test: cover boundary link preservation on subgraph creation

The only e2e coverage of Convert to Subgraph selects every node in the
workflow, so no boundary link exists and the rewiring code in
_convertToSubgraphImpl is never exercised. Partial selection - the
operation users actually perform - has no coverage at all.

Packs KSampler + VAE Decode out of the default workflow, leaving five
boundary input links from four distinct source outputs and one boundary
output link, and asserts each one lands on a type-compatible slot on the
new subgraph node and survives a serialize/reload round trip.

Author: Connor Byrne

browser_tests/tests/subgraph/subgraphCreationBoundaryLinks.spec.ts

@@ -0,0 +1,100 @@
+import { expect } from '@playwright/test'
+
+import { comfyPageFixture as test } from '@e2e/fixtures/ComfyPage'
+
+test.describe(
+  'Subgraph creation boundary links',
+  { tag: ['@slow', '@subgraph'] },
+  () => {
+    test.beforeEach(async ({ comfyPage }) => {
+      await comfyPage.settings.setSetting('Comfy.UseNewMenu', 'Disabled')
+      await comfyPage.workflow.loadWorkflow('default')
+      await comfyPage.nodeOps.selectNodes(['KSampler', 'VAE Decode'])
+      const ksampler = await comfyPage.nodeOps.getNodeRefById('3')
+      await ksampler.convertToSubgraph()
+    })
+
+    test('rewires every boundary link onto the new subgraph node', async ({
+      comfyPage
+    }) => {
+      await expect
+        .poll(() =>
+          comfyPage.page.evaluate(() => {
+            const graph = window.app!.graph!
+            const host = graph.nodes.find((node) => node.isSubgraphNode())
+            if (!host) return { error: 'no subgraph node' }
+
+            const links = [...graph.links.values()]
+            return {
+              rootLinkCount: links.length,
+              inputCount: host.inputs.length,
+              outputCount: host.outputs.length,
+              unconnectedInputs: host.inputs.filter(
+                (input) => input.link == null
+              ).length,
+              sources: links
+                .filter((link) => link.target_id === host.id)
+                .map((link) => `${link.origin_id}:${link.origin_slot}`)
+                .sort(),
+              saveImageFedByHost:
+                links.find((link) => String(link.target_id) === '9')
+                  ?.origin_id === host.id
+            }
+          })
+        )
+        .toEqual({
+          rootLinkCount: 6,
+          inputCount: 5,
+          outputCount: 1,
+          unconnectedInputs: 0,
+          sources: ['4:0', '4:2', '5:0', '6:0', '7:0'],
+          saveImageFedByHost: true
+        })
+    })
+
+    test('lands each boundary link on a type-compatible slot', async ({
+      comfyPage
+    }) => {
+      await expect
+        .poll(() =>
+          comfyPage.page.evaluate(() => {
+            const graph = window.app!.graph!
+            const host = graph.nodes.find((node) => node.isSubgraphNode())
+            if (!host) return ['no subgraph node']
+
+            return [...graph.links.values()]
+              .filter((link) => link.target_id === host.id)
+              .filter(
+                (link) => host.inputs[link.target_slot]?.type !== link.type
+              )
+              .map(
+                (link) =>
+                  `${link.type} link landed on slot ${link.target_slot} typed ${host.inputs[link.target_slot]?.type}`
+              )
+          })
+        )
+        .toEqual([])
+    })
+
+    test('preserves the rewiring across a save and reload', async ({
+      comfyPage
+    }) => {
+      const serialisedLinks = () =>
+        comfyPage.page.evaluate(() =>
+          [...window.app!.graph!.links.values()]
+            .map(
+              (link) =>
+                `${link.origin_id}:${link.origin_slot}->${link.target_id}:${link.target_slot}`
+            )
+            .sort()
+        )
+
+      const beforeReload = await serialisedLinks()
+      await comfyPage.nodeOps.loadGraph(
+        await comfyPage.nodeOps.getSerializedGraph()
+      )
+
+      await expect.poll(serialisedLinks).toEqual(beforeReload)
+    })
+  }
+)