Fix CCDF age group crashing on households with adults

[MaxGhenis]

Summary

Calculating spm_unit_ccdf_subsidy (or ccdf_market_rate, or ccdf_age_group itself) crashed for any household containing a person aged 13 or older. For a Virginia household with two adults (35 and 33) and a 3-year-old, Simulation(situation=...).calculate("spm_unit_ccdf_subsidy", 2026) raised:

ValueError: Invalid value(s) ['0', 'CCDFAgeGroup.PRESCHOOLER'] for enum CCDFAgeGroup. Valid values are: ['INFANT', 'TODDLER', 'PRESCHOOLER', 'SCHOOL_AGE']

The exact text depends on who is listed first. A child listed first gives AttributeError: 'int' object has no attribute 'index', and an adults-only household gives Invalid value(s) ['0']. The state path (va_child_care_subsidies) computed fine; only the federal generic path failed.

Root cause

ccdf_age_group built its result with select(conditions, [CCDFAgeGroup items]) and no default. select here is numpy's np.select, whose default is the integer 0. For every person no condition matched (age ≥ 13, so every adult) the result was an object array mixing 0 with CCDFAgeGroup members.

policyengine-core's Enum.encode takes its Enum-item fast path only when the first element is an Enum. With an adult first, the array is cast to strings ('0', 'CCDFAgeGroup.PRESCHOOLER') and the string lookup rejects both. With a child first, the fast path hits AttributeError on 0.index.

Before policyengine-core 3.22.0 the string path encoded unmatched values as index 0 (INFANT) with no warning, so the adults-first case silently produced INFANT for adults and, because str(CCDFAgeGroup.PRESCHOOLER) is not a member name, for the children too. Core 3.22.0 added a warning and 3.23.0 (December 2025) made it raise. This repo requires core ≥ 3.30.1, which is what surfaced the bug. The child-first ordering has always raised.

Fix

Drop the redundant age < 13 branch and give the select an explicit default=CCDFAgeGroup.SCHOOL_AGE. Children under 13 get the same answer as before (verified over a dense age grid for both home-based and center-based care). Anyone 13 or older (the CCDF age limit in gov.hhs.ccdf.age_limit) now resolves to SCHOOL_AGE instead of an unencodable 0. is_ccdf_age_eligible already screens them out of the subsidy, so no subsidy amount changes for eligible children. in_ccdf_age_group already uses this pattern.

Tests

• ccdf_age_group.yaml: age 13 boundary, an adult, and a mixed adult/preschooler household with the adults listed first.
• New integration.yaml: the reported Virginia household (computes, subsidy 0 with no childcare hours) and a Nassau County household with a preschooler in full-time center care ($310/wk × 52 = $16,120 market rate, $3,536 copay, $12,584 subsidy).
• All 71 tests under policyengine_us/tests/policy/baseline/gov/hhs/ccdf pass. All 5 new cases fail on unfixed main (04a961a) with the same ValueError: the three mixed-household cases with the exact message above, the two single-person cases with Invalid value(s) ['0'].
• A 55-person vectorised simulation with adults first across five states computes the whole chain without error.

Related

• Remove the inert New York-data federal CCDF path (part 1 of #9355) #9401 (commit 1 of Remove the inert federal CCDF implementation #9355, split out) deletes this whole path; if it lands first, this PR closes. Issue Remove the inert federal CCDF implementation (New York data under gov/hhs/ccdf) #9283 and PR Remove the inert federal CCDF implementation #9355 propose deleting the federal (legacy New York) CCDF path as inert; Clean up NY-specific federal CCDF variables and parameters #7766 is the older tracking issue. This fix is small and self-contained so the crash stops for anyone calling these variables today. If Remove the inert federal CCDF implementation #9355 lands first, this PR can simply close. If this lands first, Remove the inert federal CCDF implementation #9355 needs a rebase that also deletes the new integration.yaml.
• Swept every Enum-valued variable for select calls without a default keyword: 111 calls, 5 without it. Three are exhaustive by construction (pell_grant_household_type, state_filing_status_if_married_filing_separately_on_same_return, age_group) and il_personal_exemption_eligibility_status passes its default positionally. md_ccs_service_unit would hit the same failure only for negative or NaN childcare hours, which its bracket maps to unit 0; left for a follow-up.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (e21799b) to head (c7c4c8c).
⚠️ Report is 15 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #9400   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files            3         1    -2     
  Lines           33        18   -15     
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- Hits            33        18   -15     

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[MaxGhenis]

Superseded by #9401, which removed ccdf_age_group and the rest of the legacy New York CCDF path outright (merge commit f627b0b). The crash this PR fixed no longer has a file to live in.