Add refundable credit conversion contrib reform

[DTrim99]

Summary

Adds a new structural contrib reform gov.contrib.refundable_credit_conversion that swaps the federal standard deduction, itemized deductions, above-the-line deductions, Head of Household filing status, CTC, CDCC, and EITC for a flat refundable credit composed of per-taxpayer, per-dependent, per-household, and wage-credit components. Each repeal is toggleable independently.

The reform mirrors the ECPA pattern (PR #6831) so that repeals only affect the federal computation; the underlying eitc, ctc, cdcc, standard_deduction, itemized_taxable_income_deductions, above_the_line_deductions, and head_of_household_eligible variables continue to compute their baseline values for state programs to reference.

Implementation

New parameters under gov.contrib.refundable_credit_conversion/:

• in_effect.yaml — bool gate for the structural reform.
• repeals/{itemized, standard_deduction, head_of_household, above_the_line_deductions, ctc, cdcc, eitc}.yaml — bool toggles, default false.
• credit/{per_taxpayer, per_dependent, per_household}.yaml — currency-USD, default 0.
• credit/dependent_definition.yaml — int (0 = EITC-qualifying child, 1 = CTC-qualifying child, 2 = all claimed dependents).
• wage_credit/{rate, cap}.yaml — /1 rate and currency-USD per-worker cap.

Reform Python at policyengine_us/reforms/refundable_credit_conversion/refundable_credit_conversion.py:

• New flat_refundable_credit (TaxUnit) variable computes taxpayers * per_taxpayer + dependents * per_dependent + per_household + sum_over_persons(min(earned_income, cap) * rate).
• standard_deduction, itemized_taxable_income_deductions, above_the_line_deductions, and head_of_household_eligible are overridden to early-return 0 / False when their repeal toggle is on, and otherwise reproduce the baseline formula.
• income_tax_refundable_credits and income_tax_non_refundable_credits are overridden to filter eitc, refundable_ctc, non_refundable_ctc, and cdcc out of the federal credit lists when their toggle is on, then append flat_refundable_credit to the refundable list.
• create_refundable_credit_conversion_reform is registered in policyengine_us/reforms/reforms.py following the streamlined-EITC and ECPA gating pattern (5-year in_effect lookahead).

Tests at policyengine_us/tests/policy/contrib/refundable_credit_conversion/:

• flat_credit.yaml — credit math for single, MFJ, and MFJ-with-dependents shapes.
• repeals.yaml — one assertion per repeal toggle.
• dependent_definition.yaml — three cases switching the integer enum.
• wage_credit.yaml — per-wage-earner cap arithmetic.
• integration.yaml — full reform with all toggles on.

Test plan

• make format
• policyengine-core test policyengine_us/tests/policy/contrib/refundable_credit_conversion/ -c policyengine_us
• pytest policyengine_us/tests/microsimulation/test_microsim.py (regression)
• Verify state EITC / state CTC / state standard deduction values are unchanged when the federal reform is active

🤖 Generated with Claude Code