diff --git a/src/ZB.MOM.WW.LmxOpcUa.Host/OpcUaService.cs b/src/ZB.MOM.WW.LmxOpcUa.Host/OpcUaService.cs
index 25fcd3a..40979aa 100644
--- a/src/ZB.MOM.WW.LmxOpcUa.Host/OpcUaService.cs
+++ b/src/ZB.MOM.WW.LmxOpcUa.Host/OpcUaService.cs
@@ -267,6 +267,11 @@ namespace ZB.MOM.WW.LmxOpcUa.Host
             Log.Fatal(e.ExceptionObject as Exception, "Unhandled exception (IsTerminating={IsTerminating})", e.IsTerminating);
         }
 
+        /// <summary>
+        /// Triggers an address space rebuild from the current Galaxy repository data. For testing.
+        /// </summary>
+        internal void TriggerRebuild() => OnGalaxyChanged();
+
         // Accessors for testing
         internal IMxAccessClient? MxClient => (IMxAccessClient?)_mxAccessClient ?? _mxAccessClientForWiring;
         internal PerformanceMetrics? Metrics => _metrics;
diff --git a/tests/ZB.MOM.WW.LmxOpcUa.Tests/Helpers/OpcUaServerFixture.cs b/tests/ZB.MOM.WW.LmxOpcUa.Tests/Helpers/OpcUaServerFixture.cs
index c66dee5..bb4bbba 100644
--- a/tests/ZB.MOM.WW.LmxOpcUa.Tests/Helpers/OpcUaServerFixture.cs
+++ b/tests/ZB.MOM.WW.LmxOpcUa.Tests/Helpers/OpcUaServerFixture.cs
@@ -25,15 +25,37 @@ namespace ZB.MOM.WW.LmxOpcUa.Tests.Helpers
         public int OpcUaPort { get; }
         public string EndpointUrl => $"opc.tcp://localhost:{OpcUaPort}/LmxOpcUa";
 
+        /// <summary>
+        /// The fake Galaxy repository injected into the service. Mutate Hierarchy/Attributes
+        /// then call Service.TriggerRebuild() to simulate a Galaxy redeployment.
+        /// </summary>
+        public FakeGalaxyRepository? GalaxyRepository { get; }
+
+        /// <summary>
+        /// The fake MxAccess client injected into the service (when using WithFakeMxAccessClient).
+        /// </summary>
+        public FakeMxAccessClient? MxAccessClient { get; }
+
+        /// <summary>
+        /// The fake MxProxy injected into the service (when using WithFakes).
+        /// </summary>
+        public FakeMxProxy? MxProxy { get; }
+
         private readonly OpcUaServiceBuilder _builder;
         private bool _started;
 
-        public OpcUaServerFixture(OpcUaServiceBuilder builder)
+        private OpcUaServerFixture(OpcUaServiceBuilder builder,
+            FakeGalaxyRepository? repo = null,
+            FakeMxAccessClient? mxClient = null,
+            FakeMxProxy? mxProxy = null)
         {
             OpcUaPort = Interlocked.Increment(ref _nextPort);
             _builder = builder;
             _builder.WithOpcUaPort(OpcUaPort);
             _builder.DisableDashboard();
+            GalaxyRepository = repo;
+            MxAccessClient = mxClient;
+            MxProxy = mxProxy;
         }
 
         /// <summary>
@@ -56,7 +78,7 @@ namespace ZB.MOM.WW.LmxOpcUa.Tests.Helpers
                 .WithGalaxyRepository(r)
                 .WithGalaxyName("TestGalaxy");
 
-            return new OpcUaServerFixture(builder);
+            return new OpcUaServerFixture(builder, repo: r, mxProxy: p);
         }
 
         /// <summary>
@@ -79,7 +101,7 @@ namespace ZB.MOM.WW.LmxOpcUa.Tests.Helpers
                 .WithGalaxyRepository(r)
                 .WithGalaxyName("TestGalaxy");
 
