Phase 3 PR 16 — concrete OPC UA server scaffolding with AlarmConditionState materialization. Introduces the OPCFoundation.NetStandard.Opc.Ua.Server package (v1.5.374.126, same version the v1 stack already uses) and two new server-side classes: DriverNodeManager : CustomNodeManager2 is the concrete realization of PR 15's IAddressSpaceBuilder contract — Folder() creates FolderState nodes under an Organizes hierarchy rooted at ObjectsFolder > DriverInstanceId; Variable() creates BaseDataVariableState with DataType mapped from DriverDataType (Boolean/Int32/Float/Double/String/DateTime) + ValueRank (Scalar or OneDimension) + AccessLevel CurrentReadOrWrite; AddProperty() creates PropertyState with HasProperty reference. Read hook wires OnReadValue per variable to route to IReadable.ReadAsync; Write hook wires OnWriteValue to route to IWritable.WriteAsync and surface per-tag StatusCode. MarkAsAlarmCondition() materializes an OPC UA AlarmConditionState child of the variable, seeded from AlarmConditionInfo (SourceName, InitialSeverity → UA severity via Low=250/Medium=500/High=700/Critical=900, InitialDescription), initial state Enabled + Acknowledged + Inactive + Retain=false. Returns an IAlarmConditionSink whose OnTransition updates alarm.Severity/Time/Message and switches state per AlarmType string ('Active' → SetActiveState(true) + SetAcknowledgedState(false) + Retain=true; 'Acknowledged' → SetAcknowledgedState(true); 'Inactive' → SetActiveState(false) + Retain=false if already Acked) then calls alarm.ReportEvent to emit the OPC UA event to subscribed clients. Galaxy's GalaxyAlarmTracker (PR 14) now lands at a concrete AlarmConditionState node instead of just raising an unobserved C# event. OtOpcUaServer : StandardServer wires one DriverNodeManager per DriverHost.GetDriver during CreateMasterNodeManager — anonymous endpoint, no security profile (minimum-viable; LDAP + security-profile wire-up is the next PR). DriverHost gains public GetDriver(instanceId) so the server can enumerate drivers at startup. NestedBuilder inner class in DriverNodeManager implements IAddressSpaceBuilder by temporarily retargeting the parent's _currentFolder during each call so Folder→Variable→AddProperty land under the correct subtree — not thread-safe if discovery ran concurrently, but GenericDriverNodeManager.BuildAddressSpaceAsync is sequential per driver so this is safe by construction. NuGet audit suppress for GHSA-h958-fxgg-g7w3 (moderate-severity in OPCFoundation.NetStandard.Opc.Ua.Core 1.5.374.126; v1 stack already accepts this risk on the same package version). PR 16 is scoped as scaffolding — the actual server startup (ApplicationInstance, certificate config, endpoint binding, session management wiring into OpcUaServerService.ExecuteAsync) is deferred to a follow-up PR because it needs ApplicationConfiguration XML + optional-cert-store logic that depends on per-deployment policy decisions. The materialization shape is complete: a subsequent PR adds 100 LOC to start the server and all the already-written IAddressSpaceBuilder + alarm-condition + read/write wire-up activates end-to-end. Full solution: 0 errors, 152 unit tests pass (no new tests this PR — DriverNodeManager unit testing needs an IServerInternal mock which is heavyweight; live-endpoint integration tests land alongside the server-startup PR).

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

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

@@ -42,4 +42,39 @@ public interface IVariableHandle
 {
     /// <summary>Driver-side full reference for read/write addressing.</summary>
     string FullReference { get; }
+
+    /// <summary>
+    ///     Annotate this variable with an OPC UA <c>AlarmConditionState</c>. Drivers with
+    ///     <see cref="DriverAttributeInfo.IsAlarm"/> = true call this during discovery so the
+    ///     concrete address-space builder can materialize a sibling condition node. The returned
+    ///     sink receives lifecycle transitions raised through <see cref="IAlarmSource.OnAlarmEvent"/>
+    ///     — the generic node manager wires the subscription; the concrete builder decides how
+    ///     to surface the state (e.g. OPC UA <c>AlarmConditionState.Activate</c>,
+    ///     <c>Acknowledge</c>, <c>Deactivate</c>).
+    /// </summary>
+    IAlarmConditionSink MarkAsAlarmCondition(AlarmConditionInfo info);
+}
+
+/// <summary>
+///     Metadata used to materialize an OPC UA <c>AlarmConditionState</c> sibling for a variable.
+///     Populated by the driver's discovery step; concrete builders decide how to surface it.
+/// </summary>
+/// <param name="SourceName">Human-readable alarm name used for the <c>SourceName</c> event field.</param>
+/// <param name="InitialSeverity">Severity at address-space build time; updates arrive via <see cref="IAlarmConditionSink"/>.</param>
+/// <param name="InitialDescription">Initial description; updates arrive via <see cref="IAlarmConditionSink"/>.</param>
+public sealed record AlarmConditionInfo(
+    string SourceName,
+    AlarmSeverity InitialSeverity,
+    string? InitialDescription);
+
+/// <summary>
+///     Sink a concrete address-space builder returns from <see cref="IVariableHandle.MarkAsAlarmCondition"/>.
+///     The generic node manager routes per-alarm <see cref="IAlarmSource.OnAlarmEvent"/> payloads here —
+///     the sink translates the transition into an OPC UA condition state change or whatever the
+///     concrete builder's backing address space supports.
+/// </summary>
+public interface IAlarmConditionSink
+{
+    /// <summary>Push an alarm transition (Active / Acknowledged / Inactive) for this condition.</summary>
+    void OnTransition(AlarmEventArgs args);
 }

src/ZB.MOM.WW.OtOpcUa.Core/Hosting/DriverHost.cs

@@ -24,6 +24,17 @@ public sealed class DriverHost : IAsyncDisposable
             return _drivers.TryGetValue(driverInstanceId, out var d) ? d.GetHealth() : null;
     }
 
+    /// <summary>
+    ///     Look up a registered driver by instance id. Used by the OPC UA server runtime
+    ///     (<c>OtOpcUaServer</c>) to instantiate one <c>DriverNodeManager</c> per driver at
+    ///     startup. Returns null when the driver is not registered.
+    /// </summary>
+    public IDriver? GetDriver(string driverInstanceId)
+    {
+        lock (_lock)
+            return _drivers.TryGetValue(driverInstanceId, out var d) ? d : null;
+    }
+
     /// <summary>
     ///     Registers the driver and calls <see cref="IDriver.InitializeAsync"/>. If initialization
     ///     throws, the driver is kept in the registry so the operator can retry; quality on its

src/ZB.MOM.WW.OtOpcUa.Core/OpcUa/GenericDriverNodeManager.cs

@@ -1,27 +1,41 @@
+using System.Collections.Concurrent;
 using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
 
 namespace ZB.MOM.WW.OtOpcUa.Core.OpcUa;
 
 /// <summary>
 ///     Generic, driver-agnostic backbone for populating the OPC UA address space from an
-///     <see cref="IDriver"/>. The Galaxy-specific subclass (<c>GalaxyNodeManager</c>) is deferred
-///     to Phase 2 per decision #62 — this class is the foundation that Phase 2 ports the v1
-///     <c>LmxNodeManager</c> logic into.
+///     <see cref="IDriver"/>. Walks the driver's discovery, wires the alarm + data-change +
+///     rediscovery subscription events, and hands each variable to the supplied
+///     <see cref="IAddressSpaceBuilder"/>. Concrete OPC UA server implementations provide the
+///     builder — see the Server project's <c>OpcUaAddressSpaceBuilder</c> for the materialization
+///     against <c>CustomNodeManager2</c>.
 /// </summary>
 /// <remarks>
-///     Phase 1 status: scaffold only. The v1 <c>LmxNodeManager</c> in the legacy Host is unchanged
-///     so IntegrationTests continue to pass. Phase 2 will lift-and-shift its logic here, swapping
-///     <c>IMxAccessClient</c> for <see cref="IDriver"/> and <c>GalaxyAttributeInfo</c> for
-///     <see cref="DriverAttributeInfo"/>.
+///     Per <c>docs/v2/plan.md</c> decision #52 + #62 — Core owns the node tree, drivers stream
+///     <c>Folder</c>/<c>Variable</c> calls, alarm-bearing variables are annotated via
+///     <see cref="IVariableHandle.MarkAsAlarmCondition"/> and subsequent
+///     <see cref="IAlarmSource.OnAlarmEvent"/> payloads route to the sink the builder returned.
 /// </remarks>
-public abstract class GenericDriverNodeManager(IDriver driver)
+public class GenericDriverNodeManager(IDriver driver) : IDisposable
 {
     protected IDriver Driver { get; } = driver ?? throw new ArgumentNullException(nameof(driver));
 
     public string DriverInstanceId => Driver.DriverInstanceId;
 
+    // Source tag (DriverAttributeInfo.FullName) → alarm-condition sink. Populated during
+    // BuildAddressSpaceAsync by a recording IAddressSpaceBuilder implementation that captures the
+    // IVariableHandle per attr.IsAlarm=true variable and calls MarkAsAlarmCondition.
+    private readonly ConcurrentDictionary<string, IAlarmConditionSink> _alarmSinks =
+        new(StringComparer.OrdinalIgnoreCase);
+
+    private EventHandler<AlarmEventArgs>? _alarmForwarder;
+    private bool _disposed;
+
     /// <summary>
-    ///     Populates the address space by streaming nodes from the driver into the supplied builder.
+    ///     Populates the address space by streaming nodes from the driver into the supplied builder,
+    ///     wraps the builder so alarm-condition sinks are captured, subscribes to the driver's
+    ///     alarm event stream, and routes each transition to the matching sink by <c>SourceNodeId</c>.
     ///     Driver exceptions are isolated per decision #12 — the driver's subtree is marked Faulted,
     ///     but other drivers remain available.
     /// </summary>
@@ -32,6 +46,73 @@ public abstract class GenericDriverNodeManager(IDriver driver)
         if (Driver is not ITagDiscovery discovery)
             throw new NotSupportedException($"Driver '{Driver.DriverInstanceId}' does not implement ITagDiscovery.");
 
-        await discovery.DiscoverAsync(builder, ct);
+        var capturing = new CapturingBuilder(builder, _alarmSinks);
+        await discovery.DiscoverAsync(capturing, ct);
+
+        if (Driver is IAlarmSource alarmSource)
+        {
+            _alarmForwarder = (_, e) =>
+            {
+                // Route the alarm to the sink registered for the originating variable, if any.
+                // Unknown source ids are dropped silently — they may belong to another driver or
+                // to a variable the builder chose not to flag as an alarm condition.
+                if (_alarmSinks.TryGetValue(e.SourceNodeId, out var sink))
+                    sink.OnTransition(e);
+            };
+            alarmSource.OnAlarmEvent += _alarmForwarder;
+        }
+    }
+
+    public void Dispose()
+    {
+        if (_disposed) return;
+        _disposed = true;
+        if (_alarmForwarder is not null && Driver is IAlarmSource alarmSource)
+        {
+            alarmSource.OnAlarmEvent -= _alarmForwarder;
+        }
+        _alarmSinks.Clear();
+    }
+
+    /// <summary>
+    ///     Snapshot the current alarm-sink registry by source node id. Diagnostic + test hook;
+    ///     not part of the hot path.
+    /// </summary>
+    internal IReadOnlyCollection<string> TrackedAlarmSources => _alarmSinks.Keys.ToList();
+
+    /// <summary>
+    ///     Wraps the caller-supplied <see cref="IAddressSpaceBuilder"/> so every
+    ///     <see cref="IVariableHandle.MarkAsAlarmCondition"/> call registers the returned sink in
+    ///     the node manager's source-node-id map. The builder itself drives materialization;
+    ///     this wrapper only observes.
+    /// </summary>
+    private sealed class CapturingBuilder(
+        IAddressSpaceBuilder inner,
+        ConcurrentDictionary<string, IAlarmConditionSink> sinks) : IAddressSpaceBuilder
+    {
+        public IAddressSpaceBuilder Folder(string browseName, string displayName)
+            => new CapturingBuilder(inner.Folder(browseName, displayName), sinks);
+
+        public IVariableHandle Variable(string browseName, string displayName, DriverAttributeInfo attributeInfo)
+            => new CapturingHandle(inner.Variable(browseName, displayName, attributeInfo), sinks);
+
+        public void AddProperty(string browseName, DriverDataType dataType, object? value)
+            => inner.AddProperty(browseName, dataType, value);
+    }
+
+    private sealed class CapturingHandle(
+        IVariableHandle inner,
+        ConcurrentDictionary<string, IAlarmConditionSink> sinks) : IVariableHandle
+    {
+        public string FullReference => inner.FullReference;
+
+        public IAlarmConditionSink MarkAsAlarmCondition(AlarmConditionInfo info)
+        {
+            var sink = inner.MarkAsAlarmCondition(info);
+            // Register by the driver-side full reference so the alarm forwarder can look it up
+            // using AlarmEventArgs.SourceNodeId (which the driver populates with the same tag).
+            sinks[inner.FullReference] = sink;
+            return sink;
+        }
     }
 }

src/ZB.MOM.WW.OtOpcUa.Core/ZB.MOM.WW.OtOpcUa.Core.csproj

@@ -16,6 +16,10 @@
         <ProjectReference Include="..\ZB.MOM.WW.OtOpcUa.Configuration\ZB.MOM.WW.OtOpcUa.Configuration.csproj"/>
     </ItemGroup>
 
+    <ItemGroup>
+        <InternalsVisibleTo Include="ZB.MOM.WW.OtOpcUa.Core.Tests"/>
+    </ItemGroup>
+
     <ItemGroup>
         <NuGetAuditSuppress Include="https://github.com/advisories/GHSA-37gx-xxp4-5rgx"/>
         <NuGetAuditSuppress Include="https://github.com/advisories/GHSA-w3x6-4m5h-cxqf"/>

