fix: call checkState after image input changes for proper undo tracking (#9623)

## Summary

Image input changes (dropdown selection and file upload) in app/linear
mode did not create their own undo entries, causing undo to skip or
bundle image changes with subsequent actions.

## Changes

- **What**: Add explicit `checkState()` calls in
`WidgetSelectDropdown.vue` after `modelValue` is set in
`updateSelectedItems()` (dropdown selection) and `handleFilesUpdate()`
(file upload), ensuring each image change gets its own undo entry.

## Review Focus

The fix is intentionally scoped to `WidgetSelectDropdown` rather than
the generic `updateHandler` in `NodeWidgets.vue`, which would create
excessive undo entries for text inputs. The pattern follows existing
usage in `useSelectedNodeActions.ts` and other composables.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9623-fix-call-checkState-after-image-input-changes-for-proper-undo-tracking-31d6d73d3650814781dbca5db459ab6d)
by [Unito](https://www.unito.io)

---------

Co-authored-by: GitHub Action <action@github.com>

src/renderer/extensions/vueNodes/widgets/components/WidgetSelectDropdown.test.ts

@@ -15,7 +15,34 @@ import type { SimplifiedWidget } from '@/types/simplifiedWidget'
 import WidgetSelectDropdown from '@/renderer/extensions/vueNodes/widgets/components/WidgetSelectDropdown.vue'
 import { createMockWidget } from './widgetTestUtils'
 
+const mockCheckState = vi.hoisted(() => vi.fn())
 const mockAssetsData = vi.hoisted(() => ({ items: [] as AssetItem[] }))
+
+vi.mock('@/platform/workflow/management/stores/workflowStore', async () => {
+  const actual = await vi.importActual(
+    '@/platform/workflow/management/stores/workflowStore'
+  )
+  return {
+    ...actual,
+    useWorkflowStore: () => ({
+      activeWorkflow: {
+        changeTracker: {
+          checkState: mockCheckState
+        }
+      }
+    })
+  }
+})
+
+vi.mock('@/scripts/api', () => ({
+  api: {
+    fetchApi: vi.fn(),
+    apiURL: vi.fn((url: string) => url),
+    addEventListener: vi.fn(),
+    removeEventListener: vi.fn()
+  }
+}))
+
 vi.mock(
   '@/renderer/extensions/vueNodes/widgets/composables/useAssetWidgetData',
   () => ({
@@ -456,3 +483,69 @@ describe('WidgetSelectDropdown cloud asset mode (COM-14333)', () => {
     expect(selectedSet.has('missing-missing_model.safetensors')).toBe(true)
   })
 })
+
+describe('WidgetSelectDropdown undo tracking', () => {
+  interface UndoTrackingInstance extends ComponentPublicInstance {
+    updateSelectedItems: (selectedSet: Set<string>) => void
+    handleFilesUpdate: (files: File[]) => Promise<void>
+  }
+
+  const mountForUndo = (
+    widget: SimplifiedWidget<string | undefined>,
+    modelValue: string | undefined
+  ): VueWrapper<UndoTrackingInstance> => {
+    return mount(WidgetSelectDropdown, {
+      props: {
+        widget,
+        modelValue,
+        assetKind: 'image',
+        allowUpload: true,
+        uploadFolder: 'input'
+      },
+      global: {
+        plugins: [PrimeVue, createTestingPinia(), i18n]
+      }
+    }) as unknown as VueWrapper<UndoTrackingInstance>
+  }
+
+  beforeEach(() => {
+    mockCheckState.mockClear()
+  })
+
+  it('calls checkState after dropdown selection changes modelValue', () => {
+    const widget = createMockWidget<string | undefined>({
+      value: 'img_001.png',
+      name: 'test_image',
+      type: 'combo',
+      options: { values: ['img_001.png', 'photo_abc.jpg'] }
+    })
+    const wrapper = mountForUndo(widget, 'img_001.png')
+
+    wrapper.vm.updateSelectedItems(new Set(['input-1']))
+
+    expect(wrapper.emitted('update:modelValue')?.[0]).toEqual(['photo_abc.jpg'])
+    expect(mockCheckState).toHaveBeenCalledOnce()
+  })
+
+  it('calls checkState after file upload completes', async () => {
+    const { api } = await import('@/scripts/api')
+    vi.mocked(api.fetchApi).mockResolvedValue({
+      status: 200,
+      json: () => Promise.resolve({ name: 'uploaded.png', subfolder: '' })
+    } as Response)
+
+    const widget = createMockWidget<string | undefined>({
+      value: 'img_001.png',
+      name: 'test_image',
+      type: 'combo',
+      options: { values: ['img_001.png'] }
+    })
+    const wrapper = mountForUndo(widget, 'img_001.png')
+
+    const file = new File(['test'], 'uploaded.png', { type: 'image/png' })
+    await wrapper.vm.handleFilesUpdate([file])
+
+    expect(wrapper.emitted('update:modelValue')?.[0]).toEqual(['uploaded.png'])
+    expect(mockCheckState).toHaveBeenCalledOnce()
+  })
+})

src/renderer/extensions/vueNodes/widgets/components/WidgetSelectDropdown.vue

@@ -17,6 +17,7 @@ import {
   getAssetFilename
 } from '@/platform/assets/utils/assetMetadataUtils'
 import { useToastStore } from '@/platform/updates/common/toastStore'
+import { useWorkflowStore } from '@/platform/workflow/management/stores/workflowStore'
 import FormDropdown from '@/renderer/extensions/vueNodes/widgets/components/form/dropdown/FormDropdown.vue'
 import type {
   FilterOption,
@@ -376,6 +377,7 @@ function updateSelectedItems(selectedItems: Set<string>) {
     return
   }
   modelValue.value = name
+  useWorkflowStore().activeWorkflow?.changeTracker?.checkState()
 }
 
 const uploadFile = async (
@@ -450,6 +452,9 @@ async function handleFilesUpdate(files: File[]) {
     if (props.widget.callback) {
       props.widget.callback(uploadedPaths[0])
     }
+
+    // 5. Snapshot undo state so the image change gets its own undo entry
+    useWorkflowStore().activeWorkflow?.changeTracker?.checkState()
   } catch (error) {
     console.error('Upload error:', error)
     toastStore.addAlert(`Upload failed: ${error}`)