feat: thread BrowseNext continuation token through actor + BrowseService (T15)

src/ZB.MOM.WW.ScadaBridge.CentralUI/Services/BrowseService.cs

@@ -40,6 +40,7 @@ public sealed class BrowseService : IBrowseService
         string siteId,
         string connectionName,
         string? parentNodeId,
+        string? continuationToken = null,
         CancellationToken cancellationToken = default)
     {
         // CentralUI-side role guard — sites don't enforce envelope-level roles,
@@ -57,7 +58,7 @@ public sealed class BrowseService : IBrowseService
         {
             return await _communication.BrowseNodeAsync(
                 siteId,
-                new BrowseNodeCommand(connectionName, parentNodeId),
+                new BrowseNodeCommand(connectionName, parentNodeId, continuationToken),
                 cancellationToken);
         }
         catch (TimeoutException ex)

src/ZB.MOM.WW.ScadaBridge.CentralUI/Services/IBrowseService.cs

@@ -28,11 +28,13 @@ public interface IBrowseService
     /// <param name="siteId">The target site identifier.</param>
     /// <param name="connectionName">Name of the site-local data connection to browse against — the site's <c>DataConnectionManagerActor</c> indexes its children by name.</param>
     /// <param name="parentNodeId">Node to browse, or <c>null</c> to browse from the server root.</param>
+    /// <param name="continuationToken">Opaque cursor from a prior <see cref="BrowseNodeResult.ContinuationToken"/> to fetch the NEXT page under <paramref name="parentNodeId"/>; <c>null</c> for the first page.</param>
     /// <param name="cancellationToken">Cancellation token.</param>
     /// <returns>A task that resolves to a <see cref="BrowseNodeResult"/> containing child nodes or a <see cref="BrowseFailure"/> on error.</returns>
     Task<BrowseNodeResult> BrowseChildrenAsync(
         string siteId,
         string connectionName,
         string? parentNodeId,
+        string? continuationToken = null,
         CancellationToken cancellationToken = default);
 }

src/ZB.MOM.WW.ScadaBridge.Commons/Messages/Management/BrowseCommands.cs

@@ -15,14 +15,30 @@ namespace ZB.MOM.WW.ScadaBridge.Commons.Messages.Management;
 /// </remarks>
 /// <param name="ConnectionName">Name of the site-local data connection to browse against.</param>
 /// <param name="ParentNodeId">Node to browse, or null to browse from the server root (ObjectsFolder).</param>
+/// <param name="ContinuationToken">
+/// Opaque adapter cursor for fetching the NEXT page of children under
+/// <see cref="ParentNodeId"/>. Null on the first request; on a subsequent
+/// request carry back the token from the prior <see cref="BrowseNodeResult.ContinuationToken"/>.
+/// Additive (appended last) so positional construction stays source-compatible.
+/// </param>
 public record BrowseNodeCommand(
     string ConnectionName,
-    string? ParentNodeId);
+    string? ParentNodeId,
+    string? ContinuationToken = null);
 
+/// <param name="Children">Immediate children resolved for the browsed node (this page only).</param>
+/// <param name="Truncated">True when the result was clipped (frame-budget cap or adapter-reported truncation).</param>
+/// <param name="Failure">Structured failure, or null on success.</param>
+/// <param name="ContinuationToken">
+/// Opaque adapter cursor for the NEXT page when more children remain, or null
+/// when this is the final page. Surface it back in a follow-up
+/// <see cref="BrowseNodeCommand.ContinuationToken"/>. Additive (appended last).
+/// </param>
 public record BrowseNodeResult(
     IReadOnlyList<BrowseNode> Children,
     bool Truncated,
-    BrowseFailure? Failure);
+    BrowseFailure? Failure,
+    string? ContinuationToken = null);
 
 public record BrowseFailure(
     BrowseFailureKind Kind,

src/ZB.MOM.WW.ScadaBridge.DataConnectionLayer/Actors/DataConnectionActor.cs

@@ -1163,14 +1163,16 @@ public class DataConnectionActor : UntypedActor, IWithStash, IWithTimers
 
         _log.Debug("[{0}] Browsing children of {1}", _connectionName, command.ParentNodeId ?? "(root)");
 
