Turbopack: set window.next.turbopack instead (#82580)

Closes PACK-5239

https://vercel.slack.com/archives/C04RPSD7EPM/p1753968554253779

Author: mischnic

packages/next/src/client/app-next-turbopack.ts

@@ -1,7 +1,7 @@
 import { appBootstrap } from './app-bootstrap'
 import { isRecoverableError } from './react-client-callbacks/on-recoverable-error'
 
-window.next.version += '-turbo'
+window.next.turbopack = true
 ;(self as any).__webpack_hash__ = ''
 
 // eslint-disable-next-line @next/internal/typechecked-require

packages/next/src/client/next-dev-turbopack.ts

@@ -8,7 +8,8 @@ import { connect } from '@vercel/turbopack-ecmascript-runtime/browser/dev/hmr-cl
 import type { TurbopackMsgToBrowser } from '../server/dev/hot-reloader-types'
 
 window.next = {
-  version: `${version}-turbo`,
+  version,
+  turbopack: true,
   // router is initialized later so it has to be live-binded
   get router() {
     return router

packages/next/src/client/next-turbopack.ts

@@ -9,7 +9,8 @@ import { initialize, version, router, emitter, hydrate } from './'
 import { displayContent } from './dev/fouc'
 
 window.next = {
-  version: `${version}-turbo`,
+  version,
+  turbopack: true,
   // router is initialized later so it has to be live-binded
   get router() {
     return router

test/production/pages-dir/production/test/index.test.ts

@@ -1156,9 +1156,15 @@ describe('Production Usage', () => {
       const version = await browser.eval('window.next.version')
       expect(version).toBeTruthy()
       expect(version).toBe(
-        (await next.readJSON('node_modules/next/package.json')).version +
-          (process.env.IS_TURBOPACK_TEST ? '-turbo' : '')
+        (await next.readJSON('node_modules/next/package.json')).version
       )
+
+      const turbopack = await browser.eval('window.next.turbopack')
+      if (process.env.IS_TURBOPACK_TEST) {
+        expect(turbopack).toBeTrue()
+      } else {
+        expect(turbopack).toBeFalsy()
+      }
     } finally {
       if (browser) {
         await browser.close()