Function version_merge 

pub fn version_merge(
    conn: &Connection,
    source_ids: &[i64],
    target_name: &str,
    strategy: MergeStrategy,
) -> Result<i64>

Merge two or more versions into a new version.

The entire merge — new-version creation, is_merged flag, and all validity updates — runs in one transaction, so a failure leaves no half-built version.