor(handler);
         Guid g = Guid.NewGuid();
 
@@ -143,7 +143,10 @@ public sealed class AlarmCommandExecutorTests
         Assert.NotNull(reply.AcknowledgeAlarm);
         Assert.Equal(0, reply.AcknowledgeAlarm.NativeStatus);
         Assert.Equal(g, handler.LastAckGuid);
-        Assert.Equal("alice", handler.LastAckOperatorName);
+        Assert.Equal("ack", handler.LastComment);
+        Assert.Equal("alice", handler.LastOperator!.UserName);
+        Assert.Equal("CORP", handler.LastOperator.Domain);
+        Assert.Equal(string.Empty, handler.LastOperator.Password);
     }
 
     /// <summary>Verifies that invalid alarm GUID returns invalid request.</summary>
@@ -168,11 +171,14 @@ public sealed class AlarmCommandExecutorTests
         Assert.Equal(ProtocolStatusCode.InvalidRequest, reply.ProtocolStatus.Code);
     }
 
-    /// <summary>Verifies that nonzero native status carries a diagnostic message.</summary>
+    /// <summary>Verifies that a rejected write carries its native status and diagnostic.</summary>
     [Fact]
     public void AcknowledgeAlarm_WithNonzeroNativeStatus_CarriesDiagnostic()
     {
-        FakeAlarmHandler handler = new FakeAlarmHandler { AcknowledgeReturn = -123 };
+        FakeAlarmHandler handler = new FakeAlarmHandler
+        {
+            AckResult = AlarmAckResult.Create(AlarmAckOutcome.WriteRejected, -123, "AckMsg write rejected: detail -123."),
+        };
         MxAccessCommandExecutor executor = NewExecutor(handler);
 
         StaCommand command = new StaCommand(
@@ -188,7 +194,9 @@ public sealed class AlarmCommandExecutorTests
 
         MxCommandReply reply = executor.Execute(command);
 
+        Assert.Equal(ProtocolStatusCode.MxaccessFailure, reply.ProtocolStatus.Code);
         Assert.Equal(-123, reply.Hresult);
+        Assert.Equal(-123, reply.AcknowledgeAlarm.NativeStatus);
         Assert.Contains("-123", reply.DiagnosticMessage);
     }
 
@@ -196,7 +204,7 @@ public sealed class AlarmCommandExecutorTests
     [Fact]
     public void AcknowledgeAlarmByName_WithHandler_RoutesTupleToHandler()
     {
-        FakeAlarmHandler handler = new FakeAlarmHandler { AcknowledgeReturn = 0 };
+        FakeAlarmHandler handler = new FakeAlarmHandler();
         MxAccessCommandExecutor executor = NewExecutor(handler);
 
         StaCommand command = new StaCommand(
@@ -223,7 +231,133 @@ public sealed class AlarmCommandExecutorTests
         Assert.Equal("TestMachine_001.TestAlarm001", handler.LastAckByNameTuple!.Value.Name);
         Assert.Equal("Galaxy", handler.LastAckByNameTuple!.Value.Provider);
         Assert.Equal("TestArea", handler.LastAckByNameTuple!.Value.Group);
-        Assert.Equal("alice", handler.LastAckOperatorName);
+        Assert.Equal("ack", handler.LastComment);
+        Assert.Equal("alice", handler.LastOperator!.UserName);
+    }
+
+    /// <summary>
+    ///     Every ack outcome maps to its protocol status, carries the native
+    ///     status, and never echoes the operator password.
+    /// </summary>
+    /// <param name="outcome">The writer outcome.</param>
+    /// <param name="expected">The expected protocol status.</param>
+    [Theory]
+    [InlineData(AlarmAckOutcome.Applied, ProtocolStatusCode.Ok)]
+    [InlineData(AlarmAckOutcome.Unconfirmed, ProtocolStatusCode.Ok)]
+    [InlineData(AlarmAckOutcome.AlarmNotFound, ProtocolStatusCode.InvalidRequest)]
+    [InlineData(AlarmAckOutcome.NotAckable, ProtocolStatusCode.InvalidRequest)]
+    [InlineData(AlarmAckOutcome.AuthenticationFailed, ProtocolStatusCode.MxaccessFailure)]
+    [InlineData(AlarmAckOutcome.WriteRejected, ProtocolStatusCode.MxaccessFailure)]
+    public void AcknowledgeAlarm_MapsOutcomeWithoutLeakingPassword(AlarmAckOutcome outcome, ProtocolStatusCode expected)
+    {
+        int native = outcome is AlarmAckOutcome.Applied or AlarmAckOutcome.Unconfirmed ? 0 : 1008;
+        FakeAlarmHandler handler = new FakeAlarmHandler
+        {
+            AckResult = AlarmAckResult.Create(outcome, native, "diagnostic for alice"),
+        };
+
+        MxCommandReply reply = Execute(handler, new MxCommand
+        {
+            Kind = MxCommandKind.AcknowledgeAlarm,
+            AcknowledgeAlarmCommand = new AcknowledgeAlarmCommand
+            {
+                AlarmGuid = Guid.NewGuid().ToString(),
+                Comment = "checked",
+                OperatorUser = "alice",
+                OperatorDomain = "CORP",
+                OperatorPassword = "pw-secret",
+            },
+        });
+
+        AssertAckReply(reply, handler, expected, native);
+    }
+
+    /// <summary>The by-name ack maps outcomes identically and never echoes the operator password.</summary>
+    /// <param name="outcome">The writer outcome.</param>
+    /// <param name="expected">The expected protocol status.</param>
+    [Theory]
+    [InlineData(AlarmAckOutcome.Applied, ProtocolStatusCode.Ok)]
+    [InlineData(AlarmAckOutcome.Unconfirmed, ProtocolStatusCode.Ok)]
+    [InlineData(AlarmAckOutcome.AlarmNotFound, ProtocolStatusCode.InvalidRequest)]
+    [InlineData(AlarmAckOutcome.NotAckable, ProtocolStatusCode.InvalidRequest)]
+    [InlineData(AlarmAckOutcome.AuthenticationFailed, ProtocolStatusCode.MxaccessFailure)]
+    [InlineData(AlarmAckOutcome.WriteRejected, ProtocolStatusCode.MxaccessFailure)]
+    public void AcknowledgeAlarmByName_MapsOutcomeWithoutLeakingPassword(AlarmAckOutcome outcome, ProtocolStatusCode expected)
+    {
+        int native = outcome is AlarmAckOutcome.Applied or AlarmAckOutcome.Unconfirmed ? 0 : 1008;
+        FakeAlarmHandler handler = new FakeAlarmHandler
+        {
+            AckResult = AlarmAckResult.Create(outcome, native, "diagnostic for alice"),
+        };
+
+        MxCommandReply reply = Execute(handler, new MxCommand
+        {
+            Kind = MxCommandKind.AcknowledgeAlarmByName,
+            AcknowledgeAlarmByNameCommand = new AcknowledgeAlarmByNameCommand
+            {
+                AlarmName = "TestMachine_001.TestAlarm001",
+                ProviderName = "Galaxy",
+                GroupName = "TestArea",
+                Comment = "checked",
+                OperatorUser = "alice",
+                OperatorDomain = "CORP",
+                OperatorPassword = "pw-secret",
+            },
+        });
+
+        AssertAckReply(reply, handler, expected, native);
+    }
+
+    /// <summary>The writer's OnWriteComplete statuses are copied onto the reply.</summary>
+    [Fact]
+    public void AcknowledgeAlarm_CopiesWriteStatusesIntoReply()
+    {
+        MxStatusProxy status = new MxStatusProxy { Category = MxStatusCategory.Ok, Success = 1 };
+        FakeAlarmHandler handler = new FakeAlarmHandler
+        {
+            AckResult = AlarmAckResult.Create(AlarmAckOutcome.Applied, 0, string.Empty, new[] { status }),
+        };
+
+        MxCommandReply reply = Execute(handler, new MxCommand
+        {
+            Kind = MxCommandKind.AcknowledgeAlarm,
+            AcknowledgeAlarmCommand = new AcknowledgeAlarmCommand { AlarmGuid = Guid.NewGuid().ToString(), OperatorUser = "alice" },
+        });
+
+        Assert.Equal(status, Assert.Single(reply.Statuses));
+    }
+
+    /// <summary>
+    ///     An exception escaping the ack path (e.g. the writer's MXAccess
+    ///     Register failing) maps to MxaccessFailure with only the exception type
+    ///     and HRESULT — never the exception text, which is not under our control.
+    /// </summary>
+    [Fact]
+    public void AcknowledgeAlarmByName_WhenHandlerThrows_ReportsTypeAndHresultOnly()
+    {
+        FakeAlarmHandler handler = new FakeAlarmHandler
+        {
+            AcknowledgeException = new System.Runtime.InteropServices.COMException("echo pw-secret", unchecked((int)0x80004005)),
+        };
+
+        MxCommandReply reply = Execute(handler, new MxCommand
+        {
+            Kind = MxCommandKind.AcknowledgeAlarmByName,
+            AcknowledgeAlarmByNameCommand = new AcknowledgeAlarmByNameCommand
+            {
+                AlarmName = "TestMachine_001.TestAlarm001",
+                ProviderName = "Galaxy",
+                OperatorUser = "alice",
+                OperatorPassword = "pw-secret",
+            },
+        });
+
+        Assert.Equal(ProtocolStatusCode.MxaccessFailure, reply.ProtocolStatus.Code);
+        Assert.Equal(unchecked((int)0x80004005), reply.Hresult);
+        Assert.Contains("COMException", reply.DiagnosticMessage, StringComparison.Ordinal);
+        Assert.Contains("0x80004005", reply.DiagnosticMessage, StringComparison.Ordinal);
+        Assert.DoesNotContain("pw-secret", reply.DiagnosticMessage, StringComparison.Ordinal);
+        Assert.DoesNotContain("pw-secret", reply.ProtocolStatus.Message, StringComparison.Ordinal);
     }
 
     /// <summary>Verifies that empty alarm name returns invalid request.</summary>
@@ -393,7 +527,10 @@ public sealed class AlarmCommandExecutorTests
     [Fact]
     public void AcknowledgeAlarm_WhenHandlerThrows_ReturnsMxaccessFailure()
     {
-        FakeAlarmHandler handler = new FakeAlarmHandler { AcknowledgeThrow = true };
+        FakeAlarmHandler handler = new FakeAlarmHandler
+        {
+            AcknowledgeException = new InvalidOperationException("simulated alarm-handler failure"),
+        };
         MxAccessCommandExecutor executor = NewExecutor(handler);
 
         StaCommand command = new StaCommand(
@@ -410,7 +547,25 @@ public sealed class AlarmCommandExecutorTests
         MxCommandReply reply = executor.Execute(command);
 
         Assert.Equal(ProtocolStatusCode.MxaccessFailure, reply.ProtocolStatus.Code);
-        Assert.Contains("simulated", reply.DiagnosticMessage);
+        Assert.Contains("InvalidOperationException", reply.DiagnosticMessage, StringComparison.Ordinal);
+        Assert.DoesNotContain("simulated", reply.DiagnosticMessage, StringComparison.Ordinal);
+    }
+
+    private static MxCommandReply Execute(IAlarmCommandHandler handler, MxCommand command) =>
+        NewExecutor(handler).Execute(new StaCommand(SessionId, CorrelationId, command));
+
+    private static void AssertAckReply(MxCommandReply reply, FakeAlarmHandler handler, ProtocolStatusCode expected, int native)
+    {
+        Assert.Equal(expected, reply.ProtocolStatus.Code);
+        Assert.Equal(native, reply.Hresult);
+        Assert.Equal(native, reply.AcknowledgeAlarm.NativeStatus);
+        Assert.Equal("diagnostic for alice", reply.DiagnosticMessage);
+        Assert.Equal("checked", handler.LastComment);
+        Assert.Equal("alice", handler.LastOperator!.UserName);
+        Assert.Equal("CORP", handler.LastOperator.Domain);
+        Assert.Equal("pw-secret", handler.LastOperator.Password);
+        Assert.DoesNotContain("pw-secret", reply.DiagnosticMessage ?? string.Empty, StringComparison.Ordinal);
+        Assert.DoesNotContain("pw-secret", reply.ProtocolStatus.Message ?? string.Empty, StringComparison.Ordinal);
     }
 
     private static MxAccessCommandExecutor NewExecutor(IAlarmCommandHandler? alarmHandler)
@@ -442,14 +597,17 @@ public sealed class AlarmCommandExecutorTests
         /// <summary>Gets the last acknowledge alarm GUID.</summary>
         public Guid LastAckGuid { get; private set; }
 
-        /// <summary>Gets the last acknowledge operator name.</summary>
-        public string? LastAckOperatorName { get; private set; }
+        /// <summary>Gets the last acknowledge comment.</summary>
+        public string? LastComment { get; private set; }
 
-        /// <summary>Gets or sets the value returned by acknowledge.</summary>
-        public int AcknowledgeReturn { get; set; }
+        /// <summary>Gets the last acknowledge operator.</summary>
+        public AlarmAckOperator? LastOperator { get; private set; }
 
-        /// <summary>Gets or sets a value indicating whether acknowledge throws.</summary>
-        public bool AcknowledgeThrow { get; set; }
+        /// <summary>Gets or sets the result returned by both acknowledge methods.</summary>
+        public AlarmAckResult AckResult { get; set; } = AlarmAckResult.Create(AlarmAckOutcome.Applied, 0, string.Empty);
+
+        /// <summary>Gets or sets an exception both acknowledge methods throw.</summary>
+        public Exception? AcknowledgeException { get; set; }
 
         /// <summary>Gets or sets the query result snapshots.</summary>
         public IReadOnlyList<ActiveAlarmSnapshot> QueryResult { get; set; } =
@@ -484,28 +642,32 @@ public sealed class AlarmCommandExecutorTests
         }
 
         /// <inheritdoc />
-        public int Acknowledge(
-            Guid alarmGuid, string comment, string operatorUser,
-            string operatorNode, string operatorDomain, string operatorFullName)
+        public AlarmAckResult Acknowledge(Guid alarmGuid, string comment, AlarmAckOperator ackOperator)
         {
             LastAckGuid = alarmGuid;
-            LastAckOperatorName = operatorUser;
-            if (AcknowledgeThrow)
+            LastComment = comment;
+            LastOperator = ackOperator;
+            if (AcknowledgeException is not null)
             {
-                throw new InvalidOperationException("simulated alarm-handler failure");
+                throw AcknowledgeException;
             }
-            return AcknowledgeReturn;
+
+            return AckResult;
         }
 
         /// <inheritdoc />
-        public int AcknowledgeByName(
-            string alarmName, string providerName, string groupName,
-            string comment, string operatorUser, string operatorNode,
-            string operatorDomain, string operatorFullName)
+        public AlarmAckResult AcknowledgeByName(
+            string alarmName, string providerName, string groupName, string comment, AlarmAckOperator ackOperator)
         {
             LastAckByNameTuple = (alarmName, providerName, groupName);
-            LastAckOperatorName = operatorUser;
-            return AcknowledgeReturn;
+            LastComment = comment;
+            LastOperator = ackOperator;
+            if (AcknowledgeException is not null)
+            {
+                throw AcknowledgeException;
+            }
+
+            return AckResult;
         }
 
         /// <summary>Gets the last acknowledge by name tuple.</summary>

src/ZB.MOM.WW.MxGateway.Worker.Tests/MxAccess/AlarmCommandHandlerTests.cs

@@ -96,22 +96,100 @@ public sealed class AlarmCommandHandlerTests
         Assert.False(handler.IsSubscribed);
     }
 
-    /// <summary>Verifies that acknowledge forwards to consumer with full operator identity when subscribed.</summary>
+    /// <summary>Verifies that acknowledge resolves via the consumer and writes through the injected writer as the operator.</summary>
     [Fact]
-    public void Acknowledge_WhenSubscribed_ForwardsToConsumerWithFullOperatorIdentity()
+    public void Acknowledge_WhenSubscribed_ResolvesTargetAndWritesAsOperator()
     {
-        FakeConsumer consumer = new FakeConsumer { AcknowledgeReturn = 0 };
-        AlarmCommandHandler handler = new AlarmCommandHandler(
-            new MxAccessEventQueue(),
-            () => consumer);
+        FakeConsumer consumer = new FakeConsumer { AckTarget = AlarmAckTarget.For("T.A.AckMsg") };
+        RecordingAckWriter writer = new RecordingAckWriter();
+        AlarmCommandHandler handler = NewHandlerWithWriter(() => consumer, writer);
         handler.Subscribe(new SubscribeAlarmsCommand { SubscriptionExpression = @"\\HOST\Galaxy!A" }, "s1");
 
         Guid g = Guid.NewGuid();
-        int rc = handler.Acknowledge(g, "c", "u", "n", "d", "F");
+        AlarmAckOperator op = new AlarmAckOperator { UserName = "u", Domain = "d", Password = "p" };
+        AlarmAckResult result = handler.Acknowledge(g, "c", op);
 
-        Assert.Equal(0, rc);
-        Assert.Equal(g, consumer.LastAckGuid);
-        Assert.Equal("u", consumer.LastAckOperatorName);
+        Assert.Equal(AlarmAckOutcome.Applied, result.Outcome);
+        Assert.Equal(g, consumer.LastResolvedGuid);
+        Assert.Equal("T.A.AckMsg", writer.LastItemAddress);
+        Assert.Equal("c", writer.LastComment);
+        Assert.Same(op, writer.LastOperator);
+    }
+
+    /// <summary>Verifies acknowledge-by-name forwards the tuple and a null comment becomes empty.</summary>
+    [Fact]
+    public void AcknowledgeByName_WhenSubscribed_ForwardsTupleAndNormalizesComment()
+    {
+        FakeConsumer consumer = new FakeConsumer();
+        RecordingAckWriter writer = new RecordingAckWriter();
+        AlarmCommandHandler handler = NewHandlerWithWriter(() => consumer, writer);
+        handler.Subscribe(new SubscribeAlarmsCommand { SubscriptionExpression = @"\\HOST\Galaxy!A" }, "s1");
+
+        handler.AcknowledgeByName("Tag1", "Galaxy", "Area", null!, new AlarmAckOperator { UserName = "u" });
+
+        Assert.Equal(("Tag1", "Galaxy", "Area"), consumer.LastResolvedName);
+        Assert.Equal(string.Empty, writer.LastComment);
+    }
+
+    /// <summary>Verifies a null operator is rejected.</summary>
+    [Fact]
+    public void Acknowledge_NullOperator_Throws()
+    {
+        AlarmCommandHandler handler = NewHandlerWithWriter(() => new FakeConsumer(), new RecordingAckWriter());
+        handler.Subscribe(new SubscribeAlarmsCommand { SubscriptionExpression = @"\\HOST\Galaxy!A" }, "s1");
+
+        Assert.Throws<ArgumentNullException>(() => handler.Acknowledge(Guid.NewGuid(), "c", null!));
+    }
+
+    /// <summary>
+    ///     The ack writer is created once, on first acknowledgement, survives an
+    ///     unsubscribe/resubscribe cycle, and is disposed with the handler.
+    /// </summary>
+    [Fact]
+    public void AckWriter_CreatedLazilyOnce_AndDisposedWithHandler()
+    {
+        RecordingAckWriter writer = new RecordingAckWriter();
+        int created = 0;
+        AlarmCommandHandler handler = new AlarmCommandHandler(
+            new MxAccessEventQueue(),
+            () => new FakeConsumer(),
+            threadAffinityCheck: null,
+            comFactory: null,
+            standbyFactory: null,
+            ackWriterFactory: () =>
+            {
+                created++;
+                return writer;
+            });
+
+        handler.Subscribe(new SubscribeAlarmsCommand { SubscriptionExpression = @"\\HOST\Galaxy!A" }, "s1");
+        Assert.Equal(0, created);
+
+        handler.Acknowledge(Guid.NewGuid(), "c", new AlarmAckOperator());
+        handler.Unsubscribe();
+        Assert.False(writer.Disposed);
+
+        handler.Subscribe(new SubscribeAlarmsCommand { SubscriptionExpression = @"\\HOST\Galaxy!A" }, "s1");
+        handler.AcknowledgeByName("a", "Galaxy", "g", "c", new AlarmAckOperator());
+        Assert.Equal(1, created);
+
+        handler.Dispose();
+        Assert.True(writer.Disposed);
+    }
+
+    /// <summary>
+    ///     Without a COM factory or writer factory, subscribing still works and
+    ///     the acknowledgement fails with a diagnosable InvalidOperationException.
+    /// </summary>
+    [Fact]
+    public void Acknowledge_WithoutComFactoryOrWriterFactory_ThrowsInvalidOperation()
+    {
+        AlarmCommandHandler handler = new AlarmCommandHandler(new MxAccessEventQueue(), () => new FakeConsumer());
+        handler.Subscribe(new SubscribeAlarmsCommand { SubscriptionExpression = @"\\HOST\Galaxy!A" }, "s1");
+
+        InvalidOperationException ex = Assert.Throws<InvalidOperationException>(
+            () => handler.Acknowledge(Guid.NewGuid(), "c", new AlarmAckOperator()));
+        Assert.Contains("IMxAccessComObjectFactory", ex.Message);
     }
 
     /// <summary>Verifies that acknowledge throws invalid operation when called before subscribe.</summary>
@@ -123,7 +201,7 @@ public sealed class AlarmCommandHandlerTests
             () => new FakeConsumer());
 
         Assert.Throws<InvalidOperationException>(
-            () => handler.Acknowledge(Guid.Empty, "", "", "", "", ""));
+            () => handler.Acknowledge(Guid.Empty, "", new AlarmAckOperator()));
     }
 
     /// <summary>Verifies that query active returns mapped proto snapshots when consumer has alarms.</summary>
@@ -266,7 +344,10 @@ public sealed class AlarmCommandHandlerTests
         AlarmCommandHandler handler = new AlarmCommandHandler(
             new MxAccessEventQueue(),
             () => consumer,
-            () => guardInvocations++);
+            () => guardInvocations++,
+            comFactory: null,
+            standbyFactory: null,
+            ackWriterFactory: () => new RecordingAckWriter());
 
         // Subscribe is the first call — guard must run before the consumer
         // factory is invoked. We tally invocation counts after each call so
@@ -275,10 +356,10 @@ public sealed class AlarmCommandHandlerTests
         handler.Subscribe(new SubscribeAlarmsCommand { SubscriptionExpression = @"\\HOST\Galaxy!A" }, "s1");
         Assert.Equal(1, guardInvocations);
 
-        handler.Acknowledge(Guid.NewGuid(), "c", "u", "n", "d", "F");
+        handler.Acknowledge(Guid.NewGuid(), "c", new AlarmAckOperator { UserName = "u" });
         Assert.Equal(2, guardInvocations);
 
-        handler.AcknowledgeByName("a", "p", "g", "c", "u", "n", "d", "F");
+        handler.AcknowledgeByName("a", "p", "g", "c", new AlarmAckOperator { UserName = "u" });
         Assert.Equal(3, guardInvocations);
 
