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 18af656..0aca018 100644
--- a/src/ZB.MOM.WW.MxGateway.Worker.Tests/MxAccess/AlarmDispatcherTests.cs
+++ b/src/ZB.MOM.WW.MxGateway.Worker.Tests/MxAccess/AlarmDispatcherTests.cs
@@ -64,6 +64,41 @@ public sealed class AlarmDispatcherTests
         Assert.Equal(ts, body.TransitionTimestamp.ToDateTime());
     }
 
+    /// <summary>
+    ///     Verifies that a transition enqueued via the subtag fallback
+    ///     (<c>degraded: true</c>) is marked <see cref="OnAlarmTransitionEvent.Degraded"/>
+    ///     with <see cref="AlarmProviderMode.Subtag"/>, while the default path
+    ///     stays on the alarmmgr parity contract.
+    /// </summary>
+    [Fact]
+    public void EnqueueTransition_WhenDegraded_MarksDegradedAndSubtagProvider()
+    {
+        MxAccessEventQueue queue = new MxAccessEventQueue();
+        MxAccessAlarmEventSink sink = new MxAccessAlarmEventSink(queue, new MxAccessEventMapper());
+        sink.Attach(new object(), SessionId);
+
+        DateTime ts = new DateTime(2026, 5, 1, 17, 26, 14, 709, DateTimeKind.Utc);
+        sink.EnqueueTransition(
+            alarmFullReference: "Galaxy!TestArea.TestMachine_001.TestAlarm001",
+            sourceObjectReference: "TestMachine_001.TestAlarm001",
+            alarmTypeName: "DSC",
+            transitionKind: AlarmTransitionKind.Raise,
+            severity: 500,
+            originalRaiseTimestampUtc: null,
+            transitionTimestampUtc: ts,
+            operatorUser: string.Empty,
+            operatorComment: string.Empty,
+            category: "TestArea",
+            description: string.Empty,
+            degraded: true);
+
+        Assert.Equal(1, queue.Count);
+        Assert.True(queue.TryDequeue(out WorkerEvent? workerEvent));
+        OnAlarmTransitionEvent body = workerEvent!.Event.OnAlarmTransition;
+        Assert.True(body.Degraded);
+        Assert.Equal(AlarmProviderMode.Subtag, body.SourceProvider);
+    }
+
     /// <summary>Verifies that unchanged alarm states do not emit transitions.</summary>
     [Fact]
     public void OnTransition_WithConsecutiveUnchangedState_DoesNotEmitTransition()
diff --git a/src/ZB.MOM.WW.MxGateway.Worker.Tests/MxAccess/SyntheticAlarmGuidTests.cs b/src/ZB.MOM.WW.MxGateway.Worker.Tests/MxAccess/SyntheticAlarmGuidTests.cs
new file mode 100644
index 0000000..6877bf3
--- /dev/null
+++ b/src/ZB.MOM.WW.MxGateway.Worker.Tests/MxAccess/SyntheticAlarmGuidTests.cs
@@ -0,0 +1,27 @@
+using System;
+using ZB.MOM.WW.MxGateway.Worker.MxAccess;
+
+namespace ZB.MOM.WW.MxGateway.Worker.Tests.MxAccess;
+
+/// <summary>
+///     Unit tests for <see cref="SyntheticAlarmGuid"/>: the subtag-fallback
+///     path derives a deterministic GUID from the alarm reference, so identical
+///     references must collide and distinct references must not.
