fix: add debugging context to NullGraphError throws

- Add node ID to NullGraphError messages for easier debugging
- Add test verifying rootGraph throws after node removal

Amp-Thread-ID: https://ampcode.com/threads/T-019c0dad-0101-74ca-92fd-0fd1a992d889
Co-authored-by: Amp <amp@ampcode.com>

src/lib/litegraph/src/subgraph/ExecutableNodeDTO.ts

@@ -194,7 +194,10 @@ export class ExecutableNodeDTO implements ExecutableLGraphNode {
         }
       }
 
-      if (!subgraphNode.graph) throw new NullGraphError()
+      if (!subgraphNode.graph)
+        throw new NullGraphError(
+          `SubgraphNode ${subgraphNode.id} has no graph during input resolution`
+        )
       const outerLink = subgraphNode.graph.getLink(linkId)
       if (!outerLink)
         throw new InvalidLinkError(

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

@@ -59,6 +59,18 @@ describe.skip('SubgraphNode Construction', () => {
     expect(subgraphNode.rootGraph).toBe(parentGraph.rootGraph)
   })
 
+  it('should throw NullGraphError when accessing rootGraph after removal', () => {
+    const subgraph = createTestSubgraph()
+    const subgraphNode = createTestSubgraphNode(subgraph)
+    const parentGraph = subgraphNode.graph!
+    parentGraph.add(subgraphNode)
+
+    parentGraph.remove(subgraphNode)
+
+    expect(() => subgraphNode.rootGraph).toThrow()
+    expect(subgraphNode.graph).toBeNull()
+  })
+
   subgraphTest(
     'should synchronize slots with subgraph definition',
     ({ subgraphWithNode }) => {

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

@@ -51,7 +51,8 @@ export class SubgraphNode extends LGraphNode implements BaseLGraph {
   override graph: GraphOrSubgraph | null
 
   get rootGraph(): LGraph {
-    if (!this.graph) throw new NullGraphError()
+    if (!this.graph)
+      throw new NullGraphError(`SubgraphNode ${this.id} has no graph`)
     return this.graph.rootGraph
   }