Backdate Kentucky K-TAP parameters

[hua7450]

Summary

Backdates Kentucky K-TAP (TANF) parameters to 1997 (program inception), adds a unified earned income disregard formula supporting both the pre-2023 AFDC-era "$30 + 1/3" and post-2023 "50%" disregards, and makes all deductions fully per-person per MS 2840.

Closes #7496

Changes

• Parameters backdated: 11 files, 1997-07-01 entries added (frozen AFDC-era values)
• Nov 2025 reduction: Payment maximums reduced ~35% (2025-11-01)
• New parameters: earned_income_flat_disregard ($30 pre-2023), earned_income_flat_disregard_in_effect boolean toggle
• EID formula: Unified formula — flat + rate * (earned - flat) — handles both eras via parameter toggle
• Per-person deductions: All three deductions (work expense, dependent care, EID) applied per-person per MS 2840, then summed to unit. This matters for the pre-2023 $30+1/3 formula in two-earner households because the $30 flat makes it non-linear.
• Dependent care allocation: New ky_ktap_dependent_care_disregard_person variable allocates unit-level dependent care to the primary earner per MS 2840 B.2.c
• Dependent care fix: Added is_tax_unit_dependent filter so bracket lookup only applies to dependents
• Reference fixes: Subsection citations corrected (5(3)(c)-(d) → 5(3)(e)), Nov 2025 news source added
• Tests added: 93 new test cases (47 historical/boundary + 45 edge cases + 1 two-earner with dependent care)

Three Parameter Eras

Era	Dates	Payment Max (family of 3)	EID Formula
ERA 1 (AFDC-era)	1997-07-01 – 2023-02-15	$262	$30 flat + 1/3 of remainder
ERA 2 (2023 reform)	2023-02-16 – 2025-10-31	$524	50% of earned income
ERA 3 (Nov 2025 cut)	2025-11-01 – present	$341	50% (unchanged)

Regulatory Sources

• 921 KAR 2:016 (current) — effective 2023-03-01
• 921 KAR 2:016 (pre-2023 superseded) — AFDC-era values
• KY DCBS Operation Manual Vol III — MS 2840 (deduction order), MS 2857 (EID time limits)
• WKMS: K-TAP benefit reduction — Nov 2025 payment maximums

Known Limitations

• Pre-2023 EID time limits (4 months at $30+1/3, then 8 months at $30 only) not modeled (PolicyEngine is point-in-time)
• Post-2023 EID 6-month limit not enforced (calendar month proxy used instead)
• MS 2520 six-month 100% earned income exclusion for new employment not modeled (requires employment history tracking)
• Part-time dependent care cap ($150/month) not separately modeled
• Gross income limit uses formula (185% * SoN) rather than regulation's pre-computed table (max ~$1.65 rounding difference)

Test Plan

• All 145 K-TAP tests pass
• Microsimulation runs without errors (no entity broadcast bugs)
• make format clean
• Full CI suite (pending)

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (55a0045) to head (59a12ea).
⚠️ Report is 20 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #7497      +/-   ##
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+ Coverage   97.82%   100.00%   +2.17%     
===========================================
  Files           3         5       +2     
  Lines          92        87       -5     
  Branches        2         1       -1     
===========================================
- Hits           90        87       -3     
+ Misses          1         0       -1     
+ Partials        1         0       -1     

Flag	Coverage Δ
unittests	100.00% <100.00%> (+2.17%)	⬆️

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