+/// </summary>
+public sealed class SyntheticAlarmGuidTests
+{
+    /// <summary>Verifies the same reference yields the same GUID.</summary>
+    [Fact]
+    public void SameReference_SameGuid() =>
+        Assert.Equal(SyntheticAlarmGuid.ForReference("A.B.C"), SyntheticAlarmGuid.ForReference("A.B.C"));
+
+    /// <summary>Verifies distinct references yield distinct GUIDs.</summary>
+    [Fact]
+    public void DifferentReference_DifferentGuid() =>
+        Assert.NotEqual(SyntheticAlarmGuid.ForReference("A.B.C"), SyntheticAlarmGuid.ForReference("A.B.D"));
+
+    /// <summary>Verifies a reference produces a non-empty GUID.</summary>
+    [Fact]
+    public void Reference_ProducesNonEmptyGuid() =>
+        Assert.NotEqual(Guid.Empty, SyntheticAlarmGuid.ForReference("A.B.C"));
+}
diff --git a/src/ZB.MOM.WW.MxGateway.Worker/MxAccess/MxAccessAlarmEventSink.cs b/src/ZB.MOM.WW.MxGateway.Worker/MxAccess/MxAccessAlarmEventSink.cs
index 8948396..f732952 100644
--- a/src/ZB.MOM.WW.MxGateway.Worker/MxAccess/MxAccessAlarmEventSink.cs
+++ b/src/ZB.MOM.WW.MxGateway.Worker/MxAccess/MxAccessAlarmEventSink.cs
@@ -86,6 +86,12 @@ public sealed class MxAccessAlarmEventSink : IMxAccessEventSink
     /// <param name="operatorComment">The operator's comment, if any.</param>
     /// <param name="category">The alarm category.</param>
     /// <param name="description">The alarm description.</param>
+    /// <param name="degraded">
+    ///     <see langword="true"/> when the transition was synthesized by the
+    ///     subtag-provider fallback rather than the native alarmmgr path.
+    ///     Defaults to <see langword="false"/> so existing alarmmgr callers
+    ///     compile unchanged and stay on the parity (alarmmgr) path.
+    /// </param>
     internal void EnqueueTransition(
         string alarmFullReference,
         string sourceObjectReference,
@@ -97,10 +103,16 @@ public sealed class MxAccessAlarmEventSink : IMxAccessEventSink
         string operatorUser,
         string operatorComment,
         string category,
-        string description)
+        string description,
+        bool degraded = false)
     {
         try
         {
+            // Degraded transitions come from the subtag fallback; the native
+            // alarmmgr (wnwrap) path stays degraded=false / ALARMMGR for parity.
+            AlarmProviderMode sourceProvider = degraded
+                ? AlarmProviderMode.Subtag
+                : AlarmProviderMode.Alarmmgr;
             MxEvent mxEvent = eventMapper.CreateOnAlarmTransition(
                 sessionId,
                 alarmFullReference,
@@ -114,7 +126,9 @@ public sealed class MxAccessAlarmEventSink : IMxAccessEventSink
                 operatorComment,
                 category,
                 description,
-                statuses: null);
+                statuses: null,
+                degraded: degraded,
+                sourceProvider: sourceProvider);
             eventQueue.Enqueue(mxEvent);
         }
         catch (Exception exception)
diff --git a/src/ZB.MOM.WW.MxGateway.Worker/MxAccess/MxAccessEventMapper.cs b/src/ZB.MOM.WW.MxGateway.Worker/MxAccess/MxAccessEventMapper.cs
index 3f3f40b..08f844f 100644
--- a/src/ZB.MOM.WW.MxGateway.Worker/MxAccess/MxAccessEventMapper.cs
+++ b/src/ZB.MOM.WW.MxGateway.Worker/MxAccess/MxAccessEventMapper.cs
@@ -124,6 +124,15 @@ public sealed class MxAccessEventMapper
     /// <param name="category">Alarm taxonomy bucket from the Galaxy template.</param>
     /// <param name="description">Human-readable alarm description.</param>
     /// <param name="statuses">Array of MxStatusProxy values from MXAccess.</param>
+    /// <param name="degraded">
+    ///     <see langword="true"/> when this transition was synthesized by the
+    ///     subtag-provider fallback rather than the native alarmmgr path.
+    ///     Defaults to <see langword="false"/> to preserve alarmmgr parity.
+    /// </param>
+    /// <param name="sourceProvider">
+    ///     The alarm provider that sourced this transition. Defaults to
+    ///     <see cref="AlarmProviderMode.Alarmmgr"/> for the native path.
