A developer is building an order-processing system with several independent microservices (payment, inventory, shipping). Each service must react to events without any central controller directing the flow. When an order is placed, the payment service emits an event that the inventory service consumes, which in turn emits an event the shipping service consumes. The team wants loosely coupled services that each own their own logic and can be added or removed without changing a central component. Which architectural pattern does this design represent?