test: pin regression for subgraph IO drag → Vue widget slot reveal (#9010)

Add a focused bridge regression that simulates dragging from SubgraphInputNode into a Vue multiline widget backing input and asserts the Vue slot drag UI marks it compatible and resolves it as the active candidate.

TDD proof: with useSubgraphDragBridge temporarily disabled, this test fails at state.active assertion (false !== true); restoring the bridge makes the test pass.

src/renderer/core/canvas/links/useSubgraphDragBridge.test.ts

@@ -0,0 +1,122 @@
+import { createPinia, setActivePinia } from 'pinia'
+import { effectScope, nextTick } from 'vue'
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+
+import type { LGraphCanvas } from '@/lib/litegraph/src/LGraphCanvas'
+import { LGraphNode } from '@/lib/litegraph/src/litegraph'
+import { LinkConnector } from '@/lib/litegraph/src/canvas/LinkConnector'
+import { createTestSubgraph } from '@/lib/litegraph/src/subgraph/__fixtures__/subgraphHelpers'
+import { useCanvasStore } from '@/renderer/core/canvas/canvasStore'
+import { useSubgraphDragBridge } from '@/renderer/core/canvas/links/useSubgraphDragBridge'
+import { useSlotLinkDragUIState } from '@/renderer/core/canvas/links/slotLinkDragUIState'
+import { getSlotKey } from '@/renderer/core/layout/slots/slotIdentifier'
+import { layoutStore } from '@/renderer/core/layout/store/layoutStore'
+
+const { appMock } = vi.hoisted(() => ({
+  appMock: {
+    canvas: null as unknown
+  }
+}))
+
+vi.mock('@/scripts/app', () => ({
+  app: appMock
+}))
+
+describe('useSubgraphDragBridge', () => {
+  const setDirty = vi.fn()
+  let originalCanvas: unknown
+
+  beforeEach(() => {
+    originalCanvas = appMock.canvas
+    vi.useFakeTimers()
+    setActivePinia(createPinia())
+    layoutStore.clearAllSlotLayouts()
+    useSlotLinkDragUIState().endDrag()
+    setDirty.mockReset()
+  })
+
+  afterEach(() => {
+    appMock.canvas = originalCanvas
+    layoutStore.clearAllSlotLayouts()
+    useSlotLinkDragUIState().endDrag()
+    vi.restoreAllMocks()
+    vi.useRealTimers()
+  })
+
+  it('marks a multiline widget backing input as compatible during subgraph-input canvas drag', async () => {
+    const subgraph = createTestSubgraph({
+      inputs: [{ name: 'prompt', type: 'STRING' }]
+    })
+    const targetNode = new LGraphNode('Target')
+    targetNode.id = 501
+    targetNode.addInput('prompt', 'STRING')
+    targetNode.inputs[0].widget = { name: 'multiline_prompt' }
+    subgraph.add(targetNode)
+
+    const slotKey = getSlotKey(String(targetNode.id), 0, true)
+    layoutStore.updateSlotLayout(slotKey, {
+      nodeId: String(targetNode.id),
+      index: 0,
+      type: 'input',
+      position: { x: 220, y: 140 },
+      bounds: { x: 210, y: 130, width: 20, height: 20 }
+    })
+
+    const widgetContainer = document.createElement('div')
+    widgetContainer.className = 'lg-node-widget'
+    widgetContainer.dataset['nodeId'] = String(targetNode.id)
+
+    const hiddenBackingSlot = document.createElement('div')
+    hiddenBackingSlot.dataset['slotKey'] = slotKey
+    widgetContainer.appendChild(hiddenBackingSlot)
+    document.body.appendChild(widgetContainer)
+
+    vi.spyOn(document, 'elementFromPoint').mockReturnValue(widgetContainer)
+
+    const linkConnector = new LinkConnector(() => undefined)
+
+    const lgCanvas = {
+      linkConnector,
+      getCanvasWindow: () => window
+    } as unknown as LGraphCanvas
+
+    appMock.canvas = {
+      graph: subgraph,
+      linkConnector,
+      setDirty
+    }
+
+    const scope = effectScope()
+    scope.run(() => {
+      useSubgraphDragBridge()
+    })
+
+    const canvasStore = useCanvasStore()
+    canvasStore.canvas = lgCanvas
+    await nextTick()
+
+    linkConnector.dragNewFromSubgraphInput(
+      subgraph,
+      subgraph.inputNode,
+      subgraph.inputNode.slots[0]
+    )
+
+    const state = useSlotLinkDragUIState().state
+    expect(state.active).toBe(true)
+    expect(state.compatible.get(slotKey)).toBe(true)
+
+    document.dispatchEvent(
+      new PointerEvent('pointermove', { clientX: 220, clientY: 140 })
+    )
+    vi.advanceTimersByTime(20)
+    await nextTick()
+
+    expect(state.candidate).not.toBeNull()
+    expect(state.candidate?.layout.nodeId).toBe(String(targetNode.id))
+    expect(state.candidate?.layout.index).toBe(0)
+    expect(state.candidate?.compatible).toBe(true)
+
+    scope.stop()
+    widgetContainer.remove()
+  })
+})