fix(report): keep personal-report heartbeats ref'd during chapter writes

Staging lost the job lease mid-chapter because the unref'd interval never
fired outside an HTTP request. Refresh the lease on section progress and
leave the heartbeat timer ref'd so a long model await cannot starve it.

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/lib/personal-report-worker-core.ts

@@ -165,11 +165,6 @@ function reportFailureCode(code: PersonalReportWorkerErrorCode): PersonalReportF
   }
 }
 
-function timerUnref(timer: ReturnType<typeof globalThis.setInterval>): void {
-  const candidate = timer as ReturnType<typeof globalThis.setInterval> & { unref?: () => void };
-  candidate.unref?.();
-}
-
 function defaultRetryDelayMs(job: PersonalReportJobRecord): number {
   const exponent = Math.max(0, Math.min(job.attemptCount - 1, 5));
   return 5_000 * (2 ** exponent);
@@ -269,22 +264,26 @@ export function createPersonalReportWorker(deps: PersonalReportWorkerDeps) {
     const controller = new AbortController();
     let heartbeatError: unknown = null;
     let heartbeatChain = Promise.resolve();
+    const refreshLease = async () => {
+      if (heartbeatError !== null || controller.signal.aborted) return;
+      await deps.jobs.heartbeatLease({
+        jobId: job.id,
+        leaseToken: job.leaseToken!,
+        leaseSeconds,
+      });
+    };
     const heartbeatTimer = setIntervalFn(() => {
       heartbeatChain = heartbeatChain
-        .then(async () => {
-          if (heartbeatError !== null || controller.signal.aborted) return;
-          await deps.jobs.heartbeatLease({
-            jobId: job.id,
-            leaseToken: job.leaseToken!,
-            leaseSeconds,
-          });
-        })
+        .then(refreshLease)
         .catch((error) => {
           heartbeatError = error;
           controller.abort(error);
         });
     }, heartbeatIntervalMs);
-    timerUnref(heartbeatTimer);
+    // Keep this timer ref'd. The worker runs from instrumentation, not an HTTP
+    // request; unref'd intervals in Next.js standalone are skipped while the
+    // only in-flight work is a long model await, which is exactly when the
+    // lease must be extended.
 
     let report: PersonalReportRecord | null = null;
     const generationStartedAt = now().getTime();
@@ -339,6 +338,8 @@ export function createPersonalReportWorker(deps: PersonalReportWorkerDeps) {
         signal: controller.signal,
         sectionService: deps.sectionService,
         onProgress: async (progress) => {
+          await refreshLease();
+          if (heartbeatError !== null) throw heartbeatError;
           const percent = progress.total > 0
             ? Math.min(89, 30 + Math.floor((progress.completed / progress.total) * 55))
             : 30;