-            return new OpcUaServerFixture(builder);
+            return new OpcUaServerFixture(builder, repo: r, mxClient: client);
         }
 
         public Task InitializeAsync()
diff --git a/tests/ZB.MOM.WW.LmxOpcUa.Tests/Helpers/OpcUaTestClient.cs b/tests/ZB.MOM.WW.LmxOpcUa.Tests/Helpers/OpcUaTestClient.cs
new file mode 100644
index 0000000..7d6ec60
--- /dev/null
+++ b/tests/ZB.MOM.WW.LmxOpcUa.Tests/Helpers/OpcUaTestClient.cs
@@ -0,0 +1,154 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Threading.Tasks;
+using Opc.Ua;
+using Opc.Ua.Client;
+using Opc.Ua.Configuration;
+
+namespace ZB.MOM.WW.LmxOpcUa.Tests.Helpers
+{
+    /// <summary>
+    /// OPC UA client helper for integration tests. Connects to a test server,
+    /// browses, reads, and subscribes to nodes programmatically.
+    /// </summary>
+    internal class OpcUaTestClient : IDisposable
+    {
+        private Session? _session;
+
+        public Session Session => _session ?? throw new InvalidOperationException("Not connected");
+
+        /// <summary>
+        /// Resolves the namespace index for a given namespace URI (e.g., "urn:TestGalaxy:LmxOpcUa").
+        /// </summary>
+        public ushort GetNamespaceIndex(string galaxyName = "TestGalaxy")
+        {
+            var nsUri = $"urn:{galaxyName}:LmxOpcUa";
+            var idx = Session.NamespaceUris.GetIndex(nsUri);
+            if (idx < 0) throw new InvalidOperationException($"Namespace '{nsUri}' not found on server");
+            return (ushort)idx;
+        }
+
+        /// <summary>
+        /// Creates a NodeId in the LmxOpcUa namespace using the server's actual namespace index.
+        /// </summary>
+        public NodeId MakeNodeId(string identifier, string galaxyName = "TestGalaxy")
+        {
+            return new NodeId(identifier, GetNamespaceIndex(galaxyName));
+        }
+
+        public async Task ConnectAsync(string endpointUrl)
+        {
+            var config = new ApplicationConfiguration
+            {
+                ApplicationName = "OpcUaTestClient",
+                ApplicationUri = "urn:localhost:OpcUaTestClient",
+                ApplicationType = ApplicationType.Client,
+                SecurityConfiguration = new SecurityConfiguration
+                {
+                    ApplicationCertificate = new CertificateIdentifier
+                    {
+                        StoreType = CertificateStoreType.Directory,
+                        StorePath = Path.Combine(Path.GetTempPath(), "OpcUaTestClient", "pki", "own")
+                    },
+                    TrustedIssuerCertificates = new CertificateTrustList
+                    {
+                        StoreType = CertificateStoreType.Directory,
+                        StorePath = Path.Combine(Path.GetTempPath(), "OpcUaTestClient", "pki", "issuer")
+                    },
+                    TrustedPeerCertificates = new CertificateTrustList
+                    {
+                        StoreType = CertificateStoreType.Directory,
+                        StorePath = Path.Combine(Path.GetTempPath(), "OpcUaTestClient", "pki", "trusted")
+                    },
+                    RejectedCertificateStore = new CertificateTrustList
+                    {
+                        StoreType = CertificateStoreType.Directory,
+                        StorePath = Path.Combine(Path.GetTempPath(), "OpcUaTestClient", "pki", "rejected")
+                    },
+                    AutoAcceptUntrustedCertificates = true
+                },
+                ClientConfiguration = new ClientConfiguration { DefaultSessionTimeout = 30000 },
+                TransportQuotas = new TransportQuotas()
+            };
+
+            await config.Validate(ApplicationType.Client);
+            config.CertificateValidator.CertificateValidation += (_, e) => e.Accept = true;
+
+            var endpoint = CoreClientUtils.SelectEndpoint(config, endpointUrl, false);
+            var endpointConfig = EndpointConfiguration.Create(config);
+            var configuredEndpoint = new ConfiguredEndpoint(null, endpoint, endpointConfig);
+
+            _session = await Session.Create(
+                config, configuredEndpoint, false,
+                "OpcUaTestClient", 30000, null, null);
+        }
+
+        /// <summary>
+        /// Browse children of a node. Returns list of (DisplayName, NodeId, NodeClass).
+        /// </summary>
+        public async Task<List<(string Name, NodeId NodeId, NodeClass NodeClass)>> BrowseAsync(NodeId nodeId)
+        {
