Долгие serverless-задачи: цепочки шагов, fan-out и ретраи на шаг

export async function handler(event) {
  const { batchId, itemIds } = JSON.parse(event.body || '{}');
  if (!batchId || !itemIds?.length)
    return { statusCode: 400, body: JSON.stringify({ error: 'batchId and itemIds required' }) };
  const { instanceId: jobId } = await global.durable.startNew(
    'enrich-batch', undefined, { batchId, itemIds }
  );
  return { statusCode: 202, body: JSON.stringify({ jobId, status: 'started' }) };
}

export async function handler(event) {
  // step 1 — runs first, output feeds into fan-out branches
  const { batchId, itemIds } = event.payload ?? {};
  const items = await db.fetchItems(itemIds);        // may take several minutes
  await db.markBatchStarted(batchId);
  return { batchId, items };                          // passed to parallel branches via {{steps.extract.output}}
}

export async function handler(event) {
  // Each parallel branch receives the upstream node's output as its event.
  // Node retry: maxAttempts=3, backoffMs=2000, strategy=exponential
  const enriched = await externalApi.enrich(event.item);  // retry isolates this network call
  return { itemId: event.item.id, enriched };
}

export async function handler(event) {
  // Runs after ALL parallel branches complete. A merge node hands the next step
  // { inputs: { <branchNodeId>: <branchOutput>, ... } } — one entry per branch.
  const branchOutputs = Object.values(event.inputs ?? {});
  const merged = branchOutputs.map(b => b.enriched).filter(Boolean);
  await db.saveBatchResults(merged);
  return { saved: merged.length, total: branchOutputs.length };
}