diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Browser.Tests/OpcUaClientBrowseSessionAttributesTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Browser.Tests/OpcUaClientBrowseSessionAttributesTests.cs
index c8c13c09..d59a2855 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Browser.Tests/OpcUaClientBrowseSessionAttributesTests.cs
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Browser.Tests/OpcUaClientBrowseSessionAttributesTests.cs
@@ -20,23 +20,23 @@ public sealed class OpcUaClientBrowseSessionAttributesTests
     private static Mock<ISession> SessionReturning(NodeClass nodeClass, NodeId dataType, int valueRank, byte userAccess)
     {
         var mock = new Mock<ISession>(MockBehavior.Loose);
-        mock.SetupGet(s => s.MessageContext).Returns(new ServiceMessageContext(BrowseTelemetry.Context));
+        mock.SetupGet(s => s.MessageContext).Returns(ServiceMessageContext.Create(BrowseTelemetry.Context));
         mock.SetupGet(s => s.NamespaceUris).Returns(new NamespaceTable());
         mock.Setup(s => s.ReadAsync(
                 It.IsAny<RequestHeader>(), It.IsAny<double>(), It.IsAny<TimestampsToReturn>(),
-                It.IsAny<ReadValueIdCollection>(), It.IsAny<CancellationToken>()))
-            .ReturnsAsync((RequestHeader _, double _, TimestampsToReturn _, ReadValueIdCollection nodes, CancellationToken _) =>
+                It.IsAny<ArrayOf<ReadValueId>>(), It.IsAny<CancellationToken>()))
+            .ReturnsAsync((RequestHeader _, double _, TimestampsToReturn _, ArrayOf<ReadValueId> nodes, CancellationToken _) =>
                 new ReadResponse
                 {
                     ResponseHeader = new ResponseHeader(),
-                    Results = [.. nodes.Select(n => n.AttributeId switch
+                    Results = [.. nodes.ToList().Select(n => n.AttributeId switch
                     {
                         Attributes.NodeClass => new DataValue(new Variant((int)nodeClass)),
                         Attributes.DisplayName => new DataValue(new Variant(new LocalizedText("Speed"))),
                         Attributes.DataType => new DataValue(new Variant(dataType)),
                         Attributes.ValueRank => new DataValue(new Variant(valueRank)),
                         Attributes.UserAccessLevel => new DataValue(new Variant(userAccess)),
-                        _ => new DataValue(StatusCodes.BadAttributeIdInvalid),
+                        _ => DataValue.FromStatusCode(StatusCodes.BadAttributeIdInvalid),
                     })],
                     DiagnosticInfos = [],
                 });
@@ -101,19 +101,19 @@ public sealed class OpcUaClientBrowseSessionAttributesTests
             session.AttributesAsync("nsu=urn:not-in-table;s=X", TestContext.Current.CancellationToken));
     }
 
-    private sealed class TrackingCredential : IDisposable
+    private sealed class TrackingApplication : IAsyncDisposable
     {
         public int Disposed { get; private set; }
 
-        public void Dispose() => Disposed++;
+        public ValueTask DisposeAsync() { Disposed++; return ValueTask.CompletedTask; }
     }
 
-    /// <summary>Review m9: the browse session disposes the user certificate it was handed, with itself.</summary>
+    /// <summary>Review m9: the browse session disposes the SDK application it was handed, with itself.</summary>
     [Fact]
-    public async Task The_session_disposes_the_credential_it_owns()
+    public async Task The_session_disposes_the_application_it_owns()
     {
         var mock = SessionReturning(NodeClass.Variable, DataTypeIds.Int32, -1, 1);
-        var credential = new TrackingCredential();
+        var credential = new TrackingApplication();
         var session = new OpcUaClientBrowseSession(
             mock.Object, NamespaceMap.FromTable(new NamespaceTable()), ObjectIds.ObjectsFolder, credential);
 
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Browser.Tests/OpcUaClientBrowseSessionPaginationTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Browser.Tests/OpcUaClientBrowseSessionPaginationTests.cs
index 28811140..b89eaa69 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Browser.Tests/OpcUaClientBrowseSessionPaginationTests.cs
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Browser.Tests/OpcUaClientBrowseSessionPaginationTests.cs
@@ -20,7 +20,7 @@ public sealed class OpcUaClientBrowseSessionPaginationTests
     private static Mock<ISession> BuildSession(bool cancelNext)
     {
         var mock = new Mock<ISession>(MockBehavior.Loose);
-        mock.SetupGet(s => s.MessageContext).Returns(new ServiceMessageContext(BrowseTelemetry.Context));
+        mock.SetupGet(s => s.MessageContext).Returns(ServiceMessageContext.Create(BrowseTelemetry.Context));
         mock.SetupGet(s => s.NamespaceUris).Returns(new NamespaceTable());
 
         var firstRef = new ReferenceDescription
@@ -32,44 +32,44 @@ public sealed class OpcUaClientBrowseSessionPaginationTests
         };
         mock.Setup(s => s.BrowseAsync(
                 It.IsAny<RequestHeader>(), It.IsAny<ViewDescription>(), It.IsAny<uint>(),
-                It.IsAny<BrowseDescriptionCollection>(), It.IsAny<CancellationToken>()))
+                It.IsAny<ArrayOf<BrowseDescription>>(), It.IsAny<CancellationToken>()))
             .ReturnsAsync(new BrowseResponse
             {
                 ResponseHeader = new ResponseHeader(),
-                Results = new BrowseResultCollection
+                Results = new List<BrowseResult>
                 {
                     new BrowseResult
                     {
-                        ContinuationPoint = FakeContinuationPoint,
-                        References = new ReferenceDescriptionCollection { firstRef },
+                        ContinuationPoint = FakeContinuationPoint.ToByteString(),
+                        References = new List<ReferenceDescription> { firstRef },
                     },
                 },
-                DiagnosticInfos = new DiagnosticInfoCollection(),
+                DiagnosticInfos = new List<DiagnosticInfo>(),
             });
 
         var emptyPage = new BrowseNextResponse
         {
             ResponseHeader = new ResponseHeader(),
-            Results = new BrowseResultCollection
+            Results = new List<BrowseResult>
             {
                 new BrowseResult
                 {
-                    ContinuationPoint = Array.Empty<byte>(),
-                    References = new ReferenceDescriptionCollection(),
+                    ContinuationPoint = ByteString.Empty,
+                    References = new List<ReferenceDescription>(),
                 },
             },
-            DiagnosticInfos = new DiagnosticInfoCollection(),
+            DiagnosticInfos = new List<DiagnosticInfo>(),
         };
 
         var pageSetup = mock.Setup(s => s.BrowseNextAsync(
             It.IsAny<RequestHeader>(), It.Is<bool>(r => !r),
-            It.IsAny<ByteStringCollection>(), It.IsAny<CancellationToken>()));
+            It.IsAny<ArrayOf<ByteString>>(), It.IsAny<CancellationToken>()));
         if (cancelNext) pageSetup.ThrowsAsync(new OperationCanceledException("cancelled mid-page"));
         else pageSetup.ReturnsAsync(emptyPage);
 
         mock.Setup(s => s.BrowseNextAsync(
                 It.IsAny<RequestHeader>(), It.Is<bool>(r => r),
-                It.IsAny<ByteStringCollection>(), It.IsAny<CancellationToken>()))
+                It.IsAny<ArrayOf<ByteString>>(), It.IsAny<CancellationToken>()))
             .ReturnsAsync(emptyPage);
         return mock;
     }
@@ -89,7 +89,7 @@ public sealed class OpcUaClientBrowseSessionPaginationTests
 
         mock.Verify(s => s.BrowseNextAsync(
             It.IsAny<RequestHeader>(), It.Is<bool>(r => r),
-            It.IsAny<ByteStringCollection>(), It.IsAny<CancellationToken>()), Times.Once);
+            It.IsAny<ArrayOf<ByteString>>(), It.IsAny<CancellationToken>()), Times.Once);
     }
 
     /// <summary>Positive control: an uncancelled pagination never issues a release call.</summary>
@@ -104,9 +104,9 @@ public sealed class OpcUaClientBrowseSessionPaginationTests
         nodes.Count.ShouldBe(1);
         mock.Verify(s => s.BrowseNextAsync(
             It.IsAny<RequestHeader>(), It.Is<bool>(r => !r),
-            It.IsAny<ByteStringCollection>(), It.IsAny<CancellationToken>()), Times.Once);
+            It.IsAny<ArrayOf<ByteString>>(), It.IsAny<CancellationToken>()), Times.Once);
         mock.Verify(s => s.BrowseNextAsync(
             It.IsAny<RequestHeader>(), It.Is<bool>(r => r),
-            It.IsAny<ByteStringCollection>(), It.IsAny<CancellationToken>()), Times.Never);
+            It.IsAny<ArrayOf<ByteString>>(), It.IsAny<CancellationToken>()), Times.Never);
     }
 }
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Browser.Tests/OpcUaClientDriverBrowserTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Browser.Tests/OpcUaClientDriverBrowserTests.cs
index 2ae84ef6..08fc5825 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Browser.Tests/OpcUaClientDriverBrowserTests.cs
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Browser.Tests/OpcUaClientDriverBrowserTests.cs
@@ -120,7 +120,7 @@ public sealed class OpcUaClientDriverBrowserTests
         // A loose mock answers the attribute read with no response, so nothing is known about the node.
         var mockSession = new Mock<ISession>(MockBehavior.Loose);
         mockSession.SetupGet(s => s.NamespaceUris).Returns(new NamespaceTable());
-        mockSession.SetupGet(s => s.MessageContext).Returns(new ServiceMessageContext(BrowseTelemetry.Context));
+        mockSession.SetupGet(s => s.MessageContext).Returns(ServiceMessageContext.Create(BrowseTelemetry.Context));
         var nsMap = NamespaceMap.FromTable(new NamespaceTable());
         var sut = new OpcUaClientBrowseSession(mockSession.Object, nsMap, ObjectIds.ObjectsFolder);
 