         _ = handler.QueryActive(null, out _);
@@ -323,9 +404,9 @@ public sealed class AlarmCommandHandlerTests
         // assert each independently with a fresh handler. Below we reuse
         // the same throwing handler for the not-subscribed-yet entries:
         Assert.Throws<InvalidOperationException>(
-            () => handler.Acknowledge(Guid.Empty, "", "", "", "", ""));
+            () => handler.Acknowledge(Guid.Empty, "", new AlarmAckOperator()));
         Assert.Throws<InvalidOperationException>(
-            () => handler.AcknowledgeByName("", "", "", "", "", "", "", ""));
+            () => handler.AcknowledgeByName("", "", "", "", new AlarmAckOperator()));
         Assert.Throws<InvalidOperationException>(() => handler.QueryActive(null, out _));
         Assert.Throws<InvalidOperationException>(() => handler.PollOnce());
         Assert.Throws<InvalidOperationException>(
@@ -422,16 +503,17 @@ public sealed class AlarmCommandHandlerTests
     [Fact]
     public void Subscribe_AutoModeWithEmptyWatchListAndFallbackEnabled_BuildsReplaceableStandby()
     {
-        FakeConsumer primary = new FakeConsumer { AcknowledgeReturn = 11 };
-        FakeConsumer initialStandby = new FakeConsumer { AcknowledgeReturn = 22 };
-        FakeConsumer replacement = new FakeConsumer { AcknowledgeReturn = 33 };
+        FakeConsumer primary = new FakeConsumer { AckTarget = AlarmAckTarget.For("11.AckMsg") };
+        FakeConsumer initialStandby = new FakeConsumer { AckTarget = AlarmAckTarget.For("22.AckMsg") };
+        FakeConsumer replacement = new FakeConsumer { AckTarget = AlarmAckTarget.For("33.AckMsg") };
         int buildCount = 0;
         AlarmCommandHandler handler = new AlarmCommandHandler(
             new MxAccessEventQueue(),
             () => primary,
             threadAffinityCheck: null,
             comFactory: null,
-            standbyFactory: _ => ++buildCount == 1 ? initialStandby : replacement);
+            standbyFactory: _ => ++buildCount == 1 ? initialStandby : replacement,
+            ackWriterFactory: () => new RecordingAckWriter());
 
         handler.Subscribe(new SubscribeAlarmsCommand
         {
@@ -443,7 +525,7 @@ public sealed class AlarmCommandHandlerTests
         Assert.Equal(2, buildCount);
         Assert.Equal(@"\\HOST\Galaxy!Area", replacement.LastSubscription);
         Assert.True(initialStandby.Disposed);
-        Assert.Equal(11, handler.Acknowledge(Guid.Empty, "", "", "", "", ""));
+        Assert.Equal("11.AckMsg", AckItemOf(handler));
     }
 
     /// <summary>A replacement is rejected when no fallback-capable subscription is active.</summary>
@@ -471,16 +553,17 @@ public sealed class AlarmCommandHandlerTests
     [Fact]
     public void UpdateWatchList_WhenReplacementSubscribeFails_PreservesOldStandbyAndPrimaryMode()
     {
-        FakeConsumer primary = new FakeConsumer { AcknowledgeReturn = 11 };
-        FakeConsumer oldStandby = new FakeConsumer { AcknowledgeReturn = 22 };
-        FakeConsumer failedReplacement = new FakeConsumer { ThrowOnSubscribe = true, AcknowledgeReturn = 33 };
+        FakeConsumer primary = new FakeConsumer { AckTarget = AlarmAckTarget.For("11.AckMsg") };
+        FakeConsumer oldStandby = new FakeConsumer { AckTarget = AlarmAckTarget.For("22.AckMsg") };
+        FakeConsumer failedReplacement = new FakeConsumer { ThrowOnSubscribe = true, AckTarget = AlarmAckTarget.For("33.AckMsg") };
         int buildCount = 0;
         AlarmCommandHandler handler = new AlarmCommandHandler(
             new MxAccessEventQueue(),
             () => primary,
             null,
             null,
-            _ => ++buildCount == 1 ? oldStandby : failedReplacement);
+            _ => ++buildCount == 1 ? oldStandby : failedReplacement,
+            () => new RecordingAckWriter());
         SubscribeAlarmsCommand subscribe = new SubscribeAlarmsCommand
         {
             SubscriptionExpression = @"\\HOST\Galaxy!Area",
@@ -494,23 +577,24 @@ public sealed class AlarmCommandHandlerTests
 
         Assert.False(oldStandby.Disposed);
         Assert.True(failedReplacement.Disposed);
-        Assert.Equal(11, handler.Acknowledge(Guid.Empty, "", "", "", "", ""));
+        Assert.Equal("11.AckMsg", AckItemOf(handler));
     }
 
     /// <summary>A successful replacement while failed over keeps subtag mode active and delegates to the new standby.</summary>
     [Fact]
     public void UpdateWatchList_WhileSubtagActive_PreservesModeAndUsesReplacement()
     {
-        FakeConsumer primary = new FakeConsumer { ThrowOnSubscribe = true, AcknowledgeReturn = 11 };
-        FakeConsumer oldStandby = new FakeConsumer { AcknowledgeReturn = 22 };
-        FakeConsumer replacement = new FakeConsumer { AcknowledgeReturn = 33 };
+        FakeConsumer primary = new FakeConsumer { ThrowOnSubscribe = true, AckTarget = AlarmAckTarget.For("11.AckMsg") };
+        FakeConsumer oldStandby = new FakeConsumer { AckTarget = AlarmAckTarget.For("22.AckMsg") };
+        FakeConsumer replacement = new FakeConsumer { AckTarget = AlarmAckTarget.For("33.AckMsg") };
         int buildCount = 0;
         AlarmCommandHandler handler = new AlarmCommandHandler(
             new MxAccessEventQueue(),
             () => primary,
             null,
             null,
-            _ => ++buildCount == 1 ? oldStandby : replacement);
+            _ => ++buildCount == 1 ? oldStandby : replacement,
+            () => new RecordingAckWriter());
         SubscribeAlarmsCommand subscribe = new SubscribeAlarmsCommand
         {
             SubscriptionExpression = @"\\HOST\Galaxy!Area",
@@ -523,7 +607,7 @@ public sealed class AlarmCommandHandlerTests
         handler.UpdateWatchList(new[] { NewTarget("Galaxy!Area.Tank02.Alarm") });
 
         Assert.True(oldStandby.Disposed);
-        Assert.Equal(33, handler.Acknowledge(Guid.Empty, "", "", "", "", ""));
+        Assert.Equal("33.AckMsg", AckItemOf(handler));
     }
 
     /// <summary>
@@ -567,6 +651,19 @@ public sealed class AlarmCommandHandlerTests
         Assert.Equal(at, evt.OnAlarmProviderModeChanged.At.ToDateTime());
     }
 
+    private static AlarmCommandHandler NewHandlerWithWriter(Func<IMxAccessAlarmConsumer> consumerFactory, IAlarmAckWriter writer) =>
+        new AlarmCommandHandler(
+            new MxAccessEventQueue(),
+            consumerFactory,
+            threadAffinityCheck: null,
+            comFactory: null,
+            standbyFactory: null,
+            ackWriterFactory: () => writer);
+
+    /// <summary>Acks through the handler and returns the item the active consumer resolved (the fake writer echoes it as the diagnostic).</summary>
+    private static string AckItemOf(AlarmCommandHandler handler) =>
+        handler.Acknowledge(Guid.Empty, string.Empty, new AlarmAckOperator()).Diagnostic;
+
     private static MxAlarmSnapshotRecord NewRecord(string provider, string group, string tag)
     {
         return new MxAlarmSnapshotRecord
@@ -598,12 +695,12 @@ public sealed class AlarmCommandHandlerTests
 
         /// <summary>Gets the last subscription request.</summary>
         public string? LastSubscription { get; private set; }
-        /// <summary>Gets the last acknowledged alarm GUID.</summary>
-        public Guid LastAckGuid { get; private set; }
-        /// <summary>Gets the last acknowledged operator name.</summary>
-        public string? LastAckOperatorName { get; private set; }
-        /// <summary>Gets or sets the return value for acknowledge operations.</summary>
-        public int AcknowledgeReturn { get; set; }
+        /// <summary>Gets or sets the ack target both resolve methods return.</summary>
+        public AlarmAckTarget AckTarget { get; set; } = AlarmAckTarget.For("Fake.Alarm.AckMsg");
+        /// <summary>Gets the GUID from the last ResolveAckTarget call.</summary>
+        public Guid LastResolvedGuid { get; private set; }
+        /// <summary>Gets the (name, provider, group) from the last ResolveAckTargetByName call.</summary>
+        public (string Name, string Provider, string Group)? LastResolvedName { get; private set; }
         /// <summary>Gets or sets the snapshot result to return.</summary>
         public IReadOnlyList<MxAlarmSnapshotRecord> SnapshotResult { get; set; } =
             Array.Empty<MxAlarmSnapshotRecord>();
@@ -623,29 +720,19 @@ public sealed class AlarmCommandHandlerTests
         }
 
         /// <inheritdoc />
-        public int AcknowledgeByGuid(
-            Guid alarmGuid, string ackComment, string ackOperatorName,
-            string ackOperatorNode, string ackOperatorDomain, string ackOperatorFullName)
+        public AlarmAckTarget ResolveAckTarget(Guid alarmGuid)
         {
-            LastAckGuid = alarmGuid;
-            LastAckOperatorName = ackOperatorName;
-            return AcknowledgeReturn;
+            LastResolvedGuid = alarmGuid;
+            return AckTarget;
         }
 
         /// <inheritdoc />
-        public int AcknowledgeByName(
-            string alarmName, string providerName, string groupName,
-            string ackComment, string ackOperatorName, string ackOperatorNode,
-            string ackOperatorDomain, string ackOperatorFullName)
+        public AlarmAckTarget ResolveAckTargetByName(string alarmName, string providerName, string groupName)
         {
-            LastAckByNameTuple = (alarmName, providerName, groupName);
-            LastAckOperatorName = ackOperatorName;
-            return AcknowledgeReturn;
+            LastResolvedName = (alarmName, providerName, groupName);
+            return AckTarget;
         }
 
-        /// <summary>Gets the last acknowledge-by-name parameters.</summary>
-        public (string Name, string Provider, string Group)? LastAckByNameTuple { get; private set; }
-
         /// <summary>Gets or sets the truncation verdict this consumer reports with its snapshot.</summary>
         public bool SnapshotTruncated { get; set; }
 
@@ -671,4 +758,22 @@ public sealed class AlarmCommandHandlerTests
             Disposed = true;
         }
     }
+
+    private sealed class RecordingAckWriter : IAlarmAckWriter
+    {
+        public string? LastItemAddress { get; private set; }
+        public string? LastComment { get; private set; }
+        public AlarmAckOperator? LastOperator { get; private set; }
+        public bool Disposed { get; private set; }
+
+        public AlarmAckResult Acknowledge(string itemAddress, string comment, AlarmAckOperator ackOperator)
+        {
+            LastItemAddress = itemAddress;
+            LastComment = comment;
+            LastOperator = ackOperator;
+            return AlarmAckResult.Create(AlarmAckOutcome.Applied, 0, itemAddress);
+        }
+
+        public void Dispose() => Disposed = true;
+    }
 }

src/ZB.MOM.WW.MxGateway.Worker.Tests/MxAccess/AlarmDispatcherTests.cs

@@ -24,7 +24,7 @@ public sealed class AlarmDispatcherTests
         FakeAlarmConsumer consumer = new FakeAlarmConsumer();
         MxAccessEventQueue queue = new MxAccessEventQueue();
         MxAccessAlarmEventSink sink = new MxAccessAlarmEventSink(queue, new MxAccessEventMapper());
-        using AlarmDispatcher dispatcher = new AlarmDispatcher(consumer, sink, SessionId);
+        using AlarmDispatcher dispatcher = new AlarmDispatcher(consumer, sink, SessionId, new FakeAckWriter());
 
         consumer.RaiseTransition(new MxAlarmTransitionEvent
         {
@@ -56,7 +56,7 @@ public sealed class AlarmDispatcherTests
         FakeAlarmConsumer consumer = new FakeAlarmConsumer();
         MxAccessEventQueue queue = new MxAccessEventQueue();
         MxAccessAlarmEventSink sink = new MxAccessAlarmEventSink(queue, new MxAccessEventMapper());
-        using AlarmDispatcher dispatcher = new AlarmDispatcher(consumer, sink, SessionId);
+        using AlarmDispatcher dispatcher = new AlarmDispatcher(consumer, sink, SessionId, new FakeAckWriter());
 
         DateTime ts = new DateTime(2026, 5, 1, 17, 26, 14, 709, DateTimeKind.Utc);
         consumer.RaiseTransition(new MxAlarmTransitionEvent
@@ -142,7 +142,7 @@ public sealed class AlarmDispatcherTests
         FakeAlarmConsumer consumer = new FakeAlarmConsumer();
         MxAccessEventQueue queue = new MxAccessEventQueue();
         MxAccessAlarmEventSink sink = new MxAccessAlarmEventSink(queue, new MxAccessEventMapper());
-        using AlarmDispatcher dispatcher = new AlarmDispatcher(consumer, sink, SessionId);
+        using AlarmDispatcher dispatcher = new AlarmDispatcher(consumer, sink, SessionId, new FakeAckWriter());
 
         consumer.RaiseTransition(new MxAlarmTransitionEvent
         {
@@ -177,7 +177,7 @@ public sealed class AlarmDispatcherTests
         FakeAlarmConsumer consumer = new FakeAlarmConsumer();
         MxAccessEventQueue queue = new MxAccessEventQueue();
         MxAccessAlarmEventSink sink = new MxAccessAlarmEventSink(queue, new MxAccessEventMapper());
-        using AlarmDispatcher dispatcher = new AlarmDispatcher(consumer, sink, SessionId);
+        using AlarmDispatcher dispatcher = new AlarmDispatcher(consumer, sink, SessionId, new FakeAckWriter());
 
         consumer.RaiseTransition(new MxAlarmTransitionEvent
         {
@@ -205,155 +205,140 @@ public sealed class AlarmDispatcherTests
         using AlarmDispatcher dispatcher = new AlarmDispatcher(
             consumer,
             new MxAccessAlarmEventSink(new MxAccessEventQueue(), new MxAccessEventMapper()),
-            SessionId);
+            SessionId,
+            new FakeAckWriter());
 
         dispatcher.Subscribe(@"\\HOST\Galaxy!Area1");
         Assert.Equal(@"\\HOST\Galaxy!Area1", consumer.LastSubscription);
     }
 
-    /// <summary>Verifies that acknowledge calls are forwarded to the consumer with operator identity.</summary>
+    /// <summary>Verifies the dispatcher resolves the ack item via the consumer then writes it as the operator.</summary>
     [Fact]
-    public void Acknowledge_WhenInvoked_ForwardsToConsumerWithFullOperatorIdentity()
+    public void Acknowledge_ResolvesTargetThenWritesWithOperator()
     {
-        FakeAlarmConsumer consumer = new FakeAlarmConsumer();
-        consumer.AcknowledgeReturn = 0;
+        FakeAlarmConsumer consumer = new FakeAlarmConsumer { AckTarget = AlarmAckTarget.For("T.A.AckMsg") };
+        FakeAckWriter writer = new FakeAckWriter();
         using AlarmDispatcher dispatcher = new AlarmDispatcher(
-            consumer,
-            new MxAccessAlarmEventSink(new MxAccessEventQueue(), new MxAccessEventMapper()),
-            SessionId);
-
+            consumer, new MxAccessAlarmEventSink(new MxAccessEventQueue(), new MxAccessEventMapper()), SessionId, writer);
         Guid guid = Guid.NewGuid();
-        int rc = dispatcher.Acknowledge(
-            guid, "Acked", "alice", "WS01", "CORP", "Alice Smith");
+        AlarmAckOperator op = new AlarmAckOperator { UserName = "alice", Password = "pw" };
 
-        Assert.Equal(0, rc);
-        Assert.Equal(guid, consumer.LastAckGuid);
-        Assert.Equal("Acked", consumer.LastAckComment);
-        Assert.Equal("alice", consumer.LastAckOperatorName);
-        Assert.Equal("WS01", consumer.LastAckOperatorNode);
-        Assert.Equal("CORP", consumer.LastAckOperatorDomain);
-        Assert.Equal("Alice Smith", consumer.LastAckOperatorFullName);
+        AlarmAckResult result = dispatcher.Acknowledge(guid, "checked", op);
+
+        Assert.Equal(AlarmAckOutcome.Applied, result.Outcome);
+        Assert.Equal(guid, consumer.LastResolvedGuid);
+        Assert.Equal("T.A.AckMsg", writer.LastItemAddress);
+        Assert.Equal("checked", writer.LastComment);
+        Assert.Same(op, writer.LastOperator);
     }
 
-    /// <summary>Verifies that a managed ack client takes GUID acks with full operator identity.</summary>
+    /// <summary>Verifies an unresolved target short-circuits to its failure without calling the writer.</summary>
     [Fact]
-    public void Acknowledge_WithManagedAckClient_RoutesGuidAckToManagedClient()
+    public void Acknowledge_WhenTargetNotFound_DoesNotWrite()
     {
-        FakeAlarmConsumer consumer = new FakeAlarmConsumer { AcknowledgeReturn = -1 };
-        FakeManagedAckClient managed = new FakeManagedAckClient { AcknowledgeReturn = 0 };
+        FakeAlarmConsumer consumer = new FakeAlarmConsumer { AckTarget = AlarmAckTarget.NotFound("gone") };
+        FakeAckWriter writer = new FakeAckWriter();
         using AlarmDispatcher dispatcher = new AlarmDispatcher(
-            consumer,
-            new MxAccessAlarmEventSink(new MxAccessEventQueue(), new MxAccessEventMapper()),
-            SessionId,
-            managed);
-        dispatcher.Subscribe(@"\\HOST\Galaxy!Area1");
+            consumer, new MxAccessAlarmEventSink(new MxAccessEventQueue(), new MxAccessEventMapper()), SessionId, writer);
 
-        Guid guid = Guid.NewGuid();
-        int rc = dispatcher.Acknowledge(guid, "Acked", "alice", "WS01", "CORP", "Alice Smith");
+        AlarmAckResult result = dispatcher.Acknowledge(Guid.NewGuid(), "c", new AlarmAckOperator { UserName = "alice" });
 
-        Assert.Equal(0, rc);
-        Assert.Equal(@"\\HOST\Galaxy!Area1", managed.LastSubscription);
-        Assert.Equal(guid, managed.LastAckGuid);
-        Assert.Equal("CORP", managed.LastAckOperatorDomain);
-        Assert.Equal("Alice Smith", managed.LastAckOperatorFullName);
-        Assert.Equal(Guid.Empty, consumer.LastAckGuid);
+        Assert.Equal(AlarmAckOutcome.AlarmNotFound, result.Outcome);
+        Assert.Equal("gone", result.Diagnostic);
+        Assert.Null(writer.LastItemAddress);
     }
 
-    /// <summary>
-    ///     Verifies that a failed managed-client lifecycle neither fails the alarm
-    ///     subscription nor leaves acks routed to the broken client.
-    /// </summary>
+    /// <summary>Verifies acknowledge-by-name resolves with the full tuple and writes the resolved item.</summary>
     [Fact]
-    public void Subscribe_WhenManagedAckClientFails_FallsBackToConsumerAck()
+    public void AcknowledgeByName_ResolvesTupleThenWritesWithOperator()
     {
-        FakeAlarmConsumer consumer = new FakeAlarmConsumer { AcknowledgeReturn = 0 };
-        FakeManagedAckClient managed = new FakeManagedAckClient { ThrowOnSubscribe = true };
+        FakeAlarmConsumer consumer = new FakeAlarmConsumer
+        {
+            AckTarget = AlarmAckTarget.For("TestMachine_001.TestAlarm001.AckMsg"),
+        };
+        FakeAckWriter writer = new FakeAckWriter();
         using AlarmDispatcher dispatcher = new AlarmDispatcher(
-            consumer,
-            new MxAccessAlarmEventSink(new MxAccessEventQueue(), new MxAccessEventMapper()),
-            SessionId,
-            managed);
+            consumer, new MxAccessAlarmEventSink(new MxAccessEventQueue(), new MxAccessEventMapper()), SessionId, writer);
+        AlarmAckOperator op = new AlarmAckOperator { UserName = "alice", Domain = "CORP" };
 
-        dispatcher.Subscribe(@"\\HOST\Galaxy!Area1");
-        Guid guid = Guid.NewGuid();
-        int rc = dispatcher.Acknowledge(guid, "Acked", "alice", "WS01", "CORP", "Alice Smith");
+        AlarmAckResult result = dispatcher.AcknowledgeByName(
+            "TestMachine_001.TestAlarm001", "Galaxy", "TestArea", "ack", op);
 
-        Assert.Equal(@"\\HOST\Galaxy!Area1", consumer.LastSubscription);
-        Assert.True(managed.Disposed);
-        Assert.Equal(0, rc);
-        Assert.Equal(guid, consumer.LastAckGuid);
-        Assert.Equal(Guid.Empty, managed.LastAckGuid);
+        Assert.Equal(AlarmAckOutcome.Applied, result.Outcome);
+        Assert.Equal(("TestMachine_001.TestAlarm001", "Galaxy", "TestArea"), consumer.LastResolvedName);
+        Assert.Equal("TestMachine_001.TestAlarm001.AckMsg", writer.LastItemAddress);
+        Assert.Equal("ack", writer.LastComment);
+        Assert.Same(op, writer.LastOperator);
+    }
+
+    /// <summary>Verifies a NotAckable by-name target short-circuits without calling the writer.</summary>
+    [Fact]
+    public void AcknowledgeByName_WhenNotAckable_DoesNotWrite()
+    {
+        FakeAlarmConsumer consumer = new FakeAlarmConsumer { AckTarget = AlarmAckTarget.NotAckable("intouch") };
+        FakeAckWriter writer = new FakeAckWriter();
+        using AlarmDispatcher dispatcher = new AlarmDispatcher(
+            consumer, new MxAccessAlarmEventSink(new MxAccessEventQueue(), new MxAccessEventMapper()), SessionId, writer);
+
+        AlarmAckResult result = dispatcher.AcknowledgeByName("Tag1", "InTouch", "G", "c", new AlarmAckOperator());
+
+        Assert.Equal(AlarmAckOutcome.NotAckable, result.Outcome);
+        Assert.Null(writer.LastItemAddress);
     }
 
     /// <summary>
     ///     Verifies that while the failover consumer serves the subtag standby,
-    ///     GUID acks (synthetic GUIDs) stay on the consumer, not the managed client.
+    ///     GUID acks resolve through the standby (its synthetic GUIDs).
     /// </summary>
     [Fact]
-    public void Acknowledge_WhenFailoverInSubtagMode_KeepsGuidAckOnConsumer()
+    public void Acknowledge_WhenFailoverInSubtagMode_ResolvesThroughStandby()
     {
         FakeAlarmConsumer primary = new FakeAlarmConsumer { ThrowOnSubscribe = true };
-        FakeAlarmConsumer standby = new FakeAlarmConsumer { AcknowledgeReturn = 0 };
+        FakeAlarmConsumer standby = new FakeAlarmConsumer { AckTarget = AlarmAckTarget.For("Standby.AckMsg") };
         FailoverAlarmConsumer failover = new FailoverAlarmConsumer(
             primary, standby, new FailoverSettings(threshold: 1, probeIntervalSeconds: 0, stableProbes: 3));
-        FakeManagedAckClient managed = new FakeManagedAckClient { AcknowledgeReturn = -1 };
+        FakeAckWriter writer = new FakeAckWriter();
         using AlarmDispatcher dispatcher = new AlarmDispatcher(
             failover,
             new MxAccessAlarmEventSink(new MxAccessEventQueue(), new MxAccessEventMapper()),
             SessionId,
-            managed);
+            writer);
         dispatcher.Subscribe(@"\\HOST\Galaxy!Area1");
         Assert.Equal(AlarmProviderMode.Subtag, failover.Mode);
 
         Guid guid = Guid.NewGuid();
-        int rc = dispatcher.Acknowledge(guid, "Acked", "alice", "WS01", "CORP", "Alice Smith");
+        dispatcher.Acknowledge(guid, "Acked", new AlarmAckOperator { UserName = "alice" });
 
-        Assert.Equal(0, rc);
-        Assert.Equal(guid, standby.LastAckGuid);
-        Assert.Equal(Guid.Empty, managed.LastAckGuid);
+        Assert.Equal(guid, standby.LastResolvedGuid);
+        Assert.Equal(Guid.Empty, primary.LastResolvedGuid);
+        Assert.Equal("Standby.AckMsg", writer.LastItemAddress);
     }
 
