src/ZB.MOM.WW.OtOpcUa.Core.Abstractions/DriverAttributeInfo.cs

@@ -19,10 +19,17 @@ namespace ZB.MOM.WW.OtOpcUa.Core.Abstractions;
 /// <param name="ArrayDim">Declared array length when <see cref="IsArray"/> is true; null otherwise.</param>
 /// <param name="SecurityClass">Write-authorization tier for this attribute.</param>
 /// <param name="IsHistorized">True when this attribute is expected to feed historian / HistoryRead.</param>
+/// <param name="IsAlarm">
+///     True when this attribute represents an alarm condition (Galaxy: has an
+///     <c>AlarmExtension</c> primitive). The generic node-manager enriches the variable with an
+///     OPC UA <c>AlarmConditionState</c> when true. Defaults to false so existing non-Galaxy
+///     drivers aren't forced to flow a flag they don't produce.
+/// </param>
 public sealed record DriverAttributeInfo(
     string FullName,
     DriverDataType DriverDataType,
     bool IsArray,
     uint? ArrayDim,
     SecurityClassification SecurityClass,
-    bool IsHistorized);
+    bool IsHistorized,
+    bool IsAlarm = false);

src/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host/Backend/DbBackedGalaxyBackend.cs

@@ -138,6 +138,7 @@ public sealed class DbBackedGalaxyBackend(GalaxyRepository repository) : IGalaxy
         ArrayDim = row.ArrayDimension is int d and > 0 ? (uint)d : null,
         SecurityClassification = row.SecurityClassification,
         IsHistorized = row.IsHistorized,
+        IsAlarm = row.IsAlarm,
     };
 
     /// <summary>

src/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host/Backend/MxAccessGalaxyBackend.cs

@@ -313,6 +313,7 @@ public sealed class MxAccessGalaxyBackend : IGalaxyBackend, IDisposable
         ArrayDim = row.ArrayDimension is int d and > 0 ? (uint)d : null,
         SecurityClassification = row.SecurityClassification,
         IsHistorized = row.IsHistorized,
+        IsAlarm = row.IsAlarm,
     };
 
     private static string MapCategory(int categoryId) => categoryId switch

src/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Proxy/GalaxyProxyDriver.cs

@@ -123,7 +123,8 @@ public sealed class GalaxyProxyDriver(GalaxyProxyOptions options)
                         IsArray: attr.IsArray,
                         ArrayDim: attr.ArrayDim,
                         SecurityClass: MapSecurity(attr.SecurityClassification),
-                        IsHistorized: attr.IsHistorized));
+                        IsHistorized: attr.IsHistorized,
+                        IsAlarm: attr.IsAlarm));
             }
         }
     }

src/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Shared/Contracts/Discovery.cs

@@ -30,6 +30,15 @@ public sealed class GalaxyAttributeInfo
     [Key(3)] public uint? ArrayDim { get; set; }
     [Key(4)] public int SecurityClassification { get; set; }
     [Key(5)] public bool IsHistorized { get; set; }
+
+    /// <summary>
+    ///     True when the attribute has an AlarmExtension primitive in the Galaxy repository
+    ///     (<c>primitive_definition.primitive_name = 'AlarmExtension'</c>). The generic
+    ///     node-manager uses this to enrich the variable's OPC UA node with an
+    ///     <c>AlarmConditionState</c> during address-space build. Added in PR 9 as the
+    ///     discovery-side foundation for the alarm event wire-up that follows in PR 10+.
+    /// </summary>
+    [Key(6)] public bool IsAlarm { get; set; }
 }
 
 [MessagePackObject]

tests/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Tests/AlarmDiscoveryTests.cs

@@ -0,0 +1,84 @@
+using System;
+using MessagePack;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Shared.Contracts;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Tests;
+
+[Trait("Category", "Unit")]
+public sealed class AlarmDiscoveryTests
+{
+    /// <summary>
+    ///     PR 9 — IsAlarm must survive the MessagePack round-trip at Key=6 position.
+    ///     Regression guard: any reorder of keys in GalaxyAttributeInfo would silently corrupt
+    ///     the flag in the wire payload since MessagePack encodes by key number, not field name.
+    /// </summary>
+    [Fact]
+    public void GalaxyAttributeInfo_IsAlarm_round_trips_true_through_MessagePack()
+    {
+        var input = new GalaxyAttributeInfo
+        {
+            AttributeName = "TankLevel",
+            MxDataType = 2,
+            IsArray = false,
+            ArrayDim = null,
+            SecurityClassification = 1,
+            IsHistorized = true,
+            IsAlarm = true,
+        };
+
+        var bytes = MessagePackSerializer.Serialize(input);
+        var decoded = MessagePackSerializer.Deserialize<GalaxyAttributeInfo>(bytes);
+
+        decoded.IsAlarm.ShouldBeTrue();
+        decoded.IsHistorized.ShouldBeTrue();
+        decoded.AttributeName.ShouldBe("TankLevel");
+    }
+
+    [Fact]
+    public void GalaxyAttributeInfo_IsAlarm_round_trips_false_through_MessagePack()
+    {
+        var input = new GalaxyAttributeInfo { AttributeName = "ColorRgb", IsAlarm = false };
+        var bytes = MessagePackSerializer.Serialize(input);
+        var decoded = MessagePackSerializer.Deserialize<GalaxyAttributeInfo>(bytes);
+        decoded.IsAlarm.ShouldBeFalse();
+    }
+
+    /// <summary>
+    ///     Wire-compat guard: payloads serialized before PR 9 (which omit Key=6) must still
+    ///     deserialize cleanly — MessagePack treats missing keys as default. This lets a newer
+    ///     Proxy talk to an older Host during a rolling upgrade without a crash.
+    /// </summary>
+    [Fact]
+    public void Pre_PR9_payload_without_IsAlarm_key_deserializes_with_default_false()
+    {
+        // Build a 6-field payload (keys 0..5) matching the pre-PR9 shape by serializing a
+        // stand-in class with the same key layout but no Key=6.
+        var pre = new PrePR9Shape
+        {
+            AttributeName = "Legacy",
+            MxDataType = 1,
+            IsArray = false,
+            ArrayDim = null,
+            SecurityClassification = 0,
+            IsHistorized = false,
+        };
+        var bytes = MessagePackSerializer.Serialize(pre);
+
+        var decoded = MessagePackSerializer.Deserialize<GalaxyAttributeInfo>(bytes);
+        decoded.AttributeName.ShouldBe("Legacy");
+        decoded.IsAlarm.ShouldBeFalse();
+    }
+
+    [MessagePackObject]
+    public sealed class PrePR9Shape
+    {
+        [Key(0)] public string AttributeName { get; set; } = string.Empty;
+        [Key(1)] public int MxDataType { get; set; }
+        [Key(2)] public bool IsArray { get; set; }
+        [Key(3)] public uint? ArrayDim { get; set; }
+        [Key(4)] public int SecurityClassification { get; set; }
+        [Key(5)] public bool IsHistorized { get; set; }
+    }
+}