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientAcknowledgeFailureTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientAcknowledgeFailureTests.cs
index 101da754..acdd5b88 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientAcknowledgeFailureTests.cs
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientAcknowledgeFailureTests.cs
@@ -21,7 +21,7 @@ public sealed class OpcUaClientAcknowledgeFailureTests
     private static Mock<ISession> NewSession()
     {
         var mock = new Mock<ISession>(MockBehavior.Loose);
-        mock.SetupGet(s => s.MessageContext).Returns(new ServiceMessageContext(SdkTelemetry.Context));
+        mock.SetupGet(s => s.MessageContext).Returns(ServiceMessageContext.Create(SdkTelemetry.Context));
         mock.SetupGet(s => s.NamespaceUris).Returns(new NamespaceTable());
         return mock;
     }
@@ -34,7 +34,7 @@ public sealed class OpcUaClientAcknowledgeFailureTests
     {
         using var drv = new OpcUaClientDriver(new OpcUaClientDriverOptions(), "opcua-o8");
         var session = NewSession();
-        session.Setup(s => s.CallAsync(It.IsAny<RequestHeader>(), It.IsAny<CallMethodRequestCollection>(), It.IsAny<CancellationToken>()))
+        session.Setup(s => s.CallAsync(It.IsAny<RequestHeader>(), It.IsAny<ArrayOf<CallMethodRequest>>(), It.IsAny<CancellationToken>()))
             .ThrowsAsync(new ServiceResultException(StatusCodes.BadConnectionClosed));
         drv.SetSessionForTest(session.Object);
 
@@ -50,7 +50,7 @@ public sealed class OpcUaClientAcknowledgeFailureTests
     {
         using var drv = new OpcUaClientDriver(new OpcUaClientDriverOptions(), "opcua-o8-ok");
         var session = NewSession();
-        session.Setup(s => s.CallAsync(It.IsAny<RequestHeader>(), It.IsAny<CallMethodRequestCollection>(), It.IsAny<CancellationToken>()))
+        session.Setup(s => s.CallAsync(It.IsAny<RequestHeader>(), It.IsAny<ArrayOf<CallMethodRequest>>(), It.IsAny<CancellationToken>()))
             .ReturnsAsync(new CallResponse
             {
                 ResponseHeader = new ResponseHeader(),
@@ -61,10 +61,30 @@ public sealed class OpcUaClientAcknowledgeFailureTests
 
         await drv.AcknowledgeAsync(Ack(), TestContext.Current.CancellationToken);
 
-        session.Verify(s => s.CallAsync(It.IsAny<RequestHeader>(), It.IsAny<CallMethodRequestCollection>(), It.IsAny<CancellationToken>()),
+        session.Verify(s => s.CallAsync(It.IsAny<RequestHeader>(), It.IsAny<ArrayOf<CallMethodRequest>>(), It.IsAny<CancellationToken>()),
             Times.Once);
     }
 
+    [Fact]
+    public async Task Acknowledge_encodes_EventId_as_scalar_ByteString_and_never_retries_a_transport_failure()
+    {
+        using var driver = new OpcUaClientDriver(new OpcUaClientDriverOptions(), "opcua-ack-types");
+        var session = NewSession();
+        ArrayOf<CallMethodRequest> sent = default;
+        session.Setup(s => s.CallAsync(It.IsAny<RequestHeader>(), It.IsAny<ArrayOf<CallMethodRequest>>(), It.IsAny<CancellationToken>()))
+            .Callback<RequestHeader, ArrayOf<CallMethodRequest>, CancellationToken>((_, calls, _) => sent = calls)
+            .ThrowsAsync(new ServiceResultException(StatusCodes.BadConnectionClosed));
+        driver.SetSessionForTest(session.Object);
+        await Should.ThrowAsync<ServiceResultException>(() => driver.AcknowledgeAsync(Ack(), TestContext.Current.CancellationToken));
+        var arguments = sent[0].InputArguments;
+        arguments[0].TypeInfo.BuiltInType.ShouldBe(BuiltInType.ByteString);
+        arguments[0].TypeInfo.ValueRank.ShouldBe(ValueRanks.Scalar);
+        arguments[0].GetByteString().IsEmpty.ShouldBeTrue();
+        arguments[1].TypeInfo.BuiltInType.ShouldBe(BuiltInType.LocalizedText);
+        arguments[1].GetLocalizedText().Text.ShouldBe("operator ack");
+        session.Verify(s => s.CallAsync(It.IsAny<RequestHeader>(), It.IsAny<ArrayOf<CallMethodRequest>>(), It.IsAny<CancellationToken>()), Times.Once);
+    }
+
     /// <summary>A session lost while the ack queued on the gate fails the ack rather than reporting it applied.</summary>
     [Fact]
     public async Task A_session_lost_while_queued_fails_the_ack()
@@ -110,7 +130,7 @@ public sealed class OpcUaClientAcknowledgeFailureTests
 
         await drv.AcknowledgeAsync(Unresolvable(), TestContext.Current.CancellationToken);
 
-        session.Verify(s => s.CallAsync(It.IsAny<RequestHeader>(), It.IsAny<CallMethodRequestCollection>(), It.IsAny<CancellationToken>()),
+        session.Verify(s => s.CallAsync(It.IsAny<RequestHeader>(), It.IsAny<ArrayOf<CallMethodRequest>>(), It.IsAny<CancellationToken>()),
             Times.Never);
         lock (logger.Entries)
             logger.Entries.ShouldContain(e => e.Level == Microsoft.Extensions.Logging.LogLevel.Warning && e.Message.Contains("resolved none"));
@@ -127,7 +147,7 @@ public sealed class OpcUaClientAcknowledgeFailureTests
         var ct = TestContext.Current.CancellationToken;
         using var drv = new OpcUaClientDriver(new OpcUaClientDriverOptions(), "opcua-n1");
         var session = NewSession();
-        session.Setup(s => s.CallAsync(It.IsAny<RequestHeader>(), It.IsAny<CallMethodRequestCollection>(), It.IsAny<CancellationToken>()))
+        session.Setup(s => s.CallAsync(It.IsAny<RequestHeader>(), It.IsAny<ArrayOf<CallMethodRequest>>(), It.IsAny<CancellationToken>()))
             .ReturnsAsync(new CallResponse
             {
                 ResponseHeader = new ResponseHeader(),
@@ -154,7 +174,7 @@ public sealed class OpcUaClientAcknowledgeFailureTests
         await invoker.ExecuteAsync(DriverCapability.AlarmAcknowledge, "host",
             async c => await drv.AcknowledgeAsync(Ack(), c), ct);
 
-        session.Verify(s => s.CallAsync(It.IsAny<RequestHeader>(), It.IsAny<CallMethodRequestCollection>(), It.IsAny<CancellationToken>()),
+        session.Verify(s => s.CallAsync(It.IsAny<RequestHeader>(), It.IsAny<ArrayOf<CallMethodRequest>>(), It.IsAny<CancellationToken>()),
             Times.Once, "the genuine ack must still reach the server");
     }
 
@@ -166,7 +186,7 @@ public sealed class OpcUaClientAcknowledgeFailureTests
         var stamp = new DateTime(2026, 1, 1, 0, 0, 0, DateTimeKind.Utc);
         drv.SetHealthForTest(new DriverHealth(DriverState.Healthy, stamp, null));
         var session = NewSession();
-        session.Setup(s => s.CallAsync(It.IsAny<RequestHeader>(), It.IsAny<CallMethodRequestCollection>(), It.IsAny<CancellationToken>()))
+        session.Setup(s => s.CallAsync(It.IsAny<RequestHeader>(), It.IsAny<ArrayOf<CallMethodRequest>>(), It.IsAny<CancellationToken>()))
             .ThrowsAsync(new ServiceResultException(StatusCodes.BadConnectionClosed));
         drv.SetSessionForTest(session.Object);
 
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientAlarmTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientAlarmTests.cs
index b9a3d06b..10d0b9be 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientAlarmTests.cs
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientAlarmTests.cs
@@ -76,9 +76,9 @@ public sealed class OpcUaClientAlarmTests
 
     // ---- #619: v3 RawPath <-> upstream-source translation on the native-alarm path ----
 
-    private static VariantCollection EventFields(string sourceNode, string conditionNode) =>
+    private static List<Variant> EventFields(string sourceNode, string conditionNode) =>
     [
-        new Variant(new byte[] { 1 }),                       // EventId
+        Variant.From(new byte[] { 1 }.ToByteString()),       // scalar ByteString EventId
         new Variant(new NodeId("TripAlarmType", 3)),         // EventType
         new Variant(NodeId.Parse(sourceNode)),               // SourceNode
         new Variant(new LocalizedText("tripped")),           // Message
@@ -310,18 +310,18 @@ public sealed class OpcUaClientAlarmTests
         }
     }
 
-    private static VariantCollection ConditionFields(
+    private static List<Variant> ConditionFields(
         bool active, bool acked, string message = "tripped", ushort severity = 700, byte[]? eventId = null,
         NodeId? branchId = null, NodeId? eventType = null)
     {
         var f = EventFields("ns=3;s=Alarms.Trip1", "ns=3;s=Alarms.Trip1.Cond");
-        f[0] = new Variant(eventId ?? new byte[] { 1 });
-        if (eventType is not null) f[1] = new Variant(eventType);
+        f[0] = Variant.From(new ByteString((eventId ?? new byte[] { 1 }).AsMemory()));
+        if (eventType is not null) f[1] = Variant.From(eventType.Value);
         f[3] = new Variant(new LocalizedText(message));
         f[4] = new Variant(severity);
         f.Add(new Variant(active));
         f.Add(new Variant(acked));
-        f.Add(branchId is null ? Variant.Null : new Variant(branchId));
+        f.Add(branchId is null ? Variant.Null : Variant.From(branchId.Value));
         return f;
     }
 
