KIP-63 — Unify store and downstream caching in streams

Accepted Streams

Unifies the downstream forwarding cache with the local state store cache in Kafka Streams, so both write paths share the same record.cache.max.bytes.buffering budget and produce a single deduplicated stream of downstream emissions per cache flush. The separate downstream cache resulted in redundant Change-value records being forwarded (e.g., intermediate aggregation results) and caused unnecessary Kafka writes and downstream processing load.

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