Implement LmxOpcUa server — all 6 phases complete

Full OPC UA server on .NET Framework 4.8 (x86) exposing AVEVA System
Platform Galaxy tags via MXAccess. Mirrors Galaxy object hierarchy as
OPC UA address space, translating contained-name browse paths to
tag-name runtime references.

Components implemented:
- Configuration: AppConfiguration with 4 sections, validator
- Domain: ConnectionState, Quality, Vtq, MxDataTypeMapper, error codes
- MxAccess: StaComThread, MxAccessClient (partial classes), MxProxyAdapter
  using strongly-typed ArchestrA.MxAccess COM interop
- Galaxy Repository: SQL queries (hierarchy, attributes, change detection),
  ChangeDetectionService with auto-rebuild on deploy
- OPC UA Server: LmxNodeManager (CustomNodeManager2), LmxOpcUaServer,
  OpcUaServerHost with programmatic config, SecurityPolicy None
- Status Dashboard: HTTP server with HTML/JSON/health endpoints
- Integration: Full 14-step startup, graceful shutdown, component wiring

175 tests (174 unit + 1 integration), all passing.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/ZB.MOM.WW.LmxOpcUa.Tests/MxAccess/MxAccessClientSubscriptionTests.cs

@@ -0,0 +1,105 @@
+using System;
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.LmxOpcUa.Host.Configuration;
+using ZB.MOM.WW.LmxOpcUa.Host.Domain;
+using ZB.MOM.WW.LmxOpcUa.Host.Metrics;
+using ZB.MOM.WW.LmxOpcUa.Host.MxAccess;
+using ZB.MOM.WW.LmxOpcUa.Tests.Helpers;
+
+namespace ZB.MOM.WW.LmxOpcUa.Tests.MxAccess
+{
+    public class MxAccessClientSubscriptionTests : IDisposable
+    {
+        private readonly StaComThread _staThread;
+        private readonly FakeMxProxy _proxy;
+        private readonly PerformanceMetrics _metrics;
+        private readonly MxAccessClient _client;
+
+        public MxAccessClientSubscriptionTests()
+        {
+            _staThread = new StaComThread();
+            _staThread.Start();
+            _proxy = new FakeMxProxy();
+            _metrics = new PerformanceMetrics();
+            _client = new MxAccessClient(_staThread, _proxy, new MxAccessConfiguration(), _metrics);
+        }
+
+        public void Dispose()
+        {
+            _client.Dispose();
+            _staThread.Dispose();
+            _metrics.Dispose();
+        }
+
+        [Fact]
+        public async Task Subscribe_CreatesItemAndAdvises()
+        {
+            await _client.ConnectAsync();
+            await _client.SubscribeAsync("TestTag.Attr", (_, _) => { });
+
+            _proxy.Items.Count.ShouldBeGreaterThan(0);
+            _proxy.AdvisedItems.Count.ShouldBeGreaterThan(0);
+            _client.ActiveSubscriptionCount.ShouldBe(1);
+        }
+
+        [Fact]
+        public async Task Unsubscribe_RemovesItemAndUnadvises()
+        {
+            await _client.ConnectAsync();
+            await _client.SubscribeAsync("TestTag.Attr", (_, _) => { });
+            await _client.UnsubscribeAsync("TestTag.Attr");
+
+            _client.ActiveSubscriptionCount.ShouldBe(0);
+        }
+
+        [Fact]
+        public async Task OnDataChange_InvokesCallback()
+        {
+            await _client.ConnectAsync();
+
+            Vtq? received = null;
+            await _client.SubscribeAsync("TestTag.Attr", (addr, vtq) => received = vtq);
+
+            _proxy.SimulateDataChangeByAddress("TestTag.Attr", 42, 192);
+
+            received.ShouldNotBeNull();
+            received.Value.Value.ShouldBe(42);
+            received.Value.Quality.ShouldBe(Quality.Good);
+        }
+
+        [Fact]
+        public async Task OnDataChange_InvokesGlobalHandler()
+        {
+            await _client.ConnectAsync();
+
+            string? globalAddr = null;
+            _client.OnTagValueChanged += (addr, vtq) => globalAddr = addr;
+
+            await _client.SubscribeAsync("TestTag.Attr", (_, _) => { });
+            _proxy.SimulateDataChangeByAddress("TestTag.Attr", "hello", 192);
+
+            globalAddr.ShouldBe("TestTag.Attr");
+        }
+
+        [Fact]
+        public async Task StoredSubscriptions_ReplayedAfterReconnect()
+        {
+            await _client.ConnectAsync();
+            var callbackInvoked = false;
+            await _client.SubscribeAsync("TestTag.Attr", (_, _) => callbackInvoked = true);
+
+            // Reconnect
+            await _client.ReconnectAsync();
+
+            // After reconnect, subscription should be replayed
+            _client.ActiveSubscriptionCount.ShouldBe(1);
+
+            // Simulate data change on the re-subscribed item
+            _proxy.SimulateDataChangeByAddress("TestTag.Attr", "value", 192);
+            callbackInvoked.ShouldBe(true);
+        }
+    }
+}