Experience with distributed or event-driven systems, including delivery guarantees, idempotency, retries, ordering, dead-letter handling, and operational failure modes, plus hands-on work with Kafka or a comparable platform and a schema technology such as Avro, Protobuf, JSON Schema, or OpenAPI. A record of building APIs, SDKs, shared libraries, data contract systems, or event publishing frameworks used outside your team, with a solid understanding of schema design, versioning, validation, code generation, and migrations.