Fix Medicaid category assignment order - mandatory before optional

[daphnehanse11]

Summary

• Reorder medicaid_category formula to evaluate mandatory groups (parent, pregnant, SSI) before optional expansion groups
• Federal Medicaid eligibility rules require this ordering per federal policy
• Update test expected values to reflect correct category assignments

Test plan

• All 147 Medicaid tests pass
• Verified parent at 30% FPL is now correctly assigned to PARENT category instead of ADULT

Fixes #7267

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (ed78e6c) to head (7c7b8b4).
⚠️ Report is 221 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##              main     #7272    +/-   ##
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  Coverage   100.00%   100.00%            
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  Files           16         1    -15     
  Lines          228        25   -203     
  Branches         1         0     -1     
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- Hits           228        25   -203     

Flag	Coverage Δ
unittests	100.00% <ø> (ø)

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[PavelMakarchuk]

Formatting questions

[PavelMakarchuk]

📋 Review Summary

✅ Strengths

• Correct implementation: The PR correctly addresses the federal Medicaid eligibility hierarchy issue identified in Medicaid category assignment order incorrect - mandatory groups should precede optional expansion #7267
• Well-documented: Thorough comments explaining the regulatory basis (42 CFR references)
• Proper test updates: Test value correctly updated to reflect NON_EXPANSION_ADULT per-capita cost for WI ($4,631.1 = $2.862B spending / 618K enrollment)
• CI passing: All 147 Medicaid tests pass

🔍 Issues Found

Minor Documentation Issues (Agree with @PavelMakarchuk's review)

1. "mega-mandatory" terminology (line 44)

   • This term is informal and not used in federal regulations
   • Suggestion: Replace with "mandatory non-MAGI" or simply "mandatory categorically needy"

2. California state reference (line 38)

   • The "California MAGI Hierarchy guidance" reference is state-specific
   • The federal CFR citations are sufficient; consider removing or replacing with federal source
   • Alternative federal reference: CMS State Medicaid Manual, Chapter 3

3. "Order matters:" comment prefix (line 35)

   • Removing this makes the comment header cleaner while retaining the substance

📊 Validation Results

Check	Status
Federal Compliance	✅ Hierarchy aligns with 42 CFR 435.119 requirement
Test Value Accuracy	✅ $4,631.1 correctly calculated from WI data
No Hard-coded Values	✅ All values parameterized
CI Status	✅ All checks passing

📝 Regulatory Verification

The PR correctly implements the federal hierarchy per 42 CFR 435.119, which states individuals must be "not otherwise eligible for and enrolled for mandatory coverage under a State's Medicaid State plan" before qualifying under the Adult group. This establishes the hierarchy:

1. SSI Recipients (42 CFR 435.120-138)
2. Children (42 CFR 435.118)
3. Pregnant Women (42 CFR 435.116)
4. Parents/Caretaker Relatives (42 CFR 435.110)
5. Young Adults (optional state coverage)
6. Adult Expansion (42 CFR 435.119 - residual category)
7. Optional Aged/Blind/Disabled (non-SSI pathway)

🚀 Recommendation

Address the minor documentation suggestions from @PavelMakarchuk's review, then this PR is ready to merge.