Phase 2 PR 8 — wire gateway-level host-status push from MxAccessGalaxyBackend. PR 4 built the IPC infrastructure for OnHostStatusChanged (MessageKind.RuntimeStatusChange frame + ConnectionSink forwarding through FrameWriter) but no backend actually raised the event; the #pragma warning disable CS0067 around MxAccessGalaxyBackend.OnHostStatusChanged declared the event for interface symmetry while acknowledging the wire-up was Phase 2 follow-up. This PR closes the gateway-level signal: MxAccessClient.ConnectionStateChanged (already raised on false→true Register and true→false Unregister transitions, including the reconnect path in MonitorLoopAsync) now drives OnHostStatusChanged with a synthetic HostConnectivityStatus tagged HostName=MxAccessClient.ClientName, RuntimeStatus="Running" on reconnect + "Stopped" on disconnect, LastObservedUtcUnixMs set to the transition moment. The Admin UI's existing IHostConnectivityProbe subscriber on GalaxyProxyDriver (HostStatusChangedEventArgs) already handles the full translation — OnHostConnectivityUpdate parses "Running"/"Stopped"/"Faulted" into the Core.Abstractions HostState enum and fires OnHostStatusChanged downstream, so this single backend-side event wire-up produces an end-to-end signal with no further Proxy changes required. Per-platform and per-AppEngine ScanState probing (the 472 LOC GalaxyRuntimeProbeManager state machine in v1 that advises <Host>.ScanState on every deployed $WinPlatform + $AppEngine gobject, tracks Unknown → Running → Stopped transitions, handles the on-change-only delivery quirk of ScanState, and surfaces IsHostStopped(gobjectId) for the node manager's Read path to short-circuit on-demand reads against known-stopped runtimes) remains deferred to a follow-up PR — the gateway-level signal gives operators the top-level transport-health rung of the status ladder, which is what matters when the Galaxy COM proxy itself goes down (vs a specific platform going down). MxAccessClient.ClientName property exposes the previously-private _clientName field so the backend can tag its pushes with a stable gateway identity — operators configure this via OTOPCUA_GALAXY_CLIENT_NAME env var (default "OtOpcUa-Galaxy.Host" per Program.cs). MxAccessGalaxyBackend constructor subscribes the new _onConnectionStateChanged field before returning + Dispose unsubscribes it via _mx.ConnectionStateChanged -= _onConnectionStateChanged to prevent the backend's own dispose from leaving a dangling handler on the MxAccessClient (same shape as MxAccessClient.SubscriptionReplayFailed PR 6 dispose discipline). #pragma warning disable CS0067 removed from around OnHostStatusChanged since the event is now raised; the directive is narrowed to cover only OnAlarmEvent which stays unraised pending the alarm subsystem port (PR 9 candidate). Tests — HostStatusPushTests (new, 2 cases): ConnectionStateChanged_raises_OnHostStatusChanged_with_gateway_name fires mx.ConnectAsync → mx.DisconnectAsync and asserts two notifications in order with HostName="GatewayClient" (the clientName passed to MxAccessClient ctor), RuntimeStatus="Running" then "Stopped", LastObservedUtcUnixMs > 0; Dispose_unsubscribes_so_post_dispose_state_changes_do_not_fire_events asserts that after backend.Dispose() a subsequent mx.DisconnectAsync does not bump the count on a registered OnHostStatusChanged handler — guards against the subscription-leak regression where a lingering backend instance would accumulate cross-reconnect notifications for a dead writer. Host.Tests csproj gains a Reference to lib/ArchestrA.MxAccess.dll (identical to the reference PR 6 adds — conflict-free cherry-pick/merge since both PRs stage the same <Reference> node; git will collapse to one when either lands first). Full Galaxy.Host.Tests Unit suite: 26 pass / 0 fail (2 new host-status + 9 PR5 historian + 15 pre-existing PostMortemMmf/RecyclePolicy/StaPump/MemoryWatchdog/EndToEndIpc/Handshake). Galaxy.Host builds clean (0 errors, 0 warnings). Branch base — PR 8 is on phase-2-pr5-historian rather than phase-2-pr4-findings because the constructor path on MxAccessGalaxyBackend gained a new historian parameter in PR 5 and the Dispose implementation needs to coordinate the two unsubscribes; targeting the earlier base would leave a trivial conflict on Dispose.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