@@ -382,7 +382,7 @@ public sealed class OpcUaClientAlarmTests
         OpcUaClientDriver.IsRefreshRequired(EventFieldsOfType(ObjectTypeIds.RefreshEndEventType)).ShouldBeFalse();
     }
 
-    private static VariantCollection EventFieldsOfType(NodeId type)
+    private static List<Variant> EventFieldsOfType(NodeId type)
     {
         var f = EventFields("i=2253", "i=0");
         f[1] = new Variant(type);
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientCertAuthTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientCertAuthTests.cs
index b3886f03..19fd456e 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientCertAuthTests.cs
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientCertAuthTests.cs
@@ -65,4 +65,49 @@ public sealed class OpcUaClientCertAuthTests
             try { File.Delete(tmpPath); } catch { /* best-effort */ }
         }
     }
+    [Fact]
+    public async Task Certificate_identity_signs_repeatedly_and_requires_reopen_after_file_rotation()
+    {
+        var path = Path.Combine(Path.GetTempPath(), $"opcua-cert-rotation-{Guid.NewGuid():N}.pfx");
+        try
+        {
+            using var key = RSA.Create(2048);
+            var request = new CertificateRequest("CN=OpcUaSdk2Signing", key, HashAlgorithmName.SHA256, RSASignaturePadding.Pkcs1);
+            using var original = request.CreateSelfSigned(DateTimeOffset.UtcNow.AddMinutes(-5), DateTimeOffset.UtcNow.AddHours(1));
+            File.WriteAllBytes(path, original.Export(X509ContentType.Pfx, "test-password"));
+            var options = new OpcUaClientDriverOptions { AuthType = OpcUaAuthType.Certificate,
+                UserCertificatePath = path, UserCertificatePassword = "test-password" };
+            var identity = OpcUaClientDriver.BuildCertificateIdentity(options);
+            byte[] challenge = [1, 2, 3, 4];
+            for (var i = 0; i < 2; i++)
+            {
+                var signature = await identity.TokenHandler.SignAsync(challenge, Opc.Ua.SecurityPolicies.Basic256Sha256,
+                    TestContext.Current.CancellationToken);
+                using var publicKey = original.GetRSAPublicKey();
+                publicKey.ShouldNotBeNull().VerifyData(challenge, signature.Signature.Span,
+                    HashAlgorithmName.SHA256, RSASignaturePadding.Pkcs1).ShouldBeTrue();
+            }
+            using var cancelled = new CancellationTokenSource();
+            cancelled.Cancel();
+            await Should.ThrowAsync<OperationCanceledException>(async () =>
+                await identity.TokenHandler.SignAsync(challenge, Opc.Ua.SecurityPolicies.Basic256Sha256, cancelled.Token));
+
+            using var rotatedKey = RSA.Create(2048);
+            var rotatedRequest = new CertificateRequest("CN=OpcUaSdk2Signing", rotatedKey, HashAlgorithmName.SHA256, RSASignaturePadding.Pkcs1);
+            using var rotated = rotatedRequest.CreateSelfSigned(DateTimeOffset.UtcNow.AddMinutes(-5), DateTimeOffset.UtcNow.AddHours(1));
+            File.WriteAllBytes(path, rotated.Export(X509ContentType.Pfx, "test-password"));
+            var error = await Should.ThrowAsync<Opc.Ua.ServiceResultException>(async () =>
+                await identity.TokenHandler.SignAsync(challenge, Opc.Ua.SecurityPolicies.Basic256Sha256,
+                    TestContext.Current.CancellationToken));
+            error.StatusCode.ShouldBe(Opc.Ua.StatusCodes.BadIdentityTokenInvalid);
+            var fresh = OpcUaClientDriver.BuildCertificateIdentity(options);
+            var freshSignature = await fresh.TokenHandler.SignAsync(challenge, Opc.Ua.SecurityPolicies.Basic256Sha256,
+                TestContext.Current.CancellationToken);
+            using var rotatedPublicKey = rotated.GetRSAPublicKey();
+            rotatedPublicKey.ShouldNotBeNull().VerifyData(challenge, freshSignature.Signature.Span,
+                HashAlgorithmName.SHA256, RSASignaturePadding.Pkcs1).ShouldBeTrue();
+        }
+        finally { File.Delete(path); }
+    }
+
 }
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientConnectionLossSignalTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientConnectionLossSignalTests.cs
index ae0ffe91..29f9c585 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientConnectionLossSignalTests.cs
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientConnectionLossSignalTests.cs
@@ -59,7 +59,7 @@ public sealed class OpcUaClientConnectionLossSignalTests
     private static Mock<ISession> NewSession()
     {
         var mock = new Mock<ISession>(MockBehavior.Loose);
-        mock.SetupGet(s => s.MessageContext).Returns(new ServiceMessageContext(SdkTelemetry.Context));
+        mock.SetupGet(s => s.MessageContext).Returns(ServiceMessageContext.Create(SdkTelemetry.Context));
         mock.SetupGet(s => s.NamespaceUris).Returns(new NamespaceTable());
         return mock;
     }
@@ -77,18 +77,18 @@ public sealed class OpcUaClientConnectionLossSignalTests
         return (drv, session, clock, log);
     }
 
-    private static DataValue Good(object value, DateTime ts) => new(new Variant(value), StatusCodes.Good, ts, ts);
+    private static DataValue Good(object value, DateTime ts) => new(VariantHelper.CastFrom(value), StatusCodes.Good, ts, ts);
 
     /// <summary>Every read returns <paramref name="values"/> (one per requested node, in order) at <paramref name="at"/>.</summary>
     private static void SetupRead(Mock<ISession> session, Func<DateTime> at, params object[] values) =>
         session.Setup(s => s.ReadAsync(
                 It.IsAny<RequestHeader>(), It.IsAny<double>(), It.IsAny<TimestampsToReturn>(),
-                It.IsAny<ReadValueIdCollection>(), It.IsAny<CancellationToken>()))
-            .ReturnsAsync((RequestHeader _, double _, TimestampsToReturn _, ReadValueIdCollection nodes, CancellationToken _) =>
+                It.IsAny<ArrayOf<ReadValueId>>(), It.IsAny<CancellationToken>()))
+            .ReturnsAsync((RequestHeader _, double _, TimestampsToReturn _, ArrayOf<ReadValueId> nodes, CancellationToken _) =>
                 new ReadResponse
                 {
                     ResponseHeader = new ResponseHeader(),
-                    Results = [.. nodes.Select((_, i) => Good(values[i], at()))],
+                    Results = [.. nodes.ToList().Select((_, i) => Good(values[i], at()))],
                     DiagnosticInfos = [],
                 });
 
@@ -96,18 +96,18 @@ public sealed class OpcUaClientConnectionLossSignalTests
 
     public static TheoryData<uint> DefinitiveStatuses =>
     [
-        StatusCodes.BadSessionIdInvalid,
-        StatusCodes.BadSessionClosed,
-        StatusCodes.BadSessionNotActivated,
-        StatusCodes.BadServerHalted,
+        StatusCodes.BadSessionIdInvalid.Code,
+        StatusCodes.BadSessionClosed.Code,
+        StatusCodes.BadSessionNotActivated.Code,
+        StatusCodes.BadServerHalted.Code,
     ];
 
     public static TheoryData<uint> AmbiguousStatuses =>
     [
-        StatusCodes.BadNoCommunication,
-        StatusCodes.BadNotConnected,
-        StatusCodes.BadRequestTimeout,
-        StatusCodes.BadTimeout,
+        StatusCodes.BadNoCommunication.Code,
+        StatusCodes.BadNotConnected.Code,
+        StatusCodes.BadRequestTimeout.Code,
+        StatusCodes.BadTimeout.Code,
     ];
 
     [Theory]
@@ -127,7 +127,7 @@ public sealed class OpcUaClientConnectionLossSignalTests
         drv.RaiseKeepAliveForTest(StatusCodes.BadSessionIdInvalid);
 
         raised.ShouldHaveSingleItem("once per session, however many definitive keep-alives follow")
-            .Reason.ShouldContain(StatusCodes.GetBrowseName(status));
+            .Reason.ShouldContain(new StatusCode(status).SymbolicId!);
         order.ShouldBe([$"bad:{BadNoCommunication:X8}", "lost"], "subscribers see the Bad before the host tears down");
     }
 
@@ -404,7 +404,7 @@ public sealed class OpcUaClientConnectionLossSignalTests
         var reads = 0;
         session.Setup(s => s.ReadAsync(
                 It.IsAny<RequestHeader>(), It.IsAny<double>(), It.IsAny<TimestampsToReturn>(),
-                It.IsAny<ReadValueIdCollection>(), It.IsAny<CancellationToken>()))
+                It.IsAny<ArrayOf<ReadValueId>>(), It.IsAny<CancellationToken>()))
             .ReturnsAsync(() =>
             {
                 var trailing = Interlocked.Increment(ref reads) > 1;
@@ -447,7 +447,7 @@ public sealed class OpcUaClientConnectionLossSignalTests
         var reads = 0;
         session.Setup(s => s.ReadAsync(
                 It.IsAny<RequestHeader>(), It.IsAny<double>(), It.IsAny<TimestampsToReturn>(),
-                It.IsAny<ReadValueIdCollection>(), It.IsAny<CancellationToken>()))
+                It.IsAny<ArrayOf<ReadValueId>>(), It.IsAny<CancellationToken>()))
             .Returns(async () =>
             {
                 if (Interlocked.Increment(ref reads) > 1) await gate.Task; // hold the trailing read
@@ -495,7 +495,7 @@ public sealed class OpcUaClientConnectionLossSignalTests
 
         session.Verify(s => s.ReadAsync(
             It.IsAny<RequestHeader>(), It.IsAny<double>(), It.IsAny<TimestampsToReturn>(),
-            It.IsAny<ReadValueIdCollection>(), It.IsAny<CancellationToken>()), Times.Once,
+            It.IsAny<ArrayOf<ReadValueId>>(), It.IsAny<CancellationToken>()), Times.Once,
             "only the recovery read — the trailing read must not run against a session that is no longer current");
     }
 
