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/GalaxyRepository/ChangeDetectionServiceTests.cs

@@ -0,0 +1,100 @@
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.LmxOpcUa.Host.GalaxyRepository;
+using ZB.MOM.WW.LmxOpcUa.Tests.Helpers;
+
+namespace ZB.MOM.WW.LmxOpcUa.Tests.GalaxyRepository
+{
+    public class ChangeDetectionServiceTests
+    {
+        [Fact]
+        public async Task FirstPoll_AlwaysTriggers()
+        {
+            var repo = new FakeGalaxyRepository { LastDeployTime = new DateTime(2024, 1, 1) };
+            var service = new ChangeDetectionService(repo, intervalSeconds: 1);
+            var triggered = false;
+            service.OnGalaxyChanged += () => triggered = true;
+
+            service.Start();
+            await Task.Delay(500);
+            service.Stop();
+
+            triggered.ShouldBe(true);
+            service.Dispose();
+        }
+
+        [Fact]
+        public async Task SameTimestamp_DoesNotTriggerAgain()
+        {
+            var repo = new FakeGalaxyRepository { LastDeployTime = new DateTime(2024, 1, 1) };
+            var service = new ChangeDetectionService(repo, intervalSeconds: 1);
+            var triggerCount = 0;
+            service.OnGalaxyChanged += () => Interlocked.Increment(ref triggerCount);
+
+            service.Start();
+            await Task.Delay(2500); // Should have polled at least twice
+            service.Stop();
+
+            triggerCount.ShouldBe(1); // Only the first poll
+            service.Dispose();
+        }
+
+        [Fact]
+        public async Task ChangedTimestamp_TriggersAgain()
+        {
+            var repo = new FakeGalaxyRepository { LastDeployTime = new DateTime(2024, 1, 1) };
+            var service = new ChangeDetectionService(repo, intervalSeconds: 1);
+            var triggerCount = 0;
+            service.OnGalaxyChanged += () => Interlocked.Increment(ref triggerCount);
+
+            service.Start();
+            await Task.Delay(500);
+
+            // Change the deploy time
+            repo.LastDeployTime = new DateTime(2024, 2, 1);
+            await Task.Delay(1500);
+            service.Stop();
+
+            triggerCount.ShouldBeGreaterThanOrEqualTo(2);
+            service.Dispose();
+        }
+
+        [Fact]
+        public async Task FailedPoll_DoesNotCrash_RetriesNext()
+        {
+            var repo = new FakeGalaxyRepository { LastDeployTime = new DateTime(2024, 1, 1) };
+            var service = new ChangeDetectionService(repo, intervalSeconds: 1);
+            var triggerCount = 0;
+            service.OnGalaxyChanged += () => Interlocked.Increment(ref triggerCount);
+
+            service.Start();
+            await Task.Delay(500);
+
+            // Make it fail
+            repo.ShouldThrow = true;
+            await Task.Delay(1500);
+
+            // Restore and it should recover
+            repo.ShouldThrow = false;
+            repo.LastDeployTime = new DateTime(2024, 3, 1);
+            await Task.Delay(1500);
+            service.Stop();
+
+            // Should have triggered at least on first poll and on the changed timestamp
+            triggerCount.ShouldBeGreaterThanOrEqualTo(1);
+            service.Dispose();
+        }
+
+        [Fact]
+        public void Stop_BeforeStart_DoesNotThrow()
+        {
+            var repo = new FakeGalaxyRepository();
+            var service = new ChangeDetectionService(repo, intervalSeconds: 30);
+            service.Stop(); // Should not throw
+            service.Dispose();
+        }
+    }
+}