-    /// <summary>Verifies that disposing the dispatcher disposes the managed ack client.</summary>
+    /// <summary>Verifies the dispatcher does not dispose the writer: the handler owns it.</summary>
     [Fact]
-    public void Dispose_WithManagedAckClient_DisposesManagedClient()
+    public void Dispose_DoesNotDisposeAckWriter()
     {
-        FakeManagedAckClient managed = new FakeManagedAckClient();
+        FakeAckWriter writer = new FakeAckWriter();
         AlarmDispatcher dispatcher = new AlarmDispatcher(
             new FakeAlarmConsumer(),
             new MxAccessAlarmEventSink(new MxAccessEventQueue(), new MxAccessEventMapper()),
             SessionId,
-            managed);
+            writer);
 
         dispatcher.Dispose();
 
-        Assert.True(managed.Disposed);
+        Assert.False(writer.Disposed);
     }
 
-    /// <summary>Verifies that acknowledge-by-name calls are forwarded to the consumer.</summary>
+    /// <summary>Verifies the constructor rejects a null ack writer.</summary>
     [Fact]
-    public void AcknowledgeByName_WhenInvoked_ForwardsToConsumerWithFullTuple()
+    public void Constructor_NullAckWriter_Throws()
     {
-        FakeAlarmConsumer consumer = new FakeAlarmConsumer { AcknowledgeReturn = 0 };
-        using AlarmDispatcher dispatcher = new AlarmDispatcher(
-            consumer,
+        Assert.Throws<ArgumentNullException>(() => new AlarmDispatcher(
+            new FakeAlarmConsumer(),
             new MxAccessAlarmEventSink(new MxAccessEventQueue(), new MxAccessEventMapper()),
-            SessionId);
-
-        int rc = dispatcher.AcknowledgeByName(
-            alarmName: "TestMachine_001.TestAlarm001",
-            providerName: "Galaxy",
-            groupName: "TestArea",
-            ackComment: "ack",
-            ackOperatorName: "alice",
-            ackOperatorNode: "WS",
-            ackOperatorDomain: "CORP",
-            ackOperatorFullName: "Alice Smith");
-
-        Assert.Equal(0, rc);
-        Assert.NotNull(consumer.LastAckByNameTuple);
-        Assert.Equal("TestMachine_001.TestAlarm001", consumer.LastAckByNameTuple!.Value.Name);
-        Assert.Equal("Galaxy", consumer.LastAckByNameTuple!.Value.Provider);
-        Assert.Equal("TestArea", consumer.LastAckByNameTuple!.Value.Group);
+            SessionId,
+            null!));
     }
 
     /// <summary>Verifies that consumer alarm records are mapped to proto snapshots.</summary>
@@ -391,7 +376,8 @@ public sealed class AlarmDispatcherTests
         using AlarmDispatcher dispatcher = new AlarmDispatcher(
             consumer,
             new MxAccessAlarmEventSink(new MxAccessEventQueue(), new MxAccessEventMapper()),
-            SessionId);
+            SessionId,
+            new FakeAckWriter());
 
         IReadOnlyList<ActiveAlarmSnapshot> snapshots = dispatcher.SnapshotActiveAlarms(out _);
         Assert.Equal(2, snapshots.Count);
@@ -447,7 +433,8 @@ public sealed class AlarmDispatcherTests
         using AlarmDispatcher dispatcher = new AlarmDispatcher(
             consumer,
             new MxAccessAlarmEventSink(new MxAccessEventQueue(), new MxAccessEventMapper()),
-            SessionId);
+            SessionId,
+            new FakeAckWriter());
 
         IReadOnlyList<ActiveAlarmSnapshot> snapshots = dispatcher.SnapshotActiveAlarms(out _);
         Assert.Equal(2, snapshots.Count);
@@ -482,7 +469,8 @@ public sealed class AlarmDispatcherTests
         using AlarmDispatcher dispatcher = new AlarmDispatcher(
             consumer,
             new MxAccessAlarmEventSink(new MxAccessEventQueue(), new MxAccessEventMapper()),
-            SessionId);
+            SessionId,
+            new FakeAckWriter());
 
         IReadOnlyList<ActiveAlarmSnapshot> snapshots = dispatcher.SnapshotActiveAlarms(out bool truncated);
 
@@ -512,7 +500,8 @@ public sealed class AlarmDispatcherTests
         using AlarmDispatcher dispatcher = new AlarmDispatcher(
             consumer,
             new MxAccessAlarmEventSink(new MxAccessEventQueue(), new MxAccessEventMapper()),
-            SessionId);
+            SessionId,
+            new FakeAckWriter());
 
         IReadOnlyList<ActiveAlarmSnapshot> snapshots = dispatcher.SnapshotActiveAlarms(out bool truncated);
 
@@ -542,7 +531,7 @@ public sealed class AlarmDispatcherTests
         FakeAlarmConsumer consumer = new FakeAlarmConsumer();
         MxAccessEventQueue queue = new MxAccessEventQueue();
         MxAccessAlarmEventSink sink = new MxAccessAlarmEventSink(queue, new MxAccessEventMapper());
-        AlarmDispatcher dispatcher = new AlarmDispatcher(consumer, sink, SessionId);
+        AlarmDispatcher dispatcher = new AlarmDispatcher(consumer, sink, SessionId, new FakeAckWriter());
 
         dispatcher.Dispose();
 
@@ -569,20 +558,12 @@ public sealed class AlarmDispatcherTests
 
         /// <summary>Gets the last subscription reference.</summary>
         public string? LastSubscription { get; private set; }
-        /// <summary>Gets the GUID from the last acknowledge call.</summary>
-        public Guid LastAckGuid { get; private set; }
-        /// <summary>Gets the comment from the last acknowledge call.</summary>
-        public string? LastAckComment { get; private set; }
-        /// <summary>Gets the operator name from the last acknowledge call.</summary>
-        public string? LastAckOperatorName { get; private set; }
-        /// <summary>Gets the operator node from the last acknowledge call.</summary>
-        public string? LastAckOperatorNode { get; private set; }
-        /// <summary>Gets the operator domain from the last acknowledge call.</summary>
-        public string? LastAckOperatorDomain { get; private set; }
-        /// <summary>Gets the operator full name from the last acknowledge call.</summary>
-        public string? LastAckOperatorFullName { get; private set; }
-        /// <summary>Gets or sets the return code for acknowledge operations.</summary>
-        public int AcknowledgeReturn { get; set; }
+        /// <summary>Gets or sets the ack target both resolve methods return.</summary>
+        public AlarmAckTarget AckTarget { get; set; } = AlarmAckTarget.For("Fake.Alarm.AckMsg");
+        /// <summary>Gets the GUID from the last ResolveAckTarget call.</summary>
+        public Guid LastResolvedGuid { get; private set; }
+        /// <summary>Gets the (name, provider, group) from the last ResolveAckTargetByName call.</summary>
+        public (string Name, string Provider, string Group)? LastResolvedName { get; private set; }
         /// <summary>Gets or sets the result collection for snapshot operations.</summary>
         public IReadOnlyList<MxAlarmSnapshotRecord> SnapshotResult { get; set; } =
             Array.Empty<MxAlarmSnapshotRecord>();
@@ -607,37 +588,19 @@ public sealed class AlarmDispatcherTests
         }
 
         /// <inheritdoc />
-        public int AcknowledgeByGuid(
-            Guid alarmGuid,
-            string ackComment,
-            string ackOperatorName,
-            string ackOperatorNode,
-            string ackOperatorDomain,
-            string ackOperatorFullName)
+        public AlarmAckTarget ResolveAckTarget(Guid alarmGuid)
         {
-            LastAckGuid = alarmGuid;
-            LastAckComment = ackComment;
-            LastAckOperatorName = ackOperatorName;
-            LastAckOperatorNode = ackOperatorNode;
-            LastAckOperatorDomain = ackOperatorDomain;
-            LastAckOperatorFullName = ackOperatorFullName;
-            return AcknowledgeReturn;
+            LastResolvedGuid = alarmGuid;
+            return AckTarget;
         }
 
         /// <inheritdoc />
-        public int AcknowledgeByName(
-            string alarmName, string providerName, string groupName,
-            string ackComment, string ackOperatorName, string ackOperatorNode,
-            string ackOperatorDomain, string ackOperatorFullName)
+        public AlarmAckTarget ResolveAckTargetByName(string alarmName, string providerName, string groupName)
         {
-            LastAckByNameTuple = (alarmName, providerName, groupName);
-            LastAckOperatorName = ackOperatorName;
-            return AcknowledgeReturn;
+            LastResolvedName = (alarmName, providerName, groupName);
+            return AckTarget;
         }
 
-        /// <summary>Gets the last acknowledge-by-name tuple (alarm name, provider, group).</summary>
-        public (string Name, string Provider, string Group)? LastAckByNameTuple { get; private set; }
-
         /// <summary>Gets or sets the truncation verdict this consumer reports with its snapshot.</summary>
         public bool SnapshotTruncated { get; set; }
 
@@ -664,49 +627,22 @@ public sealed class AlarmDispatcherTests
         }
     }
 
-    private sealed class FakeManagedAckClient : IManagedAlarmAckClient
+    private sealed class FakeAckWriter : IAlarmAckWriter
     {
-        /// <summary>Gets the last subscription expression.</summary>
-        public string? LastSubscription { get; private set; }
-        /// <summary>Gets the GUID from the last acknowledge call.</summary>
-        public Guid LastAckGuid { get; private set; }
-        /// <summary>Gets the operator domain from the last acknowledge call.</summary>
-        public string? LastAckOperatorDomain { get; private set; }
-        /// <summary>Gets the operator full name from the last acknowledge call.</summary>
-        public string? LastAckOperatorFullName { get; private set; }
-        /// <summary>Gets or sets the return code for acknowledge operations.</summary>
-        public int AcknowledgeReturn { get; set; }
-        /// <summary>Gets or sets a value indicating whether <see cref="Subscribe"/> throws.</summary>
-        public bool ThrowOnSubscribe { get; set; }
-        /// <summary>Gets a value indicating whether this instance has been disposed.</summary>
+        public string? LastItemAddress { get; private set; }
+        public string? LastComment { get; private set; }
+        public AlarmAckOperator? LastOperator { get; private set; }
+        public AlarmAckResult Result { get; set; } = AlarmAckResult.Create(AlarmAckOutcome.Applied, 0, string.Empty);
         public bool Disposed { get; private set; }
 
-        /// <inheritdoc />
-        public void Subscribe(string subscription)
+        public AlarmAckResult Acknowledge(string itemAddress, string comment, AlarmAckOperator ackOperator)
         {
-            if (ThrowOnSubscribe) throw new InvalidOperationException("RegisterConsumer returned 5.");
-            LastSubscription = subscription;
+            LastItemAddress = itemAddress;
+            LastComment = comment;
+            LastOperator = ackOperator;
+            return Result;
         }
 
-        /// <inheritdoc />
-        public int AcknowledgeByGuid(
-            Guid alarmGuid,
-            string comment,
-            string operatorName,
-            string operatorNode,
-            string operatorDomain,
-            string operatorFullName)
-        {
-            LastAckGuid = alarmGuid;
-            LastAckOperatorDomain = operatorDomain;
-            LastAckOperatorFullName = operatorFullName;
-            return AcknowledgeReturn;
-        }
-
-        /// <inheritdoc />
-        public void Dispose()
-        {
-            Disposed = true;
-        }
+        public void Dispose() => Disposed = true;
     }
 }

src/ZB.MOM.WW.MxGateway.Worker.Tests/MxAccess/FailoverAlarmConsumerTests.cs

@@ -72,10 +72,10 @@ public sealed class FailoverAlarmConsumerTests
         }
 
         /// <inheritdoc />
-        public int AcknowledgeByGuid(Guid g, string c, string a, string b, string d, string e) => 11;
+        public AlarmAckTarget ResolveAckTarget(Guid g) => AlarmAckTarget.For("primary.guid.AckMsg");
 
         /// <inheritdoc />
-        public int AcknowledgeByName(string n, string p, string gr, string c, string a, string b, string d, string e) => 11;
+        public AlarmAckTarget ResolveAckTargetByName(string n, string p, string gr) => AlarmAckTarget.For("primary.name.AckMsg");
 
         /// <inheritdoc />
         public IReadOnlyList<MxAlarmSnapshotRecord> SnapshotActiveAlarms(out bool truncated)
@@ -122,10 +122,10 @@ public sealed class FailoverAlarmConsumerTests
         public void PollOnce() { }
 
         /// <inheritdoc />
-        public int AcknowledgeByGuid(Guid g, string c, string a, string b, string d, string e) => 22;
+        public AlarmAckTarget ResolveAckTarget(Guid g) => AlarmAckTarget.For("standby.guid.AckMsg");
 
         /// <inheritdoc />
-        public int AcknowledgeByName(string n, string p, string gr, string c, string a, string b, string d, string e) => 22;
+        public AlarmAckTarget ResolveAckTargetByName(string n, string p, string gr) => AlarmAckTarget.For("standby.name.AckMsg");
 
         /// <inheritdoc />
         public IReadOnlyList<MxAlarmSnapshotRecord> SnapshotActiveAlarms(out bool truncated)
@@ -305,9 +305,9 @@ public sealed class FailoverAlarmConsumerTests
         Assert.Equal(subscribeCountAfterSetup, primary.SubscribeCount);
     }
 
-    /// <summary>Proves that acknowledgment calls delegate to whichever child (primary or standby) is currently active.</summary>
+    /// <summary>Proves that ack-target resolution delegates to whichever child (primary or standby) is currently active.</summary>
     [Fact]
-    public void Acknowledge_DelegatesToActiveChild()
+    public void ResolveAckTarget_DelegatesToActiveChild()
     {
         FlakyPrimary primary = new FlakyPrimary { ThrowOnPoll = false };
         StubStandby standby = new StubStandby();
@@ -316,18 +316,18 @@ public sealed class FailoverAlarmConsumerTests
 
         sut.Subscribe(@"\\HOST\Galaxy!Area");
 
-        // Active = Primary → primary's sentinel value (11).
-        Assert.Equal(11, sut.AcknowledgeByGuid(Guid.NewGuid(), "c", "n", "node", "dom", "full"));
-        Assert.Equal(11, sut.AcknowledgeByName("a", "p", "g", "c", "n", "node", "dom", "full"));
+        // Active = Primary → primary's sentinel targets.
+        Assert.Equal("primary.guid.AckMsg", sut.ResolveAckTarget(Guid.NewGuid()).ItemAddress);
+        Assert.Equal("primary.name.AckMsg", sut.ResolveAckTargetByName("a", "p", "g").ItemAddress);
 
         // Force a failover by failing the primary past threshold.
         primary.ThrowOnPoll = true;
         sut.PollOnce(); // threshold=1 → switch to Standby
         Assert.Equal(AlarmProviderMode.Subtag, sut.Mode);
 
-        // Active = Standby → standby's sentinel value (22).
-        Assert.Equal(22, sut.AcknowledgeByGuid(Guid.NewGuid(), "c", "n", "node", "dom", "full"));
-        Assert.Equal(22, sut.AcknowledgeByName("a", "p", "g", "c", "n", "node", "dom", "full"));
+        // Active = Standby → standby's sentinel targets.
+        Assert.Equal("standby.guid.AckMsg", sut.ResolveAckTarget(Guid.NewGuid()).ItemAddress);
+        Assert.Equal("standby.name.AckMsg", sut.ResolveAckTargetByName("a", "p", "g").ItemAddress);
     }
 
     /// <summary>

src/ZB.MOM.WW.MxGateway.Worker.Tests/MxAccess/LmxSubtagAlarmSourceTests.cs

@@ -94,76 +94,28 @@ public sealed class LmxSubtagAlarmSourceTests
     }
 
     /// <summary>
-    ///     Verifies <see cref="LmxSubtagAlarmSource.Write"/> adds the item when
-    ///     it was not previously advised and writes with user id 0.
+    ///     Verifies <see cref="LmxSubtagAlarmSource.Dispose"/> UnAdvises and
+    ///     removes every advised handle and unregisters the server exactly once.
     /// </summary>
     [Fact]
-    public void Write_AddsItemWhenUnknownAndWrites()
-    {
-        var server = new RecordingMxAccessServer();
-        using var source = new LmxSubtagAlarmSource(server, FakeServerHandle);
-
-        source.Write("Tank1.Alarm.AckComment", "acknowledged");
-
-        Assert.Contains("Tank1.Alarm.AckComment", server.AddedItems);
-        Assert.Single(server.Writes);
-        RecordingMxAccessServer.WriteRecord write = server.Writes[0];
-        Assert.Equal(FakeServerHandle, write.ServerHandle);
-        Assert.Equal("acknowledged", write.Value);
-        Assert.Equal(0, write.UserId);
-    }
-
-    /// <summary>
-    ///     Verifies <see cref="LmxSubtagAlarmSource.Write"/> reuses an existing
-    ///     item handle (no duplicate AddItem) when the address was already
-    ///     advised.
-    /// </summary>
-    [Fact]
-    public void Write_ReusesHandleForAdvisedAddress()
-    {
-        var server = new RecordingMxAccessServer();
-        using var source = new LmxSubtagAlarmSource(server, FakeServerHandle);
-
-        source.Advise(new[] { "Tank1.Alarm.Subtag" });
-        int adviseAddCount = server.AddedItems.Count;
-
-        source.Write("Tank1.Alarm.Subtag", true);
-
-        // No second AddItem for the already-advised address.
-        Assert.Equal(adviseAddCount, server.AddedItems.Count);
-        Assert.Single(server.Writes);
-    }
-
-    /// <summary>
-    ///     Verifies <see cref="LmxSubtagAlarmSource.Dispose"/> UnAdvises only the
-    ///     handles that were actually advised — a write-only item (added by
-    ///     <see cref="LmxSubtagAlarmSource.Write"/> but never advised) is removed
-    ///     but not unadvised — and unregisters the server exactly once.
-    /// </summary>
-    [Fact]
-    public void Dispose_UnAdvisesOnlyAdvisedHandles_RemovesAll_AndUnregistersOnce()
+    public void Dispose_UnAdvisesAndRemovesAdvisedHandles_AndUnregistersOnce()
     {
         var server = new RecordingMxAccessServer();
         var source = new LmxSubtagAlarmSource(server, FakeServerHandle);
 
         source.Advise(new[] { "Tank1.Alarm.Subtag", "Tank2.Alarm.Subtag" });
-        // A write-only subtag: added by Write, never advised.
-        source.Write("Tank1.Alarm.AckComment", "acknowledged");
 
         int advised1 = server.LastItemHandleFor("Tank1.Alarm.Subtag");
         int advised2 = server.LastItemHandleFor("Tank2.Alarm.Subtag");
-        int writeOnly = server.LastItemHandleFor("Tank1.Alarm.AckComment");
 
         source.Dispose();
 
-        // Only the two advised handles are unadvised — never the write-only one.
         Assert.Equal(new[] { advised1, advised2 }, server.UnAdvisedItemHandles);
-        Assert.DoesNotContain(writeOnly, server.UnAdvisedItemHandles);
-        // Every added item (advised + write-only) is removed.
         Assert.Equal(
-            new[] { advised1, advised2, writeOnly }.OrderBy(h => h),
+            new[] { advised1, advised2 }.OrderBy(h => h),
             server.RemovedItemHandles.OrderBy(h => h));
         Assert.Equal(1, server.UnregisterCount);
+        Assert.Empty(server.Writes);
     }
 
     /// <summary>

src/ZB.MOM.WW.MxGateway.Worker.Tests/MxAccess/MxAccessStaSessionTests.cs

@@ -663,15 +663,13 @@ public sealed class MxAccessStaSessionTests
         }
 
         /// <inheritdoc />
-        public int Acknowledge(Guid alarmGuid, string comment, string operatorUser,
-            string operatorNode, string operatorDomain, string operatorFullName)
-            => 0;
+        public AlarmAckResult Acknowledge(Guid alarmGuid, string comment, AlarmAckOperator ackOperator)
+            => AlarmAckResult.Create(AlarmAckOutcome.Applied, 0, string.Empty);
 
         /// <inheritdoc />
-        public int AcknowledgeByName(string alarmName, string providerName, string groupName,
-            string comment, string operatorUser, string operatorNode,
-            string operatorDomain, string operatorFullName)
-            => 0;
+        public AlarmAckResult AcknowledgeByName(string alarmName, string providerName, string groupName,
+            string comment, AlarmAckOperator ackOperator)
+            => AlarmAckResult.Create(AlarmAckOutcome.Applied, 0, string.Empty);
 
         /// <inheritdoc />
         public IReadOnlyList<ActiveAlarmSnapshot> QueryActive(

src/ZB.MOM.WW.MxGateway.Worker.Tests/MxAccess/SubtagAlarmConsumerTests.cs

@@ -9,7 +9,7 @@ namespace ZB.MOM.WW.MxGateway.Worker.Tests.MxAccess;
 /// <summary>
 ///     Unit tests for <see cref="SubtagAlarmConsumer"/>: prove that the subtag
 ///     fallback advises the observable subtags, synthesizes degraded
-///     transitions with stable synthetic GUIDs, routes acknowledgments to the
+///     transitions with stable synthetic GUIDs, resolves acknowledgments to the
 ///     ack-comment subtag, and stamps snapshots. A <see cref="FakeSource"/>
 ///     stands in for the live MXAccess subtag source so this needs no AVEVA
 ///     install.
@@ -40,9 +40,13 @@ public sealed class SubtagAlarmConsumerTests
         return new SubtagAlarmConsumer(source, new[] { BuildTarget() });
     }
 
-    /// <summary>Verifies Subscribe advises the active, acked, priority, and ack-comment subtags (the ack-comment is advised so it is an active, writable MXAccess item).</summary>
+    /// <summary>
+    ///     Verifies Subscribe advises the observable active, acked and priority
+    ///     subtags but not the ack-comment subtag: the ack is written by
+    ///     <see cref="AlarmAckWriter"/>, which adds and advises it on its own server.
+    /// </summary>
     [Fact]
-    public void Subscribe_AdvisesAllSubtagsIncludingAckComment()
+    public void Subscribe_AdvisesObservableSubtagsButNotAckComment()
     {
         FakeSource source = new FakeSource();
         using SubtagAlarmConsumer consumer = BuildConsumer(source);
@@ -52,7 +56,7 @@ public sealed class SubtagAlarmConsumerTests
         Assert.Contains(ActiveSubtag, source.Advised);
         Assert.Contains(AckedSubtag, source.Advised);
         Assert.Contains(PrioritySubtag, source.Advised);
-        Assert.Contains(AckCommentSubtag, source.Advised);
+        Assert.DoesNotContain(AckCommentSubtag, source.Advised);
     }
 
     /// <summary>Verifies an active=true value change raises a degraded, GUID-stamped UNACK_ALM transition.</summary>
@@ -74,50 +78,49 @@ public sealed class SubtagAlarmConsumerTests
         Assert.NotEqual(Guid.Empty, emitted.Record.AlarmGuid);
     }
 
-    /// <summary>Verifies AcknowledgeByName writes the comment to the ack-comment subtag and returns success.</summary>
+    /// <summary>Verifies ResolveAckTargetByName resolves to the target's ack-comment subtag.</summary>
     [Fact]
-    public void AcknowledgeByName_WritesCommentToAckCommentSubtag()
+    public void ResolveAckTargetByName_ReturnsAckCommentSubtag()
     {
         FakeSource source = new FakeSource();
         using SubtagAlarmConsumer consumer = BuildConsumer(source);
         consumer.Subscribe(@"\\HOST\Galaxy!TestArea");
 
-        int rc = consumer.AcknowledgeByName(
-            alarmName: "Tank01.Level.HiHi",
-            providerName: "Galaxy",
-            groupName: "TestArea",
-            ackComment: "operator ack",
-            ackOperatorName: "alice",
-            ackOperatorNode: "WS01",
-            ackOperatorDomain: "CORP",
-            ackOperatorFullName: "Alice Smith");
+        AlarmAckTarget target = consumer.ResolveAckTargetByName("Tank01.Level.HiHi", "Galaxy", "TestArea");
 
-        Assert.Equal(0, rc);
-        Assert.NotNull(source.LastWrite);
-        Assert.Equal(AckCommentSubtag, source.LastWrite!.Value.Address);
-        Assert.Equal("operator ack", source.LastWrite!.Value.Value);
+        Assert.True(target.Found);
+        Assert.Equal(AckCommentSubtag, target.ItemAddress);
     }
 
