Self-requeueing jobs need their own limit

// before: on a stall, try again later from the same cursor, forever
await enqueue({ resumeFrom: cursor }, { delayMs: 120_000 });
// after: count stalls across runs, give up loudly
const stalled = madeNoProgress ? (payload.stalledRunCount ?? 0) + 1 : 0;
if (stalled >= MAX_STALLED_RUNS) throw new Error(`Backfill stuck at ${JSON.stringify(cursor)}`);
await enqueue({ resumeFrom: cursor, stalledRunCount: stalled }, { delayMs: 120_000 });