fix: skip broken subgraph links in graphToPrompt instead of crashing

Catch InvalidLinkError during input resolution so workflows with
stale or broken link references can still be converted to API
format. The broken input is silently skipped rather than aborting
the entire conversion.

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')
+  })
+})

src/utils/executionUtil.ts

@@ -7,6 +7,7 @@ import {
   ExecutableNodeDTO,
   LGraphEventMode
 } from '@/lib/litegraph/src/litegraph'
+import { InvalidLinkError } from '@/lib/litegraph/src/infrastructure/InvalidLinkError'
 import type {
   ComfyApiWorkflow,
   ComfyWorkflowJSON
@@ -117,7 +118,13 @@ export const graphToPrompt = async (
 
     // Store all node links
     for (const [i, input] of node.inputs.entries()) {
-      const resolvedInput = node.resolveInput(i)
+      let resolvedInput
+      try {
+        resolvedInput = node.resolveInput(i)
+      } catch (e) {
+        if (e instanceof InvalidLinkError) continue
+        throw e
+      }
       if (!resolvedInput) continue
 
       // Resolved to an actual widget value rather than a node connection