The department shall contract with the Health and Human Services Commission for provision of commission facilities, treatment, and habilitation for inmates with mental illness or an intellectual disability in the custody of the department. The contract must provide:
(1) detailed characteristics of the inmate population with mental illness and the inmate population with intellectual disabilities to be affected under the contract;
(2) for the respective responsibilities of the commission and the department with regard to the care and supervision of the affected inmates; and
(3) that the department remains responsible for security.