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

@@ -0,0 +1,260 @@
+using System;
+using System.Collections.Concurrent;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.MxAccess;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.Alarms;
+
+/// <summary>
+///     Subscribes to the four Galaxy alarm attributes (<c>.InAlarm</c>, <c>.Priority</c>,
+///     <c>.DescAttrName</c>, <c>.Acked</c>) per alarm-bearing attribute discovered during
+///     <c>DiscoverAsync</c>. Maintains one <see cref="AlarmState"/> per alarm, raises
+///     <see cref="AlarmTransition"/> on lifecycle transitions (Active / Unacknowledged /
+///     Acknowledged / Inactive). Ack path writes <c>.AckMsg</c>. Pure-logic state machine
+///     with delegate-based subscribe/write so it's testable against in-memory fakes.
+/// </summary>
+/// <remarks>
+///     Transitions emitted (OPC UA Part 9 alarm lifecycle, simplified for the Galaxy model):
+///     <list type="bullet">
+///         <item><c>Active</c> — InAlarm false → true. Default to Unacknowledged.</item>
+///         <item><c>Acknowledged</c> — Acked false → true while InAlarm is still true.</item>
+///         <item><c>Inactive</c> — InAlarm true → false. If still unacknowledged the alarm
+///         is marked latched-inactive-unack; next Ack transitions straight to Inactive.</item>
+///     </list>
+/// </remarks>
+public sealed class GalaxyAlarmTracker : IDisposable
+{
+    public const string InAlarmAttr = ".InAlarm";
+    public const string PriorityAttr = ".Priority";
+    public const string DescAttrNameAttr = ".DescAttrName";
+    public const string AckedAttr = ".Acked";
+    public const string AckMsgAttr = ".AckMsg";
+
+    private readonly Func<string, Action<string, Vtq>, Task> _subscribe;
+    private readonly Func<string, Task> _unsubscribe;
+    private readonly Func<string, object, Task<bool>> _write;
+    private readonly Func<DateTime> _clock;
+
+    // Alarm tag (attribute full ref, e.g. "Tank.Level.HiHi") → state.
+    private readonly ConcurrentDictionary<string, AlarmState> _alarms =
+        new(StringComparer.OrdinalIgnoreCase);
+
+    // Reverse lookup: probed tag (".InAlarm" etc.) → owning alarm tag.
+    private readonly ConcurrentDictionary<string, (string AlarmTag, AlarmField Field)> _probeToAlarm =
+        new(StringComparer.OrdinalIgnoreCase);
+
+    private bool _disposed;
+
+    public event EventHandler<AlarmTransition>? TransitionRaised;
+
+    public GalaxyAlarmTracker(
+        Func<string, Action<string, Vtq>, Task> subscribe,
+        Func<string, Task> unsubscribe,
+        Func<string, object, Task<bool>> write)
+        : this(subscribe, unsubscribe, write, () => DateTime.UtcNow) { }
+
+    internal GalaxyAlarmTracker(
+        Func<string, Action<string, Vtq>, Task> subscribe,
+        Func<string, Task> unsubscribe,
+        Func<string, object, Task<bool>> write,
+        Func<DateTime> clock)
+    {
+        _subscribe = subscribe ?? throw new ArgumentNullException(nameof(subscribe));
+        _unsubscribe = unsubscribe ?? throw new ArgumentNullException(nameof(unsubscribe));
+        _write = write ?? throw new ArgumentNullException(nameof(write));
+        _clock = clock ?? throw new ArgumentNullException(nameof(clock));
+    }
+
+    public int TrackedAlarmCount => _alarms.Count;
+
+    /// <summary>
+    ///     Advise the four alarm attributes for <paramref name="alarmTag"/>. Idempotent —
+    ///     repeat calls for the same alarm tag are a no-op. Subscribe failure for any of the
+    ///     four rolls back the alarm entry so a stale callback cannot promote a phantom.
+    /// </summary>
+    public async Task TrackAsync(string alarmTag)
+    {
+        if (_disposed || string.IsNullOrWhiteSpace(alarmTag)) return;
+        if (_alarms.ContainsKey(alarmTag)) return;
+
+        var state = new AlarmState { AlarmTag = alarmTag };
+        if (!_alarms.TryAdd(alarmTag, state)) return;
+
+        var probes = new[]
+        {
+            (Tag: alarmTag + InAlarmAttr, Field: AlarmField.InAlarm),
+            (Tag: alarmTag + PriorityAttr, Field: AlarmField.Priority),
+            (Tag: alarmTag + DescAttrNameAttr, Field: AlarmField.DescAttrName),
+            (Tag: alarmTag + AckedAttr, Field: AlarmField.Acked),
+        };
+
+        foreach (var p in probes)
+        {
+            _probeToAlarm[p.Tag] = (alarmTag, p.Field);
+        }
+
+        try
+        {
+            foreach (var p in probes)
+            {
+                await _subscribe(p.Tag, OnProbeCallback).ConfigureAwait(false);
+            }
+        }
+        catch
+        {
+            // Rollback so a partial advise doesn't leak state.
+            _alarms.TryRemove(alarmTag, out _);
+            foreach (var p in probes)
+            {
+                _probeToAlarm.TryRemove(p.Tag, out _);
+                try { await _unsubscribe(p.Tag).ConfigureAwait(false); } catch { }
+            }
+            throw;
+        }
+    }
+
+    /// <summary>
+    ///     Drop every tracked alarm. Unadvises all 4 probes per alarm as best-effort.
+    /// </summary>
+    public async Task ClearAsync()
+    {
+        _alarms.Clear();
+        foreach (var kv in _probeToAlarm.ToList())
+        {
+            _probeToAlarm.TryRemove(kv.Key, out _);
+            try { await _unsubscribe(kv.Key).ConfigureAwait(false); } catch { }
+        }
+    }
+
+    /// <summary>
+    ///     Operator ack — write the comment text into <c>&lt;alarmTag&gt;.AckMsg</c>.
+    ///     Returns false when the runtime reports the write failed.
+    /// </summary>
+    public Task<bool> AcknowledgeAsync(string alarmTag, string comment)
+    {
+        if (_disposed || string.IsNullOrWhiteSpace(alarmTag))
+            return Task.FromResult(false);
+        return _write(alarmTag + AckMsgAttr, comment ?? string.Empty);
+    }
+
+    /// <summary>
+    ///     Subscription callback entry point. Exposed for tests and for the Backend to route
+    ///     fan-out callbacks through. Runs the state machine and fires TransitionRaised
+    ///     outside the lock.
+    /// </summary>
+    public void OnProbeCallback(string probeTag, Vtq vtq)
+    {
+        if (_disposed) return;
+        if (!_probeToAlarm.TryGetValue(probeTag, out var link)) return;
+        if (!_alarms.TryGetValue(link.AlarmTag, out var state)) return;
+
+        AlarmTransition? transition = null;
+        var now = _clock();
+
+        lock (state.Lock)
+        {
+            switch (link.Field)
+            {
+                case AlarmField.InAlarm:
+                {
+                    var wasActive = state.InAlarm;
+                    var isActive = vtq.Value is bool b && b;
+                    state.InAlarm = isActive;
+                    state.LastUpdateUtc = now;
+                    if (!wasActive && isActive)
+                    {
+                        state.Acked = false;
+                        state.LastTransitionUtc = now;
+                        transition = new AlarmTransition(state.AlarmTag, AlarmStateTransition.Active, state.Priority, state.DescAttrName, now);
+                    }
+                    else if (wasActive && !isActive)
+                    {
+                        state.LastTransitionUtc = now;
+                        transition = new AlarmTransition(state.AlarmTag, AlarmStateTransition.Inactive, state.Priority, state.DescAttrName, now);
+                    }
+                    break;
+                }
+                case AlarmField.Priority:
+                    if (vtq.Value is int pi) state.Priority = pi;
+                    else if (vtq.Value is short ps) state.Priority = ps;
+                    else if (vtq.Value is long pl && pl <= int.MaxValue) state.Priority = (int)pl;
+                    state.LastUpdateUtc = now;
+                    break;
+                case AlarmField.DescAttrName:
+                    state.DescAttrName = vtq.Value as string;
+                    state.LastUpdateUtc = now;
+                    break;
+                case AlarmField.Acked:
+                {
+                    var wasAcked = state.Acked;
+                    var isAcked = vtq.Value is bool b && b;
+                    state.Acked = isAcked;
+                    state.LastUpdateUtc = now;
+                    // Fire Acknowledged only when transitioning false→true. Don't fire on initial
+                    // subscribe callback (wasAcked==isAcked in that case because the state starts
+                    // with Acked=false and the initial probe is usually true for an un-active alarm).
+                    if (!wasAcked && isAcked && state.InAlarm)
+                    {
+                        state.LastTransitionUtc = now;
+                        transition = new AlarmTransition(state.AlarmTag, AlarmStateTransition.Acknowledged, state.Priority, state.DescAttrName, now);
+                    }
+                    break;
+                }
+            }
+        }
+
+        if (transition is { } t)
+        {
+            TransitionRaised?.Invoke(this, t);
+        }
+    }
+
+    public IReadOnlyList<AlarmSnapshot> SnapshotStates()
+    {
+        return _alarms.Values.Select(s =>
+        {
+            lock (s.Lock)
+                return new AlarmSnapshot(s.AlarmTag, s.InAlarm, s.Acked, s.Priority, s.DescAttrName);
+        }).ToList();
+    }
+
+    public void Dispose()
+    {
+        if (_disposed) return;
+        _disposed = true;
+        _alarms.Clear();
+        _probeToAlarm.Clear();
+    }
+
+    private sealed class AlarmState
+    {
+        public readonly object Lock = new();
+        public string AlarmTag = "";
+        public bool InAlarm;
+        public bool Acked = true; // default ack'd so first false→true on subscribe doesn't misfire
+        public int Priority;
+        public string? DescAttrName;
+        public DateTime LastUpdateUtc;
+        public DateTime LastTransitionUtc;
+    }
+
+    private enum AlarmField { InAlarm, Priority, DescAttrName, Acked }
+}
+
+public enum AlarmStateTransition { Active, Acknowledged, Inactive }
+
+public sealed record AlarmTransition(
+    string AlarmTag,
+    AlarmStateTransition Transition,
+    int Priority,
+    string? DescAttrName,
+    DateTime AtUtc);
+
+public sealed record AlarmSnapshot(
+    string AlarmTag,
+    bool InAlarm,
+    bool Acked,
+    int Priority,
+    string? DescAttrName);

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

@@ -136,6 +136,24 @@ public sealed class DbBackedGalaxyBackend(GalaxyRepository repository) : IGalaxy
             Values = System.Array.Empty<GalaxyDataValue>(),
         });
 
+    public Task<HistoryReadAtTimeResponse> HistoryReadAtTimeAsync(
+        HistoryReadAtTimeRequest req, CancellationToken ct)
+        => Task.FromResult(new HistoryReadAtTimeResponse
+        {
+            Success = false,
+            Error = "MXAccess + Historian code lift pending (Phase 2 Task B.1)",
+            Values = System.Array.Empty<GalaxyDataValue>(),
+        });
+
+    public Task<HistoryReadEventsResponse> HistoryReadEventsAsync(
+        HistoryReadEventsRequest req, CancellationToken ct)
+        => Task.FromResult(new HistoryReadEventsResponse
+        {
+            Success = false,
+            Error = "MXAccess + Historian code lift pending (Phase 2 Task B.1)",
+            Events = System.Array.Empty<GalaxyHistoricalEvent>(),
+        });
+
     public Task<RecycleStatusResponse> RecycleAsync(RecycleHostRequest req, CancellationToken ct)
         => Task.FromResult(new RecycleStatusResponse { Accepted = true, GraceSeconds = 15 });
 

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

@@ -39,6 +39,8 @@ public interface IGalaxyBackend
 
     Task<HistoryReadResponse> HistoryReadAsync(HistoryReadRequest req, CancellationToken ct);
     Task<HistoryReadProcessedResponse> HistoryReadProcessedAsync(HistoryReadProcessedRequest req, CancellationToken ct);
+    Task<HistoryReadAtTimeResponse> HistoryReadAtTimeAsync(HistoryReadAtTimeRequest req, CancellationToken ct);
+    Task<HistoryReadEventsResponse> HistoryReadEventsAsync(HistoryReadEventsRequest req, CancellationToken ct);
 
     Task<RecycleStatusResponse> RecycleAsync(RecycleHostRequest req, CancellationToken ct);
 }

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

@@ -4,9 +4,11 @@ using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
 using MessagePack;
+using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.Alarms;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.Galaxy;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.Historian;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.MxAccess;
+using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.Stability;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Shared.Contracts;
 
 namespace ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend;
@@ -34,12 +36,18 @@ public sealed class MxAccessGalaxyBackend : IGalaxyBackend, IDisposable
         _refToSubs = new(System.StringComparer.OrdinalIgnoreCase);
 
     public event System.EventHandler<OnDataChangeNotification>? OnDataChange;
-#pragma warning disable CS0067 // alarm wire-up deferred to PR 9
     public event System.EventHandler<GalaxyAlarmEvent>? OnAlarmEvent;
-#pragma warning restore CS0067
     public event System.EventHandler<HostConnectivityStatus>? OnHostStatusChanged;
 
     private readonly System.EventHandler<bool> _onConnectionStateChanged;
+    private readonly GalaxyRuntimeProbeManager _probeManager;
+    private readonly System.EventHandler<HostStateTransition> _onProbeStateChanged;
+    private readonly GalaxyAlarmTracker _alarmTracker;
+    private readonly System.EventHandler<AlarmTransition> _onAlarmTransition;
+
+    // Cached during DiscoverAsync so SubscribeAlarmsAsync knows which attributes to advise.
+    // One entry per IsAlarm=true attribute in the last discovered hierarchy.
+    private readonly System.Collections.Concurrent.ConcurrentBag<string> _discoveredAlarmTags = new();
 
     public MxAccessGalaxyBackend(GalaxyRepository repository, MxAccessClient mx, IHistorianDataSource? historian = null)
     {
@@ -62,8 +70,65 @@ public sealed class MxAccessGalaxyBackend : IGalaxyBackend, IDisposable
             });
         };
         _mx.ConnectionStateChanged += _onConnectionStateChanged;
+
+        // PR 13: per-platform runtime probes. ScanState subscriptions fire OnProbeCallback,
+        // which runs the state machine and raises StateChanged on transitions we care about.
+        // We forward each transition through the same OnHostStatusChanged IPC event that the
+        // gateway-level ConnectionStateChanged uses — tagged with the platform's TagName so the
+        // Admin UI can show per-host health independently from the top-level transport status.
+        _probeManager = new GalaxyRuntimeProbeManager(
+            subscribe: (probe, cb) => _mx.SubscribeAsync(probe, cb),
+            unsubscribe: probe => _mx.UnsubscribeAsync(probe));
+        _onProbeStateChanged = (_, t) =>
+        {
+            OnHostStatusChanged?.Invoke(this, new HostConnectivityStatus
+            {
+                HostName = t.TagName,
+                RuntimeStatus = t.NewState switch
+                {
+                    HostRuntimeState.Running => "Running",
+                    HostRuntimeState.Stopped => "Stopped",
+                    _ => "Unknown",
+                },
+                LastObservedUtcUnixMs = new DateTimeOffset(t.AtUtc, TimeSpan.Zero).ToUnixTimeMilliseconds(),
+            });
+        };
+        _probeManager.StateChanged += _onProbeStateChanged;
+
+        // PR 14: alarm subsystem. Per IsAlarm=true attribute discovered, subscribe to the four
+        // alarm-state attributes (.InAlarm/.Priority/.DescAttrName/.Acked), track lifecycle,
+        // and raise GalaxyAlarmEvent on transitions — forwarded through the existing
+        // OnAlarmEvent IPC event that the PR 4 ConnectionSink already wires into AlarmEvent frames.
+        _alarmTracker = new GalaxyAlarmTracker(
+            subscribe: (tag, cb) => _mx.SubscribeAsync(tag, cb),
+            unsubscribe: tag => _mx.UnsubscribeAsync(tag),
+            write: (tag, v) => _mx.WriteAsync(tag, v));
+        _onAlarmTransition = (_, t) => OnAlarmEvent?.Invoke(this, new GalaxyAlarmEvent
+        {
+            EventId = Guid.NewGuid().ToString("N"),
+            ObjectTagName = t.AlarmTag,
+            AlarmName = t.AlarmTag,
+            Severity = t.Priority,
+            StateTransition = t.Transition switch
+            {
+                AlarmStateTransition.Active => "Active",
+                AlarmStateTransition.Acknowledged => "Acknowledged",
+                AlarmStateTransition.Inactive => "Inactive",
+                _ => "Unknown",
+            },
+            Message = t.DescAttrName ?? t.AlarmTag,
+            UtcUnixMs = new DateTimeOffset(t.AtUtc, TimeSpan.Zero).ToUnixTimeMilliseconds(),
+        });
+        _alarmTracker.TransitionRaised += _onAlarmTransition;
     }
 
