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/MxAccessClientReadWriteTests.cs

@@ -0,0 +1,126 @@
+using System;
+using System.Threading;
+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 MxAccessClientReadWriteTests : IDisposable
+    {
+        private readonly StaComThread _staThread;
+        private readonly FakeMxProxy _proxy;
+        private readonly PerformanceMetrics _metrics;
+        private readonly MxAccessClient _client;
+
+        public MxAccessClientReadWriteTests()
+        {
+            _staThread = new StaComThread();
+            _staThread.Start();
+            _proxy = new FakeMxProxy();
+            _metrics = new PerformanceMetrics();
+            var config = new MxAccessConfiguration { ReadTimeoutSeconds = 2, WriteTimeoutSeconds = 2 };
+            _client = new MxAccessClient(_staThread, _proxy, config, _metrics);
+        }
+
+        public void Dispose()
+        {
+            _client.Dispose();
+            _staThread.Dispose();
+            _metrics.Dispose();
+        }
+
+        [Fact]
+        public async Task Read_NotConnected_ReturnsBad()
+        {
+            var result = await _client.ReadAsync("Tag.Attr");
+            result.Quality.ShouldBe(Quality.BadNotConnected);
+        }
+
+        [Fact]
+        public async Task Read_ReturnsValueOnDataChange()
+        {
+            await _client.ConnectAsync();
+
+            // Start read in background
+            var readTask = _client.ReadAsync("TestTag.Attr");
+
+            // Give it a moment to set up subscription, then simulate data change
+            await Task.Delay(50);
+            _proxy.SimulateDataChangeByAddress("TestTag.Attr", 42, 192);
+
+            var result = await readTask;
+            result.Value.ShouldBe(42);
+            result.Quality.ShouldBe(Quality.Good);
+        }
+
+        [Fact]
+        public async Task Read_Timeout_ReturnsBadCommFailure()
+        {
+            await _client.ConnectAsync();
+
+            // No data change simulated, so it will timeout
+            var result = await _client.ReadAsync("TestTag.Attr");
+            result.Quality.ShouldBe(Quality.BadCommFailure);
+        }
+
+        [Fact]
+        public async Task Write_NotConnected_ReturnsFalse()
+        {
+            var result = await _client.WriteAsync("Tag.Attr", 42);
+            result.ShouldBe(false);
+        }
+
+        [Fact]
+        public async Task Write_Success_ReturnsTrue()
+        {
+            await _client.ConnectAsync();
+            _proxy.WriteCompleteStatus = 0;
+
+            var result = await _client.WriteAsync("TestTag.Attr", 42);
+            result.ShouldBe(true);
+            _proxy.WrittenValues.ShouldContain(w => w.Address == "TestTag.Attr" && (int)w.Value == 42);
+        }
+
+        [Fact]
+        public async Task Write_ErrorCode_ReturnsFalse()
+        {
+            await _client.ConnectAsync();
+            _proxy.WriteCompleteStatus = 1012; // Wrong data type
+
+            var result = await _client.WriteAsync("TestTag.Attr", "bad_value");
+            result.ShouldBe(false);
+        }
+
+        [Fact]
+        public async Task Read_RecordsMetrics()
+        {
+            await _client.ConnectAsync();
+
+            var readTask = _client.ReadAsync("TestTag.Attr");
+            await Task.Delay(50);
+            _proxy.SimulateDataChangeByAddress("TestTag.Attr", 1, 192);
+            await readTask;
+
+            var stats = _metrics.GetStatistics();
+            stats.ShouldContainKey("Read");
+            stats["Read"].TotalCount.ShouldBe(1);
+        }
+
+        [Fact]
+        public async Task Write_RecordsMetrics()
+        {
+            await _client.ConnectAsync();
+            await _client.WriteAsync("TestTag.Attr", 42);
+
+            var stats = _metrics.GetStatistics();
+            stats.ShouldContainKey("Write");
+            stats["Write"].TotalCount.ShouldBe(1);
+        }
+    }
+}