diff --git a/docs/AlarmClientDiscovery.md b/docs/AlarmClientDiscovery.md
index 6caa43f..7878f81 100644
--- a/docs/AlarmClientDiscovery.md
+++ b/docs/AlarmClientDiscovery.md
@@ -793,6 +793,28 @@ in the codebase for the forward-compat shape, but the gateway-side
 `AcknowledgeAlarmByName` when the public RPC supplies a recognizable
 `Provider!Group.Tag` reference.
 
+**Opt-in managed GUID ack.** Setting `MXGATEWAY_USE_MANAGED_ALARM_ACK=1`
+in the gateway's environment (workers inherit it) routes GUID-keyed acks
+through `aaAlarmManagedClient.AlarmClient.AlarmAckByGUID` instead of the
+wnwrap method. That managed method is implemented on this build and
+carries operator domain and full name natively. The worker reaches it by
+reflection (`AaManagedAlarmAckConsumer`) because the members are
+non-public, and runs its own Initialize → Register → Subscribe lifecycle
+against the alarm subscription expression. The path is deliberately
+conservative:
+
+- If the DLL cannot load or the lifecycle returns a non-zero status, the
+  worker drops back to the wnwrap ack path; alarm reads never fail
+  because of it.
+- Subtag-mode acks (forced subtag, or failover currently on the standby)
+  stay on the subtag consumer: their GUIDs are synthetic and only it can
+  resolve them.
+- By-name acks stay on wnwrap — `AlarmClient` has no by-name ack.
+
+A zero return still means *accepted*, not *applied*; a secured
+(`MxSecurityOperate`) alarm needs an authenticated operator. The skip-gated
+`AlarmManagedGuidAckLiveSmokeTests` asserts the ack actually lands.
+
 ### 5. STA / threading — resolved
 
 The wnwrap COM is `ThreadingModel=Apartment`. The consumer's
diff --git a/docs/GatewayConfiguration.md b/docs/GatewayConfiguration.md
index b80266e..4b0c0af 100644
--- a/docs/GatewayConfiguration.md
+++ b/docs/GatewayConfiguration.md
@@ -446,6 +446,13 @@ behavior.
 The alarm monitor is independent of client sessions: `AcknowledgeAlarm` and
 `StreamAlarms` are session-less RPCs served by the monitor.
 
+GUID-keyed acknowledges can opt into AVEVA's managed alarm client by setting
+the environment variable `MXGATEWAY_USE_MANAGED_ALARM_ACK=1` on the gateway
+process (workers inherit it; under NSSM, add it to the service environment).
+It is off by default and has no `MxGateway:*` option because it is still
+awaiting live confirmation on the rig. See
+[AlarmClientDiscovery](./AlarmClientDiscovery.md) ("Opt-in managed GUID ack").
+
 ### Alarm fallback options
 
 The `Fallback` sub-section controls how the alarm feed selects between the
diff --git a/src/ZB.MOM.WW.MxGateway.Worker.Tests/MxAccess/AlarmDispatcherTests.cs b/src/ZB.MOM.WW.MxGateway.Worker.Tests/MxAccess/AlarmDispatcherTests.cs
index d41b42f..7c85796 100644
--- a/src/ZB.MOM.WW.MxGateway.Worker.Tests/MxAccess/AlarmDispatcherTests.cs
+++ b/src/ZB.MOM.WW.MxGateway.Worker.Tests/MxAccess/AlarmDispatcherTests.cs
@@ -203,6 +203,100 @@ public sealed class AlarmDispatcherTests
         Assert.Equal("Alice Smith", consumer.LastAckOperatorFullName);
     }
 