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

@@ -19,17 +19,10 @@ 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 IsAlarm = false);
+    bool IsHistorized);

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

@@ -138,7 +138,6 @@ 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/MxAccess/MxAccessClient.cs

@@ -54,6 +54,13 @@ public sealed class MxAccessClient : IDisposable
     public int SubscriptionCount => _subscriptions.Count;
     public int ReconnectCount => _reconnectCount;
 
+    /// <summary>
+    ///     Wonderware client identity used when registering with the LMXProxyServer. Surfaced so
+    ///     <see cref="Backend.MxAccessGalaxyBackend"/> can tag its <c>OnHostStatusChanged</c> IPC
+    ///     pushes with a stable gateway name per PR 8.
+    /// </summary>
+    public string ClientName => _clientName;
+
     /// <summary>Connects on the STA thread. Idempotent. Starts the reconnect monitor on first call.</summary>
     public async Task<int> ConnectAsync()
     {

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

@@ -34,16 +34,34 @@ public sealed class MxAccessGalaxyBackend : IGalaxyBackend, IDisposable
         _refToSubs = new(System.StringComparer.OrdinalIgnoreCase);
 
     public event System.EventHandler<OnDataChangeNotification>? OnDataChange;
-#pragma warning disable CS0067 // event not yet raised — alarm + host-status wire-up in PR #4 follow-up
+#pragma warning disable CS0067 // alarm wire-up deferred to PR 9
     public event System.EventHandler<GalaxyAlarmEvent>? OnAlarmEvent;
-    public event System.EventHandler<HostConnectivityStatus>? OnHostStatusChanged;
 #pragma warning restore CS0067
+    public event System.EventHandler<HostConnectivityStatus>? OnHostStatusChanged;
+
+    private readonly System.EventHandler<bool> _onConnectionStateChanged;
 
     public MxAccessGalaxyBackend(GalaxyRepository repository, MxAccessClient mx, IHistorianDataSource? historian = null)
     {
         _repository = repository;
         _mx = mx;
         _historian = historian;
+
+        // PR 8: gateway-level host-status push. When the MXAccess COM proxy transitions
+        // connected↔disconnected, raise OnHostStatusChanged with a synthetic host entry named
+        // after the Wonderware client identity so the Admin UI surfaces top-level transport
+        // health even before per-platform/per-engine probing lands (deferred to a later PR that
+        // ports v1's GalaxyRuntimeProbeManager with ScanState subscriptions).
+        _onConnectionStateChanged = (_, connected) =>
+        {
+            OnHostStatusChanged?.Invoke(this, new HostConnectivityStatus
+            {
+                HostName = _mx.ClientName,
+                RuntimeStatus = connected ? "Running" : "Stopped",
+                LastObservedUtcUnixMs = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds(),
+            });
+        };
+        _mx.ConnectionStateChanged += _onConnectionStateChanged;
     }
 
     public async Task<OpenSessionResponse> OpenSessionAsync(OpenSessionRequest req, CancellationToken ct)
@@ -267,7 +285,11 @@ public sealed class MxAccessGalaxyBackend : IGalaxyBackend, IDisposable
     public Task<RecycleStatusResponse> RecycleAsync(RecycleHostRequest req, CancellationToken ct)
         => Task.FromResult(new RecycleStatusResponse { Accepted = true, GraceSeconds = 15 });
 
-    public void Dispose() => _historian?.Dispose();
+    public void Dispose()
+    {
+        _mx.ConnectionStateChanged -= _onConnectionStateChanged;
+        _historian?.Dispose();
+    }
 
     private static GalaxyDataValue ToWire(string reference, Vtq vtq) => new()
     {
@@ -313,7 +335,6 @@ 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

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

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

@@ -30,15 +30,6 @@ 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

@@ -1,84 +0,0 @@
-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; }
-    }
-}