-    /// <summary>Verifies AcknowledgeByName returns non-zero when no target matches the supplied name.</summary>
+    /// <summary>Verifies ResolveAckTargetByName reports AlarmNotFound when no target matches the supplied name.</summary>
     [Fact]
-    public void AcknowledgeByName_UnknownAlarm_ReturnsNonZero()
+    public void ResolveAckTargetByName_UnknownAlarm_IsNotFound()
     {
         FakeSource source = new FakeSource();
         using SubtagAlarmConsumer consumer = BuildConsumer(source);
         consumer.Subscribe(@"\\HOST\Galaxy!TestArea");
 
-        int rc = consumer.AcknowledgeByName(
-            alarmName: "DoesNotExist.NoSuchAlarm",
-            providerName: "Galaxy",
-            groupName: "TestArea",
-            ackComment: "operator ack",
-            ackOperatorName: "alice",
-            ackOperatorNode: "WS01",
-            ackOperatorDomain: "CORP",
-            ackOperatorFullName: "Alice Smith");
+        AlarmAckTarget target = consumer.ResolveAckTargetByName("DoesNotExist.NoSuchAlarm", "Galaxy", "TestArea");
 
-        Assert.NotEqual(0, rc);
-        Assert.Null(source.LastWrite);
+        Assert.False(target.Found);
+        Assert.Equal(AlarmAckOutcome.AlarmNotFound, target.Failure);
+    }
+
+    /// <summary>Verifies a target with no ack-comment subtag resolves as NotAckable, by name and by GUID.</summary>
+    [Fact]
+    public void ResolveAckTarget_EmptyAckCommentSubtag_IsNotAckable()
+    {
+        AlarmSubtagTarget noAck = BuildTarget();
+        noAck.AckCommentSubtag = string.Empty;
+        FakeSource source = new FakeSource();
+        using SubtagAlarmConsumer consumer = new SubtagAlarmConsumer(source, new[] { noAck });
+
+        Assert.Equal(
+            AlarmAckOutcome.NotAckable,
+            consumer.ResolveAckTargetByName("Tank01.Level.HiHi", "Galaxy", "TestArea").Failure);
+        Assert.Equal(
+            AlarmAckOutcome.NotAckable,
+            consumer.ResolveAckTarget(SyntheticAlarmGuid.ForReference(Reference)).Failure);
     }
 
     /// <summary>Verifies a snapshot of an active alarm stamps Degraded and a non-empty synthetic GUID.</summary>
@@ -160,11 +163,11 @@ public sealed class SubtagAlarmConsumerTests
 
     /// <summary>
     ///     Verifies that when two alarm targets share a prefix (e.g. Level.Hi vs Level.HiHi),
-    ///     AcknowledgeByName routes each ack to its own ack-comment subtag and never
+    ///     ResolveAckTargetByName resolves each to its own ack-comment subtag and never
     ///     conflates the shorter name with the longer one.
     /// </summary>
     [Fact]
-    public void AcknowledgeByName_PrefixNameDoesNotFalseMatch()
+    public void ResolveAckTargetByName_PrefixNameDoesNotFalseMatch()
     {
         const string ReferenceHi = "Galaxy!Area.Tank01.Level.Hi";
         const string ReferenceHiHi = "Galaxy!Area.Tank01.Level.HiHi";
@@ -195,42 +198,19 @@ public sealed class SubtagAlarmConsumerTests
             source, new[] { targetHi, targetHiHi });
         consumer.Subscribe(@"\\HOST\Galaxy!Area");
 
-        // Ack the shorter name — must write to the shorter target's subtag only.
-        int rcHi = consumer.AcknowledgeByName(
-            alarmName: "Tank01.Level.Hi",
-            providerName: "Galaxy",
-            groupName: "Area",
-            ackComment: "ack hi",
-            ackOperatorName: "op", ackOperatorNode: "WS01",
-            ackOperatorDomain: "CORP", ackOperatorFullName: "Operator");
-
-        Assert.Equal(0, rcHi);
-        Assert.NotNull(source.LastWrite);
-        Assert.Equal(AckCommentHi, source.LastWrite!.Value.Address);
-        Assert.Equal("ack hi", source.LastWrite.Value.Value);
-
-        // Ack the longer name — must write to the longer target's subtag.
-        int rcHiHi = consumer.AcknowledgeByName(
-            alarmName: "Tank01.Level.HiHi",
-            providerName: "Galaxy",
-            groupName: "Area",
-            ackComment: "ack hihi",
-            ackOperatorName: "op", ackOperatorNode: "WS01",
-            ackOperatorDomain: "CORP", ackOperatorFullName: "Operator");
-
-        Assert.Equal(0, rcHiHi);
-        Assert.NotNull(source.LastWrite);
-        Assert.Equal(AckCommentHiHi, source.LastWrite!.Value.Address);
-        Assert.Equal("ack hihi", source.LastWrite.Value.Value);
+        Assert.Equal(AckCommentHi, consumer.ResolveAckTargetByName("Tank01.Level.Hi", "Galaxy", "Area").ItemAddress);
+        Assert.Equal(AckCommentHiHi, consumer.ResolveAckTargetByName("Tank01.Level.HiHi", "Galaxy", "Area").ItemAddress);
+        Assert.Equal(
+            AlarmAckOutcome.AlarmNotFound,
+            consumer.ResolveAckTargetByName("Tank01.Level.H", "Galaxy", "Area").Failure);
     }
 
     /// <summary>
-    ///     Verifies AcknowledgeByGuid resolves the synthetic GUID (computed from
-    ///     the alarm's full reference) to the correct target and writes the comment
-    ///     to that target's ack-comment subtag.
+    ///     Verifies ResolveAckTarget resolves the synthetic GUID (computed from
+    ///     the alarm's full reference) to that target's ack-comment subtag.
     /// </summary>
     [Fact]
-    public void AcknowledgeByGuid_WritesCommentToAckCommentSubtag()
+    public void ResolveAckTarget_SyntheticGuid_ReturnsAckCommentSubtag()
     {
         FakeSource source = new FakeSource();
         using SubtagAlarmConsumer consumer = BuildConsumer(source);
@@ -246,41 +226,21 @@ public sealed class SubtagAlarmConsumerTests
         Guid syntheticGuid = emitted!.Record.AlarmGuid;
         Assert.NotEqual(Guid.Empty, syntheticGuid);
 
-        int rc = consumer.AcknowledgeByGuid(
-            alarmGuid: syntheticGuid,
-            ackComment: "guid ack",
-            ackOperatorName: "op",
-            ackOperatorNode: "WS01",
-            ackOperatorDomain: "CORP",
-            ackOperatorFullName: "Operator");
+        AlarmAckTarget target = consumer.ResolveAckTarget(syntheticGuid);
 
-        Assert.Equal(0, rc);
-        Assert.NotNull(source.LastWrite);
-        Assert.Equal(AckCommentSubtag, source.LastWrite!.Value.Address);
-        Assert.Equal("guid ack", source.LastWrite.Value.Value);
+        Assert.True(target.Found);
+        Assert.Equal(AckCommentSubtag, target.ItemAddress);
     }
 
-    /// <summary>
-    ///     Verifies AcknowledgeByGuid returns non-zero and performs no write when
-    ///     the supplied GUID is not known to the consumer.
-    /// </summary>
+    /// <summary>Verifies ResolveAckTarget reports AlarmNotFound for a GUID unknown to the consumer.</summary>
     [Fact]
-    public void AcknowledgeByGuid_UnknownGuid_ReturnsNonZero()
+    public void ResolveAckTarget_UnknownGuid_IsNotFound()
     {
         FakeSource source = new FakeSource();
         using SubtagAlarmConsumer consumer = BuildConsumer(source);
         consumer.Subscribe(@"\\HOST\Galaxy!TestArea");
 
-        int rc = consumer.AcknowledgeByGuid(
-            alarmGuid: Guid.NewGuid(),
-            ackComment: "should not write",
-            ackOperatorName: "op",
-            ackOperatorNode: "WS01",
-            ackOperatorDomain: "CORP",
-            ackOperatorFullName: "Operator");
-
-        Assert.NotEqual(0, rc);
-        Assert.Null(source.LastWrite);
+        Assert.Equal(AlarmAckOutcome.AlarmNotFound, consumer.ResolveAckTarget(Guid.NewGuid()).Failure);
     }
 
     private sealed class FakeSource : ISubtagAlarmSource
@@ -291,21 +251,12 @@ public sealed class SubtagAlarmConsumerTests
         /// <summary>Gets the subtag addresses passed to <see cref="Advise"/>.</summary>
         public List<string> Advised { get; } = new List<string>();
 
-        /// <summary>Gets the most recent (address, value) pair passed to <see cref="Write"/>.</summary>
-        public (string Address, object? Value)? LastWrite { get; private set; }
-
         /// <inheritdoc />
         public void Advise(IReadOnlyCollection<string> itemAddresses)
         {
             Advised.AddRange(itemAddresses);
         }
 
-        /// <inheritdoc />
-        public void Write(string itemAddress, object? value)
-        {
-            LastWrite = (itemAddress, value);
-        }
-
         /// <summary>Raises a <see cref="SubtagValueChange"/> for the given subtag.</summary>
         /// <param name="address">The subtag address whose value changed.</param>
         /// <param name="value">The new value.</param>

src/ZB.MOM.WW.MxGateway.Worker.Tests/MxAccess/WnWrapAlarmConsumerXmlTests.cs

@@ -824,4 +824,58 @@ public sealed class WnWrapAlarmConsumerXmlTests
         Assert.Equal("mgack-authwrite 180714", record.AckComment);
         Assert.Equal("Test alarm #1", record.AlarmComment);
     }
+
+    /// <summary>A Galaxy-provider record resolves to its <c>&lt;tag&gt;.AckMsg</c> item; an unknown GUID is not found.</summary>
+    [Fact]
+    public void ResolveAckTarget_GalaxyRecord_ReturnsAckMsgItem()
+    {
+        Guid guid = Guid.NewGuid();
+        using WnWrapAlarmConsumer consumer = CreateConsumerWithSnapshot(new MxAlarmSnapshotRecord
+        {
+            AlarmGuid = guid, ProviderName = "Galaxy", Group = "TestArea", TagName = "TestMachine_001.TestAlarm001", State = MxAlarmStateKind.UnackAlm,
+        });
+
+        AlarmAckTarget target = consumer.ResolveAckTarget(guid);
+
+        Assert.True(target.Found);
+        Assert.Equal("TestMachine_001.TestAlarm001.AckMsg", target.ItemAddress);
+        Assert.Equal(AlarmAckOutcome.AlarmNotFound, consumer.ResolveAckTarget(Guid.NewGuid()).Failure);
+    }
+
+    /// <summary>A non-Galaxy provider has no MXAccess ack attribute, so it is not ackable.</summary>
+    [Fact]
+    public void ResolveAckTarget_NonGalaxyProvider_IsNotAckable()
+    {
+        Guid guid = Guid.NewGuid();
+        using WnWrapAlarmConsumer consumer = CreateConsumerWithSnapshot(new MxAlarmSnapshotRecord
+        {
+            AlarmGuid = guid, ProviderName = "InTouch", Group = "G", TagName = "Tag1", State = MxAlarmStateKind.UnackAlm,
+        });
+
+        Assert.Equal(AlarmAckOutcome.NotAckable, consumer.ResolveAckTarget(guid).Failure);
+    }
+
+    /// <summary>By-name resolution needs no snapshot: a Galaxy name maps straight to its AckMsg item.</summary>
+    [Fact]
+    public void ResolveAckTargetByName_Galaxy_ReturnsAckMsgItem()
+    {
+        using WnWrapAlarmConsumer consumer = CreateConsumerWithSnapshot();
+
+        Assert.Equal("TestMachine_001.TestAlarm001.AckMsg",
+            consumer.ResolveAckTargetByName("TestMachine_001.TestAlarm001", "Galaxy", "TestArea").ItemAddress);
+        Assert.Equal(AlarmAckOutcome.NotAckable, consumer.ResolveAckTargetByName("Tag1", "InTouch", "G").Failure);
+    }
+
+    private static WnWrapAlarmConsumer CreateConsumerWithSnapshot(params MxAlarmSnapshotRecord[] records)
+    {
+        WnWrapAlarmConsumer consumer = new WnWrapAlarmConsumer(1024);
+        Dictionary<Guid, MxAlarmSnapshotRecord> next = new Dictionary<Guid, MxAlarmSnapshotRecord>();
+        foreach (MxAlarmSnapshotRecord record in records)
+        {
+            next[record.AlarmGuid] = record;
+        }
+
+        consumer.FoldFetch(next, truncated: false, out _);
+        return consumer;
+    }
 }

src/ZB.MOM.WW.MxGateway.Worker.Tests/Probes/AlarmManagedGuidAckLiveSmokeTests.cs

@@ -1,229 +0,0 @@
-using System;
-using System.Collections.Concurrent;
-using System.Diagnostics;
-using System.Linq;
-using System.Threading;
-using ZB.MOM.WW.MxGateway.Contracts.Proto;
-using ZB.MOM.WW.MxGateway.Worker.MxAccess;
-using Xunit;
-using Xunit.Abstractions;
-
-namespace ZB.MOM.WW.MxGateway.Worker.Tests.Probes;
-
-/// <summary>
-///     Live dev-rig smoke test for the MANAGED GUID-ack path — the
-///     <see cref="AaManagedAlarmAckConsumer"/> wired into
-///     <see cref="AlarmDispatcher"/>. Where <c>AlarmsLiveSmokeTests</c> acks by
-///     name through the wnwrap COM consumer, this acks by GUID through AVEVA's
-///     modern <c>aaAlarmManagedClient.AlarmClient.AlarmAckByGUID</c> — the path
-///     that carries operator domain + full name and is not <c>E_NOTIMPL</c>.
-///
-///     Flow: subscribe a wnwrap reader + a managed ack client to
-///     <c>\\&lt;machine&gt;\Galaxy!DEV</c>; wait for a Raise; pull a real
-///     (non-degraded) alarm GUID from the reader's snapshot; ack it by GUID via
-///     the dispatcher (which routes to the managed client); then assert the ack
-///     registers as a subsequent <see cref="AlarmTransitionKind.Acknowledge"/>
-///     transition (and that the active snapshot shows the alarm acked).
-///
-///     This is the runtime confirmation the static work could not close: that an
-///     authenticated GUID ack actually flips state. rc=0 alone is "accepted",
-///     not "applied" — the Acknowledge transition is the real assertion. For a
-///     SECURED alarm the ack must run under an operator with Operate permission;
-///     run the dev-rig flip script and, if the test UDA is secured, an
-///     authenticated operator session (see docs/AlarmProbeFindings.md).
-///
-///     Skip-gated; flip <c>Skip=null</c> on the dev rig with AVEVA +
-///     aaAlarmManagedClient.dll present and the flip script running.
-/// </summary>
-public sealed class AlarmManagedGuidAckLiveSmokeTests
-{
-    private static readonly string SubscriptionExpression =
-        $@"\\{Environment.MachineName}\Galaxy!DEV";
-    private static readonly TimeSpan TransitionWaitTimeout = TimeSpan.FromSeconds(20);
-    private static readonly TimeSpan RaiseWait = TimeSpan.FromSeconds(30);
-    private static readonly TimeSpan AckConfirmWait = TimeSpan.FromSeconds(30);
-
-    private const string SessionId = "alarms-managed-guid-ack-smoke";
-
-    private readonly ITestOutputHelper output;
-    private readonly Stopwatch elapsed = Stopwatch.StartNew();
-    private readonly ConcurrentQueue<string> log = new ConcurrentQueue<string>();
-
-    /// <summary>Initializes a new instance of the AlarmManagedGuidAckLiveSmokeTests class.</summary>
-    /// <param name="output">Test output helper for logging.</param>
-    public AlarmManagedGuidAckLiveSmokeTests(ITestOutputHelper output)
-    {
-        this.output = output;
-    }
-
-    /// <summary>Acks a live alarm by GUID through the managed client and verifies the acked transition.</summary>
-    [Fact(Skip = "Live dev-rig smoke test — flip Skip=null with AVEVA + aaAlarmManagedClient.dll + the alarm flip script, and an operator authorized to ack.")]
-    public void ManagedGuidAck_AcksActiveAlarm_RegistersAcknowledge()
-    {
-        Exception? threadException = null;
-        var done = new ManualResetEventSlim(false);
-        var thread = new Thread(() =>
-        {
-            try { RunSmoke(); }
-            catch (Exception ex) { threadException = ex; }
-            finally { done.Set(); }
-        });
-        thread.IsBackground = false;
-        thread.SetApartmentState(ApartmentState.STA);
-        thread.Start();
-        done.Wait();
-        thread.Join();
-
-        output.WriteLine($"Captured {log.Count} log line(s):");
-        while (log.TryDequeue(out string? line)) output.WriteLine(line);
-
-        if (threadException != null) throw threadException;
-    }
-
-    private void RunSmoke()
-    {
-        Log($"Subscription expression: {SubscriptionExpression}");
-
-        MxAccessEventQueue queue = new MxAccessEventQueue();
-        WnWrapAlarmConsumer consumer = new WnWrapAlarmConsumer(
-            new WNWRAPCONSUMERLib.wwAlarmConsumerClass(),
-            maxAlarmsPerFetch: 1024);
-        MxAccessAlarmEventSink sink = new MxAccessAlarmEventSink(queue, new MxAccessEventMapper());
-
-        // Construct the managed ack client directly (production selects it via
-        // AaManagedAlarmAckConsumer.EnvGatedFactory when MXGATEWAY_USE_MANAGED_ALARM_ACK=1).
-        using IManagedAlarmAckClient managedAck =
-            new AaManagedAlarmAckConsumer(SessionId + ".ack");
-        using AlarmDispatcher dispatcher =
-            new AlarmDispatcher(consumer, sink, SessionId, managedAck);
-
-        Log("Constructed reader + managed ack client + dispatcher.");
-        dispatcher.Subscribe(SubscriptionExpression);
-        Log("Subscribe (reader + managed ack) -> ok. Driving PollOnce from this STA...");
-
-        // 1. Wait for a Raise so there is an active, unacked alarm to ack.
-        OnAlarmTransitionEvent? raiseBody = null;
-        DateTime raiseDeadline = DateTime.UtcNow + RaiseWait;
-        while (DateTime.UtcNow < raiseDeadline && raiseBody is null)
-        {
-            WorkerEvent? evt = WaitForTransition(queue, TransitionWaitTimeout, "raise", consumer);
-            if (evt is null) break;
-            OnAlarmTransitionEvent body = evt.Event.OnAlarmTransition;
-            Log("Transition: " + DescribeTransition(body));
-            Assert.Equal(SessionId, evt.Event.SessionId);
-            if (body.TransitionKind == AlarmTransitionKind.Raise) raiseBody = body;
-        }
-        Assert.NotNull(raiseBody);
-
-        // 2. Pull a REAL alarm GUID from the reader's snapshot (alarmmgr mode).
-        //    Skip degraded/subtag records — their GUID is synthetic and not
-        //    valid for AlarmAckByGUID.
-        var records = consumer.SnapshotActiveAlarms(out _);
-        Log($"Snapshot records: {records.Count}");
-        foreach (var r in records)
-            Log($"  rec guid={r.AlarmGuid} state={r.State} degraded={r.Degraded} ref={r.ProviderName}!{r.Group}.{r.TagName}");
-
-        MxAlarmSnapshotRecord? target = records.FirstOrDefault(r =>
-            !r.Degraded &&
-            r.AlarmGuid != Guid.Empty &&
-            r.State == MxAlarmStateKind.UnackAlm);
-        Assert.NotNull(target);
-        Log($"Ack target GUID={target!.AlarmGuid} ref={target.ProviderName}!{target.Group}.{target.TagName}");
-
-        // 3. Ack by GUID through the dispatcher -> managed AlarmAckByGUID, with
-        //    the current Windows identity (domain + full name are carried
-        //    natively on this path, unlike the wnwrap 6-arg AckByName).
-        string user = Environment.UserName;
-        string node = Environment.MachineName;
-        string domain = Environment.UserDomainName ?? string.Empty;
-        Log($"Ack identity user='{user}' node='{node}' domain='{domain}'");
-
-        int rc = dispatcher.Acknowledge(
-            alarmGuid: target.AlarmGuid,
-            ackComment: "managed-guid-ack smoke",
-            ackOperatorName: user,
-            ackOperatorNode: node,
-            ackOperatorDomain: domain,
-            ackOperatorFullName: user);
-        Log($"dispatcher.Acknowledge(managed GUID) -> rc={rc}");
-        Assert.Equal(0, rc);
-
-        // 4. The ack must APPLY, not merely be accepted: wait for an
-        //    Acknowledge transition on the same alarm, or the snapshot showing
-        //    it acked. rc=0 with neither is the inert-ack failure the probe saw.
-        bool acked = false;
-        DateTime confirmDeadline = DateTime.UtcNow + AckConfirmWait;
-        while (DateTime.UtcNow < confirmDeadline && !acked)
-        {
-            WorkerEvent? evt = WaitForTransition(queue, TransitionWaitTimeout, "post-ack", consumer);
-            if (evt is not null)
-            {
-                OnAlarmTransitionEvent body = evt.Event.OnAlarmTransition;
-                Log("Post-ack transition: " + DescribeTransition(body));
-                if (body.TransitionKind == AlarmTransitionKind.Acknowledge)
-                {
-                    acked = true;
-                    break;
-                }
-            }
-
-            // Also accept the active snapshot flipping to an acked state for the
-            // target GUID, in case the ack delta was folded without a discrete
-            // Acknowledge transition.
-            var now = consumer.SnapshotActiveAlarms(out _);
-            if (now.Any(r => r.AlarmGuid == target.AlarmGuid &&
-                             (r.State == MxAlarmStateKind.AckAlm || !string.IsNullOrEmpty(r.OperatorName))))
-            {
-                Log("Snapshot shows target GUID acked (AckAlm / operator populated).");
-                acked = true;
-            }
-        }
-
-        Assert.True(
-            acked,
-            "Managed GUID ack returned rc=0 but no Acknowledge transition or acked snapshot was observed " +
-            "within the confirm window — the ack was accepted but not applied (see docs/AlarmProbeFindings.md; " +
-            "most likely the alarm's MxSecurityOperate classification requires an authenticated operator).");
-    }
-
-    private WorkerEvent? WaitForTransition(
-        MxAccessEventQueue queue,
-        TimeSpan timeout,
-        string label,
-        WnWrapAlarmConsumer consumer)
-    {
-        DateTime deadline = DateTime.UtcNow + timeout;
-        int pollCount = 0;
-        while (DateTime.UtcNow < deadline)
-        {
-            try
-            {
-                consumer.PollOnce();
-                pollCount++;
-            }
-            catch (Exception ex)
-            {
-                Log($"PollOnce threw on poll #{pollCount + 1}: {ex.GetType().Name}: {ex.Message}");
-                throw;
-            }
-            if (queue.TryDequeue(out WorkerEvent? evt) && evt is not null)
-            {
-                if (evt.Event.Family == MxEventFamily.OnAlarmTransition) return evt;
-                Log($"Skipped non-alarm event (family={evt.Event.Family}) while waiting for {label}.");
-            }
-            Thread.Sleep(500);
-        }
-        Log($"Timed out waiting for {label} transition after {timeout.TotalSeconds:F0}s (polls={pollCount}).");
-        return null;
-    }
-
-    private static string DescribeTransition(OnAlarmTransitionEvent body)
-    {
-        return string.Format(
-            "kind={0} ref='{1}' operator='{2}' comment='{3}' ts={4:o}",
-            body.TransitionKind, body.AlarmFullReference, body.OperatorUser, body.OperatorComment,
-            body.TransitionTimestamp?.ToDateTime() ?? DateTime.MinValue);
-    }
-
-    private void Log(string line) => log.Enqueue($"[t={elapsed.Elapsed.TotalSeconds:F3}s] {line}");
-}

src/ZB.MOM.WW.MxGateway.Worker.Tests/Probes/AlarmSubtagLiveSmokeTests.cs

@@ -2,7 +2,7 @@
 //
 // Validates the subtag-fallback pipeline against a real Galaxy + MXAccess install:
 //   LmxSubtagAlarmSource (own LMXProxyServerClass) ->
-//   SubtagAlarmConsumer (state machine + AcknowledgeByName write) ->
+//   SubtagAlarmConsumer (state machine + ResolveAckTargetByName) + AlarmAckWriter (AckMsg write) ->
 //   synthesized MxAlarmTransitionEvent (Raise / Clear, Degraded=true, SyntheticGuid)
 //
 // FIELD NAMES CONFIRMED: InAlarm/Acked/AckMsg/Priority are the confirmed AVEVA
@@ -49,8 +49,9 @@ namespace ZB.MOM.WW.MxGateway.Worker.Tests.Probes;
 ///     synthesize <see cref="MxAlarmTransitionEvent"/> records from Galaxy
 ///     alarm subtags using the confirmed AVEVA <c>AlarmExtension</c> field
 ///     names (InAlarm/Acked/AckMsg/Priority), and that
-///     <see cref="SubtagAlarmConsumer.AcknowledgeByName"/> writes the
-///     ack-comment subtag (AckMsg) successfully.
+///     <see cref="SubtagAlarmConsumer.ResolveAckTargetByName"/> resolves the
+///     ack-comment subtag (AckMsg) that <see cref="AlarmAckWriter"/> then
+///     writes successfully.
 ///
 ///     Skip-gated; flip <c>Skip=null</c> on the dev rig with an alarm being
 ///     driven (flip script or a manual operator/IDE toggle of the alarm
@@ -119,7 +120,7 @@ public sealed class AlarmSubtagLiveSmokeTests
     ///     real <c>LMXProxyServerClass</c>, collects a Raise then a Clear
     ///     transition synthesized by <see cref="SubtagAlarmConsumer"/>, confirms
     ///     the Degraded flag and synthetic GUID are stamped, then
-    ///     AcknowledgeByName and verifies the ack-comment write returns 0.
+    ///     acknowledges through the resolved ack-comment subtag and verifies the write succeeds.
     /// </summary>
     [Fact(Skip = "Live dev-rig smoke test — flip Skip=null with AVEVA + an alarm being driven (flip script or manual operator/IDE toggle of the alarm attribute). Subtag fallback path. Field names confirmed (InAlarm/Acked/AckMsg/Priority); live-validate runtime path resolves without intermediate alarm-condition segment.")]
     public void SubtagFallback_FullPipelineRoundTrip_SynthesizesRaiseAndAcknowledges()
@@ -257,17 +258,9 @@ public sealed class AlarmSubtagLiveSmokeTests
         Log("InAlarm subtag delivered a value: " + inAlarmResolved);
 