+    /// <summary>Verifies that a managed ack client takes GUID acks with full operator identity.</summary>
+    [Fact]
+    public void Acknowledge_WithManagedAckClient_RoutesGuidAckToManagedClient()
+    {
+        FakeAlarmConsumer consumer = new FakeAlarmConsumer { AcknowledgeReturn = -1 };
+        FakeManagedAckClient managed = new FakeManagedAckClient { AcknowledgeReturn = 0 };
+        using AlarmDispatcher dispatcher = new AlarmDispatcher(
+            consumer,
+            new MxAccessAlarmEventSink(new MxAccessEventQueue(), new MxAccessEventMapper()),
+            SessionId,
+            managed);
+        dispatcher.Subscribe(@"\\HOST\Galaxy!Area1");
+
+        Guid guid = Guid.NewGuid();
+        int rc = dispatcher.Acknowledge(guid, "Acked", "alice", "WS01", "CORP", "Alice Smith");
+
+        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);
+    }
+
+    /// <summary>
+    ///     Verifies that a failed managed-client lifecycle neither fails the alarm
+    ///     subscription nor leaves acks routed to the broken client.
+    /// </summary>
+    [Fact]
+    public void Subscribe_WhenManagedAckClientFails_FallsBackToConsumerAck()
+    {
+        FakeAlarmConsumer consumer = new FakeAlarmConsumer { AcknowledgeReturn = 0 };
+        FakeManagedAckClient managed = new FakeManagedAckClient { ThrowOnSubscribe = true };
+        using AlarmDispatcher dispatcher = new AlarmDispatcher(
+            consumer,
+            new MxAccessAlarmEventSink(new MxAccessEventQueue(), new MxAccessEventMapper()),
+            SessionId,
+            managed);
+
+        dispatcher.Subscribe(@"\\HOST\Galaxy!Area1");
+        Guid guid = Guid.NewGuid();
+        int rc = dispatcher.Acknowledge(guid, "Acked", "alice", "WS01", "CORP", "Alice Smith");
+
+        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);
+    }
+
+    /// <summary>
+    ///     Verifies that while the failover consumer serves the subtag standby,
+    ///     GUID acks (synthetic GUIDs) stay on the consumer, not the managed client.
+    /// </summary>
+    [Fact]
+    public void Acknowledge_WhenFailoverInSubtagMode_KeepsGuidAckOnConsumer()
+    {
+        FakeAlarmConsumer primary = new FakeAlarmConsumer { ThrowOnSubscribe = true };
+        FakeAlarmConsumer standby = new FakeAlarmConsumer { AcknowledgeReturn = 0 };
+        FailoverAlarmConsumer failover = new FailoverAlarmConsumer(
+            primary, standby, new FailoverSettings(threshold: 1, probeIntervalSeconds: 0, stableProbes: 3));
+        FakeManagedAckClient managed = new FakeManagedAckClient { AcknowledgeReturn = -1 };
+        using AlarmDispatcher dispatcher = new AlarmDispatcher(
+            failover,
+            new MxAccessAlarmEventSink(new MxAccessEventQueue(), new MxAccessEventMapper()),
+            SessionId,
+            managed);
+        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");
+
+        Assert.Equal(0, rc);
+        Assert.Equal(guid, standby.LastAckGuid);
+        Assert.Equal(Guid.Empty, managed.LastAckGuid);
+    }
+
+    /// <summary>Verifies that disposing the dispatcher disposes the managed ack client.</summary>
+    [Fact]
+    public void Dispose_WithManagedAckClient_DisposesManagedClient()
+    {
+        FakeManagedAckClient managed = new FakeManagedAckClient();
+        AlarmDispatcher dispatcher = new AlarmDispatcher(
+            new FakeAlarmConsumer(),
+            new MxAccessAlarmEventSink(new MxAccessEventQueue(), new MxAccessEventMapper()),
+            SessionId,
+            managed);
+
+        dispatcher.Dispose();
+
+        Assert.True(managed.Disposed);
+    }
+
     /// <summary>Verifies that acknowledge-by-name calls are forwarded to the consumer.</summary>
     [Fact]
     public void AcknowledgeByName_WhenInvoked_ForwardsToConsumerWithFullTuple()
@@ -470,9 +564,13 @@ public sealed class AlarmDispatcherTests
             AlarmTransitionEmitted?.Invoke(this, transition);
         }
 
+        /// <summary>Gets or sets a value indicating whether <see cref="Subscribe"/> throws.</summary>
+        public bool ThrowOnSubscribe { get; set; }
+
         /// <inheritdoc />
         public void Subscribe(string subscription)
         {
+            if (ThrowOnSubscribe) throw new InvalidOperationException("subscribe failed");
             LastSubscription = subscription;
         }
 
