Resilient WooCommerce Commerce System

Revenue is lost at the seams, not on the product page. A retried webhook double-books an order; two concurrent checkouts oversell the last unit; float arithmetic drifts a tax total by a penny per line; a refund path lets you return more than was captured. Each is invisible in a design review and expensive in production.

Webhooks land in a replay-safe inbox

Every inbound webhook is signature-verified and written to an atomic dedup store backed by a database unique constraint. A replayed delivery is accepted and ignored, not processed twice — and the E2E test proves it against a real MySQL.

Money is integer minor units, never floats

The tax calculator works in pence/cents throughout. Float arithmetic is not "close enough" on a line-item total that gets multiplied and summed hundreds of times a day.

Invariants are enforced, not documented

Stock cannot go oversold, a refund can never exceed what was captured, and order-state transitions are a closed set. These are unit-tested rules in code rather than notes in a wiki.

Stack

• ▸ WordPress · WooCommerce extension APIs
• ▸ PHP 8.1+ · Composer
• ▸ $wpdb-backed atomic dedup store · MySQL
• ▸ HMAC signature verification · timestamp window
• ▸ REST API route · webhook inbox
• ▸ PHPUnit · Playwright · wp-env
• ▸ GitHub Actions · dedicated E2E workflow

Tooling

• ✓ kept Composer · wp-env · GitHub Actions · MySQL fixture