MO WFTC missing Missouri-specific investment income limit

[hua7450]

Bug

Missouri applies its own investment income limit to the Working Families Tax Credit — far below the federal EITC limit — and PolicyEngine does not model it. mo_wftc_potential is eitc × match with no investment income check (parameters/gov/states/mo/tax/income/credits/wftc/ contains only match.yaml), so only the federal limit ($11,000 TY23 / $11,600 TY24 / $11,950 TY25) applies implicitly.

Missouri's limits per Form MO-WFTC:

Tax year	Limit	Form checklist wording
2023	$4,050	"equal to or greater than $4,050" (Form MO-WFTC 2023)
2024	$4,300	"greater than $4,300" (Form MO-WFTC 2024)
2025	$4,400	"greater than $4,400" (2025 MO-1040 Instructions)

Examples:

• MO filer with $4,401 of taxable interest, 2025 → PolicyEngine pays $192.81 of mo_wftc; the correct amount is $0.
• MO filer with exactly $4,050 of investment income, 2023 → PolicyEngine pays $40.11; the 2023 form checklist disqualifies at "equal to or greater than" $4,050 (but see the boundary note below).

Legal basis

No Missouri statute or regulation states these amounts — RSMo 143.177 never uses the words "investment," "disqualified," "interest," "dividend," or "capital gain," and no implementing CSR rule exists. The chain is:

1. RSMo 143.177.3(1): the credit is a percentage of the federal EITC "as such credit existed under 26 U.S.C. Section 32 as of January 1, 2021" — overriding Missouri's default rolling conformity (RSMo 143.091). https://revisor.mo.gov/main/OneSection.aspx?section=143.177&bid=49978&hl=
2. Pre-ARPA 26 U.S.C. 32(i) denied the EITC when disqualified income "exceeds $2,200," indexed under 32(j) — $3,650 for TY2021 (Rev. Proc. 2020-45). ARPA Sec. 9624 later raised the federal limit to $10,000 indexed, but Missouri's frozen reference keeps the old test.
3. The IRS no longer publishes the pre-ARPA indexed value, so MO DOR computes it each year and publishes it only on the form and its FAQ.

Boundary semantics (needs a decision)

DOR's own publications disagree on the boundary:

Source	2023	2024	2025
Form checklist Q3	">="	">"	">"
Form info page ("cannot exceed")	">"	">"	">"
DOR FAQ	">="	">="	">="
Frozen IRC 32(i) ("exceeds")	">"	">"	">"

The only reading with statutory grounding is strict ">" in all years; the year-to-year flip on the form checklists appears to be DOR drafting inconsistency, not a legal change. Suggest encoding strict ">" uniformly and documenting the discrepancy in a comment. The entire difference is a filer sitting exactly at the limit.

Implementation notes

• Missouri's investment income definition (form p. 2: tax-exempt interest + taxable interest + ordinary dividends + positive capital gain net income, with an IRS Pub 596 Worksheet 1 fallback) is close to but not identical to the federal eitc_relevant_investment_income (which also nets rental/passive income). Reusing the federal variable is the pragmatic choice; document the divergence.
• The parameter cannot be given an uprating — there is no federal source to uprate from. Each year's value only exists once DOR releases the new form, so the parameter needs a new dated value annually.
• The parameter reference should cite the DOR form/FAQ for the values plus RSMo 143.177.3(1) for why the check exists, with a comment noting the statute itself contains no dollar amount.

Related: #9177 (MFS exclusion) shares the same root cause — the frozen IRC Section 32 reference in RSMo 143.177.3(1) is not modeled.