         // Decisive write: AckMsg. Returns 0 only if the address resolves and is writable.
-        Log("AcknowledgeByName (writes AckMsg subtag) ...");
-        int rc = consumer.AcknowledgeByName(
-            alarmName: AlarmTagName,
-            providerName: Provider,
-            groupName: Group,
-            ackComment: "subtag-resolution-probe",
-            ackOperatorName: Environment.UserName,
-            ackOperatorNode: Environment.MachineName,
-            ackOperatorDomain: Environment.UserDomainName ?? string.Empty,
-            ackOperatorFullName: Environment.UserName);
-        Log(string.Format("AcknowledgeByName(AckMsg write) -> rc={0}", rc));
+        Log("Acknowledge (writes AckMsg subtag via AlarmAckWriter) ...");
+        int rc = AckViaWriter(consumer, "subtag-resolution-probe").NativeStatus;
+        Log(string.Format("Ack (AckMsg write) -> rc={0}", rc));
 
         DateTime settle = DateTime.UtcNow + TimeSpan.FromSeconds(2);
         while (DateTime.UtcNow < settle)
@@ -392,21 +385,13 @@ public sealed class AlarmSubtagLiveSmokeTests
         Assert.True(foundInSnapshot,
             string.Format("Active alarm snapshot must contain '{0}' after a Raise.", AlarmFullReference));
 
-        // 3. AcknowledgeByName — writes the ack-comment subtag.
+        // 3. Resolve the ack-comment subtag and write it as the operator.
         //    The dispatcher derives (alarmName, provider, group) via the same
         //    TryParseReference logic as AlarmsLiveSmokeTests.
-        Log("Calling AcknowledgeByName ...");
-        int rc = consumer.AcknowledgeByName(
-            alarmName: AlarmTagName,
-            providerName: Provider,
-            groupName: Group,
-            ackComment: "subtag-fallback-smoke ack",
-            ackOperatorName: Environment.UserName,
-            ackOperatorNode: Environment.MachineName,
-            ackOperatorDomain: Environment.UserDomainName ?? string.Empty,
-            ackOperatorFullName: Environment.UserName);
+        Log("Acknowledging via AlarmAckWriter ...");
+        int rc = AckViaWriter(consumer, "subtag-fallback-smoke ack").NativeStatus;
 
-        Log(string.Format("AcknowledgeByName -> rc={0}", rc));
+        Log(string.Format("Ack -> rc={0}", rc));
         Assert.Equal(0, rc);
 
         // 4. Wait for a Clear or Acknowledge transition to confirm the state
@@ -501,6 +486,29 @@ public sealed class AlarmSubtagLiveSmokeTests
     ///     Mirrors the pump pattern documented in
     ///     <c>docs/MxAccessWorkerInstanceDesign.md</c>.
     /// </summary>
+    /// <summary>
+    ///     Resolves the probe alarm's ack item through the consumer and writes it
+    ///     with <see cref="AlarmAckWriter"/> as the operator named by
+    ///     <c>MXGATEWAY_PROBE_ACK_USER</c>/<c>MXGATEWAY_PROBE_ACK_PASSWORD</c>
+    ///     (default: current user, empty password).
+    /// </summary>
+    private static AlarmAckResult AckViaWriter(SubtagAlarmConsumer consumer, string comment)
+    {
+        AlarmAckTarget target = consumer.ResolveAckTargetByName(AlarmTagName, Provider, Group);
+        if (!target.Found)
+        {
+            return AlarmAckResult.FromTarget(target);
+        }
+
+        using AlarmAckWriter writer = new AlarmAckWriter(
+            new MxAccessComObjectFactory(), PumpMessages, TimeSpan.FromSeconds(5), AlarmAckWriter.DefaultClientName);
+        return writer.Acknowledge(target.ItemAddress, comment, new AlarmAckOperator
+        {
+            UserName = Environment.GetEnvironmentVariable("MXGATEWAY_PROBE_ACK_USER") ?? Environment.UserName,
+            Password = Environment.GetEnvironmentVariable("MXGATEWAY_PROBE_ACK_PASSWORD") ?? string.Empty,
+        });
+    }
+
     private static void PumpMessages()
     {
         NativeMethods.MSG msg;

src/ZB.MOM.WW.MxGateway.Worker.Tests/Probes/AlarmsLiveSmokeTests.cs

@@ -86,7 +86,12 @@ public sealed class AlarmsLiveSmokeTests
             new WNWRAPCONSUMERLib.wwAlarmConsumerClass(),
             maxAlarmsPerFetch: 1024);
         MxAccessAlarmEventSink sink = new MxAccessAlarmEventSink(queue, new MxAccessEventMapper());
-        using AlarmDispatcher dispatcher = new AlarmDispatcher(consumer, sink, SessionId);
+        using AlarmAckWriter ackWriter = new AlarmAckWriter(
+            new MxAccessComObjectFactory(),
+            () => new ZB.MOM.WW.MxGateway.Worker.Sta.StaMessagePump().PumpPendingMessages(),
+            TimeSpan.FromSeconds(5),
+            AlarmAckWriter.DefaultClientName);
+        using AlarmDispatcher dispatcher = new AlarmDispatcher(consumer, sink, SessionId, ackWriter);
 
         Log("Constructed consumer + sink + dispatcher.");
         dispatcher.Subscribe(SubscriptionExpression);
@@ -139,26 +144,23 @@ public sealed class AlarmsLiveSmokeTests
             $"Captured reference '{raiseBody.AlarmFullReference}' did not parse as Provider!Group.Tag.");
         Log($"Ack target: provider='{provider}' group='{group}' name='{alarmName}'");
 
-        // Try the ack with real Windows identity. AVEVA's AlarmAckByName
-        // may reject synthetic operator strings; using the current process
-        // identity gives the alarm-history a recognizable principal.
-        string realUser = Environment.UserName;
-        string realNode = Environment.MachineName;
-        string realDomain = Environment.UserDomainName ?? string.Empty;
-        Log($"Ack identity: user='{realUser}' node='{realNode}' domain='{realDomain}'");
+        // The ack authenticates a Galaxy operator and writes <tag>.AckMsg.
+        // Operator credentials come from the environment (never logged);
+        // the user defaults to the current process identity.
+        AlarmAckOperator ackOperator = new AlarmAckOperator
+        {
+            UserName = Environment.GetEnvironmentVariable("MXGATEWAY_PROBE_ACK_USER") ?? Environment.UserName,
+            Password = Environment.GetEnvironmentVariable("MXGATEWAY_PROBE_ACK_PASSWORD") ?? string.Empty,
+        };
+        Log($"Ack identity: {ackOperator}");
 
-        int rc = dispatcher.AcknowledgeByName(
-            alarmName: alarmName,
-            providerName: provider,
-            groupName: group,
-            ackComment: "alarms-live-smoke ack",
-            ackOperatorName: realUser,
-            ackOperatorNode: realNode,
-            ackOperatorDomain: realDomain,
-            ackOperatorFullName: realUser);
-        Log($"AcknowledgeByName(real identity) -> rc={rc}");
+        AlarmAckResult result = dispatcher.AcknowledgeByName(
+            alarmName, provider, group, "alarms-live-smoke ack", ackOperator);
+        Log($"AcknowledgeByName -> outcome={result.Outcome} native={result.NativeStatus} diag='{result.Diagnostic}'");
 
-        Assert.Equal(0, rc);
+        Assert.True(
+            result.Outcome == AlarmAckOutcome.Applied || result.Outcome == AlarmAckOutcome.Unconfirmed,
+            $"Ack outcome {result.Outcome}: {result.Diagnostic}");
 
         // 4. Wait for the post-ack transition. With the alarm flipping every
         //    10s and the consumer polling every 500ms, the next state

src/ZB.MOM.WW.MxGateway.Worker/Ipc/WorkerPipeSession.cs

@@ -76,7 +76,7 @@ public sealed class WorkerPipeSession
             options,
             () => Process.GetCurrentProcess().Id,
             new WorkerPipeSessionOptions(),
-            () => new MxAccessStaSession((eq, affinity, comFactory) => new AlarmCommandHandler(eq, () => new WnWrapAlarmConsumer(), affinity, comFactory, standbyFactory: null, managedAckFactory: AaManagedAlarmAckConsumer.EnvGatedFactory)),
+            () => new MxAccessStaSession((eq, affinity, comFactory) => new AlarmCommandHandler(eq, () => new WnWrapAlarmConsumer(), affinity, comFactory, standbyFactory: null)),
             logger,
             stream)
     {
@@ -98,7 +98,7 @@ public sealed class WorkerPipeSession
             options,
             processIdProvider,
             new WorkerPipeSessionOptions(),
-            () => new MxAccessStaSession((eq, affinity, comFactory) => new AlarmCommandHandler(eq, () => new WnWrapAlarmConsumer(), affinity, comFactory, standbyFactory: null, managedAckFactory: AaManagedAlarmAckConsumer.EnvGatedFactory)),
+            () => new MxAccessStaSession((eq, affinity, comFactory) => new AlarmCommandHandler(eq, () => new WnWrapAlarmConsumer(), affinity, comFactory, standbyFactory: null)),
             logger: null)
     {
     }
@@ -1585,7 +1585,7 @@ public sealed class WorkerPipeSession
         // parameterless CompleteStartupHandshakeAsync is used without a
         // prior factory call.
         _runtimeSession ??= new MxAccessStaSession(
-            (eq, affinity, comFactory) => new AlarmCommandHandler(eq, () => new WnWrapAlarmConsumer(), affinity, comFactory, standbyFactory: null, managedAckFactory: AaManagedAlarmAckConsumer.EnvGatedFactory));
+            (eq, affinity, comFactory) => new AlarmCommandHandler(eq, () => new WnWrapAlarmConsumer(), affinity, comFactory, standbyFactory: null));
         IWorkerRuntimeSession session = _runtimeSession;
         try
         {

src/ZB.MOM.WW.MxGateway.Worker/MxAccess/AaManagedAlarmAckConsumer.cs

@@ -1,231 +0,0 @@
-using System;
-using System.IO;
-using System.Reflection;
-using WNWRAPCONSUMERLib;
-
-namespace ZB.MOM.WW.MxGateway.Worker.MxAccess;
-
-/// <summary>
-///     Acknowledge path over AVEVA's modern managed alarm client,
-///     <c>aaAlarmManagedClient.AlarmClient</c> (the C++/CLI assembly the AVEVA
-///     Alarm Control itself uses: <c>AlarmClient → CwwAlarmConsumer →
-///     alarmlst.dll → alarmmgr.exe</c>). Preferred over a hand-rolled native
-///     WNAL consumer because <c>AlarmAckByGUID</c> performs the
-///     register → match-by-GUID → submit sequence internally — the record
-///     layout and selection semantics that are provider-defined (and therefore
-///     NOT safely recoverable by static RE of alarmlst.dll) stay inside AVEVA's
-///     own code. See <see cref="WnalNativeAckConsumer"/> for why the native
-///     acquisition path is deliberately unfinished.
-///
-///     The <c>AlarmClient</c> members are <c>famorasm</c> (protected-internal)
-///     and mxaccessgw is not an <c>InternalsVisibleTo</c> friend, so everything
-///     here is invoked by reflection. In full-trust .NET Framework 4.8 that is
-///     permitted. Method shapes are confirmed from the assembly metadata:
-///       .ctor()                                                   (internal)
-///       int InitializeConsumer(string appName)
-///       int RegisterConsumer(int hWnd, string product, string app, string version, bool)
-///       int Subscribe(string expr, short fromPri, short toPri,
-///                     localQueryType, localSortFlags,
-///                     localAlarmFilterState mask, localAlarmFilterState spec)
-///       int AlarmAckByGUID(System.Guid guid, string comment, string oper,
-///                          string node, string domain, string fullName)
-///       int DeregisterConsumer()  /  int UninitializeConsumer()  /  Dispose()
-///
-///     THREADING: the underlying consumer is apartment-affine (same as the
-///     wnwrap COM path). Construct and call this only on the worker STA
-///     (marshal via <c>StaRuntime.InvokeAsync</c>).
-///
-///     x86 ONLY — aaAlarmManagedClient.dll is a 32-bit mixed-mode PE.
-///
-///     OPEN (confirm at runtime, flagged inline): the trailing <c>bool</c> of
-///     <c>RegisterConsumer</c> (passed <c>false</c> here); whether
-///     <c>Subscribe</c> is actually required before an ack by GUID; and the
-///     native status returned on a real secured ack.
-/// </summary>
-public sealed class AaManagedAlarmAckConsumer : IManagedAlarmAckClient
-{
-    /// <summary>Default install location of the managed alarm client (eac.dll folder).</summary>
-    public const string DefaultAssemblyPath =
-        @"C:\Program Files (x86)\ArchestrA\Framework\Bin\Invensys_Systems__Inc__eac.dll\aaAlarmManagedClient.dll";
-
-    /// <summary>
-    ///     Env var that opts the worker into the managed ack path. Unset/anything
-    ///     other than "1" keeps the existing wnwrap ack behavior.
-    /// </summary>
-    public const string EnableEnvVar = "MXGATEWAY_USE_MANAGED_ALARM_ACK";
-
-    private const string AckApplicationName = "ZB.MOM.WW.MxGateway.ack";
-
-    /// <summary>
-    ///     Production factory for the <see cref="AlarmCommandHandler"/> seam:
-    ///     returns a managed ack client only when <see cref="EnableEnvVar"/> == "1",
-    ///     otherwise <see langword="null"/> (ack stays on the wnwrap path). Never
-    ///     throws — a construction failure (missing DLL, etc.) degrades to the
-    ///     wnwrap path rather than breaking the alarm subscription.
-    /// </summary>
-    public static IManagedAlarmAckClient? EnvGatedFactory()
-    {
-        if (!string.Equals(Environment.GetEnvironmentVariable(EnableEnvVar), "1", StringComparison.Ordinal))
-            return null;
-        try
-        {
-            return new AaManagedAlarmAckConsumer(AckApplicationName);
-        }
-        catch
-        {
-            // Opt-in enhancement only: if the managed client can't load, fall
-            // back to the wnwrap ack path rather than failing alarm reads.
-            return null;
-        }
-    }
-
-    private const string TypeName = "aaAlarmManagedClient.AlarmClient";
-    private const BindingFlags Inst = BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic;
-
-    private readonly object syncRoot = new();
-    private readonly object client;
-    private readonly MethodInfo initializeConsumer;
-    private readonly MethodInfo registerConsumer;
-    private readonly MethodInfo subscribe;
-    private readonly MethodInfo alarmAckByGuid;
-    private readonly MethodInfo? deregisterConsumer;
-    private readonly MethodInfo? uninitializeConsumer;
-
-    private bool subscribed;
-    private bool disposed;
-
-    /// <param name="applicationName">Consumer application name (e.g. "MxGateway.ack").</param>
-    /// <param name="assemblyPath">Override for <see cref="DefaultAssemblyPath"/>.</param>
-    public AaManagedAlarmAckConsumer(string applicationName, string? assemblyPath = null)
-    {
-        if (string.IsNullOrWhiteSpace(applicationName))
-            throw new ArgumentException("Application name is required.", nameof(applicationName));
-
-        string path = assemblyPath ?? DefaultAssemblyPath;
-        if (!File.Exists(path))
-            throw new FileNotFoundException($"aaAlarmManagedClient.dll not found at '{path}'.", path);
-
-        Assembly asm = Assembly.LoadFrom(path);
-        Type type = asm.GetType(TypeName, throwOnError: true)
-            ?? throw new InvalidOperationException($"Type '{TypeName}' not found in {path}.");
-
-        initializeConsumer = Resolve(type, "InitializeConsumer");
-        registerConsumer = Resolve(type, "RegisterConsumer");
-        subscribe = Resolve(type, "Subscribe");
-        alarmAckByGuid = Resolve(type, "AlarmAckByGUID");
-        deregisterConsumer = type.GetMethod("DeregisterConsumer", Inst, null, Type.EmptyTypes, null);
-        uninitializeConsumer = type.GetMethod("UninitializeConsumer", Inst, null, Type.EmptyTypes, null);
-
-        client = Activator.CreateInstance(type, nonPublic: true)
-            ?? throw new InvalidOperationException($"Could not construct '{TypeName}'.");
-
-        ApplicationName = applicationName;
-    }
-
-    /// <summary>The consumer application name this instance registered under.</summary>
-    public string ApplicationName { get; }
-
-    private static MethodInfo Resolve(Type type, string name) =>
-        type.GetMethod(name, Inst)
-        ?? throw new MissingMethodException(TypeName, name);
-
-    /// <summary>
-    ///     Run the Initialize → Register → Subscribe lifecycle once, mirroring the
-    ///     proven wnwrap argument values. <paramref name="subscription"/> is the
-    ///     alarm query root, e.g. <c>\\NODE\Galaxy!Area</c>. Throws if any native
-    ///     status is non-zero.
-    /// </summary>
-    public void Subscribe(string subscription)
-    {
-        if (subscription is null) throw new ArgumentNullException(nameof(subscription));
-        lock (syncRoot)
-        {
-            if (disposed) throw new ObjectDisposedException(nameof(AaManagedAlarmAckConsumer));
-            if (subscribed) throw new InvalidOperationException("Subscribe was already called.");
-
-            int init = (int)initializeConsumer.Invoke(client, new object[] { ApplicationName })!;
-            if (init != 0) throw new InvalidOperationException($"InitializeConsumer returned {init}.");
-
-            // RegisterConsumer(hWnd, product, app, version, bool). hWnd=0 => pull model.
-            // The trailing bool is unconfirmed; false = client/non-modal is the safe default.
-            int reg = (int)registerConsumer.Invoke(client, new object[]
-            {
-                0, "ZB.MOM.WW.MxGateway", ApplicationName, "1.0", false,
-            })!;
-            if (reg != 0) throw new InvalidOperationException($"RegisterConsumer returned {reg}.");
-
-            int sub = (int)subscribe.Invoke(client, BuildSubscribeArgs(subscription))!;
-            if (sub != 0) throw new InvalidOperationException($"Subscribe('{subscription}') returned {sub}.");
-
-            subscribed = true;
-        }
-    }
-
-    /// <summary>
-    ///     Acknowledge a single alarm by GUID with full operator identity. Returns
-    ///     AVEVA's native status (0 = success). A zero return means accepted, not
-    ///     necessarily applied — verify the alarm's acked state / Historian row
-    ///     (see docs/AlarmProbeFindings.md).
-    /// </summary>
-    public int AcknowledgeByGuid(
-        Guid alarmGuid,
-        string comment,
-        string operatorName,
-        string operatorNode,
-        string operatorDomain,
-        string operatorFullName)
-    {
-        lock (syncRoot)
-        {
-            if (disposed) throw new ObjectDisposedException(nameof(AaManagedAlarmAckConsumer));
-            if (!subscribed) throw new InvalidOperationException("Subscribe must be called before acknowledging.");
-
-            return (int)alarmAckByGuid.Invoke(client, new object[]
-            {
-                alarmGuid,
-                comment ?? string.Empty,
-                operatorName ?? string.Empty,
-                operatorNode ?? string.Empty,
-                operatorDomain ?? string.Empty,
-                operatorFullName ?? string.Empty,
-            })!;
-        }
-    }
-
-    /// <summary>
-    ///     Build the 7 Subscribe args, boxing the proven wnwrap enum integers into
-    ///     aaAlarmManagedClient's own enum parameter types (localQueryType /
-    ///     localSortFlags / localAlarmFilterState) via <see cref="Enum.ToObject(Type,object)"/>.
-    /// </summary>
-    private object[] BuildSubscribeArgs(string subscription)
-    {
-        ParameterInfo[] p = subscribe.GetParameters();
-        if (p.Length != 7)
-            throw new InvalidOperationException($"Unexpected AlarmClient.Subscribe arity {p.Length}; expected 7.");
-
-        return new object[]
-        {
-            subscription,
-            (short)1,                                                        // wFromPri
-            (short)999,                                                      // wToPri
-            Enum.ToObject(p[3].ParameterType, (int)eQueryType.qtSummary),
-            Enum.ToObject(p[4].ParameterType, (int)eSortFlags.sfReturnNewestFirst),
-            Enum.ToObject(p[5].ParameterType, (int)eAlarmFilterState.asAlarmActiveNow),
-            Enum.ToObject(p[6].ParameterType, (int)eAlarmFilterState.asAlarmActiveNow),
-        };
-    }
-
-    /// <inheritdoc />
-    public void Dispose()
-    {
-        lock (syncRoot)
-        {
-            if (disposed) return;
-            disposed = true;
-
-            try { if (subscribed) deregisterConsumer?.Invoke(client, Array.Empty<object>()); } catch { /* best effort */ }
-            try { uninitializeConsumer?.Invoke(client, Array.Empty<object>()); } catch { /* best effort */ }
-            (client as IDisposable)?.Dispose();
-        }
-    }
-}

src/ZB.MOM.WW.MxGateway.Worker/MxAccess/AlarmCommandHandler.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using ZB.MOM.WW.MxGateway.Contracts.Proto;
+using ZB.MOM.WW.MxGateway.Worker.Sta;
 
 namespace ZB.MOM.WW.MxGateway.Worker.MxAccess;
 
