Oh you would ask that. It's in section 104(a)

-(disabled is included because they're under Medicare)

-(Section 631(d) prevents revisions to a state Medicaid plan that would vreat a gap in coverage - i.e preserving it's safety net function)

Section 104(a):

Subject to section 631(d), the Secretary, States, and health insurance issuers shall ensure that any nondisabled, nonelderly adult individual eligible under title XIX of the Social Security Act (including any nondisabled, nonelderly adult individual eligible under a waiver under such title or under section 1115 of such Act (42 U.S.C. 1315)) covered under a HAPI plan provided through the State HHA receives medical assistance under State Medicaid plans in a manner that--

(1) is provided in coordination with, and as a supplement to, the coverage provided the nondisabled, nonelderly adult individual under the HAPI plan in which the individual is enrolled;

(2) does not supplant the nondisabled, nonelderly adult individual's coverage under a HAPI plan;

(3) ensures that the nondisabled, nonelderly adult individual receives all items or services that are not available (or are otherwise limited) under the HAPI plan in which they are enrolled but that is provided under the State plan (or provided to a greater extent or in a less restrictive manner) under title XIX of the Social Security Act (including any waiver under such title or under section 1115 of such Act (42 U.S.C. 1315)) of the State in which the nondisabled, nonelderly adult individual resides; and

(4) ensures that the family of the nondisabled, nonelderly adult individual is not charged premiums, deductibles, or other cost-sharing that is greater than would have been charged under the State plan under title XIX of the Social Security Act of the State in which the nondisabled, nonelderly adult individual resides if such coverage was not provided as a supplement to the coverage provided the child under the HAPI plan in which the nondisabled, nonelderly adult individual is enrolled.