KIP-1340 — Expose Both Mapped Key and Stream Key in Streams-GlobalKTable Joins

Accepted Streams

Adds a ValueJoinerWithStreamAndMappedKey functional interface for stream-GlobalKTable joins whose apply() receives both the original KStream record key and the mapped join key produced by the KeyValueMapper. KStreamKTableJoinProcessor#doJoin passes record.key() into ValueJoinerWithKey for global-table joins, which type-checks because both keys share type K but contradicts KIP-149's contract that readOnlyKey is the join key, leaving users no way to see the lookup key without recomputing it themselves.

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