@@ -39,10 +40,12 @@ public sealed class AlarmCommandHandler : IAlarmCommandHandler
     private readonly Action? threadAffinityCheck;
     private readonly IMxAccessComObjectFactory? comFactory;
     private readonly Func<IReadOnlyList<AlarmSubtagTarget>, IMxAccessAlarmConsumer>? standbyFactory;
-    private readonly Func<IManagedAlarmAckClient?>? managedAckFactory;
+    private readonly Func<IAlarmAckWriter>? ackWriterFactory;
     private readonly MxAccessEventMapper mapper = new MxAccessEventMapper();
     private readonly object syncRoot = new object();
+    private readonly IAlarmAckWriter deferredAckWriter;
     private AlarmDispatcher? dispatcher;
+    private IAlarmAckWriter? ackWriter;
     private FailoverAlarmConsumer? failoverConsumer;
     private EventHandler<AlarmProviderModeChange>? providerModeChangedHandler;
     private string subscribeSessionId = string.Empty;
@@ -118,14 +121,15 @@ public sealed class AlarmCommandHandler : IAlarmCommandHandler
     ///     <paramref name="comFactory"/>. Tests inject a fake so they need no
     ///     live COM factory.
     /// </param>
-    /// <param name="managedAckFactory">
-    ///     Optional per-subscription factory for a managed ack client
-    ///     (<see cref="IManagedAlarmAckClient"/>). When it yields a non-null
-    ///     client, GUID-keyed acknowledges route through AVEVA's modern
-    ///     <c>AlarmClient.AlarmAckByGUID</c> instead of the wnwrap COM path.
-    ///     Defaults to <see langword="null"/> (wnwrap ack). Production supplies
-    ///     <see cref="AaManagedAlarmAckConsumer.EnvGatedFactory"/>, which is a
-    ///     no-op unless <c>MXGATEWAY_USE_MANAGED_ALARM_ACK=1</c>.
+    /// <param name="ackWriterFactory">
+    ///     Optional seam that builds the <see cref="IAlarmAckWriter"/> used for
+    ///     every acknowledgement. Defaults to an <see cref="AlarmAckWriter"/> over
+    ///     <paramref name="comFactory"/> that registers its own MXAccess server
+    ///     (client name from <see cref="AlarmAckWriter.ResolveClientName"/>).
+    ///     The writer is created once per handler, on the first acknowledgement
+    ///     (so a subscription never fails because ack is unavailable), survives
+    ///     unsubscribe/resubscribe, and is disposed with the handler. Tests
+    ///     inject a fake.
     /// </param>
     public AlarmCommandHandler(
         MxAccessEventQueue eventQueue,
@@ -133,14 +137,15 @@ public sealed class AlarmCommandHandler : IAlarmCommandHandler
         Action? threadAffinityCheck,
         IMxAccessComObjectFactory? comFactory,
         Func<IReadOnlyList<AlarmSubtagTarget>, IMxAccessAlarmConsumer>? standbyFactory,
-        Func<IManagedAlarmAckClient?>? managedAckFactory = null)
+        Func<IAlarmAckWriter>? ackWriterFactory = null)
     {
         this.eventQueue = eventQueue ?? throw new ArgumentNullException(nameof(eventQueue));
         this.consumerFactory = consumerFactory ?? throw new ArgumentNullException(nameof(consumerFactory));
         this.threadAffinityCheck = threadAffinityCheck;
         this.comFactory = comFactory;
         this.standbyFactory = standbyFactory;
-        this.managedAckFactory = managedAckFactory;
+        this.ackWriterFactory = ackWriterFactory;
+        this.deferredAckWriter = new DeferredAckWriter(this);
     }
 
     /// <summary>Gets a value indicating whether the handler is subscribed.</summary>
@@ -181,14 +186,8 @@ public sealed class AlarmCommandHandler : IAlarmCommandHandler
                 failover.ProviderModeChanged += providerModeChangedHandler;
             }
 
-            // Optional managed ack client (opt-in via env); null → wnwrap ack.
-            // A forced-subtag session never has alarmmgr GUIDs to ack, so it
-            // skips the extra managed consumer entirely.
-            IManagedAlarmAckClient? managedAck = command.ForcedMode == AlarmProviderMode.Subtag
-                ? null
-                : managedAckFactory?.Invoke();
             MxAccessAlarmEventSink sink = new MxAccessAlarmEventSink(eventQueue, mapper);
-            dispatcher = new AlarmDispatcher(consumer, sink, subscribeSessionId, managedAck);
+            dispatcher = new AlarmDispatcher(consumer, sink, subscribeSessionId, deferredAckWriter);
             try
             {
                 dispatcher.Subscribe(subscriptionExpression);
@@ -323,47 +322,31 @@ public sealed class AlarmCommandHandler : IAlarmCommandHandler
     }
 
     /// <inheritdoc />
-    public int Acknowledge(
-        Guid alarmGuid,
-        string comment,
-        string operatorUser,
-        string operatorNode,
-        string operatorDomain,
-        string operatorFullName)
+    public AlarmAckResult Acknowledge(Guid alarmGuid, string comment, AlarmAckOperator ackOperator)
     {
+        if (ackOperator is null) throw new ArgumentNullException(nameof(ackOperator));
         threadAffinityCheck?.Invoke();
-        AlarmDispatcher? d = GetDispatcherOrThrow();
-        return d.Acknowledge(
-            alarmGuid,
-            comment ?? string.Empty,
-            operatorUser ?? string.Empty,
-            operatorNode ?? string.Empty,
-            operatorDomain ?? string.Empty,
-            operatorFullName ?? string.Empty);
+        AlarmDispatcher d = GetDispatcherOrThrow();
+        return d.Acknowledge(alarmGuid, comment ?? string.Empty, ackOperator);
     }
 
     /// <inheritdoc />
-    public int AcknowledgeByName(
+    public AlarmAckResult AcknowledgeByName(
         string alarmName,
         string providerName,
         string groupName,
         string comment,
-        string operatorUser,
-        string operatorNode,
-        string operatorDomain,
-        string operatorFullName)
+        AlarmAckOperator ackOperator)
     {
+        if (ackOperator is null) throw new ArgumentNullException(nameof(ackOperator));
         threadAffinityCheck?.Invoke();
-        AlarmDispatcher? d = GetDispatcherOrThrow();
+        AlarmDispatcher d = GetDispatcherOrThrow();
         return d.AcknowledgeByName(
             alarmName ?? string.Empty,
             providerName ?? string.Empty,
             groupName ?? string.Empty,
             comment ?? string.Empty,
-            operatorUser ?? string.Empty,
-            operatorNode ?? string.Empty,
-            operatorDomain ?? string.Empty,
-            operatorFullName ?? string.Empty);
+            ackOperator);
     }
 
     /// <inheritdoc />
@@ -398,6 +381,60 @@ public sealed class AlarmCommandHandler : IAlarmCommandHandler
         d?.PollOnce();
     }
 
+    private IAlarmAckWriter GetOrCreateAckWriter()
+    {
+        lock (syncRoot)
+        {
+            if (disposed) throw new ObjectDisposedException(nameof(AlarmCommandHandler));
+            if (ackWriter is not null) return ackWriter;
+            if (ackWriterFactory is not null)
+            {
+                ackWriter = ackWriterFactory() ?? throw new InvalidOperationException("Alarm ack writer factory returned null.");
+                return ackWriter;
+            }
+
+            if (comFactory is null)
+            {
+                throw new InvalidOperationException(
+                    "Alarm acknowledgement requires an IMxAccessComObjectFactory; the alarm command handler was constructed without one.");
+            }
+
+            // StaMessagePump.PumpPendingMessages is PeekMessage/DispatchMessage on
+            // the calling thread — the STA, since acks run there — which is what
+            // delivers the writer's OnWriteComplete callback.
+            ackWriter = new AlarmAckWriter(
+                comFactory,
+                () => new StaMessagePump().PumpPendingMessages(),
+                MxAccessStaSession.ResolveWriteCompletionTimeout(),
+                AlarmAckWriter.ResolveClientName());
+            return ackWriter;
+        }
+    }
+
+    /// <summary>
+    ///     The writer handed to each <see cref="AlarmDispatcher"/>. Resolves the
+    ///     handler's real writer on first acknowledgement so the writer (and its
+    ///     MXAccess server registration) is created only when an ack happens and
+    ///     outlives dispatcher churn. Disposing it is a no-op; the handler owns
+    ///     the real writer.
+    /// </summary>
+    private sealed class DeferredAckWriter : IAlarmAckWriter
+    {
+        private readonly AlarmCommandHandler owner;
+
+        public DeferredAckWriter(AlarmCommandHandler owner)
+        {
+            this.owner = owner;
+        }
+
+        public AlarmAckResult Acknowledge(string itemAddress, string comment, AlarmAckOperator ackOperator) =>
+            owner.GetOrCreateAckWriter().Acknowledge(itemAddress, comment, ackOperator);
+
+        public void Dispose()
+        {
+        }
+    }
+
     private AlarmDispatcher GetDispatcherOrThrow()
     {
         if (disposed) throw new ObjectDisposedException(nameof(AlarmCommandHandler));
@@ -418,5 +455,13 @@ public sealed class AlarmCommandHandler : IAlarmCommandHandler
         if (disposed) return;
         disposed = true;
         Unsubscribe();
+        IAlarmAckWriter? writerToDispose;
+        lock (syncRoot)
+        {
+            writerToDispose = ackWriter;
+            ackWriter = null;
+        }
+
+        try { writerToDispose?.Dispose(); } catch { /* swallow */ }
     }
 }

src/ZB.MOM.WW.MxGateway.Worker/MxAccess/AlarmDispatcher.cs

@@ -18,7 +18,9 @@ namespace ZB.MOM.WW.MxGateway.Worker.MxAccess;
 ///         worker's IPC layer issues <c>SubscribeAlarmsCommand</c> /
 ///         <c>AcknowledgeAlarmCommand</c> / <c>QueryActiveAlarmsCommand</c>
 ///         through <see cref="AlarmCommandHandler"/>, which owns one
-///         dispatcher per session.
+///         dispatcher per session. Acknowledgement resolves the alarm to its
+///         MXAccess ack item through the consumer and hands the write to the
+///         <see cref="IAlarmAckWriter"/>, which authenticates as the operator.
 ///     </para>
 ///     <para>
 ///         Threading: <see cref="WnWrapAlarmConsumer"/> owns no internal
@@ -36,30 +38,29 @@ public sealed class AlarmDispatcher : IDisposable
     private readonly MxAccessAlarmEventSink sink;
     private readonly string sessionId;
     private readonly EventHandler<MxAlarmTransitionEvent> handler;
-    private IManagedAlarmAckClient? managedAck;
+    private readonly IAlarmAckWriter ackWriter;
     private bool disposed;
 
-    /// <summary>Initializes a new alarm dispatcher for the given consumer, sink, and session ID.</summary>
+    /// <summary>Initializes a new alarm dispatcher for the given consumer, sink, session ID and ack writer.</summary>
     /// <param name="consumer">The alarm consumer.</param>
     /// <param name="sink">The alarm event sink.</param>
     /// <param name="sessionId">The session identifier.</param>
-    /// <param name="managedAck">
-    ///     Optional managed ack client. When non-null, GUID-keyed acknowledges
-    ///     route to it (AVEVA's modern <c>AlarmClient.AlarmAckByGUID</c>) instead
-    ///     of the wnwrap consumer while the alarmmgr provider is active; null
-    ///     keeps the existing wnwrap ack path. Subtag-mode acks always stay on
-    ///     the consumer because their GUIDs are synthetic.
+    /// <param name="ackWriter">
+    ///     Writes the resolved ack item as the authenticated operator. Owned by
+    ///     the caller (<see cref="AlarmCommandHandler"/>), which disposes it; the
+    ///     dispatcher never does, so the writer's registered MXAccess server
+    ///     outlives an unsubscribe/resubscribe cycle.
     /// </param>
     public AlarmDispatcher(
         IMxAccessAlarmConsumer consumer,
         MxAccessAlarmEventSink sink,
         string sessionId,
-        IManagedAlarmAckClient? managedAck = null)
+        IAlarmAckWriter ackWriter)
     {
         this.consumer = consumer ?? throw new ArgumentNullException(nameof(consumer));
         this.sink = sink ?? throw new ArgumentNullException(nameof(sink));
         this.sessionId = sessionId ?? string.Empty;
-        this.managedAck = managedAck;
+        this.ackWriter = ackWriter ?? throw new ArgumentNullException(nameof(ackWriter));
         // Sink.Attach is the seam that propagates the session id onto the
         // proto SessionId field of every emitted MxEvent. Pass the consumer
         // as the "associated COM object" — sink ignores the object reference
@@ -80,113 +81,37 @@ public sealed class AlarmDispatcher : IDisposable
     {
         if (disposed) throw new ObjectDisposedException(nameof(AlarmDispatcher));
         consumer.Subscribe(subscription);
-        // The managed ack client maintains its own registered/subscribed
-        // consumer; run its lifecycle against the same expression so a later
-        // AlarmAckByGUID has a live consumer to act through. It is an opt-in
-        // enhancement, so a failed lifecycle drops back to the wnwrap ack path
-        // rather than failing the alarm subscription.
-        if (managedAck is not null)
-        {
-            try
-            {
-                managedAck.Subscribe(subscription);
-            }
-            catch
-            {
-                try { managedAck.Dispose(); } catch { /* swallow */ }
-                managedAck = null;
-            }
-        }
     }
 
-    /// <summary>
-    ///     True when the consumer is currently serving alarms from the subtag
-    ///     fallback, whose alarm GUIDs are synthetic and unknown to alarmmgr.
-    /// </summary>
-    private bool IsSubtagActive() =>
-        consumer is SubtagAlarmConsumer ||
-        (consumer is FailoverAlarmConsumer failover && failover.Mode == AlarmProviderMode.Subtag);
-
-    /// <summary>
-    ///     Forward an <c>AcknowledgeAlarm</c> request to the underlying
-    ///     consumer's <c>AlarmAckByGUID</c>. Returns the AVEVA-native
-    ///     status code (0 = success).
-    /// </summary>
+    /// <summary>Acknowledges the alarm with the given GUID by writing its ack item as the operator.</summary>
     /// <param name="alarmGuid">The alarm GUID.</param>
-    /// <param name="ackComment">The acknowledgment comment.</param>
-    /// <param name="ackOperatorName">The operator name.</param>
-    /// <param name="ackOperatorNode">The operator node.</param>
-    /// <param name="ackOperatorDomain">The operator domain.</param>
-    /// <param name="ackOperatorFullName">The operator full name.</param>
-    /// <returns>The AVEVA-native status code.</returns>
-    public int Acknowledge(
-        Guid alarmGuid,
-        string ackComment,
-        string ackOperatorName,
-        string ackOperatorNode,
-        string ackOperatorDomain,
-        string ackOperatorFullName)
+    /// <param name="ackComment">The acknowledgement comment.</param>
+    /// <param name="ackOperator">The operator to authenticate as.</param>
+    /// <returns>The outcome.</returns>
+    public AlarmAckResult Acknowledge(Guid alarmGuid, string ackComment, AlarmAckOperator ackOperator)
     {
         if (disposed) throw new ObjectDisposedException(nameof(AlarmDispatcher));
-        if (managedAck is not null && !IsSubtagActive())
-        {
-            // Preferred path: AVEVA's modern AlarmClient.AlarmAckByGUID carries
-            // operator domain + full name and is not E_NOTIMPL like the wnwrap
-            // COM AlarmAckByGUID. Skipped in subtag mode: those GUIDs are
-            // synthetic and only the subtag consumer can resolve them (it acks
-            // via an AckMsg write).
-            return managedAck.AcknowledgeByGuid(
-                alarmGuid,
-                ackComment,
-                ackOperatorName,
-                ackOperatorNode,
-                ackOperatorDomain,
-                ackOperatorFullName);
-        }
-
-        return consumer.AcknowledgeByGuid(
-            alarmGuid,
-            ackComment,
-            ackOperatorName,
-            ackOperatorNode,
-            ackOperatorDomain,
-            ackOperatorFullName);
+        AlarmAckTarget target = consumer.ResolveAckTarget(alarmGuid);
+        return target.Found
+            ? ackWriter.Acknowledge(target.ItemAddress, ackComment, ackOperator)
+            : AlarmAckResult.FromTarget(target);
     }
 
-    /// <summary>
-    ///     Acknowledge an alarm by its (name, provider, group) tuple.
-    ///     Routes to the consumer's <c>AcknowledgeByName</c> path which
-    ///     maps to <c>wwAlarmConsumerClass.AlarmAckByName</c>.
-    /// </summary>
-    /// <param name="alarmName">The alarm name.</param>
-    /// <param name="providerName">The provider name.</param>
-    /// <param name="groupName">The group name.</param>
-    /// <param name="ackComment">The acknowledgment comment.</param>
-    /// <param name="ackOperatorName">The operator name.</param>
-    /// <param name="ackOperatorNode">The operator node.</param>
-    /// <param name="ackOperatorDomain">The operator domain.</param>
-    /// <param name="ackOperatorFullName">The operator full name.</param>
-    /// <returns>The AVEVA-native status code.</returns>
-    public int AcknowledgeByName(
-        string alarmName,
-        string providerName,
-        string groupName,
-        string ackComment,
-        string ackOperatorName,
-        string ackOperatorNode,
-        string ackOperatorDomain,
-        string ackOperatorFullName)
+    /// <summary>Acknowledges the alarm identified by name/provider/group as the operator.</summary>
+    /// <param name="alarmName">The tag/alarm name.</param>
+    /// <param name="providerName">The provider.</param>
+    /// <param name="groupName">The group/area.</param>
+    /// <param name="ackComment">The acknowledgement comment.</param>
+    /// <param name="ackOperator">The operator to authenticate as.</param>
+    /// <returns>The outcome.</returns>
+    public AlarmAckResult AcknowledgeByName(
+        string alarmName, string providerName, string groupName, string ackComment, AlarmAckOperator ackOperator)
     {
         if (disposed) throw new ObjectDisposedException(nameof(AlarmDispatcher));
-        return consumer.AcknowledgeByName(
-            alarmName,
-            providerName,
-            groupName,
-            ackComment,
-            ackOperatorName,
-            ackOperatorNode,
-            ackOperatorDomain,
-            ackOperatorFullName);
+        AlarmAckTarget target = consumer.ResolveAckTargetByName(alarmName, providerName, groupName);
+        return target.Found
+            ? ackWriter.Acknowledge(target.ItemAddress, ackComment, ackOperator)
+            : AlarmAckResult.FromTarget(target);
     }
 
     /// <summary>
@@ -327,6 +252,5 @@ public sealed class AlarmDispatcher : IDisposable
         try { consumer.AlarmTransitionEmitted -= handler; } catch { /* swallow */ }
         try { sink.Detach(); } catch { /* swallow */ }
         try { consumer.Dispose(); } catch { /* swallow */ }
-        try { managedAck?.Dispose(); } catch { /* swallow */ }
     }
 }

src/ZB.MOM.WW.MxGateway.Worker/MxAccess/FailoverAlarmConsumer.cs

@@ -41,7 +41,7 @@ namespace ZB.MOM.WW.MxGateway.Worker.MxAccess;
 ///         <strong>Threading.</strong> Like its children, this type is driven
 ///         entirely on the worker's STA: <see cref="Subscribe"/>,
 ///         <see cref="PollOnce"/>, <see cref="ProbeOnce"/>, and the
-///         <c>AcknowledgeBy*</c> calls are all invoked from the apartment that
+///         <c>ResolveAckTarget*</c> calls are all invoked from the apartment that
 ///         owns the underlying COM objects. It owns no locks of its own and no
 ///         internal timer; the worker drives <see cref="PollOnce"/> on a timer.
 ///     </para>
@@ -259,34 +259,17 @@ public sealed class FailoverAlarmConsumer : IMxAccessAlarmConsumer
     }
 
     /// <inheritdoc />
-    public int AcknowledgeByGuid(
-        Guid alarmGuid,
-        string ackComment,
-        string ackOperatorName,
-        string ackOperatorNode,
-        string ackOperatorDomain,
-        string ackOperatorFullName)
+    public AlarmAckTarget ResolveAckTarget(Guid alarmGuid)
     {
         if (disposed) throw new ObjectDisposedException(nameof(FailoverAlarmConsumer));
-        return ActiveChild.AcknowledgeByGuid(
-            alarmGuid, ackComment, ackOperatorName, ackOperatorNode, ackOperatorDomain, ackOperatorFullName);
+        return ActiveChild.ResolveAckTarget(alarmGuid);
     }
 
     /// <inheritdoc />
-    public int AcknowledgeByName(
-        string alarmName,
-        string providerName,
-        string groupName,
-        string ackComment,
-        string ackOperatorName,
-        string ackOperatorNode,
-        string ackOperatorDomain,
-        string ackOperatorFullName)
+    public AlarmAckTarget ResolveAckTargetByName(string alarmName, string providerName, string groupName)
     {
         if (disposed) throw new ObjectDisposedException(nameof(FailoverAlarmConsumer));
-        return ActiveChild.AcknowledgeByName(
-            alarmName, providerName, groupName, ackComment,
-            ackOperatorName, ackOperatorNode, ackOperatorDomain, ackOperatorFullName);
+        return ActiveChild.ResolveAckTargetByName(alarmName, providerName, groupName);
     }
 
     /// <inheritdoc />

src/ZB.MOM.WW.MxGateway.Worker/MxAccess/IAlarmCommandHandler.cs

@@ -35,44 +35,21 @@ public interface IAlarmCommandHandler : IDisposable
     /// <summary>Tear down the active subscription. No-op if not subscribed.</summary>
     void Unsubscribe();
 
-    /// <summary>Acknowledge a single alarm by GUID. Returns AVEVA's native status (0 = success).</summary>
+    /// <summary>Acknowledges an alarm by GUID as <paramref name="ackOperator"/>.</summary>
     /// <param name="alarmGuid">The alarm GUID.</param>
-    /// <param name="comment">The acknowledgment comment.</param>
-    /// <param name="operatorUser">The operator user name.</param>
-    /// <param name="operatorNode">The operator node name.</param>
-    /// <param name="operatorDomain">The operator domain name.</param>
-    /// <param name="operatorFullName">The operator full name.</param>
-    /// <returns>AVEVA's native alarm status code (0 = success).</returns>
-    int Acknowledge(
-        Guid alarmGuid,
-        string comment,
-        string operatorUser,
-        string operatorNode,
-        string operatorDomain,
-        string operatorFullName);
+    /// <param name="comment">The acknowledgement comment written to the alarm's ack item.</param>
+    /// <param name="ackOperator">The operator to authenticate as (credential-sensitive).</param>
+    /// <returns>The acknowledgement outcome.</returns>
+    AlarmAckResult Acknowledge(Guid alarmGuid, string comment, AlarmAckOperator ackOperator);
 
-    /// <summary>
-    ///     Acknowledge a single alarm by (name, provider, group) — used when
-    ///     the caller has the human-readable reference but not the GUID.
-    /// </summary>
-    /// <param name="alarmName">The alarm name.</param>
+    /// <summary>Acknowledges an alarm by name/provider/group as <paramref name="ackOperator"/>.</summary>
+    /// <param name="alarmName">The alarm (tag) name.</param>
     /// <param name="providerName">The provider name.</param>
     /// <param name="groupName">The group name.</param>
-    /// <param name="comment">The acknowledgment comment.</param>
-    /// <param name="operatorUser">The operator user name.</param>
-    /// <param name="operatorNode">The operator node name.</param>
-    /// <param name="operatorDomain">The operator domain name.</param>
-    /// <param name="operatorFullName">The operator full name.</param>
-    /// <returns>AVEVA's native alarm status code (0 = success).</returns>
-    int AcknowledgeByName(
-        string alarmName,
-        string providerName,
-        string groupName,
-        string comment,
-        string operatorUser,
-        string operatorNode,
-        string operatorDomain,
-        string operatorFullName);
+    /// <param name="comment">The acknowledgement comment written to the alarm's ack item.</param>
+    /// <param name="ackOperator">The operator to authenticate as (credential-sensitive).</param>
+    /// <returns>The acknowledgement outcome.</returns>
+    AlarmAckResult AcknowledgeByName(string alarmName, string providerName, string groupName, string comment, AlarmAckOperator ackOperator);
 