@@ -506,7 +506,7 @@ public sealed class OpcUaClientConnectionLossSignalTests
         var reads = 0;
         session.Setup(s => s.ReadAsync(
                 It.IsAny<RequestHeader>(), It.IsAny<double>(), It.IsAny<TimestampsToReturn>(),
-                It.IsAny<ReadValueIdCollection>(), It.IsAny<CancellationToken>()))
+                It.IsAny<ArrayOf<ReadValueId>>(), It.IsAny<CancellationToken>()))
             .ReturnsAsync(() => new ReadResponse
             {
                 ResponseHeader = new ResponseHeader(),
@@ -559,7 +559,7 @@ public sealed class OpcUaClientConnectionLossSignalTests
         var handle = drv.AddSubscriptionForTest([SpeedRef]);
         var t0 = clock.Now.UtcDateTime;
         DataValue NoSource(object v, DateTime server) =>
-            new(new Variant(v), StatusCodes.Good, DateTime.MinValue, server);
+            new(VariantHelper.CastFrom(v), StatusCodes.Good, DateTime.MinValue, server);
         drv.DeliverNotificationForTest(handle, SpeedRef, NoSource(10f, t0));
         var reads = SetupRecoveryThenTrailing(session, NoSource(10f, t0.AddSeconds(1)), NoSource(40f, t0.AddSeconds(9)));
 
@@ -587,7 +587,7 @@ public sealed class OpcUaClientConnectionLossSignalTests
         var reads = 0;
         session.Setup(s => s.ReadAsync(
                 It.IsAny<RequestHeader>(), It.IsAny<double>(), It.IsAny<TimestampsToReturn>(),
-                It.IsAny<ReadValueIdCollection>(), It.IsAny<CancellationToken>()))
+                It.IsAny<ArrayOf<ReadValueId>>(), It.IsAny<CancellationToken>()))
             .ReturnsAsync(() => new ReadResponse
             {
                 ResponseHeader = new ResponseHeader(),
@@ -677,12 +677,12 @@ public sealed class OpcUaClientConnectionLossSignalTests
         drv.PostRecoveryReconcileDelay = () => TimeSpan.Zero;
         var handle = drv.AddSubscriptionForTest([SpeedRef]);
         var t0 = clock.Now.UtcDateTime;
-        DataValue NoSource(object v, DateTime server) => new(new Variant(v), StatusCodes.Good, DateTime.MinValue, server);
+        DataValue NoSource(object v, DateTime server) => new(VariantHelper.CastFrom(v), StatusCodes.Good, DateTime.MinValue, server);
         drv.DeliverNotificationForTest(handle, SpeedRef, NoSource(10f, t0));
         var reads = 0;
         session.Setup(s => s.ReadAsync(
                 It.IsAny<RequestHeader>(), It.IsAny<double>(), It.IsAny<TimestampsToReturn>(),
-                It.IsAny<ReadValueIdCollection>(), It.IsAny<CancellationToken>()))
+                It.IsAny<ArrayOf<ReadValueId>>(), It.IsAny<CancellationToken>()))
             .ReturnsAsync(() =>
             {
                 DataValue result;
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientContinuationPointReleaseTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientContinuationPointReleaseTests.cs
index e4fcc323..62b9a6b1 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientContinuationPointReleaseTests.cs
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientContinuationPointReleaseTests.cs
@@ -37,7 +37,7 @@ public sealed class OpcUaClientContinuationPointReleaseTests
     private static Mock<ISession> BuildCancellingSessionMock()
     {
         var mock = new Mock<ISession>(MockBehavior.Loose);
-        mock.SetupGet(s => s.MessageContext).Returns(new ServiceMessageContext(ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.SdkTelemetry.Context));
+        mock.SetupGet(s => s.MessageContext).Returns(ServiceMessageContext.Create(ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.SdkTelemetry.Context));
         mock.SetupGet(s => s.NamespaceUris).Returns(new NamespaceTable());
 
         // BrowseAsync — return one Object child plus a non-empty continuation point so
@@ -52,20 +52,20 @@ public sealed class OpcUaClientContinuationPointReleaseTests
         };
         var browseResult = new BrowseResult
         {
-            ContinuationPoint = FakeContinuationPoint,
-            References = new ReferenceDescriptionCollection { firstRef },
+            ContinuationPoint = FakeContinuationPoint.ToByteString(),
+            References = new List<ReferenceDescription> { firstRef },
         };
         var browseResp = new BrowseResponse
         {
             ResponseHeader = new ResponseHeader(),
-            Results = new BrowseResultCollection { browseResult },
-            DiagnosticInfos = new DiagnosticInfoCollection(),
+            Results = new List<BrowseResult> { browseResult },
+            DiagnosticInfos = new List<DiagnosticInfo>(),
         };
         mock.Setup(s => s.BrowseAsync(
                 It.IsAny<RequestHeader>(),
                 It.IsAny<ViewDescription>(),
                 It.IsAny<uint>(),
-                It.IsAny<BrowseDescriptionCollection>(),
+                It.IsAny<ArrayOf<BrowseDescription>>(),
                 It.IsAny<CancellationToken>()))
             .ReturnsAsync(browseResp);
 
@@ -73,7 +73,7 @@ public sealed class OpcUaClientContinuationPointReleaseTests
         mock.Setup(s => s.BrowseNextAsync(
                 It.IsAny<RequestHeader>(),
                 It.Is<bool>(release => !release),
-                It.IsAny<ByteStringCollection>(),
+                It.IsAny<ArrayOf<ByteString>>(),
                 It.IsAny<CancellationToken>()))
             .ThrowsAsync(new OperationCanceledException("ct cancelled during BrowseNext"));
 
@@ -82,19 +82,19 @@ public sealed class OpcUaClientContinuationPointReleaseTests
         // there is no separate BrowseNextResult type in the OPC UA SDK.
         var emptyReleaseResult = new BrowseResult
         {
-            ContinuationPoint = Array.Empty<byte>(),
-            References = new ReferenceDescriptionCollection(),
+            ContinuationPoint = ByteString.Empty,
+            References = new List<ReferenceDescription>(),
         };
         var releaseResp = new BrowseNextResponse
         {
             ResponseHeader = new ResponseHeader(),
-            Results = new BrowseResultCollection { emptyReleaseResult },
-            DiagnosticInfos = new DiagnosticInfoCollection(),
+            Results = new List<BrowseResult> { emptyReleaseResult },
+            DiagnosticInfos = new List<DiagnosticInfo>(),
         };
         mock.Setup(s => s.BrowseNextAsync(
                 It.IsAny<RequestHeader>(),
                 It.Is<bool>(release => release),
-                It.IsAny<ByteStringCollection>(),
+                It.IsAny<ArrayOf<ByteString>>(),
                 It.IsAny<CancellationToken>()))
             .ReturnsAsync(releaseResp);
 
@@ -127,7 +127,7 @@ public sealed class OpcUaClientContinuationPointReleaseTests
         sessionMock.Verify(s => s.BrowseNextAsync(
             It.IsAny<RequestHeader>(),
             It.Is<bool>(release => release),
-            It.IsAny<ByteStringCollection>(),
+            It.IsAny<ArrayOf<ByteString>>(),
             It.IsAny<CancellationToken>()),
             Times.Once,
             "DiscoverAsync must release the server-side continuation point on cancellation " +
@@ -148,7 +148,7 @@ public sealed class OpcUaClientContinuationPointReleaseTests
         using var drv = new OpcUaClientDriver(new OpcUaClientDriverOptions(), "opcua-cp-norelease");
 
         var mock = new Mock<ISession>(MockBehavior.Loose);
-        mock.SetupGet(s => s.MessageContext).Returns(new ServiceMessageContext(ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.SdkTelemetry.Context));
+        mock.SetupGet(s => s.MessageContext).Returns(ServiceMessageContext.Create(ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.SdkTelemetry.Context));
         mock.SetupGet(s => s.NamespaceUris).Returns(new NamespaceTable());
 
         // BrowseAsync — return a result with a continuation point so the loop is entered.
@@ -161,27 +161,27 @@ public sealed class OpcUaClientContinuationPointReleaseTests
         };
         var browseResult = new BrowseResult
         {
-            ContinuationPoint = FakeContinuationPoint,
-            References = new ReferenceDescriptionCollection { firstRef },
+            ContinuationPoint = FakeContinuationPoint.ToByteString(),
+            References = new List<ReferenceDescription> { firstRef },
         };
         mock.Setup(s => s.BrowseAsync(
                 It.IsAny<RequestHeader>(),
                 It.IsAny<ViewDescription>(),
                 It.IsAny<uint>(),
-                It.IsAny<BrowseDescriptionCollection>(),
+                It.IsAny<ArrayOf<BrowseDescription>>(),
                 It.IsAny<CancellationToken>()))
             .ReturnsAsync(new BrowseResponse
             {
                 ResponseHeader = new ResponseHeader(),
-                Results = new BrowseResultCollection { browseResult },
-                DiagnosticInfos = new DiagnosticInfoCollection(),
+                Results = new List<BrowseResult> { browseResult },
+                DiagnosticInfos = new List<DiagnosticInfo>(),
             });
 