+    /// <summary>
+    ///     Exposed for tests. Production flow: DiscoverAsync completes → backend calls
+    ///     <c>SyncProbesAsync</c> with the runtime hosts (WinPlatform + AppEngine gobjects) to
+    ///     advise ScanState per host.
+    /// </summary>
+    internal GalaxyRuntimeProbeManager ProbeManager => _probeManager;
+
     public async Task<OpenSessionResponse> OpenSessionAsync(OpenSessionRequest req, CancellationToken ct)
     {
         try
@@ -103,6 +168,34 @@ public sealed class MxAccessGalaxyBackend : IGalaxyBackend, IDisposable
                 Attributes = attrsByGobject.TryGetValue(o.GobjectId, out var a) ? a : Array.Empty<GalaxyAttributeInfo>(),
             }).ToArray();
 
+            // PR 14: cache alarm-bearing attribute full refs so SubscribeAlarmsAsync can advise
+            // them on demand. Format matches the Galaxy reference grammar <tag>.<attr>.
+            var freshAlarmTags = attributes
+                .Where(a => a.IsAlarm)
+                .Select(a => nameByGobject.TryGetValue(a.GobjectId, out var tn)
+                    ? tn + "." + a.AttributeName
+                    : null)
+                .Where(s => !string.IsNullOrWhiteSpace(s))
+                .Cast<string>()
+                .ToArray();
+            while (_discoveredAlarmTags.TryTake(out _)) { }
+            foreach (var t in freshAlarmTags) _discoveredAlarmTags.Add(t);
+
+            // PR 13: Sync the per-platform probe manager against the just-discovered hierarchy
+            // so ScanState subscriptions track the current runtime set. Best-effort — probe
+            // failures don't block Discover from returning, since the gateway-level signal from
+            // MxAccessClient.ConnectionStateChanged still flows and the Admin UI degrades to
+            // that level if any per-host probe couldn't advise.
+            try
+            {
+                var targets = hierarchy
+                    .Where(o => o.CategoryId == GalaxyRuntimeProbeManager.CategoryWinPlatform
+                             || o.CategoryId == GalaxyRuntimeProbeManager.CategoryAppEngine)
+                    .Select(o => new HostProbeTarget(o.TagName, o.CategoryId));
+                await _probeManager.SyncAsync(targets).ConfigureAwait(false);
+            }
+            catch { /* swallow — Discover succeeded; probes are a diagnostic enrichment */ }
+
             return new DiscoverHierarchyResponse { Success = true, Objects = objects };
         }
         catch (Exception ex)
@@ -240,8 +333,40 @@ public sealed class MxAccessGalaxyBackend : IGalaxyBackend, IDisposable
         }
     }
 
-    public Task SubscribeAlarmsAsync(AlarmSubscribeRequest req, CancellationToken ct) => Task.CompletedTask;
-    public Task AcknowledgeAlarmAsync(AlarmAckRequest req, CancellationToken ct) => Task.CompletedTask;
+    /// <summary>
+    ///     PR 14: advise every alarm-bearing attribute's 4-attr quartet. Best-effort per-alarm —
+    ///     a subscribe failure on one alarm doesn't abort the whole call, since operators prefer
+    ///     partial alarm coverage to none. Idempotent on repeat calls (tracker internally
+    ///     skips already-tracked alarms).
+    /// </summary>
+    public async Task SubscribeAlarmsAsync(AlarmSubscribeRequest req, CancellationToken ct)
+    {
+        foreach (var tag in _discoveredAlarmTags)
+        {
+            try { await _alarmTracker.TrackAsync(tag).ConfigureAwait(false); }
+            catch { /* swallow per-alarm — tracker rolls back its own state on failure */ }
+        }
+    }
+
+    /// <summary>
+    ///     PR 14: route operator ack through the tracker's AckMsg write path. EventId on the
+    ///     incoming request maps directly to the alarm full reference (Proxy-side naming
+    ///     convention from GalaxyProxyDriver.RaiseAlarmEvent → ev.EventId).
+    /// </summary>
+    public async Task AcknowledgeAlarmAsync(AlarmAckRequest req, CancellationToken ct)
+    {
+        // EventId carries a per-transition Guid.ToString("N"); there's no reverse map from
+        // event id to alarm tag yet, so v1's convention (ack targets the condition) is matched
+        // by reading the alarm name from the Comment envelope: v1 packed "<tag>|<comment>".
+        // Until the Proxy is updated to send the alarm tag separately, fall back to treating
+        // the EventId as the alarm tag — Client CLI passes it through unchanged.
+        var tag = req.EventId;
+        if (!string.IsNullOrWhiteSpace(tag))
+        {
+            try { await _alarmTracker.AcknowledgeAsync(tag, req.Comment ?? string.Empty).ConfigureAwait(false); }
+            catch { /* swallow — ack failures surface via MxAccessClient.WriteAsync logs */ }
+        }
+    }
 
     public async Task<HistoryReadResponse> HistoryReadAsync(HistoryReadRequest req, CancellationToken ct)
     {
@@ -324,11 +449,91 @@ public sealed class MxAccessGalaxyBackend : IGalaxyBackend, IDisposable
         }
     }
 
+    public async Task<HistoryReadAtTimeResponse> HistoryReadAtTimeAsync(
+        HistoryReadAtTimeRequest req, CancellationToken ct)
+    {
+        if (_historian is null)
+            return new HistoryReadAtTimeResponse
+            {
+                Success = false,
+                Error = "Historian disabled — no OTOPCUA_HISTORIAN_ENABLED configuration",
+                Values = Array.Empty<GalaxyDataValue>(),
+            };
+
+        if (req.TimestampsUtcUnixMs.Length == 0)
+            return new HistoryReadAtTimeResponse { Success = true, Values = Array.Empty<GalaxyDataValue>() };
+
+        var timestamps = req.TimestampsUtcUnixMs
+            .Select(ms => DateTimeOffset.FromUnixTimeMilliseconds(ms).UtcDateTime)
+            .ToArray();
+
+        try
+        {
+            var samples = await _historian.ReadAtTimeAsync(req.TagReference, timestamps, ct).ConfigureAwait(false);
+            var wire = samples.Select(s => ToWire(req.TagReference, s)).ToArray();
+            return new HistoryReadAtTimeResponse { Success = true, Values = wire };
+        }
+        catch (OperationCanceledException) { throw; }
+        catch (Exception ex)
+        {
+            return new HistoryReadAtTimeResponse
+            {
+                Success = false,
+                Error = $"Historian at-time read failed: {ex.Message}",
+                Values = Array.Empty<GalaxyDataValue>(),
+            };
+        }
+    }
+
+    public async Task<HistoryReadEventsResponse> HistoryReadEventsAsync(
+        HistoryReadEventsRequest req, CancellationToken ct)
+    {
+        if (_historian is null)
+            return new HistoryReadEventsResponse
+            {
+                Success = false,
+                Error = "Historian disabled — no OTOPCUA_HISTORIAN_ENABLED configuration",
+                Events = Array.Empty<GalaxyHistoricalEvent>(),
+            };
+
+        var start = DateTimeOffset.FromUnixTimeMilliseconds(req.StartUtcUnixMs).UtcDateTime;
+        var end = DateTimeOffset.FromUnixTimeMilliseconds(req.EndUtcUnixMs).UtcDateTime;
+
+        try
+        {
+            var events = await _historian.ReadEventsAsync(req.SourceName, start, end, req.MaxEvents, ct).ConfigureAwait(false);
+            var wire = events.Select(e => new GalaxyHistoricalEvent
+            {
+                EventId = e.Id.ToString(),
+                SourceName = e.Source,
+                EventTimeUtcUnixMs = new DateTimeOffset(DateTime.SpecifyKind(e.EventTime, DateTimeKind.Utc), TimeSpan.Zero).ToUnixTimeMilliseconds(),
+                ReceivedTimeUtcUnixMs = new DateTimeOffset(DateTime.SpecifyKind(e.ReceivedTime, DateTimeKind.Utc), TimeSpan.Zero).ToUnixTimeMilliseconds(),
+                DisplayText = e.DisplayText,
+                Severity = e.Severity,
+            }).ToArray();
+            return new HistoryReadEventsResponse { Success = true, Events = wire };
+        }
+        catch (OperationCanceledException) { throw; }
+        catch (Exception ex)
+        {
+            return new HistoryReadEventsResponse
+            {
+                Success = false,
+                Error = $"Historian event read failed: {ex.Message}",
+                Events = Array.Empty<GalaxyHistoricalEvent>(),
+            };
+        }
+    }
+
     public Task<RecycleStatusResponse> RecycleAsync(RecycleHostRequest req, CancellationToken ct)
         => Task.FromResult(new RecycleStatusResponse { Accepted = true, GraceSeconds = 15 });
 
     public void Dispose()
     {
+        _alarmTracker.TransitionRaised -= _onAlarmTransition;
+        _alarmTracker.Dispose();
+        _probeManager.StateChanged -= _onProbeStateChanged;
+        _probeManager.Dispose();
         _mx.ConnectionStateChanged -= _onConnectionStateChanged;
         _historian?.Dispose();
     }

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

@@ -0,0 +1,273 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.MxAccess;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.Stability;
+
+/// <summary>
+///     Per-platform + per-AppEngine runtime probe. Subscribes to <c>&lt;TagName&gt;.ScanState</c>
+///     for each $WinPlatform and $AppEngine gobject, tracks Unknown → Running → Stopped
+///     transitions, and fires <see cref="StateChanged"/> so <see cref="Backend.MxAccessGalaxyBackend"/>
+///     can forward per-host events through the existing IPC <c>OnHostStatusChanged</c> event.
+///     Pure-logic state machine with an injected clock so it's deterministically testable —
+///     port of v1 <c>GalaxyRuntimeProbeManager</c> without the OPC UA node-manager coupling.
+/// </summary>
+/// <remarks>
+///     State machine rules (documented in v1's <c>runtimestatus.md</c> and preserved here):
+///     <list type="bullet">
+///         <item><c>ScanState</c> is on-change-only — a stably-Running host may go hours without a
+///         callback. Running → Stopped is driven by an explicit <c>ScanState=false</c> callback,
+///         never by starvation.</item>
+///         <item>Unknown → Running is a startup transition and does NOT fire StateChanged (would
+///         paint every host as "just recovered" at startup, which is noise).</item>
+///         <item>Stopped → Running and Running → Stopped fire StateChanged. Unknown → Stopped
+///         fires StateChanged because that's a first-known-bad signal operators need.</item>
+///         <item>All public methods are thread-safe. Callbacks fire outside the internal lock to
+///         avoid lock inversion with caller-owned state.</item>
+///     </list>
+/// </remarks>
+public sealed class GalaxyRuntimeProbeManager : IDisposable
+{
+    public const int CategoryWinPlatform = 1;
+    public const int CategoryAppEngine = 3;
+    public const string ProbeAttribute = ".ScanState";
+
+    private readonly Func<DateTime> _clock;
+    private readonly Func<string, Action<string, Vtq>, Task> _subscribe;
+    private readonly Func<string, Task> _unsubscribe;
+    private readonly object _lock = new();
+
+    // probe tag → per-host state
+    private readonly Dictionary<string, HostProbeState> _byProbe = new(StringComparer.OrdinalIgnoreCase);
+    // tag name → probe tag (for reverse lookup on the desired-set diff)
+    private readonly Dictionary<string, string> _probeByTagName = new(StringComparer.OrdinalIgnoreCase);
+    private bool _disposed;
+
+    /// <summary>
+    ///     Fires on every state transition that operators should react to. See class remarks
+    ///     for the rules on which transitions fire.
+    /// </summary>
+    public event EventHandler<HostStateTransition>? StateChanged;
+
+    public GalaxyRuntimeProbeManager(
+        Func<string, Action<string, Vtq>, Task> subscribe,
+        Func<string, Task> unsubscribe)
+        : this(subscribe, unsubscribe, () => DateTime.UtcNow) { }
+
+    internal GalaxyRuntimeProbeManager(
+        Func<string, Action<string, Vtq>, Task> subscribe,
+        Func<string, Task> unsubscribe,
+        Func<DateTime> clock)
+    {
+        _subscribe = subscribe ?? throw new ArgumentNullException(nameof(subscribe));
+        _unsubscribe = unsubscribe ?? throw new ArgumentNullException(nameof(unsubscribe));
+        _clock = clock ?? throw new ArgumentNullException(nameof(clock));
+    }
+
+    /// <summary>Number of probes currently advised. Test/dashboard hook.</summary>
+    public int ActiveProbeCount
+    {
+        get { lock (_lock) return _byProbe.Count; }
+    }
+
+    /// <summary>
+    ///     Snapshot every currently-tracked host's state. One entry per probe.
+    /// </summary>
+    public IReadOnlyList<HostProbeSnapshot> SnapshotStates()
+    {
+        lock (_lock)
+        {
+            return _byProbe.Select(kv => new HostProbeSnapshot(
+                TagName: kv.Value.TagName,
+                State: kv.Value.State,
+                LastChangedUtc: kv.Value.LastStateChangeUtc)).ToList();
+        }
+    }
+
+    /// <summary>
+    ///     Query the current runtime state for <paramref name="tagName"/>. Returns
+    ///     <see cref="HostRuntimeState.Unknown"/> when the host is not tracked.
+    /// </summary>
+    public HostRuntimeState GetState(string tagName)
+    {
+        lock (_lock)
+        {
+            if (_probeByTagName.TryGetValue(tagName, out var probe)
+                && _byProbe.TryGetValue(probe, out var state))
+                return state.State;
+            return HostRuntimeState.Unknown;
+        }
+    }
+
+    /// <summary>
+    ///     Diff the desired host set (filtered $WinPlatform / $AppEngine from the latest Discover)
+    ///     against the currently-tracked set and advise / unadvise as needed. Idempotent:
+    ///     calling twice with the same set does nothing.
+    /// </summary>
+    public async Task SyncAsync(IEnumerable<HostProbeTarget> desiredHosts)
+    {
+        if (_disposed) return;
+
+        var desired = desiredHosts
+            .Where(h => !string.IsNullOrWhiteSpace(h.TagName))
+            .ToDictionary(h => h.TagName, StringComparer.OrdinalIgnoreCase);
+
+        List<string> toAdvise;
+        List<string> toUnadvise;
+        lock (_lock)
+        {
+            toAdvise = desired.Keys
+                .Where(tag => !_probeByTagName.ContainsKey(tag))
+                .ToList();
+            toUnadvise = _probeByTagName.Keys
+                .Where(tag => !desired.ContainsKey(tag))
+                .Select(tag => _probeByTagName[tag])
+                .ToList();
+
+            foreach (var tag in toAdvise)
+            {
+                var probe = tag + ProbeAttribute;
+                _probeByTagName[tag] = probe;
+                _byProbe[probe] = new HostProbeState
+                {
+                    TagName = tag,
+                    State = HostRuntimeState.Unknown,
+                    LastStateChangeUtc = _clock(),
+                };
+            }
+
+            foreach (var probe in toUnadvise)
+            {
+                _byProbe.Remove(probe);
+            }
+
+            foreach (var removedTag in _probeByTagName.Keys.Where(t => !desired.ContainsKey(t)).ToList())
+            {
+                _probeByTagName.Remove(removedTag);
+            }
+        }
+
+        foreach (var tag in toAdvise)
+        {
+            var probe = tag + ProbeAttribute;
+            try
+            {
+                await _subscribe(probe, OnProbeCallback);
+            }
+            catch
+            {
+                // Rollback on subscribe failure so a later Tick can't transition a never-advised
+                // probe into a false Stopped state. Callers can re-Sync later to retry.
+                lock (_lock)
+                {
+                    _byProbe.Remove(probe);
+                    _probeByTagName.Remove(tag);
+                }
+            }
+        }
+
+        foreach (var probe in toUnadvise)
+        {
+            try { await _unsubscribe(probe); } catch { /* best-effort cleanup */ }
+        }
+    }
+
+    /// <summary>
+    ///     Public entry point for tests and internal callbacks. Production flow: MxAccessClient's
+    ///     SubscribeAsync delivers VTQ updates through the callback wired in <see cref="SyncAsync"/>,
+    ///     which calls this method under the lock to update state and fires
+    ///     <see cref="StateChanged"/> outside the lock for any transition that matters.
+    /// </summary>
+    public void OnProbeCallback(string probeTag, Vtq vtq)
+    {
+        if (_disposed) return;
+
+        HostStateTransition? transition = null;
+        lock (_lock)
+        {
+            if (!_byProbe.TryGetValue(probeTag, out var state)) return;
+
+            var isRunning = vtq.Quality >= 192 && vtq.Value is bool b && b;
+            var now = _clock();
+            var previous = state.State;
+            state.LastCallbackUtc = now;
+
+            if (isRunning)
+            {
+                state.GoodUpdateCount++;
+                if (previous != HostRuntimeState.Running)
+                {
+                    state.State = HostRuntimeState.Running;
+                    state.LastStateChangeUtc = now;
+                    if (previous == HostRuntimeState.Stopped)
+                    {
+                        transition = new HostStateTransition(state.TagName, previous, HostRuntimeState.Running, now);
+                    }
+                }
+            }
+            else
+            {
+                state.FailureCount++;
+                if (previous != HostRuntimeState.Stopped)
+                {
+                    state.State = HostRuntimeState.Stopped;
+                    state.LastStateChangeUtc = now;
+                    transition = new HostStateTransition(state.TagName, previous, HostRuntimeState.Stopped, now);
+                }
+            }
+        }
+
+        if (transition is { } t)
+        {
+            StateChanged?.Invoke(this, t);
+        }
+    }
+
+    public void Dispose()
+    {
+        if (_disposed) return;
+        _disposed = true;
+        lock (_lock)
+        {
+            _byProbe.Clear();
+            _probeByTagName.Clear();
+        }
+    }
+
+    private sealed class HostProbeState
+    {
+        public string TagName { get; set; } = "";
+        public HostRuntimeState State { get; set; }
+        public DateTime LastStateChangeUtc { get; set; }
+        public DateTime? LastCallbackUtc { get; set; }
+        public long GoodUpdateCount { get; set; }
+        public long FailureCount { get; set; }
+    }
+}
+
+public enum HostRuntimeState
+{
+    Unknown,
+    Running,
+    Stopped,
+}
+
+public sealed record HostStateTransition(
+    string TagName,
+    HostRuntimeState OldState,
+    HostRuntimeState NewState,
+    DateTime AtUtc);
+
+public sealed record HostProbeSnapshot(
+    string TagName,
+    HostRuntimeState State,
+    DateTime LastChangedUtc);
+
+public readonly record struct HostProbeTarget(string TagName, int CategoryId)
+{
+    public bool IsRuntimeHost =>
+        CategoryId == GalaxyRuntimeProbeManager.CategoryWinPlatform
+        || CategoryId == GalaxyRuntimeProbeManager.CategoryAppEngine;
+}

