Head-of-household filer-share untargeted; HoH-repeal has no external anchor to validate against

Surfaced on the RCC dashboard's Build P validation refresh: https://github.com/PolicyEngine/refundable-credit-conversion/pull/72

Observation

The RCC head_of_household toggle applies gov.contrib.congress.romney.family_security_act.remove_head_of_household, which reassigns HoH filers to SINGLE. Modal endpoint on policyengine 5.0.1 bundling populace-us-2024-buildp-sparse-rmloss100-cae8640-20260728T011454Z:

Two gaps:

1. No published HoH-repeal revenue benchmark — the RCC validation row ships with externalBillions: null and no diff can be computed. QBI, ALD, OBBBA all have JCT/CBO comparators; HoH does not.
2. No HoH filer-share target in populace calibration — zero hits for head_of_household, hoh, or filing_status substring in Build P's calibration_diagnostics.json (5,659 targets). HoH filer share is therefore wholly inherited from the donor CPS/PUF distribution with no target-side correction.

Whether the $9.4B is right, low, or high is unknowable with the current setup.

Ask

1. Add a HoH filer-count / mass target so the share is anchored. Candidate source: IRS SOI Publication 1304 Table 1.2 (returns by filing status).
2. Identify a published HoH-repeal benchmark to slot into the RCC validation surface and #535's repeal_revenue_benchmarks.json. Candidates worth checking:
   • Romney Family Security Act scoring (JCT ad-hoc for §102(b)(2)(A))
   • Tax Foundation options briefs
   • CBO Budget Options — the 2018 volume scored "Eliminate Head of Household Filing Status"; unclear whether 2024/2025 volumes re-scored.

Reproducer

reform = {
    "gov.contrib.congress.romney.family_security_act.remove_head_of_household":
        {"2026-01-01.2100-12-31": True},
}
# expected: ??? (no published anchor)
# observed on Build P (Modal endpoint, PE 5.0.1): $9.4B

Refs

• RCC validation surface refresh: refundable-credit-conversion#72
• Per-component repeal-revenue surface: #535

Start with Build P's calibration_diagnostics.json and the RCC validation refresh in refundable-credit-conversion#72, then inspect #535's repeal_revenue_benchmarks.json. Check IRS SOI Publication 1304 Table 1.2 and the listed JCT, Tax Foundation, and CBO sources for filing-status and HoH-repeal anchors. Done means a HoH target is added and a defensible published benchmark is integrated into the validation surfaces.