Fix Vermont CDCC: TY2022 AGI cap, low-income credit sunset, and pre-2022 24% nonrefundable credit

[hua7450]

Summary

Fixes the three Vermont CDCC divergences confirmed by verbatim reading of the enacted acts (#8879, part of the #8826 state CDCC verification). All three are grounded in the act texts quoted below.

Closes #8879

Regulatory basis

2022 Act 138, Sec. 3 amended 32 V.S.A. § 5828c for TY2022 to read:

"LOW-INCOME CHILD AND DEPENDENT CARE CREDIT — A resident of this State with federal adjusted gross income less than $30,000.00 (or $40,000.00 for married, filing jointly) shall be eligible for a refundable credit… equal to 50 72 percent of the federal child and dependent care credit… provided in this State in a registered home or licensed facility certified by the Agency of Human Services…"

2023 Act 72, Sec. 14 (eff. Jan 1, 2023) rewrote § 5828c without the AGI cap, the certified-facility requirement, or the "low-income" title — matching the current statute.

2022 Act 138, Sec. 2 struck "child care and dependent care credits" from old § 5822(d)(1): "A taxpayer shall be entitled to a credit… of 24 percent of each of the credits allowed against the taxpayer's federal income tax… and child care and dependent care credits." (2021 codified text)

Changes

1. TY2022 AGI cap on vt_cdcc. New income_limit_in_effect boolean (true 2022, false 2023+) gates the 72% credit on the existing vt_low_income_cdcc_eligible AGI test ($30,000, or $40,000 joint — thresholds unchanged from the prior low-income credit). Previously the model paid 72% to all filers from 2022, over-granting above-threshold TY2022 filers.
2. Sunset the 50% low-income credit after 2021 (low_income/rate.yaml → 0 at 2022-01-01) and remove vt_low_income_cdcc from the 2022+ state_cdccs.yaml entries, which double-listed both Vermont credits in the taxsim_state_cdcc aggregate (0.72 + 0.5 × federal for a low-income filer). Tax liability was unaffected (the refundable-credits list was already year-exclusive); the aggregate was not.
3. New vt_nonrefundable_cdcc (§ 5822(d)(1)): 24% of the capped federal credit through 2021, ending 2022 per Act 138 Sec. 2. Low-income-eligible filers are excluded — § 5828c is claimed "in lieu of" the 5822(d) credit, and its 50% refundable match always dominates 24% nonrefundable. Registered in non_refundable.yaml (2021 entry; new 2022 entry drops it) and in the pre-2022 state_cdccs.yaml blocks. Mirrors the sibling vt_elderly_or_disabled_credit, the other modeled leg of the same § 5822(d)(1) match. Previously an above-threshold pre-2022 filer received $0 where law gave 24%.
4. Also adds a 2021-01-01: 0 entry to the 72% rate so pre-2022 queries don't back-extrapolate it, fixes vt_cdcc.py's reference tuple (three URLs were concatenated into one string), and adds missing period: metadata to the touched parameter files.

Not modeled (by design)

What	Source	Why
Certified-facility requirement (pre-2023 § 5828c; pre-2022 § 5822(d) had none)	Act 138 Sec. 3	We don't track provider certification at the moment; noted in code comments
In-state-care requirement	§ 5828c	We don't track where care is provided at the moment

Flagged for review: the 24% § 5822(d)(1) rate is verified for 2021 via Act 138's before-text; continuity back to 2005 (the low-income parameters' start) is assumed and noted in the parameter comment.

Reproductions

Scenario	Before	After
TY2022, AGI $50,000, $1,000 federal CDCC	$720	$0
TY2022, joint, AGI $40,000 (at threshold)	$720	$720
TY2023, AGI $50,000	$720	$720 (cap removed)
TY2021, AGI $50,000 (above low-income threshold)	$0	$240 nonrefundable
TY2021, AGI $20,000	$500 low-income credit	$500 (unchanged; still in lieu of the 24%)
Low-income filer's state-CDCC aggregate, TY2022+	0.72 + 0.5 × federal	0.72 × federal

Tests

Seven new/appended cases covering every row above plus the vt_non_refundable_credits pickup. Full VT income tax tree passes locally: 168 tests.

Independent of #8855/#8878 — no shared files.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (f9e58e7) to head (adff77a).
⚠️ Report is 46 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         2    -1     
  Lines           55        30   -25     
  Branches         0         1    +1     
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- Hits            55        30   -25     

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

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