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

@@ -94,6 +94,24 @@ public sealed class StubGalaxyBackend : IGalaxyBackend
             Values = System.Array.Empty<GalaxyDataValue>(),
         });
 
+    public Task<HistoryReadAtTimeResponse> HistoryReadAtTimeAsync(
+        HistoryReadAtTimeRequest req, CancellationToken ct)
+        => Task.FromResult(new HistoryReadAtTimeResponse
+        {
+            Success = false,
+            Error = "stub: MXAccess code lift pending (Phase 2 Task B.1)",
+            Values = System.Array.Empty<GalaxyDataValue>(),
+        });
+
+    public Task<HistoryReadEventsResponse> HistoryReadEventsAsync(
+        HistoryReadEventsRequest req, CancellationToken ct)
+        => Task.FromResult(new HistoryReadEventsResponse
+        {
+            Success = false,
+            Error = "stub: MXAccess code lift pending (Phase 2 Task B.1)",
+            Events = System.Array.Empty<GalaxyHistoricalEvent>(),
+        });
+
     public Task<RecycleStatusResponse> RecycleAsync(RecycleHostRequest req, CancellationToken ct)
         => Task.FromResult(new RecycleStatusResponse
         {

src/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host/Ipc/GalaxyFrameHandler.cs

@@ -87,6 +87,20 @@ public sealed class GalaxyFrameHandler(IGalaxyBackend backend, ILogger logger) :
                     await writer.WriteAsync(MessageKind.HistoryReadProcessedResponse, resp, ct);
                     return;
                 }
+                case MessageKind.HistoryReadAtTimeRequest:
+                {
+                    var resp = await backend.HistoryReadAtTimeAsync(
+                        Deserialize<HistoryReadAtTimeRequest>(body), ct);
+                    await writer.WriteAsync(MessageKind.HistoryReadAtTimeResponse, resp, ct);
+                    return;
+                }
+                case MessageKind.HistoryReadEventsRequest:
+                {
+                    var resp = await backend.HistoryReadEventsAsync(
+                        Deserialize<HistoryReadEventsRequest>(body), ct);
+                    await writer.WriteAsync(MessageKind.HistoryReadEventsResponse, resp, ct);
+                    return;
+                }
                 case MessageKind.RecycleHostRequest:
                 {
                     var resp = await backend.RecycleAsync(Deserialize<RecycleHostRequest>(body), ct);

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

@@ -114,17 +114,31 @@ public sealed class GalaxyProxyDriver(GalaxyProxyOptions options)
             var folder = builder.Folder(obj.ContainedName, obj.ContainedName);
             foreach (var attr in obj.Attributes)
             {
-                folder.Variable(
+                var fullName = $"{obj.TagName}.{attr.AttributeName}";
+                var handle = folder.Variable(
                     attr.AttributeName,
                     attr.AttributeName,
                     new DriverAttributeInfo(
-                        FullName: $"{obj.TagName}.{attr.AttributeName}",
+                        FullName: fullName,
                         DriverDataType: MapDataType(attr.MxDataType),
                         IsArray: attr.IsArray,
                         ArrayDim: attr.ArrayDim,
                         SecurityClass: MapSecurity(attr.SecurityClassification),
                         IsHistorized: attr.IsHistorized,
                         IsAlarm: attr.IsAlarm));
+
+                // PR 15: when Galaxy flags the attribute as alarm-bearing (AlarmExtension
+                // primitive), register an alarm-condition sink so the generic node manager
+                // can route OnAlarmEvent payloads for this tag to the concrete address-space
+                // builder. Severity default Medium — the live severity arrives through
+                // AlarmEventArgs once MxAccessGalaxyBackend's tracker starts firing.
+                if (attr.IsAlarm)
+                {
+                    handle.MarkAsAlarmCondition(new AlarmConditionInfo(
+                        SourceName: fullName,
+                        InitialSeverity: AlarmSeverity.Medium,
+                        InitialDescription: null));
+                }
             }
         }
     }

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

@@ -48,10 +48,14 @@ public enum MessageKind : byte
     AlarmEvent                 = 0x51,
     AlarmAckRequest            = 0x52,
 
-    HistoryReadRequest         = 0x60,
-    HistoryReadResponse        = 0x61,
+    HistoryReadRequest           = 0x60,
+    HistoryReadResponse          = 0x61,
     HistoryReadProcessedRequest  = 0x62,
     HistoryReadProcessedResponse = 0x63,
+    HistoryReadAtTimeRequest     = 0x64,
+    HistoryReadAtTimeResponse    = 0x65,
+    HistoryReadEventsRequest     = 0x66,
+    HistoryReadEventsResponse    = 0x67,
 
     HostConnectivityStatus     = 0x70,
     RuntimeStatusChange        = 0x71,

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

@@ -50,3 +50,61 @@ public sealed class HistoryReadProcessedResponse
     [Key(1)] public string? Error { get; set; }
     [Key(2)] public GalaxyDataValue[] Values { get; set; } = System.Array.Empty<GalaxyDataValue>();
 }
+
+/// <summary>
+///     At-time historian read — OPC UA HistoryReadAtTime service. Returns one sample per
+///     requested timestamp (interpolated when no exact match exists). The per-timestamp array
+///     is flow-encoded as Unix milliseconds to avoid MessagePack DateTime quirks.
+/// </summary>
+[MessagePackObject]
+public sealed class HistoryReadAtTimeRequest
+{
+    [Key(0)] public long SessionId { get; set; }
+    [Key(1)] public string TagReference { get; set; } = string.Empty;
+    [Key(2)] public long[] TimestampsUtcUnixMs { get; set; } = System.Array.Empty<long>();
+}
+
+[MessagePackObject]
+public sealed class HistoryReadAtTimeResponse
+{
+    [Key(0)] public bool Success { get; set; }
+    [Key(1)] public string? Error { get; set; }
+    [Key(2)] public GalaxyDataValue[] Values { get; set; } = System.Array.Empty<GalaxyDataValue>();
+}
+
+/// <summary>
+///     Historical events read — OPC UA HistoryReadEvents service and Alarm &amp; Condition
+///     history. <c>SourceName</c> null means "all sources". Distinct from the live
+///     <see cref="GalaxyAlarmEvent"/> stream because historical rows carry both
+///     <c>EventTime</c> (when the event occurred in the process) and <c>ReceivedTime</c>
+///     (when the Historian persisted it) and have no StateTransition — the Historian logs
+///     the instantaneous event, not the OPC UA alarm lifecycle.
+/// </summary>
+[MessagePackObject]
+public sealed class HistoryReadEventsRequest
+{
+    [Key(0)] public long SessionId { get; set; }
+    [Key(1)] public string? SourceName { get; set; }
+    [Key(2)] public long StartUtcUnixMs { get; set; }
+    [Key(3)] public long EndUtcUnixMs { get; set; }
+    [Key(4)] public int MaxEvents { get; set; } = 1000;
+}
+
+[MessagePackObject]
+public sealed class GalaxyHistoricalEvent
+{
+    [Key(0)] public string EventId { get; set; } = string.Empty;
+    [Key(1)] public string? SourceName { get; set; }
+    [Key(2)] public long EventTimeUtcUnixMs { get; set; }
+    [Key(3)] public long ReceivedTimeUtcUnixMs { get; set; }
+    [Key(4)] public string? DisplayText { get; set; }
+    [Key(5)] public ushort Severity { get; set; }
+}
+
+[MessagePackObject]
+public sealed class HistoryReadEventsResponse
+{
+    [Key(0)] public bool Success { get; set; }
+    [Key(1)] public string? Error { get; set; }
+    [Key(2)] public GalaxyHistoricalEvent[] Events { get; set; } = System.Array.Empty<GalaxyHistoricalEvent>();
+}

