The state pledges and agrees with the holders of bonds issued under the Regional Transit District Act and with those parties who enter into contracts with a district or a member of a combination pursuant to the Regional Transit District Act that the state will not impair the rights vested in the district or the rights or obligations of a person with which the district contracts to fulfill the terms of an agreement made pursuant to the Regional Transit District Act. The state further agrees that it will not impair the rights or remedies of the holders of the bonds of a district until the bonds have been paid or until adequate provision for payment has been made. A district may include this provision and undertaking for the state in bonds.