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Proposed Changes

Coordinator Changes

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When processing an EndTxnRequest, the coordinator already determines the transaction version (legacy or TV2) and stores it in the transaction’s TransactionMetadata.

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With this KIP, the coordinator will

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propagate the transaction version to partition leaders by including a new TransactionVersion field

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when building a WriteTxnMarkersRequest. This field is only included if the target broker supports request version 2; otherwise, the coordinator falls back to version 1, which omits the field. This allows leaders to apply the correct epoch validation rule while maintaining compatibility across mixed-version clusters.

Broker/Leader Changes

Leaders must apply strict validation when TV is known to be TV2:

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