fix: ensure lint worker errors aren't silenced (#75766)

Errors thrown by the lint worker would only surface the error if
`JEST_WORKER_ID` is present. This check was not reliably truthy in all
cases (eg, when run with the vercel CLI, `JEST_WORKER_ID` wasn't
present) which meant the build would fail with no helpful error message.
Outside of that, it was a brittle check because if jest-worker ever
changed or removed this env, or we replaced the underlying worker
library, this would start failing.

This updates the check to be a more explicit env variable that we
control.

Fixes NEXT-3994

packages/next/src/lib/verify-typescript-setup.ts

@@ -164,7 +164,7 @@ export async function verifyTypeScriptSetup({
      */
 
     // we are in a worker, print the error message and exit the process
-    if (process.env.JEST_WORKER_ID) {
+    if (process.env.IS_NEXT_WORKER) {
       if (err instanceof Error) {
         console.error(err.message)
       } else {

packages/next/src/lib/worker.ts

@@ -48,6 +48,7 @@ export class Worker {
           env: {
             ...((farmOptions.forkOptions?.env || {}) as any),
             ...process.env,
+            IS_NEXT_WORKER: 'true',
           } as any,
         },
       }) as JestWorker
@@ -73,7 +74,7 @@ export class Worker {
           worker._child?.on('exit', (code, signal) => {
             if ((code || (signal && signal !== 'SIGINT')) && this._worker) {
               logger.error(
-                `Static worker exited with code: ${code} and signal: ${signal}`
+                `Next.js build worker exited with code: ${code} and signal: ${signal}`
               )
 
               // We're restarting the worker, so we don't want to exit the parent process

test/production/app-dir/worker-restart/worker-restart.test.ts

@@ -41,7 +41,7 @@ describe('worker-restart', () => {
 
     const output = stdout + stderr
     expect(output).toContain(
-      'Static worker exited with code: null and signal: SIGKILL'
+      'Next.js build worker exited with code: null and signal: SIGKILL'
     )
   })
 })