Fix CDCC returning $0 for disabled adult dependents (with section 21(d)(2) deemed income)

[hua7450]

Summary

Fixes the Child and Dependent Care Credit (CDCC) for households whose qualifying individual is a disabled adult — which previously returned $0. Extends the original expense-gate fix with a correct IRC § 21 qualifying-individual definition, handling of a disabled spouse the model assigns as head, and the § 21(d)(2) deemed-earned-income floor.

The bug

CDCC eligibility and the dollar limit already counted a disabled non-head dependent/spouse of any age, but expense attribution was gated on is_child (age < 18). A disabled qualifying individual aged 18+ was therefore allocated $0 of expenses → $0 federal credit and $0 state CDCCs (e.g. ks_cdcc). Separately, a lone disabled adult could still net $0 because the model infers them as a "spouse" with $0 actual earnings while the § 21(d)(2) deemed-income floor was not modeled.

Changes

1. Qualifying individual — is_cdcc_eligible (IRC § 21(b)(1))

• Child-by-age prong now requires dependency: is_dependent & (age < 13).
• Disability prong: disabled & (is_dependent | (head_or_spouse & has_spouse)) — a disabled dependent of any age, or a disabled member of a married couple (so a disabled spouse the model assigns as head is still counted).

2. Expense attribution — is_dependent_care_recipient + plumbing (IRC § 21(b)(2))

• New person-level is_dependent_care_recipient = is_child | (disabled & (dependent | member-of-couple)), used as the distribution key in pre_subsidy_childcare_expenses; tax_unit_childcare_expenses distributes by is_cdcc_eligible.

3. Deemed earned income — min_head_spouse_earned (IRC § 21(d)(2))

• A spouse who is a full-time student or incapable of self-care is deemed to earn $250/mo (one qualifying individual) or $500/mo (two or more), applied to only one spouse. Adds the deemed_earned_income parameter ($3,000 / $6,000 annual) and the cdcc_income_floor_eligible variable.

Reproduction (TY 2024, disabled dependent, only the age changed)

	Age 17	Age 18 (before)	Age 18 (after)
cdcc	$660	$0	$660
ks_cdcc	$330	$0	$330

Statutory basis

• IRC § 21(b)(1)(A)/(B)/(C) — qualifying individual (only the child prong has an age limit)
• IRC § 21(b)(2) — employment-related expenses (care of any qualifying individual)
• IRC § 21(c) — $3,000 / $6,000 dollar limits
• IRC § 21(d)(1)–(2) — earned-income limitation and deemed income for a student/incapacitated spouse
• K.S.A. 79-32,111c — Kansas CDCC (50% of federal, TY 2024+)

Modeling notes (approximations)

• Deemed income and student/incapacitated status are applied annually, not per qualifying month.
• The same-principal-place-of-abode (> ½ year) test for a disabled dependent/spouse is assumed met.
• IRC § 21(b)(1)(A) references § 152(a)(1) (qualifying child); the model uses tax-unit dependency.

Tests

494 tests pass locally across the childcare-expense plumbing, federal CDCC (including new is_cdcc_eligible, min_head_spouse_earned, and cdcc_income_floor_eligible cases), ~30 state/local CDCC mirrors, SNAP deductions, and the partner CDCC edge-case test. CI runs the full suite (including the partner contract suite).

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (47cb26b) to head (be2adf0).
⚠️ Report is 13 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
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  Coverage   100.00%   100.00%           
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  Files            3         7    +4     
  Lines           47       109   +62     
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+ Hits            47       109   +62     

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

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