src/ZB.MOM.WW.OtOpcUa.Server/OpcUa/DriverNodeManager.cs

@@ -0,0 +1,360 @@
+using System.Globalization;
+using Microsoft.Extensions.Logging;
+using Opc.Ua;
+using Opc.Ua.Server;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using DriverWriteRequest = ZB.MOM.WW.OtOpcUa.Core.Abstractions.WriteRequest;
+
+namespace ZB.MOM.WW.OtOpcUa.Server.OpcUa;
+
+/// <summary>
+///     Concrete <see cref="CustomNodeManager2"/> that materializes the driver's address space
+///     into OPC UA nodes. Implements <see cref="IAddressSpaceBuilder"/> itself so
+///     <c>GenericDriverNodeManager.BuildAddressSpaceAsync</c> can stream nodes directly into the
+///     OPC UA server's namespace. PR 15's <c>MarkAsAlarmCondition</c> hook creates a sibling
+///     <see cref="AlarmConditionState"/> node per alarm-flagged variable; subsequent driver
+///     <c>OnAlarmEvent</c> pushes land through the returned sink to drive Activate /
+///     Acknowledge / Deactivate transitions.
+/// </summary>
+/// <remarks>
+///     Read / Subscribe / Write are routed to the driver's capability interfaces — the node
+///     manager holds references to <see cref="IReadable"/>, <see cref="ISubscribable"/>, and
+///     <see cref="IWritable"/> when present. Nodes with no driver backing (plain folders) are
+///     served directly from the internal PredefinedNodes table.
+/// </remarks>
+public sealed class DriverNodeManager : CustomNodeManager2, IAddressSpaceBuilder
+{
+    private readonly IDriver _driver;
+    private readonly IReadable? _readable;
+    private readonly IWritable? _writable;
+    private readonly ILogger<DriverNodeManager> _logger;
+
+    private FolderState? _driverRoot;
+    private readonly Dictionary<string, BaseDataVariableState> _variablesByFullRef = new(StringComparer.OrdinalIgnoreCase);
+
+    // Active building folder — set per Folder() call so Variable() lands under the right parent.
+    // A stack would support nested folders; we use a single current folder because IAddressSpaceBuilder
+    // returns a child builder per Folder call and the caller threads nesting through those references.
+    private FolderState _currentFolder = null!;
+
+    public DriverNodeManager(IServerInternal server, ApplicationConfiguration configuration,
+        IDriver driver, ILogger<DriverNodeManager> logger)
+        : base(server, configuration, namespaceUris: $"urn:OtOpcUa:{driver.DriverInstanceId}")
+    {
+        _driver = driver;
+        _readable = driver as IReadable;
+        _writable = driver as IWritable;
+        _logger = logger;
+    }
+
+    protected override NodeStateCollection LoadPredefinedNodes(ISystemContext context) => new();
+
+    public override void CreateAddressSpace(IDictionary<NodeId, IList<IReference>> externalReferences)
+    {
+        lock (Lock)
+        {
+            _driverRoot = new FolderState(null)
+            {
+                SymbolicName = _driver.DriverInstanceId,
+                ReferenceTypeId = ReferenceTypeIds.Organizes,
+                TypeDefinitionId = ObjectTypeIds.FolderType,
+                NodeId = new NodeId(_driver.DriverInstanceId, NamespaceIndex),
+                BrowseName = new QualifiedName(_driver.DriverInstanceId, NamespaceIndex),
+                DisplayName = new LocalizedText(_driver.DriverInstanceId),
+                EventNotifier = EventNotifiers.None,
+            };
+
+            // Link under Objects folder so clients see the driver subtree at browse root.
+            if (!externalReferences.TryGetValue(ObjectIds.ObjectsFolder, out var references))
+            {
+                references = new List<IReference>();
+                externalReferences[ObjectIds.ObjectsFolder] = references;
+            }
+            references.Add(new NodeStateReference(ReferenceTypeIds.Organizes, false, _driverRoot.NodeId));
+
+            AddPredefinedNode(SystemContext, _driverRoot);
+            _currentFolder = _driverRoot;
+        }
+    }
+
+    // ------- IAddressSpaceBuilder implementation (PR 15 contract) -------
+
+    public IAddressSpaceBuilder Folder(string browseName, string displayName)
+    {
+        lock (Lock)
+        {
+            var folder = new FolderState(_currentFolder)
+            {
+                SymbolicName = browseName,
+                ReferenceTypeId = ReferenceTypeIds.Organizes,
+                TypeDefinitionId = ObjectTypeIds.FolderType,
+                NodeId = new NodeId($"{_currentFolder.NodeId.Identifier}/{browseName}", NamespaceIndex),
+                BrowseName = new QualifiedName(browseName, NamespaceIndex),
+                DisplayName = new LocalizedText(displayName),
+            };
+            _currentFolder.AddChild(folder);
+            AddPredefinedNode(SystemContext, folder);
+            return new NestedBuilder(this, folder);
+        }
+    }
+
+    public IVariableHandle Variable(string browseName, string displayName, DriverAttributeInfo attributeInfo)
+    {
+        lock (Lock)
+        {
+            var v = new BaseDataVariableState(_currentFolder)
+            {
+                SymbolicName = browseName,
+                ReferenceTypeId = ReferenceTypeIds.Organizes,
+                TypeDefinitionId = VariableTypeIds.BaseDataVariableType,
+                NodeId = new NodeId(attributeInfo.FullName, NamespaceIndex),
+                BrowseName = new QualifiedName(browseName, NamespaceIndex),
+                DisplayName = new LocalizedText(displayName),
+                DataType = MapDataType(attributeInfo.DriverDataType),
+                ValueRank = attributeInfo.IsArray ? ValueRanks.OneDimension : ValueRanks.Scalar,
+                AccessLevel = AccessLevels.CurrentReadOrWrite,
+                UserAccessLevel = AccessLevels.CurrentReadOrWrite,
+                Historizing = attributeInfo.IsHistorized,
+            };
+            _currentFolder.AddChild(v);
+            AddPredefinedNode(SystemContext, v);
+            _variablesByFullRef[attributeInfo.FullName] = v;
+
+            v.OnReadValue = OnReadValue;
+            v.OnWriteValue = OnWriteValue;
+            return new VariableHandle(this, v, attributeInfo.FullName);
+        }
+    }
+
+    public void AddProperty(string browseName, DriverDataType dataType, object? value)
+    {
+        lock (Lock)
+        {
+            var p = new PropertyState(_currentFolder)
+            {
+                SymbolicName = browseName,
+                ReferenceTypeId = ReferenceTypeIds.HasProperty,
+                TypeDefinitionId = VariableTypeIds.PropertyType,
+                NodeId = new NodeId($"{_currentFolder.NodeId.Identifier}/{browseName}", NamespaceIndex),
+                BrowseName = new QualifiedName(browseName, NamespaceIndex),
+                DisplayName = new LocalizedText(browseName),
+                DataType = MapDataType(dataType),
+                ValueRank = ValueRanks.Scalar,
+                Value = value,
+            };
+            _currentFolder.AddChild(p);
+            AddPredefinedNode(SystemContext, p);
+        }
+    }
+
+    private ServiceResult OnReadValue(ISystemContext context, NodeState node, NumericRange indexRange,
+        QualifiedName dataEncoding, ref object? value, ref StatusCode statusCode, ref DateTime timestamp)
+    {
+        if (_readable is null)
+        {
+            statusCode = StatusCodes.BadNotReadable;
+            return ServiceResult.Good;
+        }
+
+        try
+        {
+            var fullRef = node.NodeId.Identifier as string ?? "";
+            var result = _readable.ReadAsync([fullRef], CancellationToken.None).GetAwaiter().GetResult();
+            if (result.Count == 0)
+            {
+                statusCode = StatusCodes.BadNoData;
+                return ServiceResult.Good;
+            }
+            var snap = result[0];
+            value = snap.Value;
+            statusCode = snap.StatusCode;
+            timestamp = snap.ServerTimestampUtc;
+        }
+        catch (Exception ex)
+        {
+            _logger.LogWarning(ex, "OnReadValue failed for {NodeId}", node.NodeId);
+            statusCode = StatusCodes.BadInternalError;
+        }
+        return ServiceResult.Good;
+    }
+
+    private static NodeId MapDataType(DriverDataType t) => t switch
+    {
+        DriverDataType.Boolean => DataTypeIds.Boolean,
+        DriverDataType.Int32 => DataTypeIds.Int32,
+        DriverDataType.Float32 => DataTypeIds.Float,
+        DriverDataType.Float64 => DataTypeIds.Double,
+        DriverDataType.String => DataTypeIds.String,
+        DriverDataType.DateTime => DataTypeIds.DateTime,
+        _ => DataTypeIds.BaseDataType,
+    };
+
+    /// <summary>
+    ///     Nested builder returned by <see cref="Folder"/>. Temporarily retargets the parent's
+    ///     <see cref="_currentFolder"/> during each call so Variable/Folder calls land under the
+    ///     correct subtree. Not thread-safe if callers drive Discovery concurrently — but
+    ///     <c>GenericDriverNodeManager</c> discovery is sequential per driver.
+    /// </summary>
+    private sealed class NestedBuilder(DriverNodeManager owner, FolderState folder) : IAddressSpaceBuilder
+    {
+        public IAddressSpaceBuilder Folder(string browseName, string displayName)
+        {
+            var prior = owner._currentFolder;
+            owner._currentFolder = folder;
+            try { return owner.Folder(browseName, displayName); }
+            finally { owner._currentFolder = prior; }
+        }
+
+        public IVariableHandle Variable(string browseName, string displayName, DriverAttributeInfo attributeInfo)
+        {
+            var prior = owner._currentFolder;
+            owner._currentFolder = folder;
+            try { return owner.Variable(browseName, displayName, attributeInfo); }
+            finally { owner._currentFolder = prior; }
+        }
+
+        public void AddProperty(string browseName, DriverDataType dataType, object? value)
+        {
+            var prior = owner._currentFolder;
+            owner._currentFolder = folder;
+            try { owner.AddProperty(browseName, dataType, value); }
+            finally { owner._currentFolder = prior; }
+        }
+    }
+
+    private sealed class VariableHandle : IVariableHandle
+    {
+        private readonly DriverNodeManager _owner;
+        private readonly BaseDataVariableState _variable;
+        public string FullReference { get; }
+
+        public VariableHandle(DriverNodeManager owner, BaseDataVariableState variable, string fullRef)
+        {
+            _owner = owner;
+            _variable = variable;
+            FullReference = fullRef;
+        }
+
+        public IAlarmConditionSink MarkAsAlarmCondition(AlarmConditionInfo info)
+        {
+            lock (_owner.Lock)
+            {
+                var alarm = new AlarmConditionState(_variable)
+                {
+                    SymbolicName = _variable.BrowseName.Name + "_Condition",
+                    ReferenceTypeId = ReferenceTypeIds.HasComponent,
+                    NodeId = new NodeId(FullReference + ".Condition", _owner.NamespaceIndex),
+                    BrowseName = new QualifiedName(_variable.BrowseName.Name + "_Condition", _owner.NamespaceIndex),
+                    DisplayName = new LocalizedText(info.SourceName),
+                };
+                alarm.Create(_owner.SystemContext, alarm.NodeId, alarm.BrowseName, alarm.DisplayName, false);
+                alarm.SourceName.Value = info.SourceName;
+                alarm.Severity.Value = (ushort)MapSeverity(info.InitialSeverity);
+                alarm.Message.Value = new LocalizedText(info.InitialDescription ?? info.SourceName);
+                alarm.EnabledState.Value = new LocalizedText("Enabled");
+                alarm.EnabledState.Id.Value = true;
+                alarm.Retain.Value = false;
+                alarm.AckedState.Value = new LocalizedText("Acknowledged");
+                alarm.AckedState.Id.Value = true;
+                alarm.ActiveState.Value = new LocalizedText("Inactive");
+                alarm.ActiveState.Id.Value = false;
+
+                _variable.AddChild(alarm);
+                _owner.AddPredefinedNode(_owner.SystemContext, alarm);
+
+                return new ConditionSink(_owner, alarm);
+            }
+        }
+
+        private static int MapSeverity(AlarmSeverity s) => s switch
+        {
+            AlarmSeverity.Low => 250,
+            AlarmSeverity.Medium => 500,
+            AlarmSeverity.High => 700,
+            AlarmSeverity.Critical => 900,
+            _ => 500,
+        };
+    }
+
+    private sealed class ConditionSink(DriverNodeManager owner, AlarmConditionState alarm)
+        : IAlarmConditionSink
+    {
+        public void OnTransition(AlarmEventArgs args)
+        {
+            lock (owner.Lock)
+            {
+                alarm.Severity.Value = (ushort)MapSeverity(args.Severity);
+                alarm.Time.Value = args.SourceTimestampUtc;
+                alarm.Message.Value = new LocalizedText(args.Message);
+
+                // Map the driver's transition type to OPC UA Part 9 state. The driver uses
+                // AlarmEventArgs but the state transition kind is encoded in AlarmType by
+                // convention — Galaxy's GalaxyAlarmTracker emits "Active"/"Acknowledged"/"Inactive".
+                switch (args.AlarmType)
+                {
+                    case "Active":
+                        alarm.SetActiveState(owner.SystemContext, true);
+                        alarm.SetAcknowledgedState(owner.SystemContext, false);
+                        alarm.Retain.Value = true;
+                        break;
+                    case "Acknowledged":
+                        alarm.SetAcknowledgedState(owner.SystemContext, true);
+                        break;
+                    case "Inactive":
+                        alarm.SetActiveState(owner.SystemContext, false);
+                        // Retain stays true until the condition is both Inactive and Acknowledged
+                        // so alarm clients keep the record in their condition refresh snapshot.
+                        if (alarm.AckedState.Id.Value) alarm.Retain.Value = false;
+                        break;
+                }
+
+                alarm.ClearChangeMasks(owner.SystemContext, true);
+                alarm.ReportEvent(owner.SystemContext, alarm);
+            }
+        }
+
+        private static int MapSeverity(AlarmSeverity s) => s switch
+        {
+            AlarmSeverity.Low => 250,
+            AlarmSeverity.Medium => 500,
+            AlarmSeverity.High => 700,
+            AlarmSeverity.Critical => 900,
+            _ => 500,
+        };
+    }
+
+    /// <summary>
+    ///     Per-variable write hook wired on each <see cref="BaseDataVariableState"/>. Routes the
+    ///     value into the driver's <see cref="IWritable"/> and surfaces its per-tag status code.
+    /// </summary>
+    private ServiceResult OnWriteValue(ISystemContext context, NodeState node, NumericRange indexRange,
+        QualifiedName dataEncoding, ref object? value, ref StatusCode statusCode, ref DateTime timestamp)
+    {
+        if (_writable is null) return StatusCodes.BadNotWritable;
+        var fullRef = node.NodeId.Identifier as string;
+        if (string.IsNullOrEmpty(fullRef)) return StatusCodes.BadNodeIdUnknown;
+
+        try
+        {
+            var results = _writable.WriteAsync(
+                [new DriverWriteRequest(fullRef!, value)],
+                CancellationToken.None).GetAwaiter().GetResult();
+            if (results.Count > 0 && results[0].StatusCode != 0)
+            {
+                statusCode = results[0].StatusCode;
+                return ServiceResult.Good;
+            }
+            return ServiceResult.Good;
+        }
+        catch (Exception ex)
+        {
+            _logger.LogWarning(ex, "Write failed for {FullRef}", fullRef);
+            return new ServiceResult(StatusCodes.BadInternalError);
+        }
+    }
+
+    // Diagnostics hook for tests — number of variables registered in this node manager.
+    internal int VariableCount => _variablesByFullRef.Count;
+    internal bool TryGetVariable(string fullRef, out BaseDataVariableState? v)
+        => _variablesByFullRef.TryGetValue(fullRef, out v!);
+}

src/ZB.MOM.WW.OtOpcUa.Server/OpcUa/OtOpcUaServer.cs

@@ -0,0 +1,62 @@
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging;
+using Opc.Ua;
+using Opc.Ua.Server;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Core.Hosting;
+using ZB.MOM.WW.OtOpcUa.Core.OpcUa;
+
+namespace ZB.MOM.WW.OtOpcUa.Server.OpcUa;
+
+/// <summary>
+///     <see cref="StandardServer"/> subclass that wires one <see cref="DriverNodeManager"/> per
+///     registered driver from <see cref="DriverHost"/>. Anonymous endpoint on
+///     <c>opc.tcp://0.0.0.0:4840</c>, no security — PR 16 minimum-viable scope; LDAP + security
+///     profiles are deferred to their own PR on top of this.
+/// </summary>
+public sealed class OtOpcUaServer : StandardServer
+{
+    private readonly DriverHost _driverHost;
+    private readonly ILoggerFactory _loggerFactory;
+    private readonly List<DriverNodeManager> _driverNodeManagers = new();
+
+    public OtOpcUaServer(DriverHost driverHost, ILoggerFactory loggerFactory)
+    {
+        _driverHost = driverHost;
+        _loggerFactory = loggerFactory;
+    }
+
+    /// <summary>
+    ///     Read-only snapshot of the driver node managers materialized at server start. Used by
+    ///     the generic-driver-node-manager-driven discovery flow after the server starts — the
+    ///     host walks each entry and invokes
+    ///     <c>GenericDriverNodeManager.BuildAddressSpaceAsync(manager)</c> passing the manager
+    ///     as its own <see cref="IAddressSpaceBuilder"/>.
+    /// </summary>
+    public IReadOnlyList<DriverNodeManager> DriverNodeManagers => _driverNodeManagers;
+
+    protected override MasterNodeManager CreateMasterNodeManager(IServerInternal server, ApplicationConfiguration configuration)
+    {
+        foreach (var driverId in _driverHost.RegisteredDriverIds)
+        {
+            var driver = _driverHost.GetDriver(driverId);
+            if (driver is null) continue;
+
+            var logger = _loggerFactory.CreateLogger<DriverNodeManager>();
+            var manager = new DriverNodeManager(server, configuration, driver, logger);
+            _driverNodeManagers.Add(manager);
+        }
+
+        return new MasterNodeManager(server, configuration, null, _driverNodeManagers.ToArray());
+    }
+
+    protected override ServerProperties LoadServerProperties() => new()
+    {
+        ManufacturerName = "OtOpcUa",
+        ProductName = "OtOpcUa.Server",
+        ProductUri = "urn:OtOpcUa:Server",
+        SoftwareVersion = "2.0.0",
+        BuildNumber = "0",
+        BuildDate = DateTime.UtcNow,
+    };
+}

src/ZB.MOM.WW.OtOpcUa.Server/ZB.MOM.WW.OtOpcUa.Server.csproj

@@ -21,6 +21,8 @@
         <PackageReference Include="Serilog.Settings.Configuration" Version="9.0.0"/>
         <PackageReference Include="Serilog.Sinks.Console" Version="6.0.0"/>
         <PackageReference Include="Serilog.Sinks.File" Version="7.0.0"/>
+        <PackageReference Include="OPCFoundation.NetStandard.Opc.Ua.Server" Version="1.5.374.126"/>
+        <PackageReference Include="OPCFoundation.NetStandard.Opc.Ua.Configuration" Version="1.5.374.126"/>
     </ItemGroup>
 
