Ecommerce

Quick Reference

Critical Code Traps

These break production and cost real money. See code-traps.md for full patterns.

1. Payment idempotency — Store payment_intent_id, check before processing. Webhooks retry.
2. Inventory race conditions — UPDATE ... WHERE stock > 0 with rowsAffected check, not read-then-write.
3. Frontend price trust — Backend recalculates everything. Never trust client totals.
4. Webhook signatures — Verify stripe-signature or equivalent. Reject unsigned requests.
5. Stock validation timing — Verify at payment moment, not just add-to-cart.