+            var results = new List<(string, NodeId, NodeClass)>();
+            var browser = new Browser(Session)
+            {
+                NodeClassMask = (int)NodeClass.Object | (int)NodeClass.Variable,
+                ReferenceTypeId = ReferenceTypeIds.HierarchicalReferences,
+                IncludeSubtypes = true,
+                BrowseDirection = BrowseDirection.Forward
+            };
+
+            var refs = browser.Browse(nodeId);
+            foreach (var rd in refs)
+            {
+                results.Add((rd.DisplayName.Text, ExpandedNodeId.ToNodeId(rd.NodeId, Session.NamespaceUris), rd.NodeClass));
+            }
+            return results;
+        }
+
+        /// <summary>
+        /// Read a node's value.
+        /// </summary>
+        public DataValue Read(NodeId nodeId)
+        {
+            return Session.ReadValue(nodeId);
+        }
+
+        /// <summary>
+        /// Create a subscription with a monitored item on the given node.
+        /// Returns the subscription and monitored item for inspection.
+        /// </summary>
+        public async Task<(Subscription Sub, MonitoredItem Item)> SubscribeAsync(
+            NodeId nodeId, int intervalMs = 250)
+        {
+            var subscription = new Subscription(Session.DefaultSubscription)
+            {
+                PublishingInterval = intervalMs,
+                DisplayName = "TestSubscription"
+            };
+
+            var item = new MonitoredItem(subscription.DefaultItem)
+            {
+                StartNodeId = nodeId,
+                DisplayName = nodeId.ToString(),
+                SamplingInterval = intervalMs
+            };
+
+            subscription.AddItem(item);
+            Session.AddSubscription(subscription);
+            await subscription.CreateAsync();
+
+            return (subscription, item);
+        }
+
+        public void Dispose()
+        {
+            if (_session != null)
+            {
+                try { _session.Close(); }
+                catch { /* ignore */ }
+                _session.Dispose();
+            }
+        }
+    }
+}
diff --git a/tests/ZB.MOM.WW.LmxOpcUa.Tests/Integration/AddressSpaceRebuildTests.cs b/tests/ZB.MOM.WW.LmxOpcUa.Tests/Integration/AddressSpaceRebuildTests.cs
new file mode 100644
index 0000000..9609b82
--- /dev/null
+++ b/tests/ZB.MOM.WW.LmxOpcUa.Tests/Integration/AddressSpaceRebuildTests.cs
@@ -0,0 +1,263 @@
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Opc.Ua;
+using Opc.Ua.Client;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.LmxOpcUa.Host.Domain;
+using ZB.MOM.WW.LmxOpcUa.Tests.Helpers;
+
+namespace ZB.MOM.WW.LmxOpcUa.Tests.Integration
+{
+    /// <summary>
+    /// Integration tests verifying dynamic address space changes via a real OPC UA client.
+    /// Tests browse, subscribe, add/remove nodes at runtime, and subscription quality changes.
+    /// </summary>
+    public class AddressSpaceRebuildTests
+    {
+        [Fact]
+        public async Task Browse_ReturnsInitialHierarchy()
+        {
+            var fixture = OpcUaServerFixture.WithFakes();
+            await fixture.InitializeAsync();
+            try
+            {
+                using var client = new OpcUaTestClient();
+                await client.ConnectAsync(fixture.EndpointUrl);
+
+                // Browse from ZB root
+                var zbNode = client.MakeNodeId("ZB");
+                var children = await client.BrowseAsync(zbNode);
+
+                children.ShouldContain(c => c.Name == "DEV");
+            }
+            finally
+            {
+                await fixture.DisposeAsync();
+            }
+        }
+
+        [Fact]
+        public async Task Browse_AfterAddingObject_NewNodeAppears()
+        {
+            var fixture = OpcUaServerFixture.WithFakes();
+            await fixture.InitializeAsync();
+            try
+            {
+                using var client = new OpcUaTestClient();
+                await client.ConnectAsync(fixture.EndpointUrl);
+
+                // Verify initial state — browse TestMachine_001
+                var machineNode = client.MakeNodeId("TestMachine_001");
+                var initialChildren = await client.BrowseAsync(machineNode);
+                initialChildren.ShouldNotContain(c => c.Name == "NewReceiver");
+
+                // Add a new object to the hierarchy
+                fixture.GalaxyRepository!.Hierarchy.Add(new GalaxyObjectInfo
+                {
+                    GobjectId = 100, TagName = "NewReceiver_001",
