use ContractType;
use Deserialize;
/// Column-level contract definition.
///
/// Each `ColumnContracts` entry binds a column name to one or more
/// validation rules (`ContractType`). These rules are deserialized
/// from TOML/JSON/YAML contract files.
///
/// Example TOML:
/// ```toml
/// [[columns]]
/// name = "email"
/// validation = [
/// { rule = "not_null" },
/// { rule = "pattern", pattern = "^[^@]+@[^@]+$" }
/// ]
/// ```