Fix Connection of Primitive nodes to Subgraph node (#5024)

* Fix connection of primitives to subgraphNodes

* Fix loading and nested subgraphs with primitives

Medium hackyness, but this saves ~100 lines.

* Use improved type check

* Remove requirement for type assertion

* Add warning comment

---------

Co-authored-by: filtered <176114999+webfiltered@users.noreply.github.com>

src/lib/litegraph/src/subgraph/SubgraphNode.ts

@@ -313,9 +313,8 @@ export class SubgraphNode extends LGraphNode implements BaseLGraph {
     widget: Readonly<IBaseWidget>
   ) {
     // Use the first matching widget
-    const promotedWidget = toConcreteWidget(widget, this).createCopyForNode(
-      this
-    )
+    const targetWidget = toConcreteWidget(widget, this)
+    const promotedWidget = targetWidget.createCopyForNode(this)
 
     Object.assign(promotedWidget, {
       get name() {
@@ -370,7 +369,15 @@ export class SubgraphNode extends LGraphNode implements BaseLGraph {
       subgraphNode: this
     })
 
-    input.widget = { name: subgraphInput.name }
+    // NOTE: This code creates linked chains of prototypes for passing across
+    // multiple levels of subgraphs. As part of this, it intentionally avoids
+    // creating new objects. Have care when making changes.
+    const backingInput =
+      targetWidget.node.findInputSlot(widget.name, true)?.widget ?? {}
+    input.widget ??= { name: subgraphInput.name }
+    input.widget.name = subgraphInput.name
+    Object.setPrototypeOf(input.widget, backingInput)
+
     input._widget = promotedWidget
   }