+    /// </param>
     public MxEvent CreateOnAlarmTransition(
         string sessionId,
         string alarmFullReference,
@@ -137,7 +146,9 @@ public sealed class MxAccessEventMapper
         string operatorComment,
         string category,
         string description,
-        Array? statuses)
+        Array? statuses,
+        bool degraded = false,
+        AlarmProviderMode sourceProvider = AlarmProviderMode.Alarmmgr)
     {
         MxEvent mxEvent = CreateBaseEvent(
             MxEventFamily.OnAlarmTransition,
@@ -159,6 +170,8 @@ public sealed class MxAccessEventMapper
             OperatorComment = operatorComment ?? string.Empty,
             Category = category ?? string.Empty,
             Description = description ?? string.Empty,
+            Degraded = degraded,
+            SourceProvider = sourceProvider,
         };
         if (originalRaiseTimestampUtc is { } orts)
         {
diff --git a/src/ZB.MOM.WW.MxGateway.Worker/MxAccess/MxAlarmSnapshot.cs b/src/ZB.MOM.WW.MxGateway.Worker/MxAccess/MxAlarmSnapshot.cs
index 529f089..9bcee70 100644
--- a/src/ZB.MOM.WW.MxGateway.Worker/MxAccess/MxAlarmSnapshot.cs
+++ b/src/ZB.MOM.WW.MxGateway.Worker/MxAccess/MxAlarmSnapshot.cs
@@ -37,4 +37,12 @@ public sealed class MxAlarmSnapshotRecord
     public string OperatorName { get; set; } = string.Empty;
     /// <summary>Gets or sets the alarm comment.</summary>
     public string AlarmComment { get; set; } = string.Empty;
+    /// <summary>
+    ///     Gets or sets a value indicating whether this record was synthesized
+    ///     by the subtag-provider fallback rather than emitted by the native
+    ///     alarmmgr (wnwrap) path. Default <see langword="false"/> preserves
+    ///     parity for the alarmmgr path; the subtag fallback sets it to
+    ///     <see langword="true"/>.
+    /// </summary>
+    public bool Degraded { get; set; }
 }
diff --git a/src/ZB.MOM.WW.MxGateway.Worker/MxAccess/SyntheticAlarmGuid.cs b/src/ZB.MOM.WW.MxGateway.Worker/MxAccess/SyntheticAlarmGuid.cs
new file mode 100644
index 0000000..729428d
--- /dev/null
+++ b/src/ZB.MOM.WW.MxGateway.Worker/MxAccess/SyntheticAlarmGuid.cs
@@ -0,0 +1,42 @@
+using System;
+using System.Security.Cryptography;
+using System.Text;
+
+namespace ZB.MOM.WW.MxGateway.Worker.MxAccess;
+
+/// <summary>
+///     Derives a deterministic synthetic <see cref="Guid"/> from an alarm
+///     reference for the subtag-provider fallback path, which has no native
+///     MxAccess alarm GUID. Hashing the reference yields a stable identity so
+///     repeated transitions for the same alarm reference correlate downstream
+///     (acknowledge, snapshot, OPC UA mapping) without an alarmmgr-supplied GUID.
+/// </summary>
+public static class SyntheticAlarmGuid
+{
+    /// <summary>
+    ///     Produces a stable <see cref="Guid"/> for the given alarm reference.
+    ///     The same reference always maps to the same GUID; distinct references
+    ///     map to distinct GUIDs with overwhelming probability.
+    /// </summary>
+    /// <param name="reference">
+    ///     The fully-qualified alarm reference (for example
+    ///     <c>"Galaxy!Area.Tag.HiHi"</c>). Treated as UTF-8 bytes.
+    /// </param>
+    /// <returns>A deterministic, non-empty GUID derived from the reference.</returns>
+    /// <exception cref="ArgumentNullException">
+    ///     Thrown when <paramref name="reference"/> is <see langword="null"/>.
+    /// </exception>
+    public static Guid ForReference(string reference)
+    {
+        if (reference is null) throw new ArgumentNullException(nameof(reference));
+
+        byte[] bytes = Encoding.UTF8.GetBytes(reference);
+
+        // MD5 is used purely for a stable, non-cryptographic identity mapping
+        // (reference -> 16-byte GUID), never for security. Its 128-bit output
+        // fits a GUID exactly, which is why it is preferred here.
+        using MD5 md5 = MD5.Create();
+        byte[] hash = md5.ComputeHash(bytes);
+        return new Guid(hash);
+    }
+}