     /// <summary>
     ///     Snapshot the currently-active alarm set, optionally scoped to a

src/ZB.MOM.WW.MxGateway.Worker/MxAccess/IManagedAlarmAckClient.cs

@@ -1,44 +0,0 @@
-using System;
-
-namespace ZB.MOM.WW.MxGateway.Worker.MxAccess;
-
-/// <summary>
-///     Optional ack-only seam over AVEVA's modern managed alarm client
-///     (<c>aaAlarmManagedClient.AlarmClient</c>). When supplied to an
-///     <see cref="AlarmDispatcher"/>, GUID-keyed acknowledges route here
-///     instead of the wnwrap COM consumer's <c>AlarmAckByGUID</c> (which is
-///     <c>E_NOTIMPL</c> on current builds) — carrying full operator identity
-///     (domain + full name) that the wnwrap 6-arg <c>AlarmAckByName</c> drops.
-///     The production implementation is <see cref="AaManagedAlarmAckConsumer"/>.
-/// </summary>
-public interface IManagedAlarmAckClient : IDisposable
-{
-    /// <summary>
-    ///     Run the client's Initialize → Register → Subscribe lifecycle against
-    ///     the same subscription expression the read consumer uses
-    ///     (<c>\\&lt;node&gt;\Galaxy!&lt;area&gt;</c>). Must be called once,
-    ///     on the worker STA, before <see cref="AcknowledgeByGuid"/>.
-    /// </summary>
-    /// <param name="subscription">The subscription expression.</param>
-    void Subscribe(string subscription);
-
-    /// <summary>
-    ///     Acknowledge a single alarm by GUID with full operator identity.
-    ///     Returns AVEVA's native status (0 = success; 0 means accepted, not
-    ///     necessarily applied — verify the alarm's acked state / Historian row).
-    /// </summary>
-    /// <param name="alarmGuid">The alarm GUID.</param>
-    /// <param name="comment">The acknowledgment comment.</param>
-    /// <param name="operatorName">The operator name.</param>
-    /// <param name="operatorNode">The operator node.</param>
-    /// <param name="operatorDomain">The operator domain.</param>
-    /// <param name="operatorFullName">The operator full name.</param>
-    /// <returns>The AVEVA-native status code.</returns>
-    int AcknowledgeByGuid(
-        Guid alarmGuid,
-        string comment,
-        string operatorName,
-        string operatorNode,
-        string operatorDomain,
-        string operatorFullName);
-}

src/ZB.MOM.WW.MxGateway.Worker/MxAccess/IMxAccessAlarmConsumer.cs

@@ -49,51 +49,19 @@ public interface IMxAccessAlarmConsumer : IDisposable
     void Subscribe(string subscription);
 
     /// <summary>
-    ///     Acknowledges a single alarm with full operator-identity fidelity.
-    ///     Reaches AVEVA's native <c>AlarmAckByGUID</c>; operator
-    ///     user / node / domain / full-name and the comment land atomically
-    ///     with the ack transition in the alarm-history log.
+    ///     Resolves the MXAccess item whose write acknowledges the alarm with the
+    ///     given GUID (e.g. <c>Obj.Alarm.AckMsg</c>). Does not perform the ack.
     /// </summary>
-    /// <param name="alarmGuid">The alarm GUID.</param>
-    /// <param name="ackComment">The acknowledgment comment.</param>
-    /// <param name="ackOperatorName">The operator name.</param>
-    /// <param name="ackOperatorNode">The operator node.</param>
-    /// <param name="ackOperatorDomain">The operator domain.</param>
-    /// <param name="ackOperatorFullName">The operator full name.</param>
-    /// <returns>The AVEVA-native status code.</returns>
-    int AcknowledgeByGuid(
-        Guid alarmGuid,
-        string ackComment,
-        string ackOperatorName,
-        string ackOperatorNode,
-        string ackOperatorDomain,
-        string ackOperatorFullName);
+    /// <param name="alarmGuid">The alarm GUID as reported by this consumer.</param>
+    /// <returns>The resolved target or the reason none exists.</returns>
+    AlarmAckTarget ResolveAckTarget(Guid alarmGuid);
 
-    /// <summary>
-    ///     Acknowledge a single alarm by its (name, provider, group) tuple.
-    ///     Reaches AVEVA's <c>AlarmAckByName</c> on
-    ///     <c>wwAlarmConsumerClass</c>; same alarm-history outcome as
-    ///     <see cref="AcknowledgeByGuid"/>, used when the caller has the
-    ///     human-readable reference but not the canonical GUID.
-    /// </summary>
-    /// <param name="alarmName">The alarm name.</param>
-    /// <param name="providerName">The provider name.</param>
-    /// <param name="groupName">The group name.</param>
-    /// <param name="ackComment">The acknowledgment comment.</param>
-    /// <param name="ackOperatorName">The operator name.</param>
-    /// <param name="ackOperatorNode">The operator node.</param>
-    /// <param name="ackOperatorDomain">The operator domain.</param>
-    /// <param name="ackOperatorFullName">The operator full name.</param>
-    /// <returns>The AVEVA-native status code.</returns>
-    int AcknowledgeByName(
-        string alarmName,
-        string providerName,
-        string groupName,
-        string ackComment,
-        string ackOperatorName,
-        string ackOperatorNode,
-        string ackOperatorDomain,
-        string ackOperatorFullName);
+    /// <summary>Resolves the ack item for an alarm identified by name, provider and group.</summary>
+    /// <param name="alarmName">The tag/alarm name, e.g. <c>TestMachine_001.TestAlarm001</c>.</param>
+    /// <param name="providerName">The provider (literal <c>Galaxy</c> for ArchestrA).</param>
+    /// <param name="groupName">The area/group.</param>
+    /// <returns>The resolved target or the reason none exists.</returns>
+    AlarmAckTarget ResolveAckTargetByName(string alarmName, string providerName, string groupName);
 
     /// <summary>
     ///     Returns the consumer's most recently parsed snapshot of currently

src/ZB.MOM.WW.MxGateway.Worker/MxAccess/ISubtagAlarmSource.cs

@@ -16,9 +16,4 @@ public interface ISubtagAlarmSource : IDisposable
     /// <summary>Begins advising the supplied MXAccess subtag item addresses.</summary>
     /// <param name="itemAddresses">The subtag references to advise.</param>
     void Advise(IReadOnlyCollection<string> itemAddresses);
-
-    /// <summary>Writes a value to the named MXAccess subtag (e.g. an ack request).</summary>
-    /// <param name="itemAddress">The subtag reference to write.</param>
-    /// <param name="value">The value to write.</param>
-    void Write(string itemAddress, object? value);
 }

src/ZB.MOM.WW.MxGateway.Worker/MxAccess/LmxSubtagAlarmSource.cs

@@ -9,8 +9,9 @@ namespace ZB.MOM.WW.MxGateway.Worker.MxAccess;
 ///     Production <see cref="ISubtagAlarmSource"/> backed by its own MXAccess
 ///     <c>LMXProxyServerClass</c> COM object. It advises a set of alarm subtag
 ///     item addresses, normalizes each <c>OnDataChange</c> COM callback into a
-///     <see cref="SubtagValueChange"/>, and supports writing a value (e.g. an
-///     ack-comment) to a subtag.
+///     <see cref="SubtagValueChange"/>. It is observe-only: alarm
+///     acknowledgement goes through <see cref="AlarmAckWriter"/>, which
+///     authenticates the operator on its own server.
 /// </summary>
 /// <remarks>
 ///     <para>
@@ -25,7 +26,7 @@ namespace ZB.MOM.WW.MxGateway.Worker.MxAccess;
 ///         <strong>Threading.</strong> The <c>LMXProxyServerClass</c> CLSID is
 ///         apartment-threaded and delivers <c>OnDataChange</c> via the STA
 ///         message pump. Every method on this type — the lazy <see cref="Advise"/>
-///         creation, <see cref="Write"/>, and <see cref="Dispose"/> — must be
+///         creation and <see cref="Dispose"/> — must be
 ///         invoked on the worker's STA that created the source, exactly as
 ///         <see cref="MxAccessSession"/> and <see cref="WnWrapAlarmConsumer"/>
 ///         require. The <c>OnDataChange</c> COM event also arrives on that STA.
@@ -47,9 +48,7 @@ public sealed class LmxSubtagAlarmSource : ISubtagAlarmSource
         new Dictionary<int, string>();
 
     // Handles that were actually Advise()d, tracked separately from the added
-    // set so Dispose only UnAdvises advised items. Write() can AddItem a
-    // write-only subtag (e.g. an ack-comment that was never advised); calling
-    // UnAdvise on such a handle would be an unbalanced teardown.
+    // set so Dispose only UnAdvises items this source advised.
     private readonly HashSet<int> advisedItemHandles = new HashSet<int>();
 
     private object? mxAccessComObject;
@@ -85,7 +84,7 @@ public sealed class LmxSubtagAlarmSource : ISubtagAlarmSource
     ///     <see cref="IMxAccessServer"/> with a pre-registered server handle,
     ///     bypassing the live COM factory. Exposed via
     ///     <c>InternalsVisibleTo("ZB.MOM.WW.MxGateway.Worker.Tests")</c> so tests can
-    ///     exercise <see cref="Advise"/>/<see cref="Write"/> and
+    ///     exercise <see cref="Advise"/> and
     ///     <see cref="HandleDataChange"/> without a live <c>LMXProxyServerClass</c>.
     ///     No COM event source is wired in this mode — tests drive
     ///     <see cref="HandleDataChange"/> directly to simulate an
@@ -140,29 +139,6 @@ public sealed class LmxSubtagAlarmSource : ISubtagAlarmSource
         }
     }
 
-    /// <inheritdoc />
-    public void Write(string itemAddress, object? value)
-    {
-        // Writes with MXAccess user id 0 — always an unsecured Write, never WriteSecured semantics.
-        if (itemAddress is null)
-        {
-            throw new ArgumentNullException(nameof(itemAddress));
-        }
-
-        ThrowIfDisposed();
-        EnsureRegistered();
-
-        IMxAccessServer mxServer = server!;
-        if (!itemHandlesByAddress.TryGetValue(itemAddress, out int itemHandle))
-        {
-            itemHandle = mxServer.AddItem(serverHandle, itemAddress);
-            itemHandlesByAddress[itemAddress] = itemHandle;
-            addressesByItemHandle[itemHandle] = itemAddress;
-        }
-
-        mxServer.Write(serverHandle, itemHandle, value, userId: 0);
-    }
-
     /// <summary>
     ///     Normalizes an MXAccess <c>OnDataChange</c> callback into a
     ///     <see cref="SubtagValueChange"/> and raises <see cref="ValueChanged"/>
@@ -223,8 +199,7 @@ public sealed class LmxSubtagAlarmSource : ISubtagAlarmSource
         {
             foreach (KeyValuePair<int, string> entry in addressesByItemHandle)
             {
-                // Only UnAdvise handles that were actually advised; a write-only
-                // item (added by Write but never Advise'd) was never advised.
+                // Only UnAdvise handles that were actually advised.
                 if (advisedItemHandles.Contains(entry.Key))
                 {
                     try { mxServer.UnAdvise(serverHandle, entry.Key); } catch { /* swallow — best effort */ }

src/ZB.MOM.WW.MxGateway.Worker/MxAccess/MxAccessCommandExecutor.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Globalization;
 using ZB.MOM.WW.MxGateway.Contracts.Proto;
 using ZB.MOM.WW.MxGateway.Worker.Conversion;
 using ZB.MOM.WW.MxGateway.Worker.Sta;
@@ -912,30 +913,25 @@ public sealed class MxAccessCommandExecutor : IStaCommandExecutor
                 $"AcknowledgeAlarm.alarm_guid is not a valid canonical GUID: '{payload.AlarmGuid}'.");
         }
 
+        // operator_password is a raw credential: it goes into AlarmAckOperator for
+        // MXAccess AuthenticateUser and nowhere else. Never format the payload
+        // (its generated ToString renders every field) or the exception text.
         try
         {
-            int rc = alarmCommandHandler.Acknowledge(
+            AlarmAckResult result = alarmCommandHandler.Acknowledge(
                 alarmGuid,
                 payload.Comment,
-                payload.OperatorUser,
-                payload.OperatorNode,
-                payload.OperatorDomain,
-                payload.OperatorFullName);
-            MxCommandReply reply = CreateOkReply(command);
-            reply.Hresult = rc;
-            reply.AcknowledgeAlarm = new AcknowledgeAlarmReplyPayload
-            {
-                NativeStatus = rc,
-            };
-            if (rc != 0)
-            {
-                reply.DiagnosticMessage = $"AVEVA AlarmAckByGUID returned non-zero status {rc}.";
-            }
-            return reply;
+                new AlarmAckOperator
+                {
+                    UserName = payload.OperatorUser,
+                    Domain = payload.OperatorDomain,
+                    Password = payload.OperatorPassword,
+                });
+            return CreateAcknowledgeReply(command, result);
         }
         catch (Exception ex)
         {
-            return CreateAlarmFailureReply(command, ex);
+            return CreateAcknowledgeFailureReply(command, ex);
         }
     }
 
@@ -958,35 +954,80 @@ public sealed class MxAccessCommandExecutor : IStaCommandExecutor
             return CreateInvalidRequestReply(command, "AcknowledgeAlarmByName.alarm_name is required.");
         }
 
+        // See ExecuteAcknowledgeAlarm: operator_password never leaves AlarmAckOperator.
         try
         {
-            int rc = alarmCommandHandler.AcknowledgeByName(
+            AlarmAckResult result = alarmCommandHandler.AcknowledgeByName(
                 payload.AlarmName,
                 payload.ProviderName,
                 payload.GroupName,
                 payload.Comment,
-                payload.OperatorUser,
-                payload.OperatorNode,
-                payload.OperatorDomain,
-                payload.OperatorFullName);
-            MxCommandReply reply = CreateOkReply(command);
-            reply.Hresult = rc;
-            reply.AcknowledgeAlarm = new AcknowledgeAlarmReplyPayload
-            {
-                NativeStatus = rc,
-            };
-            if (rc != 0)
-            {
-                reply.DiagnosticMessage = $"AVEVA AlarmAckByName returned non-zero status {rc}.";
-            }
-            return reply;
+                new AlarmAckOperator
+                {
+                    UserName = payload.OperatorUser,
+                    Domain = payload.OperatorDomain,
+                    Password = payload.OperatorPassword,
+                });
+            return CreateAcknowledgeReply(command, result);
         }
         catch (Exception ex)
         {
-            return CreateAlarmFailureReply(command, ex);
+            return CreateAcknowledgeFailureReply(command, ex);
         }
     }
 
+    private static MxCommandReply CreateAcknowledgeReply(StaCommand command, AlarmAckResult result)
+    {
+        MxCommandReply reply = CreateOkReply(command);
+        reply.Hresult = result.NativeStatus;
+        reply.AcknowledgeAlarm = new AcknowledgeAlarmReplyPayload { NativeStatus = result.NativeStatus };
+        reply.Statuses.Add(result.Statuses);
+        reply.DiagnosticMessage = result.Diagnostic;
+        switch (result.Outcome)
+        {
+            case AlarmAckOutcome.AlarmNotFound:
+            case AlarmAckOutcome.NotAckable:
+                reply.ProtocolStatus = new ProtocolStatus { Code = ProtocolStatusCode.InvalidRequest, Message = result.Diagnostic };
+                break;
+            case AlarmAckOutcome.AuthenticationFailed:
+            case AlarmAckOutcome.WriteRejected:
+                reply.ProtocolStatus = new ProtocolStatus { Code = ProtocolStatusCode.MxaccessFailure, Message = result.Diagnostic };
+                break;
+        }
+
+        return reply;
+    }
+
+    /// <summary>
+    ///     Maps an exception escaping an acknowledgement (e.g. the ack writer's
+    ///     MXAccess Register failing, or no active subscription) to an
+    ///     <see cref="ProtocolStatusCode.MxaccessFailure"/> reply. Only the
+    ///     exception type and HRESULT are reported: exception text on this path
+    ///     is not under our control and must not be able to echo operator input.
+    /// </summary>
+    private static MxCommandReply CreateAcknowledgeFailureReply(StaCommand command, Exception exception)
+    {
+        string diagnostic = string.Format(
+            CultureInfo.InvariantCulture,
+            "Alarm acknowledgement failed: {0} (HRESULT 0x{1:X8}).",
+            exception.GetType().FullName,
+            exception.HResult);
+        return new MxCommandReply
+        {
+            SessionId = command.SessionId,
+            CorrelationId = command.CorrelationId,
+            Kind = command.Kind,
+            Hresult = exception.HResult,
+            ProtocolStatus = new ProtocolStatus
+            {
+                Code = ProtocolStatusCode.MxaccessFailure,
+                Message = diagnostic,
+            },
+            DiagnosticMessage = diagnostic,
+            AcknowledgeAlarm = new AcknowledgeAlarmReplyPayload { NativeStatus = exception.HResult },
+        };
+    }
+
     private MxCommandReply ExecuteQueryActiveAlarms(StaCommand command)
     {
         if (command.Command.PayloadCase != MxCommand.PayloadOneofCase.QueryActiveAlarmsCommand)

src/ZB.MOM.WW.MxGateway.Worker/MxAccess/SubtagAlarmConsumer.cs

@@ -27,9 +27,11 @@ namespace ZB.MOM.WW.MxGateway.Worker.MxAccess;
 ///     <para>
 ///         The subtag path is event-driven, so <see cref="PollOnce"/> is a
 ///         no-op — value changes arrive through the source's advise stream
-///         rather than an explicit poll. Acknowledgment in subtag mode writes
-///         the comment to the target's writable ack-comment subtag rather than
-///         calling a native <c>AlarmAckByGUID</c> / <c>AlarmAckByName</c>.
+///         rather than an explicit poll. Acknowledgment in subtag mode resolves
+///         to the target's writable ack-comment subtag
+///         (<see cref="ResolveAckTarget"/>); <see cref="AlarmAckWriter"/>
+///         performs the operator-authenticated write on its own MXAccess
+///         server, so this consumer neither advises nor writes that subtag.
 ///     </para>
 /// </remarks>
 public sealed class SubtagAlarmConsumer : IMxAccessAlarmConsumer
@@ -49,7 +51,7 @@ public sealed class SubtagAlarmConsumer : IMxAccessAlarmConsumer
     ///     Initializes the consumer over a subtag source and a watch list of
     ///     alarm targets.
     /// </summary>
-    /// <param name="source">The subtag value source to advise and write through.</param>
+    /// <param name="source">The subtag value source to advise.</param>
     /// <param name="watchList">The alarm subtag targets to observe.</param>
     /// <exception cref="ArgumentNullException">
     ///     Thrown when <paramref name="source"/> or <paramref name="watchList"/>
@@ -91,7 +93,6 @@ public sealed class SubtagAlarmConsumer : IMxAccessAlarmConsumer
             AddIfNotEmpty(addresses, target.ActiveSubtag);
             AddIfNotEmpty(addresses, target.AckedSubtag);
             AddIfNotEmpty(addresses, target.PrioritySubtag);
-            AddIfNotEmpty(addresses, target.AckCommentSubtag);
         }
 
         source.Advise(addresses);
@@ -104,13 +105,7 @@ public sealed class SubtagAlarmConsumer : IMxAccessAlarmConsumer
     }
 
     /// <inheritdoc />
-    public int AcknowledgeByGuid(
-        Guid alarmGuid,
-        string ackComment,
-        string ackOperatorName,
-        string ackOperatorNode,
-        string ackOperatorDomain,
-        string ackOperatorFullName)
+    public AlarmAckTarget ResolveAckTarget(Guid alarmGuid)
     {
         if (disposed)
         {
@@ -120,22 +115,14 @@ public sealed class SubtagAlarmConsumer : IMxAccessAlarmConsumer
         if (!referencesBySyntheticGuid.TryGetValue(alarmGuid, out string reference) ||
             !targetsByReference.TryGetValue(reference, out AlarmSubtagTarget target))
         {
-            return -1;
+            return AlarmAckTarget.NotFound($"Alarm {alarmGuid} is not on the subtag watch list.");
         }
 
-        return WriteAckComment(target, ackComment);
+        return ToAckTarget(target);
     }
 
     /// <inheritdoc />
-    public int AcknowledgeByName(
-        string alarmName,
-        string providerName,
-        string groupName,
-        string ackComment,
-        string ackOperatorName,
-        string ackOperatorNode,
-        string ackOperatorDomain,
-        string ackOperatorFullName)
+    public AlarmAckTarget ResolveAckTargetByName(string alarmName, string providerName, string groupName)
     {
         if (disposed)
         {
@@ -143,12 +130,9 @@ public sealed class SubtagAlarmConsumer : IMxAccessAlarmConsumer
         }
 
         AlarmSubtagTarget? target = ResolveTargetByName(alarmName, providerName, groupName);
-        if (target is null)
-        {
-            return -1;
-        }
-
-        return WriteAckComment(target, ackComment);
+        return target is null
+            ? AlarmAckTarget.NotFound($"Alarm '{providerName}!{groupName}.{alarmName}' is not on the subtag watch list.")
+            : ToAckTarget(target);
     }
 
     /// <inheritdoc />
@@ -260,16 +244,12 @@ public sealed class SubtagAlarmConsumer : IMxAccessAlarmConsumer
         return target;
     }
 
-    private int WriteAckComment(AlarmSubtagTarget target, string ackComment)
+    private static AlarmAckTarget ToAckTarget(AlarmSubtagTarget target)
     {
-        string ackCommentSubtag = target.AckCommentSubtag ?? string.Empty;
-        if (string.IsNullOrEmpty(ackCommentSubtag))
-        {
-            return -1;
-        }
-
-        source.Write(ackCommentSubtag, ackComment);
-        return 0;
+        string ackItem = target.AckCommentSubtag ?? string.Empty;
+        return ackItem.Length == 0
+            ? AlarmAckTarget.NotAckable($"Alarm '{target.AlarmFullReference}' has no ack-comment subtag configured.")
+            : AlarmAckTarget.For(ackItem);
     }
 
     private static void AddIfNotEmpty(List<string> addresses, string? address)

src/ZB.MOM.WW.MxGateway.Worker/MxAccess/WnWrapAlarmConsumer.cs

@@ -34,7 +34,7 @@ namespace ZB.MOM.WW.MxGateway.Worker.MxAccess;
 ///         and operated from an STA thread; the worker's
 ///         <see cref="MxAccessStaSession"/> runs an STA pump that hosts it.
 ///         The consumer owns <em>no</em> internal timer: every COM call
-///         (<c>Subscribe</c>, <c>PollOnce</c>, <c>AcknowledgeBy*</c>) must
+///         (<c>Subscribe</c>, <c>PollOnce</c>) must
 ///         be invoked on the STA that created the consumer. Polling cadence
 ///         is driven externally by the worker's STA via
 ///         <c>StaRuntime.InvokeAsync(() =&gt; consumer.PollOnce())</c>, which
@@ -43,6 +43,15 @@ namespace ZB.MOM.WW.MxGateway.Worker.MxAccess;
 ///         off the owning STA and can deadlock on cross-apartment marshaling
 ///         when the STA is not pumping messages, so no such timer exists.
 ///     </para>
+///     <para>
+///         <strong>Acknowledgement.</strong> This consumer only receives
+///         alarms. The wnwrap <c>AlarmAckBy*</c> calls were accepted and then
+///         inert on the dev rig (see <c>docs/AlarmProbeFindings.md</c>), so
+///         acknowledgement no longer goes through wnwrap: the consumer resolves
+///         a Galaxy alarm to its <c>&lt;tag&gt;.AckMsg</c> item
+///         (<see cref="ResolveAckTarget"/>) and <see cref="AlarmAckWriter"/>
+///         writes that item over MXAccess as the authenticated operator.
+///     </para>
 /// </remarks>
 public sealed class WnWrapAlarmConsumer : IMxAccessAlarmConsumer
 {
@@ -50,6 +59,7 @@ public sealed class WnWrapAlarmConsumer : IMxAccessAlarmConsumer
     private const string DefaultApplicationName = "OtOpcUa.ZB.MOM.WW.MxGateway.Worker";
     private const string DefaultVersion = "1.0";
     private const int DefaultMaxAlarmsPerFetch = 1024;
+    private const string GalaxyProviderName = "Galaxy";
 
