implemented string concatination node

Examples/Nodify.Calculator/EditorView.xaml

@@ -483,6 +483,28 @@
                     </nodify:Node>
                 </DataTemplate>
 
+                <DataTemplate DataType="{x:Type local:StringConcatOperationViewModel}">
+                    <nodify:Node Header="{Binding Title}"
+                                 Content="{Binding}"
+                                 Input="{Binding Input}"
+                                 Output="{Binding Output}">
+                        <nodify:Node.ContentTemplate>
+                            <DataTemplate DataType="{x:Type local:StringConcatOperationViewModel}">
+                                <StackPanel Orientation="Horizontal">
+                                    <Button Style="{StaticResource IconButton}"
+                                            Content="{StaticResource PlusIcon}"
+                                            FocusVisualStyle="{StaticResource {x:Static SystemParameters.FocusVisualStyleKey}}"
+                                            Command="{Binding AddInputCommand}" />
+                                    <Button Style="{StaticResource IconButton}"
+                                            Content="{StaticResource RemoveKeyIcon}"
+                                            FocusVisualStyle="{StaticResource {x:Static SystemParameters.FocusVisualStyleKey}}"
+                                            Command="{Binding RemoveInputCommand}" />
+                                </StackPanel>
+                            </DataTemplate>
+                        </nodify:Node.ContentTemplate>
+                    </nodify:Node>
+                </DataTemplate>
+
                 <DataTemplate DataType="{x:Type local:APIOperationViewModel}">
                     <nodify:Node Header="{Binding Title}"
                                  Content="{Binding}"

Examples/Nodify.Calculator/NodeHandlers/NodeHandlerRegistry.cs

@@ -32,6 +32,7 @@ namespace Nodify.Calculator.NodeHandlers
             // Register all handlers — order matters for CanCreate/CanRestore matching.
             // More specific handlers first (e.g. TakeHandler before generic SystemHandler).
             _handlers.Add(new KnotHandler());
+            _handlers.Add(new StringConcatHandler());
             _handlers.Add(new FunctionHandler());
             _handlers.Add(new AuthHandler());
             _handlers.Add(new TakeHandler());
@@ -79,6 +80,7 @@ namespace Nodify.Calculator.NodeHandlers
             return vm switch
             {
                 KnotOperationViewModel => _handlers.OfType<KnotHandler>().FirstOrDefault(),
+                StringConcatOperationViewModel => _handlers.OfType<StringConcatHandler>().FirstOrDefault(),
                 FunctionOperationViewModel => _handlers.OfType<FunctionHandler>().FirstOrDefault(),
                 AuthOperationViewModel => _handlers.OfType<AuthHandler>().FirstOrDefault(),
                 TakeOperationViewModel => _handlers.OfType<TakeHandler>().FirstOrDefault(),

Examples/Nodify.Calculator/NodeHandlers/StringConcatHandler.cs

@@ -0,0 +1,62 @@
+using Nodify.Calculator.Models;
+using System.Drawing;
+using System.Linq;
+
+namespace Nodify.Calculator.NodeHandlers
+{
+    public class StringConcatHandler : INodeHandler
+    {
+        public string NodeTypeKey => "System";
+
+        public bool CanCreate(OperationInfoViewModel info)
+            => info.Type == OperationType.System && info.sysOp == SystemOperations.STRING_CONCAT;
+
+        public bool CanRestore(NodeData data)
+            => data.NodeType == "System" && data.SystemOp == nameof(SystemOperations.STRING_CONCAT);
+
+        public OperationViewModel Create(OperationInfoViewModel info)
+        {
+            var strColor = ConnectorViewModel.GetColorForType("string");
+            var op = new StringConcatOperationViewModel();
+
+            // Default two string inputs
+            op.Input.Add(new ConnectorViewModel { Title = "Str 1", Shape = ConnectorShape.Circle, ConnectorColor = strColor, DataType = "string" });
+            op.Input.Add(new ConnectorViewModel { Title = "Str 2", Shape = ConnectorShape.Circle, ConnectorColor = strColor, DataType = "string" });
+
+            // Single string output
+            op.Output.Add(new ConnectorViewModel
+            {
+                Title = "Result",
+                IsInput = false,
+                Shape = ConnectorShape.Circle,
+                ConnectorColor = strColor,
+                DataType = "string"
+            });
+
+            return op;
+        }
+
+        public OperationViewModel Restore(NodeData data)
+        {
+            var strColor = ConnectorViewModel.GetColorForType("string");
+            var op = new StringConcatOperationViewModel();
+
+            // Restore inputs from saved connectors
+            foreach (var ic in data.InputConnectors)
+                op.Input.Add(NodeHandlerRegistry.DeserializeConnector(ic, true));
+
+            // Restore output
+            foreach (var oc in data.OutputConnectors)
+                op.Output.Add(NodeHandlerRegistry.DeserializeConnector(oc, false));
+
+            op.Title = data.Title;
+            return op;
+        }
+
+        public void Save(OperationViewModel vm, NodeData data)
+        {
+            data.NodeType = "System";
+            data.SystemOp = nameof(SystemOperations.STRING_CONCAT);
+        }
+    }
+}

Examples/Nodify.Calculator/Operations/OperationFactory.cs

@@ -136,6 +136,14 @@ namespace Nodify.Calculator
             assertNode.Input.Add("Actual");
             assertNode.Input.Add("Expected");
 
+            var stringConcatNode = new OperationInfoViewModel()
+            {
+                Title = "String Concat",
+                Type = OperationType.System,
+                sysOp = SystemOperations.STRING_CONCAT,
+                IsFlowNode = false
+            };
+
             systemNodes.Add(authNode);
             systemNodes.Add(copynode);
             systemNodes.Add(debugNode);
@@ -148,6 +156,7 @@ namespace Nodify.Calculator
             systemNodes.Add(takeNode);
             systemNodes.Add(forEachNode);
             systemNodes.Add(assertNode);
+            systemNodes.Add(stringConcatNode);
             return systemNodes;
         }
 

Examples/Nodify.Calculator/StringConcatOperationViewModel.cs

@@ -0,0 +1,32 @@
+using System.Drawing;
+
+namespace Nodify.Calculator
+{
+    public class StringConcatOperationViewModel : SystemOperationViewModel
+    {
+        private const uint DefaultMinInput = 2;
+
+        public INodifyCommand AddInputCommand { get; }
+        public INodifyCommand RemoveInputCommand { get; }
+
+        public StringConcatOperationViewModel()
+        {
+            Title = "String Concat";
+            SystemOperationType = SystemOperations.STRING_CONCAT;
+
+            AddInputCommand = new RequeryCommand(
+                () => Input.Add(new ConnectorViewModel
+                {
+                    Title = $"Str {Input.Count + 1}",
+                    Shape = ConnectorShape.Circle,
+                    ConnectorColor = ConnectorViewModel.GetColorForType("string"),
+                    DataType = "string"
+                }),
+                () => true);
+
+            RemoveInputCommand = new RequeryCommand(
+                () => Input.RemoveAt(Input.Count - 1),
+                () => Input.Count > DefaultMinInput);
+        }
+    }
+}

Examples/Nodify.Calculator/SystemOperationViewModel.cs

@@ -23,7 +23,8 @@ namespace Nodify.Calculator
         NEW_OBJECT,
         FOREACH,
         ASSERT,
-        KNOT
+        KNOT,
+        STRING_CONCAT
     }
 
     public class SystemOperationViewModel : OperationViewModel