         // BrowseNextAsync — throw a non-cancellation transport error.
         mock.Setup(s => s.BrowseNextAsync(
                 It.IsAny<RequestHeader>(),
                 It.Is<bool>(release => !release),
-                It.IsAny<ByteStringCollection>(),
+                It.IsAny<ArrayOf<ByteString>>(),
                 It.IsAny<CancellationToken>()))
             .ThrowsAsync(new ServiceResultException(StatusCodes.BadCommunicationError));
 
@@ -195,7 +195,7 @@ public sealed class OpcUaClientContinuationPointReleaseTests
         mock.Verify(s => s.BrowseNextAsync(
             It.IsAny<RequestHeader>(),
             It.Is<bool>(release => release),
-            It.IsAny<ByteStringCollection>(),
+            It.IsAny<ArrayOf<ByteString>>(),
             It.IsAny<CancellationToken>()),
             Times.Never,
             "A transient transport failure must not trigger a release BrowseNext call");
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientGateSplitTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientGateSplitTests.cs
index b78ba971..ef5e3565 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientGateSplitTests.cs
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientGateSplitTests.cs
@@ -28,16 +28,16 @@ public sealed class OpcUaClientGateSplitTests
     {
         var drv = new OpcUaClientDriver(new OpcUaClientDriverOptions { RawTags = Tags }, "opcua-o6");
         var session = new Mock<ISession>(MockBehavior.Loose);
-        session.SetupGet(s => s.MessageContext).Returns(new ServiceMessageContext(SdkTelemetry.Context));
+        session.SetupGet(s => s.MessageContext).Returns(ServiceMessageContext.Create(SdkTelemetry.Context));
         session.SetupGet(s => s.NamespaceUris).Returns(new NamespaceTable());
         session.Setup(s => s.ReadAsync(
                 It.IsAny<RequestHeader>(), It.IsAny<double>(), It.IsAny<TimestampsToReturn>(),
-                It.IsAny<ReadValueIdCollection>(), It.IsAny<CancellationToken>()))
-            .ReturnsAsync((RequestHeader _, double _, TimestampsToReturn _, ReadValueIdCollection nodes, CancellationToken _) =>
+                It.IsAny<ArrayOf<ReadValueId>>(), It.IsAny<CancellationToken>()))
+            .ReturnsAsync((RequestHeader _, double _, TimestampsToReturn _, ArrayOf<ReadValueId> nodes, CancellationToken _) =>
                 new ReadResponse
                 {
                     ResponseHeader = new ResponseHeader(),
-                    Results = [.. nodes.Select(_ => new DataValue(new Variant(42), StatusCodes.Good, DateTime.UtcNow, DateTime.UtcNow))],
+                    Results = [.. nodes.ToList().Select(_ => new DataValue(new Variant(42), StatusCodes.Good, DateTime.UtcNow, DateTime.UtcNow))],
                     DiagnosticInfos = [],
                 });
         drv.SetSessionForTest(session.Object);
@@ -60,15 +60,15 @@ public sealed class OpcUaClientGateSplitTests
         using var _ = drv;
         var writeOnWire = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously);
         var releaseWrite = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously);
-        session.Setup(s => s.WriteAsync(It.IsAny<RequestHeader>(), It.IsAny<WriteValueCollection>(), It.IsAny<CancellationToken>()))
-            .Returns(async (RequestHeader _, WriteValueCollection nodes, CancellationToken _) =>
+        session.Setup(s => s.WriteAsync(It.IsAny<RequestHeader>(), It.IsAny<ArrayOf<WriteValue>>(), It.IsAny<CancellationToken>()))
+            .Returns(async (RequestHeader _, ArrayOf<WriteValue> nodes, CancellationToken _) =>
             {
                 writeOnWire.TrySetResult();
                 await releaseWrite.Task;
                 return new WriteResponse
                 {
                     ResponseHeader = new ResponseHeader(),
-                    Results = [.. nodes.Select(_ => (StatusCode)StatusCodes.Good)],
+                    Results = [.. nodes.ToList().Select(_ => (StatusCode)StatusCodes.Good)],
                     DiagnosticInfos = [],
                 };
             });
@@ -111,8 +111,8 @@ public sealed class OpcUaClientGateSplitTests
         var releaseBrowse = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously);
         session.Setup(s => s.BrowseAsync(
                 It.IsAny<RequestHeader>(), It.IsAny<ViewDescription>(), It.IsAny<uint>(),
-                It.IsAny<BrowseDescriptionCollection>(), It.IsAny<CancellationToken>()))
-            .Returns(async (RequestHeader _, ViewDescription _, uint _, BrowseDescriptionCollection _, CancellationToken _) =>
+                It.IsAny<ArrayOf<BrowseDescription>>(), It.IsAny<CancellationToken>()))
+            .Returns(async (RequestHeader _, ViewDescription _, uint _, ArrayOf<BrowseDescription> _, CancellationToken _) =>
             {
                 browseOnWire.TrySetResult();
                 await releaseBrowse.Task;
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientIdlePublishErrorTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientIdlePublishErrorTests.cs
index e5a30ee6..4988fde8 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientIdlePublishErrorTests.cs
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientIdlePublishErrorTests.cs
@@ -28,7 +28,7 @@ public sealed class OpcUaClientIdlePublishErrorTests
     {
         var drv = new OpcUaClientDriver(new OpcUaClientDriverOptions { RawTags = Tags }, instance);
         var session = new Mock<ISession>(MockBehavior.Loose);
-        session.SetupGet(s => s.MessageContext).Returns(new ServiceMessageContext(SdkTelemetry.Context));
+        session.SetupGet(s => s.MessageContext).Returns(ServiceMessageContext.Create(SdkTelemetry.Context));
         session.SetupGet(s => s.NamespaceUris).Returns(new NamespaceTable());
         drv.SetSessionForTest(session.Object);
         drv.SetNamespaceMapForTest(NamespaceMap.FromTable(new NamespaceTable(), Tags));
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientLifecycleGenerationTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientLifecycleGenerationTests.cs
index ae26ca54..12d230ca 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientLifecycleGenerationTests.cs
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientLifecycleGenerationTests.cs
@@ -29,15 +29,15 @@ public sealed class OpcUaClientLifecycleGenerationTests
     private static Mock<ISession> NewSession()
     {
         var mock = new Mock<ISession>(MockBehavior.Loose);
-        mock.SetupGet(s => s.MessageContext).Returns(new ServiceMessageContext(SdkTelemetry.Context));
+        mock.SetupGet(s => s.MessageContext).Returns(ServiceMessageContext.Create(SdkTelemetry.Context));
         mock.SetupGet(s => s.NamespaceUris).Returns(new NamespaceTable());
         return mock;
     }
 
-    private static ReadResponse GoodRead(ReadValueIdCollection nodes) => new()
+    private static ReadResponse GoodRead(ArrayOf<ReadValueId> nodes) => new()
     {
         ResponseHeader = new ResponseHeader(),
-        Results = [.. nodes.Select(_ => new DataValue(new Variant(1), StatusCodes.Good, DateTime.UtcNow, DateTime.UtcNow))],
+        Results = [.. nodes.ToList().Select(_ => new DataValue(new Variant(1), StatusCodes.Good, DateTime.UtcNow, DateTime.UtcNow))],
         DiagnosticInfos = [],
     };
 
@@ -118,6 +118,26 @@ public sealed class OpcUaClientLifecycleGenerationTests
         drv.GetHealth().State.ShouldBe(DriverState.Unknown, "the abandoned init must not overwrite the newer health");
     }
 
+    [Fact]
+    public async Task Cancellation_at_session_ownership_transfer_discards_session_without_failover_or_install()
+    {
+        var session = NewSession();
+        using var cancellation = new CancellationTokenSource();
+        using var driver = new OpcUaClientDriver(new OpcUaClientDriverOptions
+            { EndpointUrls = ["opc.tcp://first:4840", "opc.tcp://second:4840"] }, "sdk2-cancel-open");
+        var opens = 0;
+        driver.OpenSessionForTest = (_, _) =>
+        {
+            opens++;
+            cancellation.Cancel();
+            return Task.FromResult(session.Object);
+        };
+        await Should.ThrowAsync<OperationCanceledException>(() => driver.InitializeAsync("{}", cancellation.Token));
+        opens.ShouldBe(1);
+        driver.Session.ShouldBeNull();
+        session.Verify(s => s.Dispose(), Times.Once);
+    }
+
     /// <summary>A read whose response arrives after a shutdown does not write Healthy over the shutdown.</summary>
     [Fact]
     public async Task A_read_that_outlives_a_shutdown_does_not_overwrite_the_shutdown_health()
@@ -160,8 +180,8 @@ public sealed class OpcUaClientLifecycleGenerationTests
         var respond = new System.Collections.Concurrent.ConcurrentQueue<TaskCompletionSource>();
         session.Setup(s => s.ReadAsync(
                 It.IsAny<RequestHeader>(), It.IsAny<double>(), It.IsAny<TimestampsToReturn>(),
-                It.IsAny<ReadValueIdCollection>(), It.IsAny<CancellationToken>()))
-            .Returns(async (RequestHeader _, double _, TimestampsToReturn _, ReadValueIdCollection nodes, CancellationToken _) =>
+                It.IsAny<ArrayOf<ReadValueId>>(), It.IsAny<CancellationToken>()))
+            .Returns(async (RequestHeader _, double _, TimestampsToReturn _, ArrayOf<ReadValueId> nodes, CancellationToken _) =>
             {
                 var gate = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously);
                 respond.Enqueue(gate);
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientNamespaceTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientNamespaceTests.cs
index 5939957c..b6c574d9 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientNamespaceTests.cs
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientNamespaceTests.cs
@@ -74,6 +74,35 @@ public sealed class OpcUaClientNamespaceTests
         NamespaceMap.TryResolve(null!, "ns=1;s=X", out _).ShouldBeFalse();
     }
 
