The existing join/leftJoin stream-globalTable overloads taking ValueJoinerWithKey are deprecated. Existing applications continue to compile and run unchanged, but the compiler will emit deprecation warnings, and the methods will be removed in a future major release.
The new joinOnMappedKey and leftJoinOnMappedKey methods are additive. Existing code compiles and runs unchanged; migration is required only before the deprecated overloads are removed.
Stream-globalTable overloads taking ValueJoiner (no key access) are unaffected.
Migration guidance for the new join methods will be added to the Streams upgrade guide.

Test Plan

Unit tests in KStreamGlobalKTableJoinTest, KStreamGlobalKTableLeftJoinTest and other related tests covering the new join methods

Rejected Alternatives

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