Can I vibe code OpenLoyalty?

Build a lightweight, headless loyalty points API service using Node.js, Express, and PostgreSQL.

1. DATA MODEL:
- Create a `customers` table (id, external_id, email, current_points, tier_level, created_at).
- Create a `points_ledger` append-only table (id, customer_id, amount_delta, event_type ['EARN', 'BURN', 'REFUND', 'EXPIRATION'], reference_id, metadata JSONB, created_at).
- Create a `tiers` table (name, min_spend, multiplier).
- Create a `rewards` table (id, title, point_cost, discount_value, code_type).

2. CORE API ENDPOINTS:
- `POST /v1/events/order-created`: Accepts order JSON (customer_id, order_id, subtotal). Wrap balance updates in a DB transaction: calculate points earned based on subtotal * tier multiplier, insert row into `points_ledger`, update `customers.current_points` using row-level locking (`FOR UPDATE`), and evaluate if total spend warrants a tier upgrade.
- `POST /v1/events/order-refunded`: Accepts refund JSON (order_id, refund_amount). Reverses points proportional to refunded amount using a negative `points_ledger` entry.
- `POST /v1/rewards/redeem`: Accepts customer_id and reward_id. Validates points balance in DB, deducts points within a locked transaction, and calls Shopify REST API to generate a single-use coupon code.
- `GET /v1/customers/:id/balance`: Returns current balance, history, and progress to next tier.

3. CONCURRENCY & FAILURES:
- Ensure database transactions enforce strict row locking on customer records during balance updates to prevent double-spending.
- Idempotency check: Reject duplicate order_id events by checking `reference_id` in `points_ledger` before processing.
- Handle negative balances gracefully if a refund occurs after points were already redeemed.

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