+                    ContainedName = "NewReceiver", BrowseName = "NewReceiver",
+                    ParentGobjectId = 3, IsArea = false // parent = TestMachine_001
+                });
+                fixture.GalaxyRepository.Attributes.Add(new GalaxyAttributeInfo
+                {
+                    GobjectId = 100, TagName = "NewReceiver_001",
+                    AttributeName = "NewAttr", FullTagReference = "NewReceiver_001.NewAttr",
+                    MxDataType = 5, IsArray = false
+                });
+
+                // Trigger rebuild
+                fixture.Service.TriggerRebuild();
+                await Task.Delay(500); // allow rebuild to complete
+
+                // Browse again — new node should appear
+                var updatedChildren = await client.BrowseAsync(machineNode);
+                updatedChildren.ShouldContain(c => c.Name == "NewReceiver");
+            }
+            finally
+            {
+                await fixture.DisposeAsync();
+            }
+        }
+
+        [Fact]
+        public async Task Browse_AfterRemovingObject_NodeDisappears()
+        {
+            var fixture = OpcUaServerFixture.WithFakes();
+            await fixture.InitializeAsync();
+            try
+            {
+                using var client = new OpcUaTestClient();
+                await client.ConnectAsync(fixture.EndpointUrl);
+
+                // Verify MESReceiver exists initially
+                var machineNode = client.MakeNodeId("TestMachine_001");
+                var initialChildren = await client.BrowseAsync(machineNode);
+                initialChildren.ShouldContain(c => c.Name == "MESReceiver");
+
+                // Remove MESReceiver and its attributes from hierarchy
+                fixture.GalaxyRepository!.Hierarchy.RemoveAll(h => h.TagName == "MESReceiver_001");
+                fixture.GalaxyRepository.Attributes.RemoveAll(a => a.TagName == "MESReceiver_001");
+
+                // Trigger rebuild
+                fixture.Service.TriggerRebuild();
+                await Task.Delay(500);
+
+                // Browse again — MESReceiver should be gone
+                var updatedChildren = await client.BrowseAsync(machineNode);
+                updatedChildren.ShouldNotContain(c => c.Name == "MESReceiver");
+            }
+            finally
+            {
+                await fixture.DisposeAsync();
+            }
+        }
+
+        [Fact]
+        public async Task Subscribe_RemovedNode_PublishesBadQuality()
+        {
+            var fixture = OpcUaServerFixture.WithFakes();
+            await fixture.InitializeAsync();
+            try
+            {
+                using var client = new OpcUaTestClient();
+                await client.ConnectAsync(fixture.EndpointUrl);
+
+                // Subscribe to an attribute that will be removed
+                var nodeId = client.MakeNodeId("MESReceiver_001.MoveInBatchID");
+                var (sub, item) = await client.SubscribeAsync(nodeId, intervalMs: 100);
+
+                // Collect notifications
+                var notifications = new List<MonitoredItemNotification>();
+                item.Notification += (_, e) =>
+                {
+                    if (e.NotificationValue is MonitoredItemNotification n)
+                        notifications.Add(n);
+                };
+
+                await Task.Delay(500); // let initial subscription settle
+
+                // Remove MESReceiver and its attributes
+                fixture.GalaxyRepository!.Hierarchy.RemoveAll(h => h.TagName == "MESReceiver_001");
+                fixture.GalaxyRepository.Attributes.RemoveAll(a => a.TagName == "MESReceiver_001");
+
+                // Trigger rebuild — nodes get deleted
+                fixture.Service.TriggerRebuild();
+
+                // Wait for publish cycle to deliver Bad status
+                await Task.Delay(2000);
+
+                // The subscription should have received a Bad quality notification
+                // after the node was deleted during rebuild
+                notifications.ShouldContain(n => StatusCode.IsBad(n.Value.StatusCode));
+
+                await sub.DeleteAsync(true);
+            }
+            finally
+            {
+                await fixture.DisposeAsync();
+            }
+        }
+
+        [Fact]
+        public async Task Subscribe_SurvivingNode_StillWorksAfterRebuild()
+        {
+            var fixture = OpcUaServerFixture.WithFakes();
+            await fixture.InitializeAsync();
+            try
