// Pseudocode for Idempotency Logic
function createLead(request) {
  const { tenantId, idempotencyKey, payload } = request;

  // 1. Check idempotency key first
  const existingRequest = findRequestByIdempotencyKey(idempotencyKey, tenantId);
  if (existingRequest) {
    return 200 (OK) with existingRequest.response;
  }

  // 2. Check for external_id if provided
  if (payload.external_id) {
    const existingLead = findLeadBy({ external_id: payload.external_id, company_id: tenantId });
    if (existingLead) {
      // Record the idempotency key and return conflict
      recordIdempotency(idempotencyKey, existingLead);
      return 409 (Conflict) with existingLead;
    }
  }

  // 3. Fallback: Hash key if no external_id
  const hashKey = createHash(payload.email, payload.phone, payload.campaign, tenantId);
  const existingLeadByHash = findLeadBy({ hash_key: hashKey, company_id: tenantId });
  if (existingLeadByHash) {
    recordIdempotency(idempotencyKey, existingLeadByHash);
    return 409 (Conflict) with existingLeadByHash;
  }

  // 4. All checks passed, create new lead
  const newLead = createNewLeadInDB(payload, tenantId, hashKey);
  recordIdempotency(idempotencyKey, newLead);
  return 201 (Created) with newLead;
}