fix(frontend): prevent subflow expansion from hiding all insertion points (#8203)

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/lib/components/graph/graphBuilder.svelte.ts

@@ -422,10 +422,6 @@ export function graphBuilder(
 				throw new Error(`Duplicated node detected: ${module.id}`)
 			}
 
-			if (module.id.startsWith('subflow:')) {
-				extra.insertable = false
-			}
-
 			nodes.push({
 				id: module.id,
 				data: {
@@ -436,7 +432,7 @@ export function graphBuilder(
 					eventHandlers: eventHandlers,
 					flowModuleState: extra.flowModuleStates?.[module.id],
 					testModuleState: extra.testModuleStates?.states?.[module.id],
-					insertable: extra.insertable,
+					insertable: extra.insertable && !module.id.startsWith('subflow:'),
 					editMode: extra.editMode,
 					isOwner: extra.isOwner,
 					flowJob: extra.flowJob,
@@ -968,11 +964,15 @@ export function graphBuilder(
 							nodes.push(startNode)
 
 							if (previousId) {
-								addEdge(previousId!, startNode.id, undefined, prefix, {
-									type: 'empty'
+								addEdge(previousId, startNode.id, branch, prefix, {
+									subModules: modules,
+									disableMoveIds
 								})
 							} else {
-								addEdge(beforeNode.id, startNode.id, undefined, prefix, { type: 'empty' })
+								addEdge(beforeNode.id, startNode.id, undefined, prefix, {
+									subModules: modules,
+									disableMoveIds
+								})
 							}
 
 							const endId = `${module.id}-subflow-end`