review(Driver.OpcUaClient.Browser): AttributesAsync updates LastUsedUtc

Review at HEAD 7286d320. -001: AttributesAsync now updates LastUsedUtc (IBrowseSession
contract) + test (InternalsVisibleTo+Moq added). -002 (continuation-point cancel leak)
deferred cross-cutting w/ runtime Driver.OpcUaClient.

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Browser.Tests/OpcUaClientDriverBrowserTests.cs

@@ -1,5 +1,9 @@
+using Moq;
+using Opc.Ua;
+using Opc.Ua.Client;
 using Shouldly;
 using Xunit;
+using ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient;
 using ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Browser;
 
 namespace ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Browser.Tests;
@@ -49,4 +53,39 @@ public sealed class OpcUaClientDriverBrowserTests
             () => _sut.OpenAsync(json, TestContext.Current.CancellationToken));
         ex.Message.ShouldContain("Certificate");
     }
+
+    // ---- Driver.OpcUaClient.Browser-001: AttributesAsync must refresh LastUsedUtc ----
+
+    /// <summary>
+    ///     <see cref="IBrowseSession.LastUsedUtc"/> must be updated on every call
+    ///     including <see cref="OpcUaClientBrowseSession.AttributesAsync"/>, which the
+    ///     <see cref="BrowseSessionReaper"/> uses for idle eviction. Before the fix
+    ///     the method returned immediately without touching the property, causing a
+    ///     session that only received <c>AttributesAsync</c> calls to be evicted early.
+    /// </summary>
+    [Fact]
+    public async Task AttributesAsync_updates_LastUsedUtc()
+    {
+        var ct = TestContext.Current.CancellationToken;
+
+        // Arrange: build a minimal OpcUaClientBrowseSession without a live server.
+        // AttributesAsync does not call ISession — MockBehavior.Loose is safe.
+        var mockSession = new Mock<ISession>(MockBehavior.Loose);
+        var nsMap = NamespaceMap.FromTable(new NamespaceTable());
+        var sut = new OpcUaClientBrowseSession(mockSession.Object, nsMap, ObjectIds.ObjectsFolder);
+
+        var before = sut.LastUsedUtc;
+
+        // Introduce a small delay so clock advances at least one tick.
+        await Task.Delay(5, ct);
+
+        // Act
+        var attrs = await sut.AttributesAsync("nsu=http://opcfoundation.org/UA/;i=85", ct);
+
+        // Assert: LastUsedUtc must have been refreshed, and the result must be empty
+        // (OPC UA picker treats variables as leaves, no attribute side-panel).
+        attrs.ShouldBeEmpty();
+        sut.LastUsedUtc.ShouldBeGreaterThan(before,
+            "AttributesAsync must refresh LastUsedUtc to satisfy the IBrowseSession contract");
+    }
 }

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Browser.Tests/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Browser.Tests.csproj

@@ -12,6 +12,7 @@
     <ItemGroup>
         <PackageReference Include="xunit.v3"/>
         <PackageReference Include="Shouldly"/>
+        <PackageReference Include="Moq"/>
         <PackageReference Include="Microsoft.NET.Test.Sdk"/>
         <PackageReference Include="xunit.runner.visualstudio">
             <PrivateAssets>all</PrivateAssets>