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

@@ -0,0 +1,91 @@
+using System;
+using System.Collections.Concurrent;
+using System.Threading;
+using System.Threading.Tasks;
+using ArchestrA.MxAccess;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend;
+using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.Galaxy;
+using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.MxAccess;
+using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Sta;
+using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Shared.Contracts;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Tests;
+
+[Trait("Category", "Unit")]
+public sealed class HostStatusPushTests
+{
+    /// <summary>
+    ///     PR 8 — when MxAccessClient.ConnectionStateChanged fires false→true→false,
+    ///     MxAccessGalaxyBackend raises OnHostStatusChanged once per transition with
+    ///     HostName=ClientName, RuntimeStatus="Running"/"Stopped", and a timestamp.
+    ///     This is the gateway-level signal; per-platform ScanState probes are deferred.
+    /// </summary>
+    [Fact]
+    public async Task ConnectionStateChanged_raises_OnHostStatusChanged_with_gateway_name()
+    {
+        using var pump = new StaPump("Test.Sta");
+        await pump.WaitForStartedAsync();
+        var proxy = new FakeProxy();
+        var mx = new MxAccessClient(pump, proxy, "GatewayClient", new MxAccessClientOptions { AutoReconnect = false });
+        using var backend = new MxAccessGalaxyBackend(
+            new GalaxyRepository(new GalaxyRepositoryOptions { ConnectionString = "Server=.;Database=ZB;Integrated Security=True;" }),
+            mx,
+            historian: null);
+
+        var notifications = new ConcurrentQueue<HostConnectivityStatus>();
+        backend.OnHostStatusChanged += (_, s) => notifications.Enqueue(s);
+
+        await mx.ConnectAsync();
+        await mx.DisconnectAsync();
+
+        notifications.Count.ShouldBe(2);
+        notifications.TryDequeue(out var first).ShouldBeTrue();
+        first!.HostName.ShouldBe("GatewayClient");
+        first.RuntimeStatus.ShouldBe("Running");
+        first.LastObservedUtcUnixMs.ShouldBeGreaterThan(0);
+
+        notifications.TryDequeue(out var second).ShouldBeTrue();
+        second!.HostName.ShouldBe("GatewayClient");
+        second.RuntimeStatus.ShouldBe("Stopped");
+    }
+
+    [Fact]
+    public async Task Dispose_unsubscribes_so_post_dispose_state_changes_do_not_fire_events()
+    {
+        using var pump = new StaPump("Test.Sta");
+        await pump.WaitForStartedAsync();
+        var proxy = new FakeProxy();
+        var mx = new MxAccessClient(pump, proxy, "GatewayClient", new MxAccessClientOptions { AutoReconnect = false });
+        var backend = new MxAccessGalaxyBackend(
+            new GalaxyRepository(new GalaxyRepositoryOptions { ConnectionString = "Server=.;Database=ZB;Integrated Security=True;" }),
+            mx,
+            historian: null);
+
+        var count = 0;
+        backend.OnHostStatusChanged += (_, _) => Interlocked.Increment(ref count);
+
+        await mx.ConnectAsync();
+        count.ShouldBe(1);
+
+        backend.Dispose();
+        await mx.DisconnectAsync();
+
+        count.ShouldBe(1); // no second notification after Dispose
+    }
+
+    private sealed class FakeProxy : IMxProxy
+    {
+        private int _next = 1;
+        public int Register(string _) => 42;
+        public void Unregister(int _) { }
+        public int AddItem(int _, string __) => Interlocked.Increment(ref _next);
+        public void RemoveItem(int _, int __) { }
+        public void AdviseSupervisory(int _, int __) { }
+        public void UnAdviseSupervisory(int _, int __) { }
+        public void Write(int _, int __, object ___, int ____) { }
+        public event MxDataChangeHandler? OnDataChange { add { } remove { } }
+        public event MxWriteCompleteHandler? OnWriteComplete { add { } remove { } }
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Tests/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Tests.csproj

@@ -24,6 +24,11 @@
     <ItemGroup>
         <ProjectReference Include="..\..\src\ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host\ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.csproj"/>
         <Reference Include="System.ServiceProcess"/>
+        <!-- IMxProxy's delegate signatures mention ArchestrA.MxAccess.MXSTATUS_PROXY, so tests
+             implementing the interface must resolve that type at compile time. -->
+        <Reference Include="ArchestrA.MxAccess">
+            <HintPath>..\..\lib\ArchestrA.MxAccess.dll</HintPath>
+        </Reference>
     </ItemGroup>
 
     <ItemGroup>