set method
Over-eager on purpose: setting a field back to its initial value still marks it dirty rather than diffing against the seed. An extra field in the payload is cheap; silently dropping a real edit is not.
Implementation
FormValues set(String name, Object? value) {
return FormValues._(
Map.unmodifiable(Map<String, Object?>.of(_values)..[name] = value),
Set.unmodifiable({..._dirty, name}),
);
}