What does Kafka 4.2 add to Kafka Streams for failing records, and what limits does the new Streams rebalance protocol have?

4.2 adds dead letter queue support to Streams exception handlers (KIP-1034): a handler can return DLQ records through a new Response class, and the raw source record bytes are available in the error context, so a bad record can be routed to a dead letter topic instead of stopping the application. The server-side Streams rebalance protocol (KIP-1071) was early access in 4.1 and reached general availability with a limited feature set in 4.2; applications opt in with group.protocol=streams. The 4.2 and 4.3 developer guide lists what it does not support yet: static membership, warmup tasks and rack-aware assignment, pattern-based topic subscription, and online migration from the classic protocol.

Expected key concepts: Streams, KIP-1034, dead letter queue, exception handler, KIP-1071, group.protocol=streams, static membership, warmup, limited feature set, 4.2