test: add Playwright e2e tests for SubgraphNode copy-paste

- Copy-paste SubgraphNode preserves promoted widgets
- Pasted SubgraphNode retains proxyWidgets in serialized properties
- Interior widget values survive copy-paste round-trip through loadGraphData

Covers the _serializeItems serialize-not-clone path introduced in this PR.
Requested by DrJKL and CodeRabbit.

browser_tests/tests/subgraphCopyPaste.spec.ts

@@ -0,0 +1,143 @@
+import { expect } from '@playwright/test'
+
+import type { ComfyPage } from '../fixtures/ComfyPage'
+import { comfyPageFixture as test } from '../fixtures/ComfyPage'
+import { TestIds } from '../fixtures/selectors'
+import {
+  getPromotedWidgetNames,
+  getPromotedWidgets
+} from '../helpers/promotedWidgets'
+
+async function getSubgraphNodeIds(comfyPage: ComfyPage): Promise<string[]> {
+  return comfyPage.page.evaluate(() => {
+    const graph = window.app!.canvas.graph!
+    return graph.nodes
+      .filter(
+        (n) => typeof n.isSubgraphNode === 'function' && n.isSubgraphNode()
+      )
+      .map((n) => String(n.id))
+  })
+}
+
+test.describe('Subgraph Copy-Paste', { tag: ['@subgraph', '@widget'] }, () => {
+  test('Copy-paste SubgraphNode preserves promoted widgets', async ({
+    comfyPage
+  }) => {
+    await comfyPage.workflow.loadWorkflow(
+      'subgraphs/subgraph-with-promoted-text-widget'
+    )
+    await comfyPage.nextFrame()
+
+    const originalNode = await comfyPage.nodeOps.getNodeRefById('11')
+    const originalPromoted = await getPromotedWidgetNames(comfyPage, '11')
+    expect(originalPromoted).toContain('text')
+
+    // Select the subgraph node
+    await originalNode.click('title')
+    await comfyPage.nextFrame()
+
+    // Copy via Ctrl+C, then paste via Ctrl+V
+    await comfyPage.clipboard.copy()
+    await comfyPage.clipboard.paste()
+    await comfyPage.nextFrame()
+
+    // Should now have 2 subgraph nodes
+    const nodeIds = await getSubgraphNodeIds(comfyPage)
+    expect(nodeIds).toHaveLength(2)
+
+    // Both should have promoted widgets with 'text'
+    for (const nodeId of nodeIds) {
+      const promotedWidgets = await getPromotedWidgets(comfyPage, nodeId)
+      expect(promotedWidgets.length).toBeGreaterThan(0)
+      expect(
+        promotedWidgets.some(([, widgetName]) => widgetName === 'text')
+      ).toBe(true)
+    }
+  })
+
+  test('Copy-paste SubgraphNode preserves proxyWidgets in serialized data', async ({
+    comfyPage
+  }) => {
+    await comfyPage.workflow.loadWorkflow(
+      'subgraphs/subgraph-with-promoted-text-widget'
+    )
+    await comfyPage.nextFrame()
+
+    const originalNode = await comfyPage.nodeOps.getNodeRefById('11')
+    await originalNode.click('title')
+    await comfyPage.nextFrame()
+
+    await comfyPage.clipboard.copy()
+    await comfyPage.clipboard.paste()
+    await comfyPage.nextFrame()
+
+    // The pasted node should have proxyWidgets in its properties
+    const nodeIds = await getSubgraphNodeIds(comfyPage)
+    const pastedId = nodeIds.find((id) => id !== '11')
+    expect(pastedId).toBeDefined()
+
+    const pastedProxyWidgets = await comfyPage.page.evaluate((id) => {
+      const node = window.app!.canvas.graph!.getNodeById(id)
+      const pw = node?.properties?.proxyWidgets
+      if (!Array.isArray(pw)) return []
+      return pw as [string, string][]
+    }, pastedId!)
+
+    expect(pastedProxyWidgets.length).toBeGreaterThan(0)
+
+    // The proxyWidgets should reference the 'text' widget
+    const hasTextWidget = pastedProxyWidgets.some(
+      ([, widgetName]) => widgetName === 'text'
+    )
+    expect(hasTextWidget).toBe(true)
+  })
+
+  test('Pasted SubgraphNode interior widget values survive round-trip', async ({
+    comfyPage
+  }) => {
+    await comfyPage.workflow.loadWorkflow(
+      'subgraphs/subgraph-with-promoted-text-widget'
+    )
+    await comfyPage.nextFrame()
+
+    const testContent = 'copy-paste-round-trip-test'
+
+    // Set a value on the promoted textarea
+    const textarea = comfyPage.page.getByTestId(
+      TestIds.widgets.domWidgetTextarea
+    )
+    await textarea.first().fill(testContent)
+    await comfyPage.nextFrame()
+
+    // Select and copy the SubgraphNode
+    const originalNode = await comfyPage.nodeOps.getNodeRefById('11')
+    await originalNode.click('title')
+    await comfyPage.nextFrame()
+
+    await comfyPage.clipboard.copy()
+    await comfyPage.clipboard.paste()
+    await comfyPage.nextFrame()
+
+    // Serialize the whole graph and reload to test full round-trip
+    const serialized = await comfyPage.page.evaluate(() => {
+      return window.app!.graph!.serialize()
+    })
+
+    await comfyPage.page.evaluate(
+      (workflow) => {
+        return window.app!.loadGraphData(workflow)
+      },
+      serialized as Parameters<typeof comfyPage.page.evaluate>[1]
+    )
+    await comfyPage.nextFrame()
+
+    // Both subgraph nodes should still have promoted widgets
+    const nodeIds = await getSubgraphNodeIds(comfyPage)
+    expect(nodeIds.length).toBeGreaterThanOrEqual(2)
+
+    for (const nodeId of nodeIds) {
+      const promoted = await getPromotedWidgetNames(comfyPage, nodeId)
+      expect(promoted).toContain('text')
+    }
+  })
+})