Fix second-pass review findings: subscription leak on rebuild, metrics accuracy, and MxAccess startup recovery

- Preserve and replay subscription ref counts across address space rebuilds to prevent MXAccess subscription leaks
- Mark read timeouts and write failures as unsuccessful in PerformanceMetrics for accurate health reporting
- Add deferred MxAccess reconnect path when initial connection fails at startup
- Update code review document with verified completions and new findings
- Add covering tests for all fixes

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

tests/ZB.MOM.WW.LmxOpcUa.Tests/Wiring/ServiceStartupSequenceTest.cs

@@ -1,4 +1,5 @@
 using System.Collections.Generic;
+using System.Threading.Tasks;
 using Shouldly;
 using Xunit;
 using ZB.MOM.WW.LmxOpcUa.Host;
@@ -69,5 +70,60 @@ namespace ZB.MOM.WW.LmxOpcUa.Tests.Wiring
                 service.Stop();
             }
         }
+
+        [Fact]
+        public async Task Start_WhenMxAccessIsInitiallyDown_MonitorReconnectsInBackground()
+        {
+            var config = new AppConfiguration
+            {
+                OpcUa = new OpcUaConfiguration
+                {
+                    Port = 14841,
+                    GalaxyName = "TestGalaxy",
+                    EndpointPath = "/LmxOpcUa"
+                },
+                MxAccess = new MxAccessConfiguration
+                {
+                    ClientName = "Test",
+                    MonitorIntervalSeconds = 1,
+                    AutoReconnect = true
+                },
+                GalaxyRepository = new GalaxyRepositoryConfiguration(),
+                Dashboard = new DashboardConfiguration { Enabled = false }
+            };
+
+            var proxy = new FakeMxProxy { ShouldFailRegister = true };
+            var repo = new FakeGalaxyRepository
+            {
+                Hierarchy = new List<GalaxyObjectInfo>
+                {
+                    new GalaxyObjectInfo { GobjectId = 1, TagName = "TestObj", BrowseName = "TestObj", ParentGobjectId = 0, IsArea = false }
+                },
+                Attributes = new List<GalaxyAttributeInfo>
+                {
+                    new GalaxyAttributeInfo { GobjectId = 1, TagName = "TestObj", AttributeName = "TestAttr", FullTagReference = "TestObj.TestAttr", MxDataType = 5, IsArray = false }
+                }
+            };
+
+            var service = new OpcUaService(config, proxy, repo);
+            service.Start();
+
+            try
+            {
+                service.ServerHost.ShouldNotBeNull();
+                service.MxClient.ShouldNotBeNull();
+                service.MxClient!.State.ShouldBe(ConnectionState.Error);
+
+                proxy.ShouldFailRegister = false;
+                await Task.Delay(2500);
+
+                service.MxClient.State.ShouldBe(ConnectionState.Connected);
+                proxy.RegisterCallCount.ShouldBeGreaterThan(1);
+            }
+            finally
+            {
+                service.Stop();
+            }
+        }
     }
 }