Load InterfaceData into a prototype

Content.Server/Stack/StackSystem.cs

@@ -200,7 +200,7 @@ private void OnStackAlternativeInteract(EntityUid uid, StackComponent stack, Get
                 args.Verbs.Add(verb);
             }
 
-            if (stack.CustomSplit)
+            if (_ui.HasUi(uid, StackCustomSplitUiKey.Key))
             {
                 AlternativeVerb custom = new()
                 {

Content.Shared/Stacks/CustomStackSplitPrototype.cs

@@ -0,0 +1,20 @@
+using Robust.Shared.Prototypes;
+using Robust.Shared.Serialization.TypeSerializers.Implementations.Custom.Prototype;
+using Robust.Shared.GameObjects;
+using Robust.Shared.Utility;
+
+namespace Content.Shared.Stacks;
+
+[Prototype]
+public sealed partial class CustomStackSplitPrototype : IPrototype
+{
+    [ViewVariables]
+    [IdDataField]
+    public string ID { get; private set; } = default!;
+
+    /// <summary>
+    ///     UI parameters for custom stack splitting.
+    /// </summary>
+    [DataField(required: true)]
+    public InterfaceData Interface { get; private set; } = default!;
+}

Content.Shared/Stacks/SharedStackSystem.cs

@@ -48,8 +48,8 @@ public override void Initialize()
 
         private void OnStackInit(EntityUid uid, StackComponent stack, ref ComponentInit args)
         {
-            if (stack.CustomSplit)
-                _ui.SetUi(uid, StackCustomSplitUiKey.Key, new InterfaceData("StackCustomSplitBoundUserInterface"));
+            if (!string.IsNullOrEmpty(stack.CustomSplit) && _prototype.TryIndex<CustomStackSplitPrototype>(stack.CustomSplit, out var customStackSplit))
+                _ui.SetUi(uid, StackCustomSplitUiKey.Key, customStackSplit.Interface);
         }
 
         // client shouldn't try to split stacks so do nothing on client

Content.Shared/Stacks/StackComponent.cs

@@ -80,11 +80,11 @@ public sealed partial class StackComponent : Component
         public List<string> LayerStates = new();
 
         /// <summary>
-        /// If true, interacting with object will show a custom split dialog.
+        /// The CustomStackSplit prototype to use for the stack interface
         /// </summary>
         [DataField("customSplit")]
         [ViewVariables(VVAccess.ReadWrite)]
-        public bool CustomSplit;
+        public string? CustomSplit;
     }
 
     [Serializable, NetSerializable]

Resources/Prototypes/custom_stack_split.yml

@@ -0,0 +1,4 @@
+- type: customStackSplit
+  id: Default
+  interface:
+    type: StackCustomSplitBoundUserInterface