     /// <summary>
     ///     Floor on the resolved per-fetch cap. Mirrors the gateway-side
@@ -93,7 +103,6 @@ public sealed class WnWrapAlarmConsumer : IMxAccessAlarmConsumer
     private long truncatedFetchCount;
     private bool lastSnapshotTruncated;
     private wwAlarmConsumerClass? client;
-    private wwAlarmConsumerClass? ackClient;
     private bool subscribed;
     private bool disposed;
 
@@ -200,7 +209,7 @@ public sealed class WnWrapAlarmConsumer : IMxAccessAlarmConsumer
             // WIN-911-style code uses against the same wnwrap library.
             // Note rc=0 means the call was
             // accepted, not that an acknowledgement was applied — see
-            // AcknowledgeByName below and docs/AlarmProbeFindings.md.
+            // docs/AlarmProbeFindings.md. Acks now go through AlarmAckWriter.
             int init = com.IwwAlarmConsumer_InitializeConsumer(DefaultApplicationName);
             if (init != 0)
             {
@@ -241,10 +250,7 @@ public sealed class WnWrapAlarmConsumer : IMxAccessAlarmConsumer
             // SetXmlAlarmQuery is mangled (see docs/AlarmClientDiscovery.md),
             // calling it is necessary for subsequent GetXmlCurrentAlarms2
             // calls to succeed. Without it, GetXmlCurrentAlarms2 returns
-            // E_FAIL (HRESULT 0x80004005) on the first poll. SetXmlAlarmQuery
-            // also breaks AlarmAckByName on the same consumer (rejects with
-            // -55), so a separate ack-only consumer is provisioned below
-            // that gets only Initialize/Register/Subscribe (no SetXmlAlarmQuery).
+            // E_FAIL (HRESULT 0x80004005) on the first poll.
             //
             // The wnwrap interop signature is `void SetXmlAlarmQuery(string)`
             // — there is no integer return code to gate on like the other v1
@@ -268,116 +274,49 @@ public sealed class WnWrapAlarmConsumer : IMxAccessAlarmConsumer
                     ex);
             }
 
-            // Provision a parallel COM consumer for ack calls. It runs the
-            // v1 lifecycle (Initialize/Register/Subscribe) only; without
-            // SetXmlAlarmQuery, AlarmAckByName succeeds. State is read-only
-            // — we never poll this consumer.
-            ackClient = new wwAlarmConsumerClass();
-            int ackInit = ackClient.IwwAlarmConsumer_InitializeConsumer(DefaultApplicationName + ".ack");
-            int ackReg = ackClient.IwwAlarmConsumer_RegisterConsumer(
-                hWnd: 0,
-                szProductName: DefaultProductName,
-                szApplicationName: DefaultApplicationName + ".ack",
-                szVersion: DefaultVersion);
-            int ackSub = ackClient.IwwAlarmConsumer_Subscribe(
-                szSubscription: subscription,
-                wFromPri: 1,
-                wToPri: 999,
-                QueryType: eQueryType.qtSummary,
-                SortFlags: eSortFlags.sfReturnNewestFirst,
-                FilterMask: eAlarmFilterState.asAlarmActiveNow,
-                FilterSpecification: eAlarmFilterState.asAlarmActiveNow);
-            if (ackInit != 0 || ackReg != 0 || ackSub != 0)
-            {
-                throw new InvalidOperationException(
-                    $"Ack consumer setup returned non-zero status: " +
-                    $"Initialize={ackInit}, Register={ackReg}, Subscribe={ackSub}.");
-            }
-
             subscribed = true;
         }
     }
 
     /// <inheritdoc />
-    public int AcknowledgeByGuid(
-        Guid alarmGuid,
-        string ackComment,
-        string ackOperatorName,
-        string ackOperatorNode,
-        string ackOperatorDomain,
-        string ackOperatorFullName)
+    public AlarmAckTarget ResolveAckTarget(Guid alarmGuid)
     {
         if (disposed) throw new ObjectDisposedException(nameof(WnWrapAlarmConsumer));
+        MxAlarmSnapshotRecord? record;
+        lock (syncRoot)
+        {
+            latestSnapshot.TryGetValue(alarmGuid, out record);
+        }
 
-        wwAlarmConsumerClass com = client
-            ?? throw new ObjectDisposedException(nameof(WnWrapAlarmConsumer));
+        if (record is null)
+        {
+            return AlarmAckTarget.NotFound($"Alarm {alarmGuid} is not in the current alarm snapshot.");
+        }
 
-        // VBGUID is wnwrap's GUID interop struct (same memory layout as
-        // System.Guid: int32 + 2x int16 + 8x byte). Convert via a single
-        // unmanaged-blittable round-trip.
-        VBGUID vb = ToVbGuid(alarmGuid);
-        return com.AlarmAckByGUID(
-            AlmGUID: vb,
-            szComment: ackComment ?? string.Empty,
-            szOprName: ackOperatorName ?? string.Empty,
-            szNode: ackOperatorNode ?? string.Empty,
-            szDomainName: ackOperatorDomain ?? string.Empty,
-            szOprFullName: ackOperatorFullName ?? string.Empty);
+        return ResolveGalaxyAckTarget(record.ProviderName, record.TagName);
     }
 
     /// <inheritdoc />
-    public int AcknowledgeByName(
-        string alarmName,
-        string providerName,
-        string groupName,
-        string ackComment,
-        string ackOperatorName,
-        string ackOperatorNode,
-        string ackOperatorDomain,
-        string ackOperatorFullName)
+    public AlarmAckTarget ResolveAckTargetByName(string alarmName, string providerName, string groupName)
     {
         if (disposed) throw new ObjectDisposedException(nameof(WnWrapAlarmConsumer));
+        return ResolveGalaxyAckTarget(providerName, alarmName);
+    }
 
-        // Use the parallel ack-only consumer (no SetXmlAlarmQuery applied)
-        // — see docs/AlarmClientDiscovery.md "Option A — captured" for the
-        // empirical justification.
-        wwAlarmConsumerClass com = ackClient
-            ?? throw new InvalidOperationException(
-                "Cannot acknowledge: WnWrapAlarmConsumer was disposed or has not been subscribed yet.");
+    private static AlarmAckTarget ResolveGalaxyAckTarget(string? providerName, string? tagName)
+    {
+        if (!string.Equals(providerName, GalaxyProviderName, StringComparison.OrdinalIgnoreCase))
+        {
+            return AlarmAckTarget.NotAckable(
+                $"Alarm provider '{providerName}' is not a Galaxy provider; only Galaxy alarms can be acknowledged over MXAccess.");
+        }
 
-        // The original observation (live dev-rig 2026-05-01) was narrower than
-        // it read: the IwwAlarmConsumer2 8-arg AlarmAckByName returned -55
-        // "and looked like a stub" while the legacy 6-arg
-        // IwwAlarmConsumer.AlarmAckByName returned 0, which is how the 6-arg
-        // overload came to be the one called here. The 2026-08-18 probe
-        // corrected both halves. The -55 tracks the *consumer*, not the
-        // overload: both overloads return -55 against a
-        // SetXmlAlarmQuery-applied consumer and 0 against the ack-only one
-        // used above. And a zero return is NOT evidence the acknowledgement
-        // was applied — the probe acked a real, freshly raised alarm six ways
-        // and watched the snapshot stay UNACK_ALM, OPERATOR_NAME stay empty,
-        // and the alarm extension's own .Acked attribute stay False for 16 s
-        // after each call. On that rig the ack is accepted and then inert, so
-        // whether any wnwrap ack reaches the alarm-history path is
-        // unverified; see docs/AlarmProbeFindings.md and the 2026-08-18
-        // correction in docs/AlarmClientDiscovery.md. The 6-arg call site
-        // below therefore stays as-is for MXAccess parity — the choice is no
-        // longer justified by the rc, and rc semantics are per the probe.
-        //
-        // Operator-domain and operator-full-name fields are accepted by the
-        // proto contract for forward-compat but are not propagated to AVEVA
-        // today — wrapped in the 6-arg call so domain/full-name go to the
-        // alarm-history operator-name field via the szOprName parameter.
-        // Suppress unused-warning explicitly:
-        _ = ackOperatorDomain;
-        _ = ackOperatorFullName;
-        return com.AlarmAckByName(
-            szAlarmName: alarmName ?? string.Empty,
-            szProviderName: providerName ?? string.Empty,
-            szGroupName: groupName ?? string.Empty,
-            szComment: ackComment ?? string.Empty,
-            szOprName: ackOperatorName ?? string.Empty,
-            szNode: ackOperatorNode ?? string.Empty);
+        if (string.IsNullOrWhiteSpace(tagName))
+        {
+            return AlarmAckTarget.NotFound("Alarm record has no tag name.");
+        }
+
+        return AlarmAckTarget.For(tagName + "." + AlarmAckWriter.AckCommentAttribute);
     }
 
     /// <inheritdoc />
@@ -944,37 +883,18 @@ public sealed class WnWrapAlarmConsumer : IMxAccessAlarmConsumer
         return sb.ToString();
     }
 
-    private static VBGUID ToVbGuid(Guid g)
-    {
-        byte[] bytes = g.ToByteArray();
-        // Guid byte layout: int32-LE + int16-LE + int16-LE + 8 bytes (Data4).
-        VBGUID vb = new VBGUID
-        {
-            Data1 = BitConverter.ToInt32(bytes, 0),
-            Data2 = BitConverter.ToInt16(bytes, 4),
-            Data3 = BitConverter.ToInt16(bytes, 6),
-            Data4 = new byte[8],
-        };
-        Array.Copy(bytes, 8, vb.Data4, 0, 8);
-        return vb;
-    }
-
     /// <inheritdoc />
     public void Dispose()
     {
         wwAlarmConsumerClass? clientToDispose;
-        wwAlarmConsumerClass? ackClientToDispose;
         lock (syncRoot)
         {
             if (disposed) return;
             disposed = true;
             clientToDispose = client;
             client = null;
-            ackClientToDispose = ackClient;
-            ackClient = null;
         }
         ReleaseConsumerCom(clientToDispose);
-        ReleaseConsumerCom(ackClientToDispose);
     }
 
     private static void ReleaseConsumerCom(wwAlarmConsumerClass? consumer)

src/ZB.MOM.WW.MxGateway.Worker/MxAccess/WnalNativeAckConsumer.cs

@@ -1,273 +0,0 @@
-using System;
-using System.Runtime.InteropServices;
-using System.Text;
-
-namespace ZB.MOM.WW.MxGateway.Worker.MxAccess;
-
-/// <summary>
-///     Native alarm-acknowledge path over <c>alarmlst.dll</c>'s public <c>WNAL*</c>
-///     C exports (the same stack the AVEVA Alarm Control uses:
-///     <c>aaAlarmManagedClient → CwwAlarmConsumer → alarmlst.dll → alarmmgr.exe</c>).
-///
-///     Why this exists alongside <see cref="WnWrapAlarmConsumer"/>: the legacy
-///     <c>WNWRAPCONSUMERLib</c> COM surface cannot carry a full/secured ack —
-///     <c>AlarmAckByGUID</c> is <c>E_NOTIMPL</c>, the 8-arg <c>AlarmAckByName</c>
-///     is a vendor stub (-55), and neither exposes the signed-ack password. The
-///     native request record built by <see cref="WnalReqSetText"/> has six text
-///     fields — node, operator, comment, <b>password</b>, domain, full name — so
-///     this path can do a fully-attributed (and signed) ack.
-///
-///     THREADING: these calls are not inherently STA-bound the way the COM
-///     consumer is, but keep all of them on the worker STA for ordering/parity
-///     with the rest of the alarm surface (marshal via <c>StaRuntime.InvokeAsync</c>).
-///
-///     x86 ONLY: <c>alarmlst.dll</c> is 32-bit; this compiles into the x86 worker.
-///
-///     STATUS: the ack-SUBMIT contract (<see cref="WnalReqSetText"/>,
-///     <see cref="WnalUserRequest"/>, <see cref="WnalUserRequestEx"/>) and the
-///     request-record layout are confirmed by disassembly (see
-///     docs/alarm-ack-findings.md in the reverse-engineering workspace). The
-///     list-ACQUISITION side (obtaining <c>hAlarmList</c> + alarm handles) is
-///     deliberately NOT implemented — see the note at the end of this class.
-///     Nothing in the worker calls this type yet; it is kept for when a real
-///     list handle can be supplied by a component that owns acquisition.
-/// </summary>
-public sealed class WnalNativeAckConsumer
-{
-    private const string AlarmLst = "alarmlst.dll";
-
-    /// <summary>Request-record version stamped at WORD offset 2; WNALUserRequest rejects anything else.</summary>
-    private const ushort AlmAckVersion = 0x104;
-
-    /// <summary>Byte offset where WNALalarmReqSetText begins the string-offset table + heap.</summary>
-    private const int StringHeapBase = 0x42;
-
-    /// <summary>Sentinel the exports reject as an invalid list handle.</summary>
-    public const int InvalidAlarmList = -1;
-
-    // ---------------------------------------------------------------------
-    //  CONFIRMED exports (disassembly-verified signatures). __stdcall, ANSI.
-    // ---------------------------------------------------------------------
-
-    /// <summary>
-    ///     Pack operator identity + comment into an existing request record.
-    ///     Arg order is confirmed from the debug format string. Per-field rule:
-    ///     pass <c>null</c> to KEEP the record's existing value, "" to CLEAR it,
-    ///     a string to SET it. Strings are single-byte ASCII (strcpy_s).
-    ///     Return: positive = bytes used; NEGATIVE = record too small, magnitude
-    ///     is the required <c>recSize</c>; 0 = <paramref name="lpAlReq"/> was null.
-    /// </summary>
-    [DllImport(AlarmLst, EntryPoint = "WNALalarmReqSetText",
-        CallingConvention = CallingConvention.StdCall, CharSet = CharSet.Ansi, ExactSpelling = true)]
-    private static extern int WnalReqSetText(
-        IntPtr lpAlReq,
-        [MarshalAs(UnmanagedType.LPStr)] string? nodeName,
-        [MarshalAs(UnmanagedType.LPStr)] string? oper,
-        [MarshalAs(UnmanagedType.LPStr)] string? comment,
-        [MarshalAs(UnmanagedType.LPStr)] string? passWd,
-        [MarshalAs(UnmanagedType.LPStr)] string? domainName,
-        [MarshalAs(UnmanagedType.LPStr)] string? fullName);
-
-    /// <summary>
-    ///     Submit a user request (an ack) over the alarms SELECTED in
-    ///     <paramref name="hAlarmList"/>. a2 is reserved (0); a3 is a capacity
-    ///     hint (the native client passes the grid row count); a4 is scope
-    ///     (0 = all, 1 = selected). Returns 0 on success (provider status),
-    ///     non-zero on error.
-    /// </summary>
-    [DllImport(AlarmLst, EntryPoint = "WNALUserRequest",
-        CallingConvention = CallingConvention.StdCall, ExactSpelling = true)]
-    private static extern int WnalUserRequest(int hAlarmList, uint a2, uint a3, int a4, IntPtr lpAlmAck);
-
-    /// <summary>
-    ///     Submit a user request (an ack) against an EXPLICIT array of
-    ///     <paramref name="count"/> 4-byte alarm handles — no selection state
-    ///     required. <paramref name="a4"/> mirrors the scope/flag scalar.
-    ///     Returns 0 on success.
-    /// </summary>
-    [DllImport(AlarmLst, EntryPoint = "WNALUserRequestEx",
-        CallingConvention = CallingConvention.StdCall, ExactSpelling = true)]
-    private static extern int WnalUserRequestEx(
-        int hAlarmList, IntPtr handleArray, int count, uint a4, IntPtr lpAlmAck);
-
-    /// <summary>Acknowledge-scope values for the a4 argument.</summary>
-    private enum AckScope
-    {
-        All = 0,
-        Selected = 1,
-    }
-
-    /// <summary>
-    ///     Build a request record and submit an ack for the given alarm
-    ///     handles via <see cref="WnalUserRequestEx"/>. Caller supplies a live
-    ///     <paramref name="hAlarmList"/> and the handle(s) obtained from the
-    ///     list's records (acquisition is not implemented — see the class note).
-    ///     Returns the native status (0 == success).
-    /// </summary>
-    /// <param name="hAlarmList">A registered, subscribed alarm-list handle.</param>
-    /// <param name="alarmHandles">The 4-byte alarm handles to acknowledge.</param>
-    /// <param name="comment">Ack comment.</param>
-    /// <param name="operatorName">Operator / user name.</param>
-    /// <param name="operatorNode">Operator node name.</param>
-    /// <param name="operatorDomain">Operator domain (carried natively, unlike the COM path).</param>
-    /// <param name="operatorFullName">Operator full name (carried natively, unlike the COM path).</param>
-    /// <param name="password">Operator password for a signed/secured ack, or null.</param>
-    public int AcknowledgeByHandles(
-        int hAlarmList,
-        int[] alarmHandles,
-        string comment,
-        string operatorName,
-        string operatorNode,
-        string operatorDomain,
-        string operatorFullName,
-        string? password)
-    {
-        if (hAlarmList == InvalidAlarmList)
-            throw new ArgumentException("Invalid alarm-list handle.", nameof(hAlarmList));
-        if (alarmHandles is null || alarmHandles.Length == 0)
-            throw new ArgumentException("At least one alarm handle is required.", nameof(alarmHandles));
-
-        IntPtr record = IntPtr.Zero;
-        IntPtr handles = IntPtr.Zero;
-        try
-        {
-            record = BuildAckRecord(
-                nodeName: operatorNode,
-                oper: operatorName,
-                comment: comment,
-                passWd: password,
-                domainName: operatorDomain,
-                fullName: operatorFullName);
-
-            handles = Marshal.AllocHGlobal(alarmHandles.Length * sizeof(int));
-            for (int i = 0; i < alarmHandles.Length; i++)
-                Marshal.WriteInt32(handles, i * sizeof(int), alarmHandles[i]);
-
-            return WnalUserRequestEx(
-                hAlarmList,
-                handles,
-                alarmHandles.Length,
-                (uint)AckScope.Selected,
-                record);
-        }
-        finally
-        {
-            if (handles != IntPtr.Zero) Marshal.FreeHGlobal(handles);
-            if (record != IntPtr.Zero) Marshal.FreeHGlobal(record);
-        }
-    }
-
-    /// <summary>
-    ///     Acknowledge whatever is currently SELECTED in the list (a4 = Selected)
-    ///     via <see cref="WnalUserRequest"/>. Use when selection has already been
-    ///     established on the list rather than passing explicit handles.
-    /// </summary>
-    public int AcknowledgeSelected(
-        int hAlarmList,
-        uint rowCountHint,
-        string comment,
-        string operatorName,
-        string operatorNode,
-        string operatorDomain,
-        string operatorFullName,
-        string? password)
-    {
-        if (hAlarmList == InvalidAlarmList)
-            throw new ArgumentException("Invalid alarm-list handle.", nameof(hAlarmList));
-
-        IntPtr record = IntPtr.Zero;
-        try
-        {
-            record = BuildAckRecord(operatorNode, operatorName, comment, password, operatorDomain, operatorFullName);
-            return WnalUserRequest(hAlarmList, a2: 0, a3: rowCountHint, a4: (int)AckScope.Selected, record);
-        }
-        finally
-        {
-            if (record != IntPtr.Zero) Marshal.FreeHGlobal(record);
-        }
-    }
-
-    /// <summary>
-    ///     Allocate a zeroed request record (header + room for the string heap),
-    ///     stamp recSize + version, then let <see cref="WnalReqSetText"/> pack the
-    ///     operator/comment text. Returns an unmanaged buffer the caller must free.
-    /// </summary>
-    private static IntPtr BuildAckRecord(
-        string nodeName, string oper, string comment, string? passWd, string domainName, string fullName)
-    {
-        // recSize must be >= 0x42 + sum(strlen+1 of each field). Size generously;
-        // SetText returns a negative "needed size" if this is too small, which we
-        // honor by growing once.
-        int capacity = EstimateCapacity(nodeName, oper, comment, passWd, domainName, fullName);
-
-        for (int attempt = 0; attempt < 2; attempt++)
-        {
-            IntPtr buf = Marshal.AllocHGlobal(capacity);
-            try
-            {
-                // Zero the whole record (fixed header 0x04..0x31 stays 0 — WNALUserRequest
-                // does not validate it; it is informational/provider-filled).
-                for (int off = 0; off < capacity; off += sizeof(long))
-                {
-                    int remaining = capacity - off;
-                    if (remaining >= sizeof(long)) Marshal.WriteInt64(buf, off, 0);
-                    else for (int b = off; b < capacity; b++) Marshal.WriteByte(buf, b, 0);
-                }
-
-                Marshal.WriteInt16(buf, 0, (short)(ushort)capacity);     // WORD recSize
-                Marshal.WriteInt16(buf, 2, unchecked((short)AlmAckVersion)); // WORD version = 0x104
-
-                int rc = WnalReqSetText(buf, nodeName, oper, comment, passWd, domainName, fullName);
-                if (rc >= 0)
-                    return buf;
-
-                // rc < 0 => record too small; |rc| is the required size. Grow and retry.
-                capacity = -rc;
-                Marshal.FreeHGlobal(buf);
-            }
-            catch
-            {
-                Marshal.FreeHGlobal(buf);
-                throw;
-            }
-        }
-
-        throw new InvalidOperationException("WNALalarmReqSetText could not size the ack record.");
-    }
-
-    private static int EstimateCapacity(params string?[] fields)
-    {
-        int bytes = StringHeapBase;
-        foreach (string? f in fields)
-            bytes += (f is null ? 0 : Encoding.ASCII.GetByteCount(f)) + 1;
-        // Round up with headroom; records are tiny, over-allocation is cheap.
-        return Math.Max(1024, bytes + 64);
-    }
-
-    // ---------------------------------------------------------------------
-    //  LIST ACQUISITION — intentionally NOT implemented here, by RE conclusion.
-    //
-    //  The ABIs of WNALSelectEntry (func 0x1d) and WNALGetAlarmRecordEx (func
-    //  0x1c) are recoverable, but their SEMANTICS are not: WNALGetAlarmRecordEx
-    //  does not define the alarm-record layout — it hands alarmmgr/the provider a
-    //  set of opaque output buffers (four 0x41-byte string buffers, a 0x8b-byte
-    //  buffer, scalars) that the PROVIDER fills. So the record's GUID offset and
-    //  the 4-byte alarm handle that WNALUserRequestEx consumes are provider-defined
-    //  and cannot be read out of alarmlst.dll; likewise WNALSelectEntry's arg
-    //  meanings live on the provider side of MakeAlarmMgrFuncCall. Hand-rolling the
-    //  acquisition from static RE alone would be guessing which bytes are the
-    //  handle/GUID — a wrong guess acks the wrong alarm.
-    //
-    //  Therefore DO NOT complete the native acquisition by inference. Obtain the
-    //  hAlarmList + handles from a component that already encapsulates
-    //  register/query/match correctly:
-    //    * Preferred: aaAlarmManagedClient.dll AlarmClient.AlarmAckByGUID
-    //      (int AlarmAckByGUID(Guid, comment, oper, node, domain, fullName)) — the
-    //      Alarm Control's own code; managed signatures are exact (no ABI risk).
-    //      It is internal, so invoke by reflection from the x86 worker.
-    //    * Or drive ack through the existing WnWrapAlarmConsumer, which already
-    //      owns a registered/subscribed consumer, and fix the auth gap (Stage 0).
-    //  Keep the confirmed SUBMIT methods above for the case where a real
-    //  hAlarmList + handles are supplied by such a component.
-    // ---------------------------------------------------------------------
-}