-        browsable.BrowseChildrenAsync(command.ParentNodeId).ContinueWith(t =>
+        browsable.BrowseChildrenAsync(command.ParentNodeId, command.ContinuationToken).ContinueWith(t =>
         {
             if (t.IsCompletedSuccessfully)
             {
                 // Bound the reply to stay under Akka's remote frame size before it
                 // crosses the site→central boundary (see CapBrowseChildren).
                 var (children, truncated) = CapBrowseChildren(t.Result.Children, t.Result.Truncated);
-                return new BrowseNodeResult(children, truncated, Failure: null);
+                // Carry the adapter's continuation cursor through so the UI can ask
+                // for the next page (BrowseNext). Null when this is the final page.
+                return new BrowseNodeResult(children, truncated, Failure: null, t.Result.ContinuationToken);
             }
 
             var baseEx = t.Exception?.GetBaseException();

tests/ZB.MOM.WW.ScadaBridge.DataConnectionLayer.Tests/Actors/DataConnectionManagerBrowseHandlerTests.cs

@@ -253,4 +253,57 @@ public class DataConnectionManagerBrowseHandlerTests : TestKit
         var keptBytes = reply.Children.Sum(n => 64 + n.NodeId.Length + n.DisplayName.Length);
         Assert.True(keptBytes <= byteBudget, $"kept estimate {keptBytes} exceeds budget {byteBudget}");
     }
+
+    [Fact]
+    public void ContinuationToken_round_trips_through_the_browse_handler()
+    {
+        // Task B3 (T15): the BrowseNext continuation token must thread through the
+        // actor plumbing in both directions — the inbound command's token must reach
+        // the adapter, and the adapter's returned token must be surfaced on the reply
+        // so the UI can request the next page. We capture the token the adapter is
+        // called with and return a fresh one, then assert both halves.
+        const string inboundToken = "page-1-cursor";
+        const string outboundToken = "page-2-cursor";
+        string? receivedToken = "NOT-CALLED";
+
+        var adapter = Substitute.For<IDataConnection, IBrowsableDataConnection>();
+        ((IDataConnection)adapter).ConnectAsync(Arg.Any<IDictionary<string, string>>(), Arg.Any<CancellationToken>())
+            .Returns(Task.CompletedTask);
+        ((IDataConnection)adapter).Status.Returns(ConnectionHealth.Connected);
+
+        var children = new[]
+        {
+            new BrowseNode("ns=2;s=Next", "Next", BrowseNodeClass.Variable, HasChildren: false),
+        };
+        ((IBrowsableDataConnection)adapter)
+            .BrowseChildrenAsync(Arg.Any<string?>(), Arg.Any<string?>(), Arg.Any<CancellationToken>())
+            .Returns(ci =>
+            {
+                receivedToken = ci.ArgAt<string?>(1);
+                return new BrowseChildrenResult(children, Truncated: true, ContinuationToken: outboundToken);
+            });
+
+        _factory.Create("OpcUa", Arg.Any<IDictionary<string, string>>())
+            .Returns((IDataConnection)adapter);
+
+        var manager = Sys.ActorOf(Props.Create(() =>
+            new DataConnectionManagerActor(_factory, _options, _healthCollector, null)));
+        manager.Tell(new CreateConnectionCommand(
+            "conn-paged", "OpcUa", new Dictionary<string, string>(), null, 3));
+
+        AwaitCondition(
+            () => _factory.ReceivedCalls().Any(c => c.GetMethodInfo().Name == "Create"),
+            TimeSpan.FromSeconds(2));
+
+        manager.Tell(new BrowseNodeCommand("conn-paged", ParentNodeId: "ns=2;s=Folder", ContinuationToken: inboundToken));
+
+        var reply = ExpectMsg<BrowseNodeResult>(TimeSpan.FromSeconds(3));
+        Assert.Null(reply.Failure);
+        // Inbound token reached the adapter verbatim.
+        Assert.Equal(inboundToken, receivedToken);
+        // Outbound token from the adapter is surfaced on the reply for the next page.
+        Assert.Equal(outboundToken, reply.ContinuationToken);
+        Assert.True(reply.Truncated);
+        Assert.Single(reply.Children);
+    }
 }