feat: deduplicate subgraph node IDs on workflow load (experimental) (#8762)

## Summary

Add `ensureGlobalIdUniqueness` to reassign duplicate node IDs across
subgraphs when loading workflows, gated behind an experimental setting.

## Changes

- **What**: Shared `LGraphState` between root graph and subgraphs so ID
counters are global. Added `ensureGlobalIdUniqueness()` method that
detects and remaps colliding node IDs in subgraphs, preserving root
graph IDs as canonical and patching link references. Gated behind
`Comfy.Graph.DeduplicateSubgraphNodeIds` (experimental, default
`false`).
- **Dependencies**: None

## Review Focus

- Shared state override on `Subgraph` (getter delegates to root, setter
is no-op) — verify no existing code sets `subgraph.state` directly.
- `Math.max` state merging in `configure()` prevents ID counter
regression when loading subgraph definitions.
- Feature flag wiring: static property on `LGraph`, synced from settings
via `useLitegraphSettings`.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8762-feat-deduplicate-subgraph-node-IDs-on-workflow-load-experimental-3036d73d36508184b6cee5876dc4d935)
by [Unito](https://www.unito.io)

---------

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

browser_tests/tests/subgraph-duplicate-ids.spec.ts

@@ -0,0 +1,107 @@
+import { expect } from '@playwright/test'
+
+import { comfyPageFixture as test } from '../fixtures/ComfyPage'
+
+test.describe('Subgraph duplicate ID remapping', { tag: ['@subgraph'] }, () => {
+  const WORKFLOW = 'subgraphs/subgraph-nested-duplicate-ids'
+
+  test.beforeEach(async ({ comfyPage }) => {
+    await comfyPage.settings.setSetting(
+      'Comfy.Graph.DeduplicateSubgraphNodeIds',
+      true
+    )
+  })
+
+  test('All node IDs are globally unique after loading', async ({
+    comfyPage
+  }) => {
+    await comfyPage.workflow.loadWorkflow(WORKFLOW)
+
+    const result = await comfyPage.page.evaluate(() => {
+      const graph = window.app!.canvas.graph!
+      // TODO: Extract allGraphs accessor (root + subgraphs) into LGraph
+      // TODO: Extract allNodeIds accessor into LGraph
+      const allGraphs = [graph, ...graph.subgraphs.values()]
+      const allIds = allGraphs
+        .flatMap((g) => g._nodes)
+        .map((n) => n.id)
+        .filter((id): id is number => typeof id === 'number')
+
+      return { allIds, uniqueCount: new Set(allIds).size }
+    })
+
+    expect(result.uniqueCount).toBe(result.allIds.length)
+    expect(result.allIds.length).toBeGreaterThanOrEqual(10)
+  })
+
+  test('Root graph node IDs are preserved as canonical', async ({
+    comfyPage
+  }) => {
+    await comfyPage.workflow.loadWorkflow(WORKFLOW)
+
+    const rootIds = await comfyPage.page.evaluate(() => {
+      const graph = window.app!.canvas.graph!
+      return graph._nodes
+        .map((n) => n.id)
+        .filter((id): id is number => typeof id === 'number')
+        .sort((a, b) => a - b)
+    })
+
+    expect(rootIds).toEqual([1, 2, 5])
+  })
+
+  test('All links reference valid nodes in their graph', async ({
+    comfyPage
+  }) => {
+    await comfyPage.workflow.loadWorkflow(WORKFLOW)
+
+    const invalidLinks = await comfyPage.page.evaluate(() => {
+      const graph = window.app!.canvas.graph!
+      const labeledGraphs: [string, typeof graph][] = [
+        ['root', graph],
+        ...[...graph.subgraphs.entries()].map(
+          ([id, sg]) => [`subgraph:${id}`, sg] as [string, typeof graph]
+        )
+      ]
+
+      const isNonNegative = (id: number | string) =>
+        typeof id === 'number' && id >= 0
+
+      return labeledGraphs.flatMap(([label, g]) =>
+        [...g._links.values()].flatMap((link) =>
+          [
+            isNonNegative(link.origin_id) &&
+              !g._nodes_by_id[link.origin_id] &&
+              `${label}: origin_id ${link.origin_id} not found`,
+            isNonNegative(link.target_id) &&
+              !g._nodes_by_id[link.target_id] &&
+              `${label}: target_id ${link.target_id} not found`
+          ].filter(Boolean)
+        )
+      )
+    })
+
+    expect(invalidLinks).toEqual([])
+  })
+
+  test('Subgraph navigation works after ID remapping', async ({
+    comfyPage
+  }) => {
+    await comfyPage.workflow.loadWorkflow(WORKFLOW)
+
+    const subgraphNode = await comfyPage.nodeOps.getNodeRefById('5')
+    await subgraphNode.navigateIntoSubgraph()
+
+    const isInSubgraph = () =>
+      comfyPage.page.evaluate(
+        () => window.app!.canvas.graph?.isRootGraph === false
+      )
+
+    expect(await isInSubgraph()).toBe(true)
+
+    await comfyPage.page.keyboard.press('Escape')
+    await comfyPage.nextFrame()
+
+    expect(await isInSubgraph()).toBe(false)
+  })
+})