test: add failing test for broken subgraph links crashing graphToPrompt

Workflows with stale link IDs in subgraph node data cause
graphToPrompt to throw InvalidLinkError, preventing execution
entirely. The conversion should skip broken inputs gracefully.

src/utils/executionUtil.test.ts

@@ -0,0 +1,45 @@
+import { createTestingPinia } from '@pinia/testing'
+import { setActivePinia } from 'pinia'
+import { beforeEach, describe, expect, it } from 'vitest'
+
+import { LGraph, LGraphNode, LiteGraph } from '@/lib/litegraph/src/litegraph'
+
+import { graphToPrompt } from './executionUtil'
+
+beforeEach(() => {
+  setActivePinia(createTestingPinia({ stubActions: false }))
+})
+
+describe('graphToPrompt', () => {
+  it('skips inputs with broken links instead of crashing', async () => {
+    LiteGraph.registerNodeType(
+      'TestSampler',
+      class extends LGraphNode {
+        static override title = 'TestSampler'
+        constructor() {
+          super('TestSampler')
+          this.comfyClass = 'TestSampler'
+          this.addInput('model', 'MODEL')
+          this.addInput('seed', 'INT')
+          this.addOutput('output', 'LATENT')
+        }
+      }
+    )
+
+    const graph = new LGraph()
+    const node = LiteGraph.createNode('TestSampler')!
+    graph.add(node)
+
+    // Inject a broken link: input references a link ID that doesn't exist
+    node.inputs[0].link = 9999
+
+    // BUG: graphToPrompt throws InvalidLinkError instead of skipping
+    // the broken input. Workflows with stale link references should
+    // still be convertible to API format.
+    const result = await graphToPrompt(graph)
+    expect(result.output).toBeDefined()
+    expect(result.output[String(node.id)]).toBeDefined()
+    // Broken 'model' input should be skipped, not crash the conversion
+    expect(result.output[String(node.id)].inputs).not.toHaveProperty('model')
+  })
+})