     <ItemGroup>
@@ -30,6 +32,9 @@
     <ItemGroup>
         <NuGetAuditSuppress Include="https://github.com/advisories/GHSA-37gx-xxp4-5rgx"/>
         <NuGetAuditSuppress Include="https://github.com/advisories/GHSA-w3x6-4m5h-cxqf"/>
+        <!-- OPCFoundation.NetStandard.Opc.Ua.Core advisory — v1 already uses this package at the
+             same version, risk already accepted in the v1 stack. -->
+        <NuGetAuditSuppress Include="https://github.com/advisories/GHSA-h958-fxgg-g7w3"/>
     </ItemGroup>
 
 </Project>

tests/ZB.MOM.WW.OtOpcUa.Core.Tests/GenericDriverNodeManagerTests.cs

@@ -0,0 +1,163 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Core.OpcUa;
+
+namespace ZB.MOM.WW.OtOpcUa.Core.Tests;
+
+[Trait("Category", "Unit")]
+public sealed class GenericDriverNodeManagerTests
+{
+    /// <summary>
+    ///     BuildAddressSpaceAsync walks the driver's discovery through the caller's builder. Every
+    ///     variable marked with MarkAsAlarmCondition captures its sink in the node manager; later,
+    ///     IAlarmSource.OnAlarmEvent payloads are routed by SourceNodeId to the matching sink.
+    ///     This is the plumbing that PR 16's concrete OPC UA builder will use to update the actual
+    ///     AlarmConditionState nodes.
+    /// </summary>
+    [Fact]
+    public async Task Alarm_events_are_routed_to_the_sink_registered_for_the_matching_source_node_id()
+    {
+        var driver = new FakeDriver();
+        var builder = new RecordingBuilder();
+        using var nm = new GenericDriverNodeManager(driver);
+
+        await nm.BuildAddressSpaceAsync(builder, CancellationToken.None);
+
+        builder.Alarms.Count.ShouldBe(2);
+        nm.TrackedAlarmSources.Count.ShouldBe(2);
+
+        // Simulate the driver raising a transition for one of the alarms.
+        var args = new AlarmEventArgs(
+            SubscriptionHandle: new FakeHandle("s1"),
+            SourceNodeId: "Tank.HiHi",
+            ConditionId: "cond-1",
+            AlarmType: "Tank.HiHi",
+            Message: "Level exceeded",
+            Severity: AlarmSeverity.High,
+            SourceTimestampUtc: DateTime.UtcNow);
+        driver.RaiseAlarm(args);
+
+        builder.Alarms["Tank.HiHi"].Received.Count.ShouldBe(1);
+        builder.Alarms["Tank.HiHi"].Received[0].Message.ShouldBe("Level exceeded");
+        // The other alarm sink never received a payload — fan-out is tag-scoped.
+        builder.Alarms["Heater.OverTemp"].Received.Count.ShouldBe(0);
+    }
+
+    [Fact]
+    public async Task Non_alarm_variables_do_not_register_sinks()
+    {
+        var driver = new FakeDriver();
+        var builder = new RecordingBuilder();
+        using var nm = new GenericDriverNodeManager(driver);
+
+        await nm.BuildAddressSpaceAsync(builder, CancellationToken.None);
+
+        // FakeDriver registers 2 alarm-bearing variables + 1 plain variable.
+        nm.TrackedAlarmSources.ShouldNotContain("Tank.Level"); // the plain one
+    }
+
+    [Fact]
+    public async Task Unknown_source_node_id_is_dropped_silently()
+    {
+        var driver = new FakeDriver();
+        var builder = new RecordingBuilder();
+        using var nm = new GenericDriverNodeManager(driver);
+        await nm.BuildAddressSpaceAsync(builder, CancellationToken.None);
+
+        driver.RaiseAlarm(new AlarmEventArgs(
+            new FakeHandle("s1"), "Unknown.Source", "c", "t", "m", AlarmSeverity.Low, DateTime.UtcNow));
+
+        builder.Alarms.Values.All(s => s.Received.Count == 0).ShouldBeTrue();
+    }
+
+    [Fact]
+    public async Task Dispose_unsubscribes_from_OnAlarmEvent()
+    {
+        var driver = new FakeDriver();
+        var builder = new RecordingBuilder();
+        var nm = new GenericDriverNodeManager(driver);
+        await nm.BuildAddressSpaceAsync(builder, CancellationToken.None);
+
+        nm.Dispose();
+
+        driver.RaiseAlarm(new AlarmEventArgs(
+            new FakeHandle("s1"), "Tank.HiHi", "c", "t", "m", AlarmSeverity.Low, DateTime.UtcNow));
+
+        // No sink should have received it — the forwarder was detached.
+        builder.Alarms["Tank.HiHi"].Received.Count.ShouldBe(0);
+    }
+
+    // --- test doubles ---
+
+    private sealed class FakeDriver : IDriver, ITagDiscovery, IAlarmSource
+    {
+        public string DriverInstanceId => "fake";
+        public string DriverType => "Fake";
+        public event EventHandler<AlarmEventArgs>? OnAlarmEvent;
+
+        public Task InitializeAsync(string driverConfigJson, CancellationToken ct) => Task.CompletedTask;
+        public Task ReinitializeAsync(string driverConfigJson, CancellationToken ct) => Task.CompletedTask;
+        public Task ShutdownAsync(CancellationToken ct) => Task.CompletedTask;
+        public DriverHealth GetHealth() => new(DriverState.Healthy, DateTime.UtcNow, null);
+        public long GetMemoryFootprint() => 0;
+        public Task FlushOptionalCachesAsync(CancellationToken ct) => Task.CompletedTask;
+
+        public Task DiscoverAsync(IAddressSpaceBuilder builder, CancellationToken ct)
+        {
+            var folder = builder.Folder("Tank", "Tank");
+            var lvl = folder.Variable("Level", "Level", new DriverAttributeInfo(
+                "Tank.Level", DriverDataType.Float64, false, null, SecurityClassification.FreeAccess, false, IsAlarm: false));
+            var hiHi = folder.Variable("HiHi", "HiHi", new DriverAttributeInfo(
+                "Tank.HiHi", DriverDataType.Boolean, false, null, SecurityClassification.FreeAccess, false, IsAlarm: true));
+            hiHi.MarkAsAlarmCondition(new AlarmConditionInfo("Tank.HiHi", AlarmSeverity.High, "High-high alarm"));
+
+            var heater = builder.Folder("Heater", "Heater");
+            var ot = heater.Variable("OverTemp", "OverTemp", new DriverAttributeInfo(
+                "Heater.OverTemp", DriverDataType.Boolean, false, null, SecurityClassification.FreeAccess, false, IsAlarm: true));
+            ot.MarkAsAlarmCondition(new AlarmConditionInfo("Heater.OverTemp", AlarmSeverity.Critical, "Over-temperature"));
+            return Task.CompletedTask;
+        }
+
+        public void RaiseAlarm(AlarmEventArgs args) => OnAlarmEvent?.Invoke(this, args);
+
+        public Task<IAlarmSubscriptionHandle> SubscribeAlarmsAsync(IReadOnlyList<string> _, CancellationToken __)
+            => Task.FromResult<IAlarmSubscriptionHandle>(new FakeHandle("sub"));
+        public Task UnsubscribeAlarmsAsync(IAlarmSubscriptionHandle _, CancellationToken __) => Task.CompletedTask;
+        public Task AcknowledgeAsync(IReadOnlyList<AlarmAcknowledgeRequest> _, CancellationToken __) => Task.CompletedTask;
+    }
+
+    private sealed class FakeHandle(string diagnosticId) : IAlarmSubscriptionHandle
+    {
+        public string DiagnosticId { get; } = diagnosticId;
+    }
+
+    private sealed class RecordingBuilder : IAddressSpaceBuilder
+    {
+        public Dictionary<string, RecordingSink> Alarms { get; } = new(StringComparer.OrdinalIgnoreCase);
+
+        public IAddressSpaceBuilder Folder(string _, string __) => this;
+
+        public IVariableHandle Variable(string _, string __, DriverAttributeInfo info)
+            => new Handle(info.FullName, Alarms);
+
+        public void AddProperty(string _, DriverDataType __, object? ___) { }
+
+        public sealed class Handle(string fullRef, Dictionary<string, RecordingSink> alarms) : IVariableHandle
+        {
+            public string FullReference { get; } = fullRef;
+            public IAlarmConditionSink MarkAsAlarmCondition(AlarmConditionInfo _)
+            {
+                var sink = new RecordingSink();
+                alarms[FullReference] = sink;
+                return sink;
+            }
+        }
+
+        public sealed class RecordingSink : IAlarmConditionSink
+        {
+            public List<AlarmEventArgs> Received { get; } = new();
+            public void OnTransition(AlarmEventArgs args) => Received.Add(args);
+        }
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.E2E/RecordingAddressSpaceBuilder.cs

@@ -12,6 +12,7 @@ public sealed class RecordingAddressSpaceBuilder : IAddressSpaceBuilder
     public List<RecordedFolder> Folders { get; } = new();
     public List<RecordedVariable> Variables { get; } = new();
     public List<RecordedProperty> Properties { get; } = new();
+    public List<RecordedAlarmCondition> AlarmConditions { get; } = new();
 
     public IAddressSpaceBuilder Folder(string browseName, string displayName)
     {
@@ -22,7 +23,7 @@ public sealed class RecordingAddressSpaceBuilder : IAddressSpaceBuilder
     public IVariableHandle Variable(string browseName, string displayName, DriverAttributeInfo attributeInfo)
     {
         Variables.Add(new RecordedVariable(browseName, displayName, attributeInfo));
-        return new RecordedVariableHandle(attributeInfo.FullName);
+        return new RecordedVariableHandle(attributeInfo.FullName, AlarmConditions);
     }
 
     public void AddProperty(string browseName, DriverDataType dataType, object? value)
@@ -33,6 +34,37 @@ public sealed class RecordingAddressSpaceBuilder : IAddressSpaceBuilder
     public sealed record RecordedFolder(string BrowseName, string DisplayName);
     public sealed record RecordedVariable(string BrowseName, string DisplayName, DriverAttributeInfo AttributeInfo);
     public sealed record RecordedProperty(string BrowseName, DriverDataType DataType, object? Value);
+    public sealed record RecordedAlarmCondition(string SourceNodeId, AlarmConditionInfo Info);
+    public sealed record RecordedAlarmTransition(string SourceNodeId, AlarmEventArgs Args);
 
-    private sealed record RecordedVariableHandle(string FullReference) : IVariableHandle;
+    /// <summary>
+    ///     Sink the tests assert on to verify the alarm event forwarder routed a transition
+    ///     to the correct source-node-id. One entry per <see cref="IAlarmSource.OnAlarmEvent"/>.
+    /// </summary>
+    public List<RecordedAlarmTransition> AlarmTransitions { get; } = new();
+
+    private sealed class RecordedVariableHandle : IVariableHandle
+    {
+        private readonly List<RecordedAlarmCondition> _conditions;
+        public string FullReference { get; }
+        public RecordedVariableHandle(string fullReference, List<RecordedAlarmCondition> conditions)
+        {
+            FullReference = fullReference;
+            _conditions = conditions;
+        }
+
+        public IAlarmConditionSink MarkAsAlarmCondition(AlarmConditionInfo info)
+        {
+            _conditions.Add(new RecordedAlarmCondition(FullReference, info));
+            return new RecordingSink(FullReference);
+        }
+
+        private sealed class RecordingSink : IAlarmConditionSink
+        {
+            public string SourceNodeId { get; }
+            public List<AlarmEventArgs> Received { get; } = new();
+            public RecordingSink(string sourceNodeId) => SourceNodeId = sourceNodeId;
+            public void OnTransition(AlarmEventArgs args) => Received.Add(args);
+        }
+    }
 }

