feat(dcl): add BrowseChildrenAsync to IOpcUaClient (NotImplementedException stubs)

src/ZB.MOM.WW.ScadaBridge.DataConnectionLayer/Adapters/IOpcUaClient.cs

@@ -1,3 +1,5 @@
+using ZB.MOM.WW.ScadaBridge.Commons.Interfaces.Protocol;
+
 namespace ZB.MOM.WW.ScadaBridge.DataConnectionLayer.Adapters;
 
 /// <summary>
@@ -102,6 +104,19 @@ public interface IOpcUaClient : IAsyncDisposable
     /// becomes unreachable. The adapter layer uses this to trigger reconnection.
     /// </summary>
     event Action? ConnectionLost;
+
+    /// <summary>
+    /// Enumerates the immediate children of <paramref name="parentNodeId"/>
+    /// (or the server's ObjectsFolder when null). Throws
+    /// <see cref="ConnectionNotConnectedException"/> when the session is not
+    /// currently up.
+    /// </summary>
+    /// <param name="parentNodeId">Node id whose children to browse, or null for the server root.</param>
+    /// <param name="cancellationToken">A cancellation token that can be used to cancel the operation.</param>
+    /// <returns>A task that completes with the immediate children of the requested node.</returns>
+    Task<BrowseChildrenResult> BrowseChildrenAsync(
+        string? parentNodeId,
+        CancellationToken cancellationToken = default);
 }
 
 /// <summary>
@@ -180,6 +195,11 @@ internal class StubOpcUaClient : IOpcUaClient
         return Task.FromResult<uint>(0); // Good status
     }
 
+    /// <inheritdoc />
+    public Task<BrowseChildrenResult> BrowseChildrenAsync(
+        string? parentNodeId, CancellationToken cancellationToken = default)
+        => throw new NotImplementedException();
+
     /// <inheritdoc />
     public ValueTask DisposeAsync()
     {

src/ZB.MOM.WW.ScadaBridge.DataConnectionLayer/Adapters/RealOpcUaClient.cs

@@ -325,6 +325,12 @@ public class RealOpcUaClient : IOpcUaClient
         string.IsNullOrWhiteSpace(configured)
             ? Path.Combine(Path.GetTempPath(), "ScadaBridge", "pki", fallbackLeaf)
             : configured;
+
+    /// <inheritdoc />
+    // Real implementation lands in Task 8 of the OPC UA tag browser plan.
+    public Task<Commons.Interfaces.Protocol.BrowseChildrenResult> BrowseChildrenAsync(
+        string? parentNodeId, CancellationToken cancellationToken = default)
+        => throw new NotImplementedException();
 }
 
 /// <summary>