Function execute_public_batch 

pub fn execute_public_batch(
    backend: &mut impl OneShotBackend,
    statements: &[SqlStatementRequest],
    idempotency_key: &str,
    aggregate_result_byte_limit: usize,
    now_ms: i64,
) -> Result<PublicOperationCommit, WritePlaneError>

Execute one public SQL batch: validate the idempotency key against the caller’s now_ms (future skew bounded — the coordinator reads no clock), check for an exact replay, then run every statement inside one backend transaction while bounding the encoded result array — the JSON array delimiters (2 bytes) and inter-result separators count toward aggregate_result_byte_limit — and commit with the outcome row. Any statement or accounting error rolls the unit back. A commit error is re-read: a concurrent request carrying the same identity may have won while this attempt was open, and its co-transactional outcome is authoritative — the exact stored bytes are returned instead of a duplicate-key/conflict error.