عرض عملي: إبطال موجّه بالأحداث من ProductUpdated

خطوة بخطوة

1. The catalog service saves the product and publishes ProductUpdated{productId, version} after the transaction commits (use the outbox pattern from the messaging phase).
2. The cache service consumes the event and calls cache.evict("products", productId).
3. Update a price and show the new price returned within one second.
4. Planned mistake: the handler evicts the cache before the database commit; a concurrent read re-caches the old row. Fix: publish after commit and evict after the commit.
5. Make the consumer idempotent (evicting twice is harmless) and add a 10-minute TTL as a safety net.

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