How routing keys isolate Kafka consumer tests on a shared broker

Kafka consumer changes are hard to validate on shared brokers because routing stops at the topic, making test traffic hard to isolate.

The proposed fix is an opaque routing key carried in request context, stamped into message headers by producers, and checked by consumers.

That lets teams run realistic end-to-end tests in ephemeral environments on a shared Kafka broker without duplicating the full stack.

The approach uses concepts like OpenTelemetry baggage and consumer-side filtering to keep async flows isolated and safe to verify.