test: harden subgraph test coverage and remove low-value tests (#9967)

## Summary

Harden subgraph test coverage: remove low-value change-detector tests,
consolidate fixtures, add behavioral coverage, and fix test
infrastructure issues. Includes minor production code corrections
discovered during test hardening.

## Changes

- **What**: Comprehensive subgraph test suite overhaul across 6 phases
  - Removed change-detector tests and redundant assertions
- Consolidated fixture helpers into `subgraphHelpers.ts` /
`subgraphFixtures.ts`
  - Added Pinia initialization and fixture reset to all test files
  - Fixed barrel import violations (circular dependency prevention)
  - Added behavioral coverage for slot connections, events, edge cases
  - Added E2E helper and smoke test for subgraph promotion
  - Exported `SubgraphSlotBase` from litegraph barrel for test access
- **Production code changes** (minor correctness fixes found during
testing):
- `resolveSubgraphInputLink.ts`: iterate forward (first-connected-wins)
to match `_resolveLinkedPromotionBySubgraphInput`
- `promotionSchema.ts`: return `[]` instead of throwing on invalid
`proxyWidgets`; console.warn always (not DEV-only)
  - `LGraph.ts`: disconnect-after-veto ordering fix
  - `litegraph.ts`: barrel export swap for `SubgraphSlotBase`
- **Stats**: 349 tests passing, 0 skipped across 26 test files

## Review Focus

- Tests that merely asserted default property values were deleted
(change detectors)
- Fixture state is now reset via `resetSubgraphFixtureState()` in
`beforeEach`
- All imports use `@/lib/litegraph/src/litegraph` barrel to avoid
circular deps
- Production changes are small and directly motivated by test findings

---------

Co-authored-by: Amp <amp@ampcode.com>
Co-authored-by: bymyself <cbyrne@comfy.org>

