The payload-returning UPDATE arms emit no within-SET value-agreement check

Two input fields can write the same SET column when at least one of them carries a @nodeId decode. The walker admits that overlap deliberately (an all-plain overlap is the PlainColumnCollision reject; a decode-involving one is meant to be reconciled at runtime), and the direct-return single-row UPDATE emits emitSetAgreementPreamble to compare the two decoded values before the DML. The two payload-returning UPDATE arms, TypeFetcherGenerator.buildCarrierUpdateChainSingle and buildCarrierBulkPerRowUpdateBody, do not. They build the SET map with emitSetMapPuts and no preamble, so the second Map.put silently clobbers the first and the caller’s other value is discarded with no error.

Found while implementing the straddling-reference partition, which closed the sibling gap on the same two arms: neither of them emitted the cross-partition (WHERE ∩ SET) check either. That half is fixed, because the walker now states those overlaps as AgreementObligation rows on the UpdateRows carrier and all four emit consumers fold over them. This item is the remaining half, and it is genuinely a different fact: a within-SET overlap is not a WHERE/SET overlap, so it is not an obligation row, and the direct-return arms derive it at emit time from ColumnOverlap.groupByColumn(setGroupWriters(setGroups)).