Populate rent (ACS donor) and childcare (CPS ASEC) — close Gate-2 zero-targets

[MaxGhenis]

Summary

Fixes the two largest residual targets on the national Gate-2 surface, both caused by MP exporting a value as $0:

1. nation/census/rent — MP $0 vs ~$735B baseline (the Advance PE rebuild diagnostics and source alignment #1 residual, +0.0017).
2. spm_unit_capped_work_childcare_expense — MP $0 vs ~$348B baseline (docs: core wiring audit for microplex primitives #2, +0.0008).

Together ~14% of MP's residual robust loss after APG calibration.

Rent — always enable the ACS donor

MP already has an ACS source-impute block for rent + real_estate_taxes (the same pair eCPS imputes from ACS), but it was gated by include_acs, so the no-ACS / "eCPS-shaped" build variants dropped it and exported rent=$0.

Per the intended architecture, ACS has two independent controls: ACS-as-spine (multispine, currently disabled) and the ACS donor (must always be enabled). The ACS donor is now always appended in default_policyengine_us_data_rebuild_source_providers. Multispine remains a separate, not-yet-enabled control.

Behavior change: the ACS donor is mandatory — include_donor_surveys=False no longer drops it. The now-dead include_acs parameter and the --include-acs CLI flag are removed entirely (they were no-ops once the donor became mandatory). Provider-assembly tests are updated accordingly.

Childcare — read it from CPS ASEC

eCPS reads childcare straight from the CPS ASEC SPM field SPM_CHILDCAREXPNS; MP never mapped it. Wire SPM_CHILDCAREXPNS -> spm_unit_pre_subsidy_childcare_expenses through the same path as spm_unit_energy_subsidy: the PERSON_VARIABLES rename, the nonnegative + zero-default value-column lists, and the _attach_spm_unit_source_columns aggregation.

PolicyEngine computes spm_unit_capped_work_childcare_expenses (the target) from this input via min(work_expenses + max(pre_subsidy_childcare, 0), earned_cap), so the computed variable is not exported — the frozen export contract excludes it as formula-owned, and exporting it would trip the deep contract gate's extra-column check.

Tests

• test_load_cps_asec_derives_policyengine_value_inputs — extends the SPM_ENGVAL mapping test with SPM_CHILDCAREXPNS (incl. negative→0 clamp).
• test_build_policyengine_entity_tables_preserves_spm_source_inputs — extends the per-person→spm_unit aggregation test with childcare.
• test_build_policyengine_us_export_variable_maps_includes_contract_inputs — guards that childcare reaches the inferred export map (not only tables.spm_units).
• Provider-assembly tests updated for the always-on ACS donor.
• ruff clean; affected unit tests pass.

Review

Independent review-fix cycle run: confirmed the ACS-always-on blast radius is contained, the childcare "first" aggregation and entity routing are correct, and (empirically) the capped target computes non-zero from the exported pre_subsidy input. The one actionable finding (missing export-map guard) is fixed; the dead include_acs param was dropped.

Validation status

Unit-level logic is validated. Numeric validation (rent → ~$735B, childcare → ~$348B in a built artifact) requires a full CPS rebuild and is left to CI / a build run — not exercised locally.

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