perf: skip folder-scope construction for separate repository imports (#19452)

* perf: skip folder-scope construction for separate repository imports

* refactor(project-groups): share one mode flag between scope skip and root guard

Also cover the separate-import path with real repo paths, which the throwing
getter test no longer exercises.

---------

Co-authored-by: m4air <m4air@m4airs-MacBook-Air.local>
Co-authored-by: Neil <4138956+nwparker@users.noreply.github.com>

src/main/project-groups/nested-repo-import.test.ts

@@ -138,7 +138,9 @@ describe('createNestedProjectGroupResolver', () => {
       parentPath: '/workspace',
       groupName: 'workspace',
       mode: 'separate',
-      repoPaths: ['/workspace/services/api', '/workspace/services/worker'],
+      get repoPaths(): readonly string[] {
+        throw new Error('separate imports must not build unused folder scopes')
+      },
       createGroup: () => {
         throw new Error('should not create a group')
       }
@@ -148,6 +150,30 @@ describe('createNestedProjectGroupResolver', () => {
     expect(resolver.getCreatedGroups()).toEqual([])
   })
 
+  it('leaves every separate-import repo ungrouped even when repo paths are supplied', () => {
+    const { groups, createGroup } = createGroupRecorder()
+    const repoPaths = [
+      '/workspace/services/api',
+      '/workspace/services/worker',
+      '/workspace/platform/packages/shared'
+    ]
+    const resolver = createNestedProjectGroupResolver({
+      parentPath: '/workspace',
+      groupName: 'workspace',
+      mode: 'separate',
+      repoPaths,
+      createGroup
+    })
+
+    expect(repoPaths.map((repoPath) => resolver.getGroupForRepo(repoPath))).toEqual([
+      undefined,
+      undefined,
+      undefined
+    ])
+    expect(resolver.getRootGroup()).toBeUndefined()
+    expect(groups).toEqual([])
+  })
+
   it('preserves filesystem root parent paths when creating the root group', () => {
     const groups: ProjectGroup[] = []
     const resolver = createNestedProjectGroupResolver({

src/main/project-groups/nested-repo-import.ts

@@ -150,10 +150,12 @@ export function createNestedProjectGroupResolver(args: {
   createGroup: (input: CreateGroupInput) => ProjectGroup
 }): NestedProjectGroupResolver {
   const createdGroups: ProjectGroup[] = []
-  const folderScopes = buildSparseFolderScopes({
-    parentPath: args.parentPath,
-    repoPaths: args.repoPaths ?? []
-  })
+  // Every folder-scope read sits behind ensureRootGroup, so outside group mode the scopes are
+  // unreachable. One flag drives both so the skip can never drift from the guard that justifies it.
+  const createsGroups = args.mode === 'group'
+  const folderScopes = createsGroups
+    ? buildSparseFolderScopes({ parentPath: args.parentPath, repoPaths: args.repoPaths ?? [] })
+    : []
   const folderScopesByRelativePath = new Map(
     folderScopes.map((scope) => [scope.relativePath, scope])
   )
@@ -161,7 +163,7 @@ export function createNestedProjectGroupResolver(args: {
   let rootGroup: ProjectGroup | undefined
 
   const ensureRootGroup = (): ProjectGroup | undefined => {
-    if (args.mode !== 'group') {
+    if (!createsGroups) {
       return undefined
     }
     if (rootGroup) {