browser_tests/tests/subgraphLifecycle.spec.ts

@@ -0,0 +1,160 @@
+import { expect } from '@playwright/test'
+
+import { comfyPageFixture as test } from '../fixtures/ComfyPage'
+import {
+  getPromotedWidgetSnapshot,
+  getPromotedWidgets
+} from '../helpers/promotedWidgets'
+
+test.describe('Subgraph Lifecycle', { tag: ['@subgraph', '@widget'] }, () => {
+  test('hydrates legacy proxyWidgets deterministically across reload', async ({
+    comfyPage
+  }) => {
+    await comfyPage.workflow.loadWorkflow(
+      'subgraphs/subgraph-nested-duplicate-ids'
+    )
+    await comfyPage.nextFrame()
+
+    const firstSnapshot = await getPromotedWidgetSnapshot(comfyPage, '5')
+    expect(firstSnapshot.proxyWidgets.length).toBeGreaterThan(0)
+    expect(
+      firstSnapshot.proxyWidgets.every(([nodeId]) => nodeId !== '-1')
+    ).toBe(true)
+
+    await comfyPage.page.reload()
+    await comfyPage.setup()
+    await comfyPage.workflow.loadWorkflow(
+      'subgraphs/subgraph-nested-duplicate-ids'
+    )
+    await comfyPage.nextFrame()
+
+    const secondSnapshot = await getPromotedWidgetSnapshot(comfyPage, '5')
+    expect(secondSnapshot.proxyWidgets).toEqual(firstSnapshot.proxyWidgets)
+    expect(secondSnapshot.widgetNames).toEqual(firstSnapshot.widgetNames)
+  })
+
+  test('promoted view falls back to disconnected placeholder after source widget removal', async ({
+    comfyPage
+  }) => {
+    await comfyPage.workflow.loadWorkflow(
+      'subgraphs/subgraph-with-promoted-text-widget'
+    )
+    await comfyPage.nextFrame()
+
+    const projection = await comfyPage.page.evaluate(() => {
+      const graph = window.app!.graph!
+      const hostNode = graph.getNodeById('11')
+      if (
+        !hostNode ||
+        typeof hostNode.isSubgraphNode !== 'function' ||
+        !hostNode.isSubgraphNode()
+      )
+        throw new Error('Expected host subgraph node 11')
+
+      const beforeType = hostNode.widgets?.[0]?.type
+      const proxyWidgets = Array.isArray(hostNode.properties?.proxyWidgets)
+        ? hostNode.properties.proxyWidgets.filter(
+            (entry): entry is [string, string] =>
+              Array.isArray(entry) &&
+              entry.length === 2 &&
+              typeof entry[0] === 'string' &&
+              typeof entry[1] === 'string'
+          )
+        : []
+      const firstPromotion = proxyWidgets[0]
+      if (!firstPromotion)
+        throw new Error('Expected at least one promoted widget entry')
+
+      const [sourceNodeId, sourceWidgetName] = firstPromotion
+      const subgraph = graph.subgraphs.get(hostNode.type)
+      const sourceNode = subgraph?.getNodeById(Number(sourceNodeId))
+      if (!sourceNode?.widgets)
+        throw new Error('Expected promoted source node widget list')
+
+      sourceNode.widgets = sourceNode.widgets.filter(
+        (widget) => widget.name !== sourceWidgetName
+      )
+
+      return {
+        beforeType,
+        afterType: hostNode.widgets?.[0]?.type
+      }
+    })
+
+    expect(projection.beforeType).toBe('customtext')
+    expect(projection.afterType).toBe('button')
+  })
+
+  test('unpacking one preview host keeps remaining pseudo-preview promotions resolvable', async ({
+    comfyPage
+  }) => {
+    await comfyPage.workflow.loadWorkflow(
+      'subgraphs/subgraph-with-multiple-promoted-previews'
+    )
+    await comfyPage.nextFrame()
+
+    const beforeNode8 = await getPromotedWidgets(comfyPage, '8')
+    expect(beforeNode8).toEqual([['6', '$$canvas-image-preview']])
+
+    const cleanupResult = await comfyPage.page.evaluate(() => {
+      const graph = window.app!.graph!
+      const invalidPseudoEntries = () => {
+        const invalid: string[] = []
+        for (const node of graph.nodes) {
+          if (
+            typeof node.isSubgraphNode !== 'function' ||
+            !node.isSubgraphNode()
+          )
+            continue
+
+          const subgraph = graph.subgraphs.get(node.type)
+          const proxyWidgets = Array.isArray(node.properties?.proxyWidgets)
+            ? node.properties.proxyWidgets.filter(
+                (entry): entry is [string, string] =>
+                  Array.isArray(entry) &&
+                  entry.length === 2 &&
+                  typeof entry[0] === 'string' &&
+                  typeof entry[1] === 'string'
+              )
+            : []
+          for (const entry of proxyWidgets) {
+            if (entry[1] !== '$$canvas-image-preview') continue
+
+            const sourceNodeId = Number(entry[0])
+            const sourceNode = subgraph?.getNodeById(sourceNodeId)
+            if (!sourceNode) invalid.push(`${node.id}:${entry[0]}`)
+          }
+        }
+        return invalid
+      }
+
+      const before = invalidPseudoEntries()
+      const hostNode = graph.getNodeById('7')
+      if (
+        !hostNode ||
+        typeof hostNode.isSubgraphNode !== 'function' ||
+        !hostNode.isSubgraphNode()
+      )
+        throw new Error('Expected preview host subgraph node 7')
+
+      ;(
+        graph as unknown as { unpackSubgraph: (node: unknown) => void }
+      ).unpackSubgraph(hostNode)
+
+      return {
+        before,
+        after: invalidPseudoEntries(),
+        hasNode7: Boolean(graph.getNodeById('7')),
+        hasNode8: Boolean(graph.getNodeById('8'))
+      }
+    })
+
+    expect(cleanupResult.before).toEqual([])
+    expect(cleanupResult.after).toEqual([])
+    expect(cleanupResult.hasNode7).toBe(false)
+    expect(cleanupResult.hasNode8).toBe(true)
+
+    const afterNode8 = await getPromotedWidgets(comfyPage, '8')
+    expect(afterNode8).toEqual([['6', '$$canvas-image-preview']])
+  })
+})