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

@@ -0,0 +1,190 @@
+using System;
+using System.Collections.Concurrent;
+using System.Threading.Tasks;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.Alarms;
+using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.MxAccess;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Tests;
+
+[Trait("Category", "Unit")]
+public sealed class GalaxyAlarmTrackerTests
+{
+    private sealed class FakeSubscriber
+    {
+        public readonly ConcurrentDictionary<string, Action<string, Vtq>> Subs = new();
+        public readonly ConcurrentQueue<string> Unsubs = new();
+        public readonly ConcurrentQueue<(string Tag, object Value)> Writes = new();
+        public bool WriteReturns { get; set; } = true;
+
+        public Task Subscribe(string tag, Action<string, Vtq> cb)
+        {
+            Subs[tag] = cb;
+            return Task.CompletedTask;
+        }
+        public Task Unsubscribe(string tag)
+        {
+            Unsubs.Enqueue(tag);
+            Subs.TryRemove(tag, out _);
+            return Task.CompletedTask;
+        }
+        public Task<bool> Write(string tag, object value)
+        {
+            Writes.Enqueue((tag, value));
+            return Task.FromResult(WriteReturns);
+        }
+    }
+
+    private static Vtq Bool(bool v) => new(v, DateTime.UtcNow, 192);
+    private static Vtq Int(int v) => new(v, DateTime.UtcNow, 192);
+    private static Vtq Str(string v) => new(v, DateTime.UtcNow, 192);
+
+    [Fact]
+    public async Task Track_subscribes_to_four_alarm_attributes()
+    {
+        var fake = new FakeSubscriber();
+        using var t = new GalaxyAlarmTracker(fake.Subscribe, fake.Unsubscribe, fake.Write);
+
+        await t.TrackAsync("Tank.Level.HiHi");
+
+        fake.Subs.ShouldContainKey("Tank.Level.HiHi.InAlarm");
+        fake.Subs.ShouldContainKey("Tank.Level.HiHi.Priority");
+        fake.Subs.ShouldContainKey("Tank.Level.HiHi.DescAttrName");
+        fake.Subs.ShouldContainKey("Tank.Level.HiHi.Acked");
+        t.TrackedAlarmCount.ShouldBe(1);
+    }
+
+    [Fact]
+    public async Task Track_is_idempotent_on_repeat_call()
+    {
+        var fake = new FakeSubscriber();
+        using var t = new GalaxyAlarmTracker(fake.Subscribe, fake.Unsubscribe, fake.Write);
+
+        await t.TrackAsync("Alarm.A");
+        await t.TrackAsync("Alarm.A");
+
+        t.TrackedAlarmCount.ShouldBe(1);
+        fake.Subs.Count.ShouldBe(4); // 4 sub calls, not 8
+    }
+
+    [Fact]
+    public async Task InAlarm_false_to_true_fires_Active_transition()
+    {
+        var fake = new FakeSubscriber();
+        using var t = new GalaxyAlarmTracker(fake.Subscribe, fake.Unsubscribe, fake.Write);
+        var transitions = new ConcurrentQueue<AlarmTransition>();
+        t.TransitionRaised += (_, tr) => transitions.Enqueue(tr);
+
+        await t.TrackAsync("Alarm.A");
+        fake.Subs["Alarm.A.Priority"]("Alarm.A.Priority", Int(500));
+        fake.Subs["Alarm.A.DescAttrName"]("Alarm.A.DescAttrName", Str("TankLevelHiHi"));
+        fake.Subs["Alarm.A.InAlarm"]("Alarm.A.InAlarm", Bool(true));
+
+        transitions.Count.ShouldBe(1);
+        transitions.TryDequeue(out var tr).ShouldBeTrue();
+        tr!.Transition.ShouldBe(AlarmStateTransition.Active);
+        tr.Priority.ShouldBe(500);
+        tr.DescAttrName.ShouldBe("TankLevelHiHi");
+    }
+
+    [Fact]
+    public async Task InAlarm_true_to_false_fires_Inactive_transition()
+    {
+        var fake = new FakeSubscriber();
+        using var t = new GalaxyAlarmTracker(fake.Subscribe, fake.Unsubscribe, fake.Write);
+        var transitions = new ConcurrentQueue<AlarmTransition>();
+        t.TransitionRaised += (_, tr) => transitions.Enqueue(tr);
+
+        await t.TrackAsync("Alarm.A");
+        fake.Subs["Alarm.A.InAlarm"]("Alarm.A.InAlarm", Bool(true));
+        fake.Subs["Alarm.A.InAlarm"]("Alarm.A.InAlarm", Bool(false));
+
+        transitions.Count.ShouldBe(2);
+        transitions.TryDequeue(out _);
+        transitions.TryDequeue(out var tr).ShouldBeTrue();
+        tr!.Transition.ShouldBe(AlarmStateTransition.Inactive);
+    }
+
+    [Fact]
+    public async Task Acked_false_to_true_fires_Acknowledged_while_InAlarm_is_true()
+    {
+        var fake = new FakeSubscriber();
+        using var t = new GalaxyAlarmTracker(fake.Subscribe, fake.Unsubscribe, fake.Write);
+        var transitions = new ConcurrentQueue<AlarmTransition>();
+        t.TransitionRaised += (_, tr) => transitions.Enqueue(tr);
+
+        await t.TrackAsync("Alarm.A");
+        fake.Subs["Alarm.A.InAlarm"]("Alarm.A.InAlarm", Bool(true));  // Active, clears Acked flag
+        fake.Subs["Alarm.A.Acked"]("Alarm.A.Acked", Bool(true));      // Acknowledged
+
+        transitions.Count.ShouldBe(2);
+        transitions.TryDequeue(out _);
+        transitions.TryDequeue(out var tr).ShouldBeTrue();
+        tr!.Transition.ShouldBe(AlarmStateTransition.Acknowledged);
+    }
+
+    [Fact]
+    public async Task Acked_transition_while_InAlarm_is_false_does_not_fire()
+    {
+        var fake = new FakeSubscriber();
+        using var t = new GalaxyAlarmTracker(fake.Subscribe, fake.Unsubscribe, fake.Write);
+        var transitions = new ConcurrentQueue<AlarmTransition>();
+        t.TransitionRaised += (_, tr) => transitions.Enqueue(tr);
+
+        await t.TrackAsync("Alarm.A");
+        // Initial Acked=true on subscribe (alarm is at rest, pre-ack'd) — should not fire.
+        fake.Subs["Alarm.A.Acked"]("Alarm.A.Acked", Bool(true));
+
+        transitions.Count.ShouldBe(0);
+    }
+
+    [Fact]
+    public async Task Acknowledge_writes_AckMsg_with_comment()
+    {
+        var fake = new FakeSubscriber();
+        using var t = new GalaxyAlarmTracker(fake.Subscribe, fake.Unsubscribe, fake.Write);
+        await t.TrackAsync("Alarm.A");
+
+        var ok = await t.AcknowledgeAsync("Alarm.A", "acknowledged by operator");
+
+        ok.ShouldBeTrue();
+        fake.Writes.Count.ShouldBe(1);
+        fake.Writes.TryDequeue(out var w).ShouldBeTrue();
+        w.Tag.ShouldBe("Alarm.A.AckMsg");
+        w.Value.ShouldBe("acknowledged by operator");
+    }
+
+    [Fact]
+    public async Task Snapshot_reports_latest_fields()
+    {
+        var fake = new FakeSubscriber();
+        using var t = new GalaxyAlarmTracker(fake.Subscribe, fake.Unsubscribe, fake.Write);
+        await t.TrackAsync("Alarm.A");
+        fake.Subs["Alarm.A.InAlarm"]("Alarm.A.InAlarm", Bool(true));
+        fake.Subs["Alarm.A.Priority"]("Alarm.A.Priority", Int(900));
+        fake.Subs["Alarm.A.DescAttrName"]("Alarm.A.DescAttrName", Str("MyAlarm"));
+        fake.Subs["Alarm.A.Acked"]("Alarm.A.Acked", Bool(true));
+
+        var snap = t.SnapshotStates();
+        snap.Count.ShouldBe(1);
+        snap[0].InAlarm.ShouldBeTrue();
+        snap[0].Acked.ShouldBeTrue();
+        snap[0].Priority.ShouldBe(900);
+        snap[0].DescAttrName.ShouldBe("MyAlarm");
+    }
+
+    [Fact]
+    public async Task Foreign_probe_callback_is_dropped()
+    {
+        var fake = new FakeSubscriber();
+        using var t = new GalaxyAlarmTracker(fake.Subscribe, fake.Unsubscribe, fake.Write);
+        var transitions = new ConcurrentQueue<AlarmTransition>();
+        t.TransitionRaised += (_, tr) => transitions.Enqueue(tr);
+
+        // No TrackAsync was called — this callback is foreign and should be silently ignored.
+        t.OnProbeCallback("Unknown.InAlarm", Bool(true));
+
+        transitions.Count.ShouldBe(0);
+    }
+}

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

@@ -0,0 +1,231 @@
+using System;
+using System.Collections.Concurrent;
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.MxAccess;
+using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Backend.Stability;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Tests;
+
+[Trait("Category", "Unit")]
+public sealed class GalaxyRuntimeProbeManagerTests
+{
+    private sealed class FakeSubscriber
+    {
+        public readonly ConcurrentDictionary<string, Action<string, Vtq>> Subs = new();
+        public readonly ConcurrentQueue<string> UnsubCalls = new();
+        public bool FailSubscribeFor { get; set; }
+        public string? FailSubscribeTag { get; set; }
+
+        public Task Subscribe(string probe, Action<string, Vtq> cb)
+        {
+            if (FailSubscribeFor && string.Equals(probe, FailSubscribeTag, StringComparison.OrdinalIgnoreCase))
+                throw new InvalidOperationException("subscribe refused");
+            Subs[probe] = cb;
+            return Task.CompletedTask;
+        }
+
+        public Task Unsubscribe(string probe)
+        {
+            UnsubCalls.Enqueue(probe);
+            Subs.TryRemove(probe, out _);
+            return Task.CompletedTask;
+        }
+    }
+
+    private static Vtq Good(bool scanState) => new(scanState, DateTime.UtcNow, 192);
+    private static Vtq Bad() => new(null, DateTime.UtcNow, 0);
+
+    [Fact]
+    public async Task Sync_subscribes_to_ScanState_per_host()
+    {
+        var subs = new FakeSubscriber();
+        using var mgr = new GalaxyRuntimeProbeManager(subs.Subscribe, subs.Unsubscribe);
+
+        await mgr.SyncAsync(new[]
+        {
+            new HostProbeTarget("PlatformA", GalaxyRuntimeProbeManager.CategoryWinPlatform),
+            new HostProbeTarget("EngineB",   GalaxyRuntimeProbeManager.CategoryAppEngine),
+        });
+
+        mgr.ActiveProbeCount.ShouldBe(2);
+        subs.Subs.ShouldContainKey("PlatformA.ScanState");
+        subs.Subs.ShouldContainKey("EngineB.ScanState");
+    }
+
+    [Fact]
+    public async Task Sync_is_idempotent_on_repeat_call_with_same_set()
+    {
+        var subs = new FakeSubscriber();
+        using var mgr = new GalaxyRuntimeProbeManager(subs.Subscribe, subs.Unsubscribe);
+        var targets = new[] { new HostProbeTarget("PlatformA", 1) };
+
+        await mgr.SyncAsync(targets);
+        await mgr.SyncAsync(targets);
+
+        mgr.ActiveProbeCount.ShouldBe(1);
+        subs.Subs.Count.ShouldBe(1);
+        subs.UnsubCalls.Count.ShouldBe(0);
+    }
+
+    [Fact]
+    public async Task Sync_unadvises_removed_hosts()
+    {
+        var subs = new FakeSubscriber();
+        using var mgr = new GalaxyRuntimeProbeManager(subs.Subscribe, subs.Unsubscribe);
+
+        await mgr.SyncAsync(new[]
+        {
+            new HostProbeTarget("PlatformA", 1),
+            new HostProbeTarget("PlatformB", 1),
+        });
+        await mgr.SyncAsync(new[] { new HostProbeTarget("PlatformA", 1) });
+
+        mgr.ActiveProbeCount.ShouldBe(1);
+        subs.UnsubCalls.ShouldContain("PlatformB.ScanState");
+    }
+
+    [Fact]
+    public async Task Subscribe_failure_rolls_back_host_entry_so_later_transitions_do_not_fire_stale_events()
+    {
+        var subs = new FakeSubscriber { FailSubscribeFor = true, FailSubscribeTag = "PlatformA.ScanState" };
+        using var mgr = new GalaxyRuntimeProbeManager(subs.Subscribe, subs.Unsubscribe);
+
+        await mgr.SyncAsync(new[] { new HostProbeTarget("PlatformA", 1) });
+
+        mgr.ActiveProbeCount.ShouldBe(0); // rolled back
+        mgr.GetState("PlatformA").ShouldBe(HostRuntimeState.Unknown);
+    }
+
+    [Fact]
+    public async Task Unknown_to_Running_does_not_fire_StateChanged()
+    {
+        var now = new DateTime(2026, 4, 18, 10, 0, 0, DateTimeKind.Utc);
+        var subs = new FakeSubscriber();
+        using var mgr = new GalaxyRuntimeProbeManager(subs.Subscribe, subs.Unsubscribe, () => now);
+        var transitions = new ConcurrentQueue<HostStateTransition>();
+        mgr.StateChanged += (_, t) => transitions.Enqueue(t);
+
+        await mgr.SyncAsync(new[] { new HostProbeTarget("PlatformA", 1) });
+        subs.Subs["PlatformA.ScanState"]("PlatformA.ScanState", Good(true));
+
+        mgr.GetState("PlatformA").ShouldBe(HostRuntimeState.Running);
+        transitions.Count.ShouldBe(0); // startup transition, operators don't care
+    }
+
+    [Fact]
+    public async Task Running_to_Stopped_fires_StateChanged_with_both_states()
+    {
+        var now = new DateTime(2026, 4, 18, 10, 0, 0, DateTimeKind.Utc);
+        var subs = new FakeSubscriber();
+        using var mgr = new GalaxyRuntimeProbeManager(subs.Subscribe, subs.Unsubscribe, () => now);
+        var transitions = new ConcurrentQueue<HostStateTransition>();
+        mgr.StateChanged += (_, t) => transitions.Enqueue(t);
+
+        await mgr.SyncAsync(new[] { new HostProbeTarget("PlatformA", 1) });
+        subs.Subs["PlatformA.ScanState"]("PlatformA.ScanState", Good(true));  // Unknown→Running (silent)
+        subs.Subs["PlatformA.ScanState"]("PlatformA.ScanState", Good(false)); // Running→Stopped (fires)
+
+        transitions.Count.ShouldBe(1);
+        transitions.TryDequeue(out var t).ShouldBeTrue();
+        t!.TagName.ShouldBe("PlatformA");
+        t.OldState.ShouldBe(HostRuntimeState.Running);
+        t.NewState.ShouldBe(HostRuntimeState.Stopped);
+    }
+
+    [Fact]
+    public async Task Stopped_to_Running_fires_StateChanged_for_recovery()
+    {
+        var now = new DateTime(2026, 4, 18, 10, 0, 0, DateTimeKind.Utc);
+        var subs = new FakeSubscriber();
+        using var mgr = new GalaxyRuntimeProbeManager(subs.Subscribe, subs.Unsubscribe, () => now);
+        var transitions = new ConcurrentQueue<HostStateTransition>();
+        mgr.StateChanged += (_, t) => transitions.Enqueue(t);
+
+        await mgr.SyncAsync(new[] { new HostProbeTarget("PlatformA", 1) });
+        subs.Subs["PlatformA.ScanState"]("PlatformA.ScanState", Good(true));  // Unknown→Running (silent)
+        subs.Subs["PlatformA.ScanState"]("PlatformA.ScanState", Good(false)); // Running→Stopped (fires)
+        subs.Subs["PlatformA.ScanState"]("PlatformA.ScanState", Good(true));  // Stopped→Running (fires)
+
+        transitions.Count.ShouldBe(2);
+    }
+
+    [Fact]
+    public async Task Unknown_to_Stopped_fires_StateChanged_for_first_known_bad_signal()
+    {
+        var now = new DateTime(2026, 4, 18, 10, 0, 0, DateTimeKind.Utc);
+        var subs = new FakeSubscriber();
+        using var mgr = new GalaxyRuntimeProbeManager(subs.Subscribe, subs.Unsubscribe, () => now);
+        var transitions = new ConcurrentQueue<HostStateTransition>();
+        mgr.StateChanged += (_, t) => transitions.Enqueue(t);
+
+        await mgr.SyncAsync(new[] { new HostProbeTarget("PlatformA", 1) });
+        // First callback is bad-quality — we must flag the host Stopped so operators see it.
+        subs.Subs["PlatformA.ScanState"]("PlatformA.ScanState", Bad());
+
+        transitions.Count.ShouldBe(1);
+        transitions.TryDequeue(out var t).ShouldBeTrue();
+        t!.OldState.ShouldBe(HostRuntimeState.Unknown);
+        t.NewState.ShouldBe(HostRuntimeState.Stopped);
+    }
+
+    [Fact]
+    public async Task Repeated_Good_Running_callbacks_do_not_fire_duplicate_events()
+    {
+        var now = new DateTime(2026, 4, 18, 10, 0, 0, DateTimeKind.Utc);
+        var subs = new FakeSubscriber();
+        using var mgr = new GalaxyRuntimeProbeManager(subs.Subscribe, subs.Unsubscribe, () => now);
+        var count = 0;
+        mgr.StateChanged += (_, _) => Interlocked.Increment(ref count);
+
+        await mgr.SyncAsync(new[] { new HostProbeTarget("PlatformA", 1) });
+        for (var i = 0; i < 5; i++)
+            subs.Subs["PlatformA.ScanState"]("PlatformA.ScanState", Good(true));
+
+        count.ShouldBe(0); // only the silent Unknown→Running on the first, no events after
+    }
+
+    [Fact]
+    public async Task Unknown_callback_for_non_tracked_probe_is_dropped()
+    {
+        var subs = new FakeSubscriber();
+        using var mgr = new GalaxyRuntimeProbeManager(subs.Subscribe, subs.Unsubscribe);
+
+        mgr.OnProbeCallback("ProbeForSomeoneElse.ScanState", Good(true));
+
+        mgr.ActiveProbeCount.ShouldBe(0);
+    }
+
+    [Fact]
+    public async Task Snapshot_reports_current_state_for_every_tracked_host()
+    {
+        var now = new DateTime(2026, 4, 18, 10, 0, 0, DateTimeKind.Utc);
+        var subs = new FakeSubscriber();
+        using var mgr = new GalaxyRuntimeProbeManager(subs.Subscribe, subs.Unsubscribe, () => now);
+
+        await mgr.SyncAsync(new[]
+        {
+            new HostProbeTarget("PlatformA", 1),
+            new HostProbeTarget("EngineB",   3),
+        });
+        subs.Subs["PlatformA.ScanState"]("PlatformA.ScanState", Good(true));  // Running
+        subs.Subs["EngineB.ScanState"]("EngineB.ScanState", Bad());            // Stopped
+
+        var snap = mgr.SnapshotStates();
+        snap.Count.ShouldBe(2);
+        snap.ShouldContain(s => s.TagName == "PlatformA" && s.State == HostRuntimeState.Running);
+        snap.ShouldContain(s => s.TagName == "EngineB" && s.State == HostRuntimeState.Stopped);
+    }
+
+    [Fact]
+    public void IsRuntimeHost_recognizes_WinPlatform_and_AppEngine_category_ids()
+    {
+        new HostProbeTarget("X", GalaxyRuntimeProbeManager.CategoryWinPlatform).IsRuntimeHost.ShouldBeTrue();
+        new HostProbeTarget("X", GalaxyRuntimeProbeManager.CategoryAppEngine).IsRuntimeHost.ShouldBeTrue();
+        new HostProbeTarget("X", 4 /* $Area */).IsRuntimeHost.ShouldBeFalse();
+        new HostProbeTarget("X", 11 /* $ApplicationObject */).IsRuntimeHost.ShouldBeFalse();
+    }
+}

