Every statement inside a withTransaction holds the single primary write connection open for another edge→primary round-trip. A chatty interactive transaction is what the primary aborts as "Transaction timed-out".

A plain batch is one round-trip however many statements it carries, and is never counted. Put the chatty writes on it. That is the whole point.

Work that grows with input size must prepare its reads outside the lock and apply its writes as one batch. The high-water mark is recreateTable on attendee_answers at 27 statements, and this sits above that.