fix(build): drain compilation events after shutdown, set TURBO_ENGINE_IGNORE_DIRTY in test

- After project.shutdown() resolves, yield to the event loop via
  setTimeout so the JS async iterator drains all buffered
  persistence/compaction TraceEvents before getTraceEvents() is called
  in waitForShutdown.
- Set TURBO_ENGINE_IGNORE_DIRTY=1 in the trace-build test so persistent
  caching works in dirty git repos (test directories are always dirty).
- Update the turbopack snapshot to expect turbopack-compaction and
  turbopack-persistence spans.

Author: lukesandberg

packages/next/src/build/turbopack-build/impl.ts

@@ -264,7 +264,15 @@ export async function turbopackBuild(): Promise<{
       await project.writeAnalyzeData(appDirOnly)
     }
 
-    const shutdownPromise = project.shutdown()
+    // Shutdown triggers persistence/compaction which emit TraceEvent
+    // compilation events via the compilationEventsSubscribe iterator.
+    // After shutdown resolves, all events have been emitted into the
+    // iterator buffer but the JS for-await loop may not have drained
+    // them yet.  We yield to the microtask queue so the buffered events
+    // are processed before getTraceEvents() is called by waitForShutdown.
+    const shutdownPromise = project
+      .shutdown()
+      .then(() => new Promise<void>((resolve) => setTimeout(resolve, 0)))
 
     const time = process.hrtime(startTime)
     return {

test/e2e/app-dir/trace-build-file/trace-build-file.test.ts

@@ -62,6 +62,12 @@ describe('trace-build-file', () => {
     files: __dirname,
     skipStart: !isNextDev,
     skipDeployment: true,
+    env: {
+      // Enable persistent caching even when the git repo is dirty (test dirs
+      // are always dirty). Without this, the cache falls back to a temp
+      // directory and persistence/compaction spans are not emitted.
+      TURBO_ENGINE_IGNORE_DIRTY: '1',
+    },
   })
 
   if (isNextStart) {
@@ -134,6 +140,8 @@ describe('trace-build-file', () => {
                   "static-generation",
                   "telemetry-flush",
                   "turbopack-build-events",
+                  "turbopack-compaction",
+                  "turbopack-persistence",
                 ]
               `)
       } else {