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

@@ -0,0 +1,147 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+using MessagePack;
+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.Historian;
+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 HistoryReadAtTimeTests
+{
+    private static MxAccessGalaxyBackend BuildBackend(IHistorianDataSource? historian, StaPump pump) =>
+        new(
+            new GalaxyRepository(new GalaxyRepositoryOptions { ConnectionString = "Server=.;Database=ZB;Integrated Security=True;" }),
+            new MxAccessClient(pump, new MxProxyAdapter(), "attime-test"),
+            historian);
+
+    [Fact]
+    public async Task Returns_disabled_error_when_no_historian_configured()
+    {
+        using var pump = new StaPump("Test.Sta");
+        await pump.WaitForStartedAsync();
+        using var backend = BuildBackend(null, pump);
+
+        var resp = await backend.HistoryReadAtTimeAsync(new HistoryReadAtTimeRequest
+        {
+            TagReference = "T",
+            TimestampsUtcUnixMs = new[] { 1L, 2L },
+        }, CancellationToken.None);
+
+        resp.Success.ShouldBeFalse();
+        resp.Error.ShouldContain("Historian disabled");
+    }
+
+    [Fact]
+    public async Task Empty_timestamp_list_short_circuits_to_success_with_no_values()
+    {
+        using var pump = new StaPump("Test.Sta");
+        await pump.WaitForStartedAsync();
+        var fake = new FakeHistorian();
+        using var backend = BuildBackend(fake, pump);
+
+        var resp = await backend.HistoryReadAtTimeAsync(new HistoryReadAtTimeRequest
+        {
+            TagReference = "T",
+            TimestampsUtcUnixMs = Array.Empty<long>(),
+        }, CancellationToken.None);
+
+        resp.Success.ShouldBeTrue();
+        resp.Values.ShouldBeEmpty();
+        fake.Calls.ShouldBe(0); // no round-trip to SDK for empty timestamp list
+    }
+
+    [Fact]
+    public async Task Timestamps_survive_Unix_ms_round_trip_to_DateTime()
+    {
+        using var pump = new StaPump("Test.Sta");
+        await pump.WaitForStartedAsync();
+        var t1 = new DateTime(2026, 4, 18, 10, 0, 0, DateTimeKind.Utc);
+        var t2 = new DateTime(2026, 4, 18, 10, 5, 0, DateTimeKind.Utc);
+        var fake = new FakeHistorian(
+            new HistorianSample { Value = 100.0, Quality = 192, TimestampUtc = t1 },
+            new HistorianSample { Value = 101.5, Quality = 192, TimestampUtc = t2 });
+        using var backend = BuildBackend(fake, pump);
+
+        var resp = await backend.HistoryReadAtTimeAsync(new HistoryReadAtTimeRequest
+        {
+            TagReference = "TankLevel",
+            TimestampsUtcUnixMs = new[]
+            {
+                new DateTimeOffset(t1, TimeSpan.Zero).ToUnixTimeMilliseconds(),
+                new DateTimeOffset(t2, TimeSpan.Zero).ToUnixTimeMilliseconds(),
+            },
+        }, CancellationToken.None);
+
+        resp.Success.ShouldBeTrue();
+        resp.Values.Length.ShouldBe(2);
+        resp.Values[0].SourceTimestampUtcUnixMs.ShouldBe(new DateTimeOffset(t1, TimeSpan.Zero).ToUnixTimeMilliseconds());
+        resp.Values[0].StatusCode.ShouldBe(0u); // Good (quality 192)
+        MessagePackSerializer.Deserialize<double>(resp.Values[0].ValueBytes!).ShouldBe(100.0);
+
+        fake.Calls.ShouldBe(1);
+        fake.LastTimestamps.Length.ShouldBe(2);
+        fake.LastTimestamps[0].ShouldBe(t1);
+        fake.LastTimestamps[1].ShouldBe(t2);
+    }
+
+    [Fact]
+    public async Task Missing_sample_maps_to_Bad_category()
+    {
+        using var pump = new StaPump("Test.Sta");
+        await pump.WaitForStartedAsync();
+        // Quality=0 means no sample at that timestamp per HistorianDataSource.ReadAtTimeAsync.
+        var fake = new FakeHistorian(new HistorianSample
+        {
+            Value = null,
+            Quality = 0,
+            TimestampUtc = DateTime.UtcNow,
+        });
+        using var backend = BuildBackend(fake, pump);
+
+        var resp = await backend.HistoryReadAtTimeAsync(new HistoryReadAtTimeRequest
+        {
+            TagReference = "T",
+            TimestampsUtcUnixMs = new[] { 1L },
+        }, CancellationToken.None);
+
+        resp.Success.ShouldBeTrue();
+        resp.Values.Length.ShouldBe(1);
+        resp.Values[0].StatusCode.ShouldBe(0x80000000u); // Bad category
+        resp.Values[0].ValueBytes.ShouldBeNull();
+    }
+
+    private sealed class FakeHistorian : IHistorianDataSource
+    {
+        private readonly HistorianSample[] _samples;
+        public int Calls { get; private set; }
+        public DateTime[] LastTimestamps { get; private set; } = Array.Empty<DateTime>();
+
+        public FakeHistorian(params HistorianSample[] samples) => _samples = samples;
+
+        public Task<List<HistorianSample>> ReadAtTimeAsync(string tag, DateTime[] ts, CancellationToken ct)
+        {
+            Calls++;
+            LastTimestamps = ts;
+            return Task.FromResult(new List<HistorianSample>(_samples));
+        }
+
+        public Task<List<HistorianSample>> ReadRawAsync(string tag, DateTime s, DateTime e, int max, CancellationToken ct)
+            => Task.FromResult(new List<HistorianSample>());
+        public Task<List<HistorianAggregateSample>> ReadAggregateAsync(string tag, DateTime s, DateTime e, double ms, string col, CancellationToken ct)
+            => Task.FromResult(new List<HistorianAggregateSample>());
+        public Task<List<HistorianEventDto>> ReadEventsAsync(string? src, DateTime s, DateTime e, int max, CancellationToken ct)
+            => Task.FromResult(new List<HistorianEventDto>());
+        public HistorianHealthSnapshot GetHealthSnapshot() => new();
+        public void Dispose() { }
+    }
+}

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

@@ -0,0 +1,129 @@
+using System;
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+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.Historian;
+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 HistoryReadEventsTests
+{
+    private static MxAccessGalaxyBackend BuildBackend(IHistorianDataSource? h, StaPump pump) =>
+        new(
+            new GalaxyRepository(new GalaxyRepositoryOptions { ConnectionString = "Server=.;Database=ZB;Integrated Security=True;" }),
+            new MxAccessClient(pump, new MxProxyAdapter(), "events-test"),
+            h);
+
+    [Fact]
+    public async Task Returns_disabled_error_when_no_historian_configured()
+    {
+        using var pump = new StaPump("Test.Sta");
+        await pump.WaitForStartedAsync();
+        using var backend = BuildBackend(null, pump);
+
+        var resp = await backend.HistoryReadEventsAsync(new HistoryReadEventsRequest
+        {
+            SourceName = "TankA",
+            StartUtcUnixMs = 0,
+            EndUtcUnixMs = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds(),
+            MaxEvents = 100,
+        }, CancellationToken.None);
+
+        resp.Success.ShouldBeFalse();
+        resp.Error.ShouldContain("Historian disabled");
+    }
+
+    [Fact]
+    public async Task Maps_HistorianEventDto_to_GalaxyHistoricalEvent_wire_shape()
+    {
+        using var pump = new StaPump("Test.Sta");
+        await pump.WaitForStartedAsync();
+
+        var eventId = Guid.NewGuid();
+        var eventTime = new DateTime(2026, 4, 18, 10, 0, 0, DateTimeKind.Utc);
+        var receivedTime = eventTime.AddMilliseconds(150);
+        var fake = new FakeHistorian(new HistorianEventDto
+        {
+            Id = eventId,
+            Source = "TankA.Level.HiHi",
+            EventTime = eventTime,
+            ReceivedTime = receivedTime,
+            DisplayText = "HiHi alarm tripped",
+            Severity = 900,
+        });
+        using var backend = BuildBackend(fake, pump);
+
+        var resp = await backend.HistoryReadEventsAsync(new HistoryReadEventsRequest
+        {
+            SourceName = "TankA.Level.HiHi",
+            StartUtcUnixMs = 0,
+            EndUtcUnixMs = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds(),
+            MaxEvents = 50,
+        }, CancellationToken.None);
+
+        resp.Success.ShouldBeTrue();
+        resp.Events.Length.ShouldBe(1);
+        var got = resp.Events[0];
+        got.EventId.ShouldBe(eventId.ToString());
+        got.SourceName.ShouldBe("TankA.Level.HiHi");
+        got.DisplayText.ShouldBe("HiHi alarm tripped");
+        got.Severity.ShouldBe<ushort>(900);
+        got.EventTimeUtcUnixMs.ShouldBe(new DateTimeOffset(eventTime, TimeSpan.Zero).ToUnixTimeMilliseconds());
+        got.ReceivedTimeUtcUnixMs.ShouldBe(new DateTimeOffset(receivedTime, TimeSpan.Zero).ToUnixTimeMilliseconds());
+
+        fake.LastSourceName.ShouldBe("TankA.Level.HiHi");
+        fake.LastMaxEvents.ShouldBe(50);
+    }
+
+    [Fact]
+    public async Task Null_source_name_is_passed_through_as_all_sources()
+    {
+        using var pump = new StaPump("Test.Sta");
+        await pump.WaitForStartedAsync();
+        var fake = new FakeHistorian();
+        using var backend = BuildBackend(fake, pump);
+
+        await backend.HistoryReadEventsAsync(new HistoryReadEventsRequest
+        {
+            SourceName = null,
+            StartUtcUnixMs = 0,
+            EndUtcUnixMs = 1,
+            MaxEvents = 10,
+        }, CancellationToken.None);
+
+        fake.LastSourceName.ShouldBeNull();
+    }
+
+    private sealed class FakeHistorian : IHistorianDataSource
+    {
+        private readonly HistorianEventDto[] _events;
+        public string? LastSourceName { get; private set; } = "<unset>";
+        public int LastMaxEvents { get; private set; }
+
+        public FakeHistorian(params HistorianEventDto[] events) => _events = events;
+
+        public Task<List<HistorianEventDto>> ReadEventsAsync(string? src, DateTime s, DateTime e, int max, CancellationToken ct)
+        {
+            LastSourceName = src;
+            LastMaxEvents = max;
+            return Task.FromResult(new List<HistorianEventDto>(_events));
+        }
+
+        public Task<List<HistorianSample>> ReadRawAsync(string tag, DateTime s, DateTime e, int max, CancellationToken ct)
+            => Task.FromResult(new List<HistorianSample>());
+        public Task<List<HistorianAggregateSample>> ReadAggregateAsync(string tag, DateTime s, DateTime e, double ms, string col, CancellationToken ct)
+            => Task.FromResult(new List<HistorianAggregateSample>());
+        public Task<List<HistorianSample>> ReadAtTimeAsync(string tag, DateTime[] ts, CancellationToken ct)
+            => Task.FromResult(new List<HistorianSample>());
+        public HistorianHealthSnapshot GetHealthSnapshot() => new();
+        public void Dispose() { }
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Server.Tests/ZB.MOM.WW.OtOpcUa.Server.Tests.csproj

@@ -27,6 +27,7 @@
     <ItemGroup>
         <NuGetAuditSuppress Include="https://github.com/advisories/GHSA-37gx-xxp4-5rgx"/>
         <NuGetAuditSuppress Include="https://github.com/advisories/GHSA-w3x6-4m5h-cxqf"/>
+        <NuGetAuditSuppress Include="https://github.com/advisories/GHSA-h958-fxgg-g7w3"/>
     </ItemGroup>
 
 </Project>