+    public static TheoryData<NodeId> IdentifierKinds =>
+    [
+        new NodeId(123u, 1),
+        new NodeId("literal;i=123", 1),
+        new NodeId(Guid.Parse("db8d57c4-316f-4517-819f-194c3a6db955"), 1),
+        new NodeId(new byte[] { 0, 1, 127, 255 }.ToByteString(), 1),
+    ];
+
+    [Theory]
+    [MemberData(nameof(IdentifierKinds))]
+    public void Stable_reference_rebinds_namespace_without_changing_identifier_type(NodeId original)
+    {
+        var stable = TestMap("http://opcfoundation.org/UA/", "urn:remote:server").ToStableReference(original);
+        var context = ServiceMessageContext.Create(SdkTelemetry.Context);
+        context.NamespaceUris.Append("urn:other");
+        context.NamespaceUris.Append("urn:remote:server");
+        var session = new Moq.Mock<Opc.Ua.Client.ISession>();
+        session.SetupGet(s => s.MessageContext).Returns(context);
+        NamespaceMap.TryResolve(session.Object, stable, out var rebound).ShouldBeTrue();
+        rebound.NamespaceIndex.ShouldBe((ushort)2);
+        rebound.IdType.ShouldBe(original.IdType);
+        rebound.IdentifierAsString.ShouldBe(original.IdentifierAsString);
+        if (original.IdType == IdType.Opaque)
+        {
+            rebound.TryGetValue(out ByteString identifier).ShouldBeTrue();
+            identifier.ToArray().ShouldBe(new byte[] { 0, 1, 127, 255 });
+        }
+    }
+
     // ---- v3: RawPath → upstream node id resolution table ----
 
     /// <summary>Verifies a RawPath resolves to the upstream node id authored in its TagConfig.nodeId.</summary>
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientSdkValueBoundaryTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientSdkValueBoundaryTests.cs
new file mode 100644
index 00000000..79fb873e
--- /dev/null
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientSdkValueBoundaryTests.cs
@@ -0,0 +1,173 @@
+using Moq;
+using Opc.Ua;
+using Opc.Ua.Client;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests;
+
+[Trait("Category", "Unit")]
+public sealed class OpcUaClientSdkValueBoundaryTests
+{
+    private const string Reference = "Plant/Upstream/Value";
+    private static readonly RawTagEntry[] Tags = [new(Reference, """{"nodeId":"i=2258"}""", false)];
+
+    private static (OpcUaClientDriver Driver, Mock<ISession> Session) Connected()
+    {
+        var session = new Mock<ISession>();
+        session.SetupGet(s => s.MessageContext).Returns(ServiceMessageContext.Create(SdkTelemetry.Context));
+        session.SetupGet(s => s.NamespaceUris).Returns(new NamespaceTable());
+        var driver = new OpcUaClientDriver(new OpcUaClientDriverOptions { RawTags = Tags }, "sdk2-values");
+        driver.SetSessionForTest(session.Object);
+        driver.SetNamespaceMapForTest(NamespaceMap.FromTable(new NamespaceTable(), Tags));
+        return (driver, session);
+    }
+
+    public static TheoryData<Variant, object?> Payloads =>
+    [
+        new(Variant.From((sbyte)-3), (sbyte)-3),
+        new(Variant.From((byte)250), (byte)250),
+        new(Variant.From((short)-30), (short)-30),
+        new(Variant.From((ushort)60000), (ushort)60000),
+        new(Variant.From(-100), -100),
+        new(Variant.From(uint.MaxValue), uint.MaxValue),
+        new(Variant.From(long.MinValue), long.MinValue),
+        new(Variant.From(ulong.MaxValue), ulong.MaxValue),
+        new(Variant.From(1.5f), 1.5f),
+        new(Variant.From(1.5d), 1.5d),
+        new(Variant.From(true), true),
+        new(Variant.From("text"), "text"),
+        new(Variant.Null, null),
+        new(Variant.From(new DateTimeUtc(new DateTime(2026, 11, 10, 1, 2, 3, DateTimeKind.Utc))), new DateTime(2026, 11, 10, 1, 2, 3, DateTimeKind.Utc)),
+        new(Variant.From(new Uuid(Guid.Parse("db8d57c4-316f-4517-819f-194c3a6db955"))), Guid.Parse("db8d57c4-316f-4517-819f-194c3a6db955")),
+        new(Variant.From(new byte[] { 1, 2 }.ToByteString()), new byte[] { 1, 2 }),
+        new(Variant.From(default(ByteString)), null),
+        new(Variant.From(ByteString.Empty), Array.Empty<byte>()),
+        new(Variant.From((ArrayOf<bool>)[true, false]), new[] { true, false }),
+        new(Variant.From((ArrayOf<sbyte>)[-1, 2]), new sbyte[] { -1, 2 }),
+        new(Variant.From((ArrayOf<byte>)[1, 250]), new byte[] { 1, 250 }),
+        new(Variant.From((ArrayOf<short>)[1, 2]), new short[] { 1, 2 }),
+        new(Variant.From((ArrayOf<ushort>)[1, 60000]), new ushort[] { 1, 60000 }),
+        new(Variant.From((ArrayOf<int>)[-1, 2]), new int[] { -1, 2 }),
+        new(Variant.From((ArrayOf<long>)[long.MinValue, long.MaxValue]), new long[] { long.MinValue, long.MaxValue }),
+        new(Variant.From((ArrayOf<ulong>)[0, ulong.MaxValue]), new ulong[] { 0, ulong.MaxValue }),
+        new(Variant.From((ArrayOf<double>)[1, 2]), new double[] { 1, 2 }),
+        new(Variant.From((ArrayOf<uint>)[1, 2]), new uint[] { 1, 2 }),
+        new(Variant.From((ArrayOf<float>)[1, 2]), new float[] { 1, 2 }),
+        new(Variant.From((ArrayOf<string>)["a", "b"]), new[] { "a", "b" }),
+        new(Variant.From((ArrayOf<DateTimeUtc>)[new DateTimeUtc(new DateTime(2026, 11, 10, 1, 2, 3, DateTimeKind.Utc))]), new[] { new DateTime(2026, 11, 10, 1, 2, 3, DateTimeKind.Utc) }),
+        new(Variant.From((ArrayOf<Uuid>)[new Uuid(Guid.Empty)]), new[] { Guid.Empty }),
+        new(Variant.From((ArrayOf<ByteString>)[new byte[] { 3 }.ToByteString(), ByteString.Empty]), new byte[][] { [3], [] }),
+        new(Variant.From(default(ArrayOf<short>)), null),
+        new(Variant.From((ArrayOf<short>)[]), Array.Empty<short>()),
+    ];
+
+    [Theory]
+    [MemberData(nameof(Payloads))]
+    public async Task Read_and_notification_preserve_CLR_type_status_and_timestamp_rules(Variant upstream, object? expected)
+    {
+        var (driver, session) = Connected();
+        using var _ = driver;
+        session.Setup(s => s.ReadAsync(It.IsAny<RequestHeader>(), It.IsAny<double>(), It.IsAny<TimestampsToReturn>(),
+            It.IsAny<ArrayOf<ReadValueId>>(), It.IsAny<CancellationToken>())).ReturnsAsync(new ReadResponse
+            { Results = [new DataValue(upstream, StatusCodes.UncertainLastUsableValue, DateTimeUtc.MinValue, DateTimeUtc.MinValue)] });
+        var before = DateTime.UtcNow;
+        var read = (await driver.ReadAsync([Reference], TestContext.Current.CancellationToken)).Single();
+        AssertPayload(read, expected, before);
+        DataValueSnapshot? notified = null;
+        driver.OnDataChange += (_, e) => notified = e.Snapshot;
+        var handle = driver.AddSubscriptionForTest([Reference]);
+        driver.DeliverNotificationForTest(handle, Reference,
+            new DataValue(upstream, StatusCodes.UncertainLastUsableValue, DateTimeUtc.MinValue, DateTimeUtc.MinValue));
+        AssertPayload(notified.ShouldNotBeNull(), expected, before);
+    }
+
+    private static void AssertPayload(DataValueSnapshot snapshot, object? expected, DateTime before)
+    {
+        snapshot.Value.ShouldBe(expected);
+        snapshot.Value?.GetType().ShouldBe(expected?.GetType());
+        snapshot.StatusCode.ShouldBe(StatusCodes.UncertainLastUsableValue.Code);
+        snapshot.SourceTimestampUtc.ShouldBeNull();
+        snapshot.ServerTimestampUtc.ShouldBeGreaterThanOrEqualTo(before);
+        snapshot.ServerTimestampUtc.Kind.ShouldBe(DateTimeKind.Utc);
+    }
+
+    [Theory]
+    [InlineData(0)]
+    [InlineData(1)]
+    [InlineData(2)]
+    public async Task Read_and_notification_detach_upstream_buffers(int shape)
+    {
+        var (driver, session) = Connected();
+        using var _ = driver;
+        byte[] bytes = [1, 2];
+        short[] numbers = [3, 4];
+        // ReadOnlyMemory constructors deliberately alias the backing SDK buffer. Copying the
+        // test input before the adapter sees it would make the ownership assertion vacuous.
+        var value = shape switch
+        {
+            0 => Variant.From(new ByteString(bytes.AsMemory())),
+            1 => Variant.From(new ArrayOf<short>(numbers.AsMemory())),
+            _ => Variant.From((ArrayOf<ByteString>)[new ByteString(bytes.AsMemory())]),
+        };
+        object expected = shape switch { 0 => new byte[] { 1, 2 }, 1 => new short[] { 3, 4 }, _ => new byte[][] { [1, 2] } };
+        session.Setup(s => s.ReadAsync(It.IsAny<RequestHeader>(), It.IsAny<double>(), It.IsAny<TimestampsToReturn>(),
+            It.IsAny<ArrayOf<ReadValueId>>(), It.IsAny<CancellationToken>())).ReturnsAsync(new ReadResponse { Results = [new DataValue(value)] });
+        var read = (await driver.ReadAsync([Reference], TestContext.Current.CancellationToken)).Single();
+        DataValueSnapshot? notified = null;
+        driver.OnDataChange += (_, e) => notified = e.Snapshot;
+        driver.DeliverNotificationForTest(driver.AddSubscriptionForTest([Reference]), Reference, new DataValue(value));
+        bytes[0] = 99;
+        numbers[0] = 99;
+        read.Value.ShouldBe(expected);
+        notified.ShouldNotBeNull().Value.ShouldBe(expected);
+    }
+
+    [Fact]
+    public async Task Matrix_read_and_notification_are_refused_per_item_without_materialization()
+    {
+        var (driver, session) = Connected();
+        using var _ = driver;
+        var sourceTime = new DateTime(2026, 11, 10, 1, 2, 3, DateTimeKind.Utc);
+        var serverTime = sourceTime.AddSeconds(1);
+        var matrix = Variant.From(new int[,] { { 1, 2 }, { 3, 4 } }.ToMatrixOf());
+        session.Setup(s => s.ReadAsync(It.IsAny<RequestHeader>(), It.IsAny<double>(), It.IsAny<TimestampsToReturn>(),
+            It.IsAny<ArrayOf<ReadValueId>>(), It.IsAny<CancellationToken>())).ReturnsAsync(new ReadResponse
+            { Results = [new DataValue(matrix, StatusCodes.Good, sourceTime, serverTime),
+                new DataValue(Variant.From(42), StatusCodes.Good, sourceTime, serverTime)] });
+        var results = await driver.ReadAsync([Reference, Reference], TestContext.Current.CancellationToken);
+        results[0].Value.ShouldBeNull();
+        results[0].StatusCode.ShouldBe(StatusCodes.BadTypeMismatch.Code);
+        results[0].SourceTimestampUtc.ShouldBe(sourceTime);
+        results[0].ServerTimestampUtc.ShouldBe(serverTime);
+        results[1].Value.ShouldBe(42);
+        results[1].StatusCode.ShouldBe(StatusCodes.Good.Code);
+        DataValueSnapshot? notified = null;
+        driver.OnDataChange += (_, e) => notified = e.Snapshot;
+        driver.DeliverNotificationForTest(driver.AddSubscriptionForTest([Reference]), Reference,
+            new DataValue(matrix, StatusCodes.UncertainLastUsableValue, sourceTime, serverTime));
+        notified.ShouldNotBeNull().Value.ShouldBeNull();
+        notified.StatusCode.ShouldBe(StatusCodes.BadTypeMismatch.Code);
+        notified.SourceTimestampUtc.ShouldBe(sourceTime);
+        notified.ServerTimestampUtc.ShouldBe(serverTime);
+    }
+
+    [Fact]
+    public async Task Write_passes_scalar_shaped_arrays_once_and_rejects_unsupported_values_before_IO()
+    {
+        var (driver, session) = Connected();
+        using var _ = driver;
+        short[] caller = [7, 8];
+        ArrayOf<WriteValue> sent = default;
+        session.Setup(s => s.WriteAsync(It.IsAny<RequestHeader>(), It.IsAny<ArrayOf<WriteValue>>(), It.IsAny<CancellationToken>()))
+            .Callback<RequestHeader, ArrayOf<WriteValue>, CancellationToken>((_, writes, _) => { sent = writes; caller[0] = 99; })
+            .ReturnsAsync(new WriteResponse { Results = [StatusCodes.Good] });
+        var result = await driver.WriteAsync([new(Reference, caller), new(Reference, new object()), new(Reference, new int[1, 1])], TestContext.Current.CancellationToken);
+        result.Select(r => r.StatusCode).ShouldBe([StatusCodes.Good.Code, StatusCodes.BadTypeMismatch.Code, StatusCodes.BadTypeMismatch.Code]);
+        sent.Count.ShouldBe(1);
+        sent[0].Value.WrappedValue.TypeInfo.ValueRank.ShouldBe(ValueRanks.OneDimension);
+        UpstreamValueMapping.ToClr(sent[0].Value.WrappedValue).ShouldBe(new short[] { 7, 8 });
+        session.Verify(s => s.WriteAsync(It.IsAny<RequestHeader>(), It.IsAny<ArrayOf<WriteValue>>(), It.IsAny<CancellationToken>()), Times.Once);
+    }
+}
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientSessionLossTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientSessionLossTests.cs
index 992f5462..36f2f344 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientSessionLossTests.cs
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientSessionLossTests.cs
@@ -41,7 +41,7 @@ public sealed class OpcUaClientSessionLossTests
     {
         var mock = new Mock<ISession>(MockBehavior.Loose);
         mock.SetupGet(s => s.MessageContext)
-            .Returns(new ServiceMessageContext(SdkTelemetry.Context));
+            .Returns(ServiceMessageContext.Create(SdkTelemetry.Context));
         mock.SetupGet(s => s.NamespaceUris).Returns(new NamespaceTable());
         return mock;
     }
@@ -60,17 +60,17 @@ public sealed class OpcUaClientSessionLossTests
     }
 
