Implement Pennsylvania CTC contributed reforms

[DTrim99]

Summary

Implements two Pennsylvania Child Tax Credit reform proposals as contributed reforms (not law).

Closes #7436

Proposals

1. Flat Amount CTC (pa_ctc_flat_amount)

• $1,000 per qualifying child under age 6
• 2% phaseout rate above $125,000 threshold (same for all filing statuses)
• Refundable credit
• Effective 2026

2. Federal CTC Match (pa_ctc_match)

• 50% match of the federal Child Tax Credit
• Limited to children under age 6
• No income phaseout
• Refundable credit
• Effective 2026

Files Added

Parameters (gov/contrib/states/pa/ctc/):

• flat_amount/ - in_effect, amount, age_limit, phaseout/threshold, phaseout/rate
• ctc_match/ - in_effect, match, age_limit

Reform Code (reforms/states/pa/ctc/):

• pa_ctc_flat_amount.py
• pa_ctc_match.py
• __init__.py files

Tests (tests/policy/contrib/states/pa/ctc/):

• 8 tests for flat amount reform
• 6 tests for CTC match reform

Test Plan

• All 14 YAML tests pass
• Tests cover income below/above threshold, phaseout calculations, age limits, filing statuses
• make format passes

🤖 Generated with Claude Code

[DTrim99]

Implementation Complete

Proposal 1: Flat Amount CTC

Parameter	Value
Credit Amount	$1,000 per child
Age Limit	Under 6
Phaseout Threshold	$125,000 (all filing statuses)
Phaseout Rate	2%
Start Date	2026

Proposal 2: Federal CTC Match

Parameter	Value
Match Rate	50%
Age Limit	Under 6
Phaseout	None
Start Date	2026

Test Coverage (14 tests)

• ✅ Income below/at/above phaseout threshold
• ✅ Credit fully phased out
• ✅ Multiple filing statuses (single, joint, HOH)
• ✅ Child at/above age limit
• ✅ Mixed age children
• ✅ Multiple young children

All tests pass locally.

[DTrim99]

Updated the CTC match implementation to use ctc_value instead of ctc_child_individual_maximum. This ensures low-income families only receive the match on their actual federal CTC amount after phase-in, not the maximum amount they would eventually receive.

Added low income test cases:

• $2,000 income: $0 match (income below $2,500 federal CTC phase-in threshold)
• $10,000 income: $562.50 match (partial federal CTC phase-in of $1,125)
• $20,000 income: $1,100 match (full federal CTC phase-in to $2,200 max)

All 9 CTC match tests and 8 flat amount tests pass.

[DTrim99]

Fix: PA CTC Match Now Uses Actual Federal CTC Received

This commit fixes an important issue with the PA CTC match formula.

Problem

The original implementation used ctc_value which represents the theoretical federal CTC after phase-in, but doesn't account for the refundable vs nonrefundable split:

• Refundable portion (ACTC): Max $1,700/child - can be received as a refund
• Nonrefundable portion: $500/child - only offsets tax liability

For families with income below the standard deduction (~$24k), they have $0 tax liability and can only receive the refundable $1,700, not the full $2,200.

Example

At $20,000 income with 1 young child:

• Old calculation: ctc_value = $2,200 → PA match = $1,100
• New calculation: actual_ctc = $1,700 (refundable only) → PA match = $850

Changes

1. Formula fix: Now uses refundable_ctc + min(non_refundable_ctc, tax_liability) to calculate actual federal CTC benefit received
2. SSN requirement: Added check for meets_ctc_child_identification_requirements to exclude children without valid SSN
3. New tests: Added tests at $15k income and for children without SSN