+            {
+                using var client = new OpcUaTestClient();
+                await client.ConnectAsync(fixture.EndpointUrl);
+
+                // Subscribe to an attribute that will survive the rebuild
+                var nodeId = client.MakeNodeId("TestMachine_001.MachineID");
+                var (sub, item) = await client.SubscribeAsync(nodeId, intervalMs: 100);
+
+                await Task.Delay(500);
+
+                // Remove only MESReceiver (MachineID on TestMachine_001 survives)
+                fixture.GalaxyRepository!.Hierarchy.RemoveAll(h => h.TagName == "MESReceiver_001");
+                fixture.GalaxyRepository.Attributes.RemoveAll(a => a.TagName == "MESReceiver_001");
+
+                fixture.Service.TriggerRebuild();
+                await Task.Delay(1000);
+
+                // The surviving node should still be browsable
+                var machineNode = client.MakeNodeId("TestMachine_001");
+                var children = await client.BrowseAsync(machineNode);
+                children.ShouldContain(c => c.Name == "MachineID");
+
+                await sub.DeleteAsync(true);
+            }
+            finally
+            {
+                await fixture.DisposeAsync();
+            }
+        }
+
+        [Fact]
+        public async Task Browse_AddAttribute_NewVariableAppears()
+        {
+            var fixture = OpcUaServerFixture.WithFakes();
+            await fixture.InitializeAsync();
+            try
+            {
+                using var client = new OpcUaTestClient();
+                await client.ConnectAsync(fixture.EndpointUrl);
+
+                var machineNode = client.MakeNodeId("TestMachine_001");
+                var initialChildren = await client.BrowseAsync(machineNode);
+                initialChildren.ShouldNotContain(c => c.Name == "NewSensor");
+
+                // Add a new attribute
+                fixture.GalaxyRepository!.Attributes.Add(new GalaxyAttributeInfo
+                {
+                    GobjectId = 3, TagName = "TestMachine_001",
+                    AttributeName = "NewSensor", FullTagReference = "TestMachine_001.NewSensor",
+                    MxDataType = 4, IsArray = false // Double
+                });
+
+                fixture.Service.TriggerRebuild();
+                await Task.Delay(500);
+
+                var updatedChildren = await client.BrowseAsync(machineNode);
+                updatedChildren.ShouldContain(c => c.Name == "NewSensor");
+            }
+            finally
+            {
+                await fixture.DisposeAsync();
+            }
+        }
+
+        [Fact]
+        public async Task Browse_RemoveAttribute_VariableDisappears()
+        {
+            var fixture = OpcUaServerFixture.WithFakes();
+            await fixture.InitializeAsync();
+            try
+            {
+                using var client = new OpcUaTestClient();
+                await client.ConnectAsync(fixture.EndpointUrl);
+
+                var machineNode = client.MakeNodeId("TestMachine_001");
+                var initialChildren = await client.BrowseAsync(machineNode);
+                initialChildren.ShouldContain(c => c.Name == "MachineCode");
+
+                // Remove MachineCode attribute
+                fixture.GalaxyRepository!.Attributes.RemoveAll(
+                    a => a.TagName == "TestMachine_001" && a.AttributeName == "MachineCode");
+
+                fixture.Service.TriggerRebuild();
+                await Task.Delay(500);
+
+                var updatedChildren = await client.BrowseAsync(machineNode);
+                updatedChildren.ShouldNotContain(c => c.Name == "MachineCode");
+            }
+            finally
+            {
+                await fixture.DisposeAsync();
+            }
+        }
+    }
+}
diff --git a/tests/ZB.MOM.WW.LmxOpcUa.Tests/ZB.MOM.WW.LmxOpcUa.Tests.csproj b/tests/ZB.MOM.WW.LmxOpcUa.Tests/ZB.MOM.WW.LmxOpcUa.Tests.csproj
index 3602e39..a23ba39 100644
--- a/tests/ZB.MOM.WW.LmxOpcUa.Tests/ZB.MOM.WW.LmxOpcUa.Tests.csproj
+++ b/tests/ZB.MOM.WW.LmxOpcUa.Tests/ZB.MOM.WW.LmxOpcUa.Tests.csproj
@@ -22,6 +22,7 @@
     <PackageReference Include="Microsoft.Extensions.Configuration.Json" Version="6.0.0" />
     <PackageReference Include="Microsoft.Extensions.Configuration.Binder" Version="6.0.0" />
     <PackageReference Include="OPCFoundation.NetStandard.Opc.Ua.Server" Version="1.5.374.126" />
+    <PackageReference Include="OPCFoundation.NetStandard.Opc.Ua.Client" Version="1.5.374.126" />
   </ItemGroup>
 
   <ItemGroup>