     private static DataValue Good(object value, DateTime ts) =>
-        new(new Variant(value), StatusCodes.Good, ts, ts);
+        new(VariantHelper.CastFrom(value), StatusCodes.Good, ts, ts);
 
     private static void SetupRead(Mock<ISession> session, params object[] values) =>
         session.Setup(s => s.ReadAsync(
                 It.IsAny<RequestHeader>(), It.IsAny<double>(), It.IsAny<TimestampsToReturn>(),
-                It.IsAny<ReadValueIdCollection>(), It.IsAny<CancellationToken>()))
-            .ReturnsAsync((RequestHeader _, double _, TimestampsToReturn _, ReadValueIdCollection nodes, CancellationToken _) =>
+                It.IsAny<ArrayOf<ReadValueId>>(), It.IsAny<CancellationToken>()))
+            .ReturnsAsync((RequestHeader _, double _, TimestampsToReturn _, ArrayOf<ReadValueId> nodes, CancellationToken _) =>
                 new ReadResponse
                 {
                     ResponseHeader = new ResponseHeader(),
-                    Results = [.. nodes.Select((_, i) => new DataValue(new Variant(values[i]), StatusCodes.Good, DateTime.UtcNow, DateTime.UtcNow))],
+                    Results = [.. nodes.ToList().Select((_, i) => new DataValue(VariantHelper.CastFrom(values[i]), StatusCodes.Good, DateTime.UtcNow, DateTime.UtcNow))],
                     DiagnosticInfos = [],
                 });
 
@@ -500,11 +500,11 @@ public sealed class OpcUaClientSessionLossTests
     private static void SetupReadAt(Mock<ISession> session, object value, DateTime sourceTime) =>
         session.Setup(s => s.ReadAsync(
                 It.IsAny<RequestHeader>(), It.IsAny<double>(), It.IsAny<TimestampsToReturn>(),
-                It.IsAny<ReadValueIdCollection>(), It.IsAny<CancellationToken>()))
+                It.IsAny<ArrayOf<ReadValueId>>(), It.IsAny<CancellationToken>()))
             .ReturnsAsync(new ReadResponse
             {
                 ResponseHeader = new ResponseHeader(),
-                Results = [new DataValue(new Variant(value), StatusCodes.Good, sourceTime, sourceTime)],
+                Results = [new DataValue(VariantHelper.CastFrom(value), StatusCodes.Good, sourceTime, sourceTime)],
                 DiagnosticInfos = [],
             });
 
