[hua7450]

Closes #10366
Closes #10367

What and why

Two formula fixes in the Medicaid medically needy pathway.

Fix	Before	After	Source
Blind people (#10366)	is_in_medicaid_medically_needy_category checked is_ssi_disabled but never is_blind, so a blind adult under 65 who is not SSI-disabled could not qualify	is_blind counts under the existing disabled flag	42 CFR 435.322 (blind) beside 435.324 (disabled)
Financial unit (#10367)	Income, medical expenses and resources were summed over the tax unit, and the couple limits applied when tax_unit_is_joint	Sums run over the marital unit, a child's resources include the parents' resources SSI deems to the child, and the couple limits apply when the marital unit has two people	42 CFR 435.602(a)(2)(i), 435.845(a), 20 CFR 416.1202(b)

Blind under the disabled flag. The disabled parameter cites KFF's 50-state survey, whose medically needy column covers "seniors and people with disabilities" and counts blindness as a disability. KFF never reports blind coverage separately, so this PR adds no blind parameter.

Marital unit. Non-MAGI Medicaid counts only the income and resources of a spouse, or of a parent for a child. ssi_countable_income already carries a child's deemed parental income, an ineligible spouse's deemed income, and each half of an eligible couple's combined income. A child's marital unit holds only the child, so the formula adds ssi_resources_deemed_from_ineligible_parent (the January value of the parents' resources above SSI's $2,000 or $3,000 allowance) to the child's own resources. The optional aged, blind and disabled pathway already sums over the marital unit in the same way (is_optional_senior_or_disabled_income_eligible, medicaid_optional_senior_or_disabled_income_limit).

The couple flag keeps its name, is_joint, so that the income-limit lines stay untouched. #10374 (closes #10357 and #10358) rewrites those lines, and git merge-file merges the formula cleanly in either order with the same result.

Examples

Massachusetts, 2026: $522 / $650 a month and $2,000 / $3,000 in resources.

Household	main	This PR
Blind adult, age 40, not SSI-disabled	Not in a medically needy category	In the disabled group
Aged filer (70): $17,760 countable income, $13,000 medical expenses, $500 resources. Claims their 92-year-old parent: $3,760 countable pension, $1,800 resources	8,520 > 6,264 and 2,300 > 2,000: ineligible	4,760 ≤ 6,264 and 500 ≤ 2,000: eligible
Aged married couple filing separately, $13,080 countable income and $8,000 medical expenses each	Each passes alone: 5,080 ≤ 6,264	10,160 > 7,800 (couple limit): ineligible
Disabled child, 10: $21,358 countable income (deemed from the parents' $80,000 wages), $16,000 medical expenses. Married parents hold $4,000 (not a test case)	Joint tax unit: couple limits; 4,000 > 3,000: ineligible	Individual limits; 4,000 - 3,000 = 1,000 deemed ≤ 2,000 and 5,358 ≤ 6,264: eligible

Microsimulation effect

• Blind people under 65 who are not SSI-disabled can now qualify as medically needy in the states with the disabled group on, if they fall in no other pathway and meet the limits after medical expenses. The flag is on in 32 states, 5 of which (AZ, ID, IN, NM, NV) have no limits, so the change reaches 27 states. Update Medicaid medically needy limits and switch on AR, IA, IL, NJ and ND #10374 also switches the flags on in AR, IA, IL, NJ and ND.
• Aged, blind and disabled people who share a tax unit with relatives other than a spouse, such as parents claimed as dependents, are now tested on their own income and resources against the individual limits. Spouses who file separately are tested together against the couple limits.
• Blind or disabled children under 18 are tested against the individual limits, counting the parents' resources only above SSI's $2,000 or $3,000 allowance, instead of the parents' full resources against the couple limits of a joint tax unit.
• The population effect has not been measured.

Relation to #10240 and #10374

A local review of #10240 flagged the tax-unit sum (once that PR counts noncitizens' income, an aged dependent's pension removes the filer's eligibility). This PR fixes it, so #10240 need not.

#10240, #10374 and this PR each append cases to is_medically_needy_for_medicaid.yaml starting at Case 3, so whichever merges later gets a conflict at the end of that file and renumbers its cases. The conflict is placement and numbering only: #10374 leaves the Massachusetts limits and the Texas flags unchanged, so this PR's expected values hold in either order. The formula itself merges cleanly with #10374 in either order.

Limitations

• When a caller omits marital units, Core puts every household member into one marital unit (Preserve supplied marital units and infer missing explicit couples #10000 addresses this). Everyone's income and resources are then summed; a household of exactly two gets the couple limits and a larger one the individual limits. The optional aged, blind and disabled pathway has the same behavior.
• is_joint uses the couple limits whenever the person is married and living with their spouse, whether or not the spouse is aged, blind or disabled. This matches the optional pathway.
• Parents' medical expenses do not reduce a child's income, although 42 CFR 435.831(d) deducts expenses of "financially responsible relatives". This makes the child's test stricter than the regulation.
• Parents' resources count for a child under 18 only, as in SSI. 42 CFR 435.602(a)(2)(i) would also allow them for an 18- to 20-year-old or a blind or disabled adult child.
• The optional aged, blind and disabled pathway's asset test still omits a child's deemed parental resources; that needs its own PR.

Tests

• is_in_medicaid_medically_needy_category.yaml: a blind adult in Massachusetts (in the group) and in Texas, which has no disabled group (not in a group).
• is_medically_needy_for_medicaid.yaml: the filer with a dependent parent (Case 3) and the couple filing separately (Case 4), both examples above. Cases 5 and 6: a disabled child of 10 whose married parents hold $20,000 (17,000 deemed > 2,000: ineligible) or $2,400 (nothing deemed: eligible).
• A static scan of the YAML suite found no existing case whose expected value changes: no multi-person case with an aged, blind or disabled member has a medically needy result that differs between the tax and marital units, and the existing blind cases already qualify through another pathway or live in states without the group. Partner contract tests (tests/policy/baseline/partners/**) are unaffected; their multi-person aged and disabled cases are in Texas, which has no medically needy aged or disabled group.

Test plan

• make format (ruff)
• Changelog fragment in changelog.d/
• Local review: regulations, Massachusetts standards and every new expectation checked by hand; formula merge with Update Medicaid medically needy limits and switch on AR, IA, IL, NJ and ND #10374 checked in both orders
• CI passes (tests were not run locally)

axiom: TheAxiomFoundation/rulespec-us#1931 queued

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