Optimistic concurrency

curl -v "https://api.novatrade24.com/v1/partners/${SELLER_ID}/orders/${ORDER_UUID}" \
  -H "Authorization: Bearer ${ACCESS_TOKEN}"

ETag: "5"

curl -X PATCH "https://api.novatrade24.com/v1/partners/${SELLER_ID}/orders/${ORDER_UUID}" \
  -H "Authorization: Bearer ${ACCESS_TOKEN}" \
  -H "Idempotency-Key: $(uuidgen)" \
  -H 'If-Match: "5"' \
  -H "Content-Type: application/json" \
  -d '{ "responsibleContact": { ... } }'

{
  "type": "https://api.novatrade24.com/problems/version-mismatch",
  "title": "Version Mismatch",
  "status": 409,
  "detail": "If-Match version 5 does not match current version 7.",
  "traceId": "req_...",
  "currentResource": {
    "uuid": "o1p2q3r4-...",
    "version": 7,
    "...": "..."
  }
}

async function updateWithRetry(orderId: string, changes: Partial<Order>) {
  for (let attempt = 0; attempt < 3; attempt++) {
    const current = await getOrder(orderId);
    const merged = { ...current, ...changes };

    const r = await patchOrder(orderId, merged, current.version);
    if (r.status === 409) {
      // Another channel edited. Loop with the fresh version.
      continue;
    }
    return r;
  }
  throw new Error('Too many concurrent conflicts');
}