Function transactionally_apply_schema_checked 

pub fn transactionally_apply_schema_checked<E>(
    conn: &Connection,
    cdc: &CaptureCtx,
    op: &'static str,
    protect_registered_tables: bool,
    allow_row_changes: bool,
    apply: impl FnOnce() -> Result<(), E>,
    validate: impl FnOnce(&Connection, usize, &[ReplicatedTableSchema]) -> Result<(), E>,
) -> Result<(), E>
where
    E: From<ReplicaError>,

transactionally_apply_schema with one caller-owned validation hook after the complete schema envelope has been introspected but before COMMIT. The generic error keeps a host’s typed policy failures intact while every connection/capture/schema failure still enters through ReplicaError.