Event-driven architecture — event catalog, schema registry, eventual consistency, saga, CQRS, event sourcing. Use when the user asks to 'design event-driven system', 'build event catalog', 'implement CQRS', 'design saga patterns', 'set up schema registry', 'implement event sourcing', or mentions Kafka, RabbitMQ, Pulsar, event bus, dead-letter queue, consumer groups, or event replay. [EXPLICIT]