@@ -533,4 +631,50 @@ public sealed class AlarmDispatcherTests
             Disposed = true;
         }
     }
+
+    private sealed class FakeManagedAckClient : IManagedAlarmAckClient
+    {
+        /// <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 bool Disposed { get; private set; }
+
+        /// <inheritdoc />
+        public void Subscribe(string subscription)
+        {
+            if (ThrowOnSubscribe) throw new InvalidOperationException("RegisterConsumer returned 5.");
+            LastSubscription = subscription;
+        }
+
+        /// <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;
+        }
+    }
 }
diff --git a/src/ZB.MOM.WW.MxGateway.Worker/MxAccess/AlarmCommandHandler.cs b/src/ZB.MOM.WW.MxGateway.Worker/MxAccess/AlarmCommandHandler.cs
index 8888e55..3b10631 100644
--- a/src/ZB.MOM.WW.MxGateway.Worker/MxAccess/AlarmCommandHandler.cs
+++ b/src/ZB.MOM.WW.MxGateway.Worker/MxAccess/AlarmCommandHandler.cs
@@ -182,7 +182,11 @@ public sealed class AlarmCommandHandler : IAlarmCommandHandler
             }
 
             // Optional managed ack client (opt-in via env); null → wnwrap ack.
-            IManagedAlarmAckClient? managedAck = managedAckFactory?.Invoke();
+            // 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);
             try
diff --git a/src/ZB.MOM.WW.MxGateway.Worker/MxAccess/AlarmDispatcher.cs b/src/ZB.MOM.WW.MxGateway.Worker/MxAccess/AlarmDispatcher.cs
index a76cdc4..388266e 100644
--- a/src/ZB.MOM.WW.MxGateway.Worker/MxAccess/AlarmDispatcher.cs
+++ b/src/ZB.MOM.WW.MxGateway.Worker/MxAccess/AlarmDispatcher.cs
@@ -36,7 +36,7 @@ public sealed class AlarmDispatcher : IDisposable
     private readonly MxAccessAlarmEventSink sink;
     private readonly string sessionId;
     private readonly EventHandler<MxAlarmTransitionEvent> handler;
-    private readonly IManagedAlarmAckClient? managedAck;
+    private IManagedAlarmAckClient? managedAck;
     private bool disposed;
 
     /// <summary>Initializes a new alarm dispatcher for the given consumer, sink, and session ID.</summary>
@@ -46,7 +46,9 @@ public sealed class AlarmDispatcher : IDisposable
     /// <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; null keeps the existing wnwrap ack path.
+    ///     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>
     public AlarmDispatcher(
         IMxAccessAlarmConsumer consumer,
@@ -80,10 +82,31 @@ public sealed class AlarmDispatcher : IDisposable
         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.
-        managedAck?.Subscribe(subscription);
+        // 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
@@ -105,11 +128,13 @@ public sealed class AlarmDispatcher : IDisposable
         string ackOperatorFullName)
     {
         if (disposed) throw new ObjectDisposedException(nameof(AlarmDispatcher));
-        if (managedAck is not null)
+        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.
+            // 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,
diff --git a/src/ZB.MOM.WW.MxGateway.Worker/MxAccess/WnalNativeAckConsumer.cs b/src/ZB.MOM.WW.MxGateway.Worker/MxAccess/WnalNativeAckConsumer.cs
index aaca704..b86daa9 100644
--- a/src/ZB.MOM.WW.MxGateway.Worker/MxAccess/WnalNativeAckConsumer.cs
+++ b/src/ZB.MOM.WW.MxGateway.Worker/MxAccess/WnalNativeAckConsumer.cs
@@ -27,10 +27,10 @@ namespace ZB.MOM.WW.MxGateway.Worker.MxAccess;
 ///     <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 exports in <see cref="Unverified"/> are declared from
-///     their export names/ordinals but their argument signatures are NOT yet
-///     reverse-engineered — DO NOT call them until the signatures are verified,
-///     or the stdcall stack will be corrupted.
+///     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
 {
@@ -101,7 +101,7 @@ public sealed class WnalNativeAckConsumer
     ///     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 (see <see cref="Unverified"/> — acquisition path).
+    ///     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>