@@ -702,7 +702,7 @@ public sealed class OpcUaClientSessionLossTests
         var readAt = t0.AddSeconds(10);
         session.Setup(s => s.ReadAsync(
                 It.IsAny<RequestHeader>(), It.IsAny<double>(), It.IsAny<TimestampsToReturn>(),
-                It.IsAny<ReadValueIdCollection>(), It.IsAny<CancellationToken>()))
+                It.IsAny<ArrayOf<ReadValueId>>(), It.IsAny<CancellationToken>()))
             .ReturnsAsync(new ReadResponse
             {
                 ResponseHeader = new ResponseHeader(),
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientStaleNoSubscriptionTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientStaleNoSubscriptionTests.cs
index 8c7ea995..1755c1eb 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientStaleNoSubscriptionTests.cs
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientStaleNoSubscriptionTests.cs
@@ -42,7 +42,7 @@ public sealed class OpcUaClientStaleNoSubscriptionTests
     {
         var drv = new OpcUaClientDriver(new OpcUaClientDriverOptions { RawTags = Tags }, "opcua-763");
         var session = new Mock<ISession>(MockBehavior.Loose);
-        session.SetupGet(s => s.MessageContext).Returns(new ServiceMessageContext(SdkTelemetry.Context));
+        session.SetupGet(s => s.MessageContext).Returns(ServiceMessageContext.Create(SdkTelemetry.Context));
         session.SetupGet(s => s.NamespaceUris).Returns(new NamespaceTable());
         var clock = new ManualClock(new DateTimeOffset(2026, 11, 9, 12, 0, 0, TimeSpan.Zero));
         drv.Clock = clock;
@@ -209,7 +209,7 @@ public sealed class OpcUaClientSlowDeleteTests
         RawTagEntry[] tags = [new(SpeedRef, JsonSerializer.Serialize(new { nodeId = "ns=0;s=Speed" }), WriteIdempotent: true)];
         var drv = new OpcUaClientDriver(new OpcUaClientDriverOptions { RawTags = tags }, "opcua-764");
         var session = new Mock<ISession>(MockBehavior.Loose);
-        session.SetupGet(s => s.MessageContext).Returns(new ServiceMessageContext(SdkTelemetry.Context));
+        session.SetupGet(s => s.MessageContext).Returns(ServiceMessageContext.Create(SdkTelemetry.Context));
         session.SetupGet(s => s.NamespaceUris).Returns(new NamespaceTable());
         var clock = new ManualClock(new DateTimeOffset(2026, 11, 10, 12, 0, 0, TimeSpan.Zero));
         drv.Clock = clock;
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientStaleSessionRaceTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientStaleSessionRaceTests.cs
index 93010f2b..9e2ece3a 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientStaleSessionRaceTests.cs
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientStaleSessionRaceTests.cs
@@ -46,20 +46,20 @@ public sealed class OpcUaClientStaleSessionRaceTests
         // MessageContext. This getter is read in the driver's synchronous prologue (before the
         // gate), so signalling here proves the pre-gate capture path has run.
         mock.SetupGet(s => s.MessageContext)
-            .Returns(new ServiceMessageContext(ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.SdkTelemetry.Context))
+            .Returns(ServiceMessageContext.Create(ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.SdkTelemetry.Context))
             .Callback(() => prologueReached?.TrySetResult());
         mock.SetupGet(s => s.NamespaceUris).Returns(new NamespaceTable());
         // Acknowledge issues its wire call via CallAsync; stub it so AcknowledgeAsync can run to
         // completion against whichever session it ends up binding to.
         mock.Setup(s => s.CallAsync(
                 It.IsAny<RequestHeader>(),
-                It.IsAny<CallMethodRequestCollection>(),
+                It.IsAny<ArrayOf<CallMethodRequest>>(),
                 It.IsAny<CancellationToken>()))
             .ReturnsAsync(new CallResponse
             {
                 ResponseHeader = new ResponseHeader(),
-                Results = new CallMethodResultCollection(),
-                DiagnosticInfos = new DiagnosticInfoCollection(),
+                Results = new List<CallMethodResult>(),
+                DiagnosticInfos = new List<DiagnosticInfo>(),
             });
         return mock;
     }
@@ -67,10 +67,10 @@ public sealed class OpcUaClientStaleSessionRaceTests
     private static void VerifyAckWireHitNewSessionNotOld(Mock<ISession> newSession, Mock<ISession> oldSession)
     {
         newSession.Verify(s => s.CallAsync(
-            It.IsAny<RequestHeader>(), It.IsAny<CallMethodRequestCollection>(), It.IsAny<CancellationToken>()),
+            It.IsAny<RequestHeader>(), It.IsAny<ArrayOf<CallMethodRequest>>(), It.IsAny<CancellationToken>()),
             Times.Once);
         oldSession.Verify(s => s.CallAsync(
-            It.IsAny<RequestHeader>(), It.IsAny<CallMethodRequestCollection>(), It.IsAny<CancellationToken>()),
+            It.IsAny<RequestHeader>(), It.IsAny<ArrayOf<CallMethodRequest>>(), It.IsAny<CancellationToken>()),
             Times.Never);
     }
 
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientSubscribeCleanupTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientSubscribeCleanupTests.cs
index b3ee7ce6..b24e111b 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientSubscribeCleanupTests.cs
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientSubscribeCleanupTests.cs
@@ -30,7 +30,7 @@ public sealed class OpcUaClientSubscribeCleanupTests
     {
         var drv = new OpcUaClientDriver(new OpcUaClientDriverOptions { RawTags = Tags }, "opcua-o1");
         var session = new Mock<ISession>(MockBehavior.Loose);
-        session.SetupGet(s => s.MessageContext).Returns(new ServiceMessageContext(SdkTelemetry.Context));
+        session.SetupGet(s => s.MessageContext).Returns(ServiceMessageContext.Create(SdkTelemetry.Context));
         session.SetupGet(s => s.NamespaceUris).Returns(new NamespaceTable());
         drv.SetSessionForTest(session.Object);
         drv.SetNamespaceMapForTest(NamespaceMap.FromTable(new NamespaceTable(), Tags));
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientWriteHealthTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientWriteHealthTests.cs
index 320d9c30..3fcfb0ae 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientWriteHealthTests.cs
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientWriteHealthTests.cs
@@ -28,7 +28,7 @@ public sealed class OpcUaClientWriteHealthTests
     {
         var drv = new OpcUaClientDriver(new OpcUaClientDriverOptions { RawTags = Tags }, "opcua-write-health");
         var session = new Mock<ISession>(MockBehavior.Loose);
-        session.SetupGet(s => s.MessageContext).Returns(new ServiceMessageContext(SdkTelemetry.Context));
+        session.SetupGet(s => s.MessageContext).Returns(ServiceMessageContext.Create(SdkTelemetry.Context));
         session.SetupGet(s => s.NamespaceUris).Returns(new NamespaceTable());
         drv.SetSessionForTest(session.Object);
         drv.SetNamespaceMapForTest(NamespaceMap.FromTable(new NamespaceTable(), Tags));
@@ -44,7 +44,7 @@ public sealed class OpcUaClientWriteHealthTests
     {
         var (drv, session) = NewConnectedDriver(new DriverHealth(DriverState.Degraded, Stale, "read failed"));
         using var _ = drv;
-        session.Setup(s => s.WriteAsync(It.IsAny<RequestHeader>(), It.IsAny<WriteValueCollection>(), It.IsAny<CancellationToken>()))
+        session.Setup(s => s.WriteAsync(It.IsAny<RequestHeader>(), It.IsAny<ArrayOf<WriteValue>>(), It.IsAny<CancellationToken>()))
             .ReturnsAsync(new WriteResponse
             {
                 ResponseHeader = new ResponseHeader(),
@@ -54,7 +54,7 @@ public sealed class OpcUaClientWriteHealthTests
 
         var results = await drv.WriteAsync(Write(), TestContext.Current.CancellationToken);
 
-        results.Single().StatusCode.ShouldBe(StatusCodes.BadNotWritable, "the upstream refusal still passes through verbatim");
+        results.Single().StatusCode.ShouldBe(StatusCodes.BadNotWritable.Code, "the upstream refusal still passes through verbatim");
         var h = drv.GetHealth();
         h.State.ShouldBe(DriverState.Healthy);
         h.LastSuccessfulRead.ShouldNotBeNull().ShouldBeGreaterThan(Stale);
@@ -67,7 +67,7 @@ public sealed class OpcUaClientWriteHealthTests
     {
         var (drv, session) = NewConnectedDriver(new DriverHealth(DriverState.Healthy, Stale, null));
         using var _ = drv;
-        session.Setup(s => s.WriteAsync(It.IsAny<RequestHeader>(), It.IsAny<WriteValueCollection>(), It.IsAny<CancellationToken>()))
+        session.Setup(s => s.WriteAsync(It.IsAny<RequestHeader>(), It.IsAny<ArrayOf<WriteValue>>(), It.IsAny<CancellationToken>()))
             .ThrowsAsync(new ServiceResultException(StatusCodes.BadConnectionClosed));
 
         var results = await drv.WriteAsync(Write(), TestContext.Current.CancellationToken);
@@ -89,8 +89,8 @@ public sealed class OpcUaClientWriteHealthTests
         var (drv, session) = NewConnectedDriver(healthy);
         using var _ = drv;
         using var cts = new CancellationTokenSource();
-        session.Setup(s => s.WriteAsync(It.IsAny<RequestHeader>(), It.IsAny<WriteValueCollection>(), It.IsAny<CancellationToken>()))
-            .Returns(async (RequestHeader _, WriteValueCollection _, CancellationToken ct) =>
+        session.Setup(s => s.WriteAsync(It.IsAny<RequestHeader>(), It.IsAny<ArrayOf<WriteValue>>(), It.IsAny<CancellationToken>()))
+            .Returns(async (RequestHeader _, ArrayOf<WriteValue> _, CancellationToken ct) =>
             {
                 cts.Cancel();
                 await Task.Delay(Timeout.Infinite, ct);
@@ -128,7 +128,7 @@ public sealed class OpcUaClientWriteHealthTests
     {
         var (drv, session) = NewConnectedDriver(new DriverHealth(DriverState.Healthy, Stale, null));
         using var _ = drv;
-        session.Setup(s => s.WriteAsync(It.IsAny<RequestHeader>(), It.IsAny<WriteValueCollection>(), It.IsAny<CancellationToken>()))
+        session.Setup(s => s.WriteAsync(It.IsAny<RequestHeader>(), It.IsAny<ArrayOf<WriteValue>>(), It.IsAny<CancellationToken>()))
             .ThrowsAsync(new OperationCanceledException("SDK request timeout"));
 
         var results = await drv.WriteAsync(Write(), TestContext.Current.CancellationToken);
@@ -149,7 +149,7 @@ public sealed class OpcUaClientWriteHealthTests
         using var _ = drv;
         drv.RaiseKeepAliveForTest(StatusCodes.BadNoCommunication);
         drv.GetHealth().State.ShouldBe(DriverState.Degraded, "positive control: the outage is published");
-        session.Setup(s => s.WriteAsync(It.IsAny<RequestHeader>(), It.IsAny<WriteValueCollection>(), It.IsAny<CancellationToken>()))
+        session.Setup(s => s.WriteAsync(It.IsAny<RequestHeader>(), It.IsAny<ArrayOf<WriteValue>>(), It.IsAny<CancellationToken>()))
             .ReturnsAsync(new WriteResponse { ResponseHeader = new ResponseHeader(), Results = [StatusCodes.Good], DiagnosticInfos = [] });
 
         await drv.WriteAsync(Write(), TestContext.Current.CancellationToken);