Add Connecticut refundable child tax credit (HB 5134)

[DTrim99]

Summary

Implements Connecticut HB 5134 (2026 session) as a reform - a refundable child tax credit against the personal income tax.

Bill Reference: https://www.cga.ct.gov/2026/TOB/H/PDF/2026HB-05134-R00-HB.PDF

Credit Details

Parameter	Value
Amount per child	$600
Maximum children	3
Child age limit	Under 18
Income threshold (single/HOH/separate)	< $100,000
Income threshold (joint/surviving spouse)	< $200,000
Refundable	Yes

Files Added

Parameters (parameters/gov/contrib/states/ct/refundable_ctc/):

• in_effect.yaml - Toggle to enable the reform (default: false)
• amount.yaml - $600 per child
• max_children.yaml - Maximum 3 children
• age_limit.yaml - Children must be under 18
• income_threshold.yaml - AGI thresholds by filing status

Reform (reforms/states/ct/refundable_ctc/):

• ct_refundable_ctc.py - Reform logic
• __init__.py - Module exports

Tests (tests/policy/reforms/states/ct/refundable_ctc/):

• ct_refundable_ctc.yaml - 10 comprehensive tests

Test Coverage

• Single filer with children under income limit ✓
• Joint filers under income limit ✓
• Child count capped at 3 ✓
• Income at/over threshold disqualifies ✓
• No children = no credit ✓
• Reform toggle (in_effect) works ✓
• Age limit enforcement (18+) ✓

🤖 Generated with Claude Code

[DTrim99]

Implementation Notes

This reform implements CT HB 5134 as a contributed policy (not enacted law). Key design decisions:

1. Parameters in contrib/: Since this is a proposed bill, all parameters are in gov/contrib/states/ct/ with an in_effect toggle defaulting to false

2. Income eligibility: The bill specifies AGI must be "less than" the thresholds for all filing statuses (strict < comparison)

3. Child definition: Uses is_tax_unit_dependent with an age limit parameter (set to 18) - not tied to federal CTC qualifying child definition

4. Filing status thresholds:

   • JOINT and SURVIVING_SPOUSE: $200,000
   • SINGLE, HEAD_OF_HOUSEHOLD, SEPARATE: $100,000

The reform can be enabled by setting gov.contrib.states.ct.refundable_ctc.in_effect to true in the PolicyEngine interface.

[DTrim99]

Fixes Applied ✅

🟡 Should-Address Issues Fixed

1. ✅ Parameter descriptions updated - All 5 parameter files now use active voice, one-sentence format:

   • amount.yaml: "Connecticut proposed to provide the following refundable child tax credit amount per qualifying child."
   • age_limit.yaml: "Connecticut proposed to set the following age limit for qualifying children under the refundable child tax credit."
   • income_threshold.yaml: "Connecticut proposed to set the following federal adjusted gross income thresholds..."
   • in_effect.yaml: "Connecticut proposed to make the refundable child tax credit effective when this parameter is true."
   • max_children.yaml: "Connecticut proposed to limit the refundable child tax credit to the following maximum number of children."

2. ✅ Removed in_effect check from formula - The in_effect parameter is now handled at the reform registration level (create_ct_refundable_ctc_reform), not in the formula itself. This is the correct pattern for contributed reforms.

3. ✅ Extended end date from 2030 to 2035 - Per user instruction, the parameter modification end date has been extended.

4. ✅ Removed obsolete test - Removed the "Credit is zero when not in effect" test since this behavior is now controlled at the reform registration layer, not the formula.

Note on age_limit parameter

The age limit of 18 is implied by other organization research and House Dem press releases but not stated explicitly in the bill. This is documented but kept in the implementation.

Verification

• ✅ All 9 tests pass locally
• ✅ Code formatted

Ready for re-review.

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[PavelMakarchuk]

@DTrim99 can you resolve the open comments?

[PavelMakarchuk]

Test and closing comments

[DTrim99]

Fixes Applied

🔴 Critical Issues Fixed

• ✅ Resolved uv.lock merge conflict: Merged upstream/main and resolved conflicts
• ✅ Fixed PR variable conflict: Removed duplicate pr_gross_income.py that was causing VariableNameConflictError after merge

🟡 Review Comment Addressed

• ✅ Added computation tree outputs: Added ct_income_tax and household_net_income as outputs to all 9 test cases in ct_refundable_ctc.yaml to verify the computation flows through correctly

Verification

• ✅ All 9 CT refundable CTC tests pass locally
• ✅ Code formatted

🤖 Generated with Claude Code

[DTrim99]

Fixes Applied

🔴 Critical Issues Fixed

• ✅ Rebased onto upstream/main: Incorporated fix from PR Fix CI Fail #7459 to resolve CI failures
• ✅ Resolved uv.lock conflict: Accepted upstream version during rebase

Verification

• ✅ All 9 CT refundable CTC tests pass locally
• ✅ Code rebased and pushed

CI should now pass with the upstream fix included.

🤖 Generated with Claude Code