Fix federal disability gates disconnected from their legal definitions

[hua7450]

Summary

Part of the disconnected-disability-inputs audit (#9330). Fixes the six federal findings: gates whose statutes define disability by SSI/SSDI receipt or by cross-reference to the Social Security Act, but which read only the generic is_disabled flag (or, inversely, an SSI-criteria flag where the law requires receipt).

Fixes #9329
Fixes #9331
Fixes #9332
Fixes #9333
Fixes #9334
Fixes #9337

Changes

Issue	Gate	Legal basis	Fix
#9332	disabled_programs.yaml → is_usda_disabled	7 CFR 271.2 item (2): "Receives supplemental security income benefits … or disability or blindness payments"	Replace is_ssi_disabled (criteria flag, no receipt test, drops blind SSI recipients) with receives_ssi + ssi (reported or modeled receipt)
#9331	SNAP ABAWD exemption, work registration, general work requirements, student rule	7 CFR 273.7(b)(1)(ii): receipt of temporary or permanent disability benefits establishes unfitness for employment; 7 CFR 273.24(c)(2)	OR is_usda_disabled into each disability leg
#9333	SSI student earned income exclusion	20 CFR 416.1112(c)(3): applies to a blind or disabled claimant under SSA's own definition	is_disabled → is_ssi_disabled
#9334	Medicaid home equity family exception	42 U.S.C. 1396p(f)(2)(A)(ii)(II): child "blind or permanently and totally disabled as defined in section 1614"	Add is_ssi_disabled to the resident-child disability legs
#9329	Medicaid work requirement (community engagement)	HR1 §71119: exemption for individuals "blind or disabled (as such terms are defined in section 1614)"	Add is_ssi_disabled to eligible_disabled
#9337	HUD elderly/disabled family + HUD dependent	42 U.S.C. 1437a(b)(3)(E): person with disabilities includes the SSA §223 (SSDI) definition	Add is_ssi_disabled and SSDI receipt paths; drop stray unit = USD on the boolean

Also clarifies the disabled_programs description and is_usda_disabled documentation: per 271.2 item (2) any SSI receipt qualifies (including aged-category recipients, who are 65+ and always also qualify under the elderly test, so no consumer's outcome changes through the aged path).

Not in this PR

• State-level findings from the same audit (AR Medicaid work requirement misses SSI-criteria disability in medically-frail exemption #9335, CA WDP and IL HBWD buy-ins omit meets_ssi_disability_criteria; IL worker income test inconsistent #9336, CO AND-CS state supplement pays people who do not receive SSI #9338, MA EAEDC SSI-eligibility exclusion lacks the income test (is_ssi_eligible vs uncapped_ssi) #9339, TANF disability classification gates ignore benefit receipt (MT two-parent, VA TANF-UP, DC resource limit) #9340) — deliberately excluded; they remain open for separate PRs.
• The 7 CFR 271.2 items with no model inputs (Railroad Retirement disability annuities, government disability retirement) — documented in Disconnected disability inputs: repo-wide audit of disability gates vs their legal definitions #9330 as not representable today.

Impact channels

• Household calculations/API: all fixes bite directly.
• Microsimulation: direction-A fixes (Medicaid work requirement: SSI-definition disability does not trigger the medically-frail exemption (disconnected disability inputs) #9329, SNAP unfitness exemptions (ABAWD, work registration, student rule) miss SSI/SSDI-based disability #9331, SSI student earned income exclusion wrongly gated on disability; 20 CFR 416.1112(c)(3) requires only under-22 student status #9333, Medicaid home equity family exception misses children disabled under SSA section 1614 #9334, HUD person-with-disabilities definition read as generic is_disabled only #9337) bite only where SSI-side flags are populated in the dataset; the is_usda_disabled: 7 CFR 271.2 requires benefit receipt; definition-only flag used and blind SSI recipients dropped #9332 receipt swap moves SNAP elderly/disabled preferences onto modeled SSI receipt, so SNAP generosity co-moves with SSI takeup assignment.

Checklist

• Code formatted (make format)
• Changelog fragment (changelog.d/fix-disability-input-disconnects.fixed.md)
• CI passes

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 30.00000% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 42.20%. Comparing base (a68c725) to head (6621f87).
⚠️ Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
.../eligibility/medicaid_work_requirement_eligible.py	0.00%	2 Missing ⚠️
...ariables/gov/hud/is_hud_elderly_disabled_family.py	0.00%	1 Missing ⚠️
.../eligibility/student/is_snap_ineligible_student.py	0.00%	1 Missing ⚠️
...gibility/work_requirements/is_snap_abawd_exempt.py	0.00%	1 Missing ⚠️
...ements/is_snap_work_registration_exempt_non_age.py	0.00%	1 Missing ⚠️
...quirements/meets_snap_general_work_requirements.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##              main    #9345       +/-   ##
============================================
- Coverage   100.00%   42.20%   -57.80%     
============================================
  Files            1       10        +9     
  Lines           37      218      +181     
  Branches         2        0        -2     
============================================
+ Hits            37       92       +55     
- Misses           0      126      +126     

Flag	Coverage Δ
unittests	42.20% <30.00%> (-57.80%)	⬇️

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