Add CPS-derived recodes: unmarried-partner, SSTB-QBI flag, ESI (G6/G8/G9)

[MaxGhenis]

Summary

Closes four eCPS export-parity gaps so Microplex exports what the Enhanced CPS exports. All four columns are REQUIRED by the frozen eCPS export contract (src/microplex_us/pipelines/ecps_export_contract.json); none are forbidden.

Follows the proven G7 (#125) / social_security_retirement (#121) pattern: map the raw Census field in PERSON_VARIABLES (or compute the leaf in _process_persons), add the leaf to the export surface, and test against the real _process_persons.

Per-column status

Column	Group	Status	eCPS source mirrored
is_unmarried_partner_of_household_head	G8	Closed (real recode)	policyengine-us-data cps.py:190-195, :1219 — perrp.isin({43,44,46,47})
reported_owns_employer_sponsored_health_insurance_at_interview	G6a	Closed (real recode)	cps.py:1576-1578 — NOW_OWNGRP == 1
employer_sponsored_insurance_premiums	G6b	Closed (real imputation)	cps.py:229-273 (impute_employer_sponsored_insurance_premiums) + MEPS-IC 2024 plan priors
sstb_self_employment_income_would_be_qualified	G9	Closed (constant, as eCPS yields)	puf.py:768 — np.where(business_is_sstb, …, False) collapses to False given MP's business_is_sstb=False

All four columns are fully closed — none are backlogged. Every required raw ASEC field (PERRP, NOW_OWNGRP, NOW_HIPAID, NOW_GRPFTYP, PHIP_VAL) is present in the CPS person file MP already downloads (verified against the cached 2023 ASEC: 829 columns, all five present, zero nulls).

Implementation notes

• G8 / G6: raw fields mapped to underscore-staging columns in PERSON_VARIABLES; the bool/float leaves are computed in _process_persons and the staging columns dropped. Leaves added to SAFE_POLICYENGINE_US_EXPORT_VARIABLES.
• G6a is not (yet) a released pe-us input variable, so — exactly like its reported_has_* siblings — its export entity is pinned in POLICYENGINE_US_LEGACY_CONTRACT_VARIABLE_ENTITIES (person). The recode itself is real (NOW_OWNGRP == 1), so the column still carries true per-record values rather than a constant.
• G6b MEPS-IC Table IV.A.1 (2024) plan-type priors are constants eCPS itself hardcodes (not external data), so reproducing them satisfies the "constants only where eCPS uses a constant" rule. The polars port matches the eCPS numpy reference bit-for-bit on the eCPS unit-test fixture.
• G9: MP has no PUF QBI simulation and already exports business_is_sstb=False for every record, so eCPS's np.where(business_is_sstb, self_employment_income_would_be_qualified, False) is False everywhere. Exported as a constant False in POLICYENGINE_US_EXPORT_DEFAULTS — the exact value eCPS emits given MP's inputs, and more correct than the pe-us default_value=True (which would wrongly QBI-qualify all SE income). Consistent with MP's existing QBI-flag default treatment.

def_formula check (pinned pe-us 1.715.3 — the eCPS pin)

Leaf	In pe-us 1.715.3?	def formula	adds/subtracts	Treatment
is_unmarried_partner_of_household_head	yes (Person, bool)	0	0 / 0	plain allowlist
employer_sponsored_insurance_premiums	yes (Person, float)	0	0 / 0	plain allowlist
sstb_self_employment_income_would_be_qualified	yes (Person, bool, default_value=True)	0	0 / 0	plain default (False)
reported_owns_employer_sponsored_health_insurance_at_interview	no (not in any released pe-us)	n/a	n/a	SAFE + legacy-contract person entity

All pe-us-present leaves are storable INPUTs, so none needs a POLICYENGINE_US_DATA_OVERRIDABLE_COMPUTED_EXPORT_VARIABLES entry.

Tests

tests/data_sources/test_cps_employer_insurance_and_partner.py — 14 tests exercising the real _process_persons (no stubbing):

• PERRP recode (incl. adjacent code 45 excluded), boolean dtype
• ESI policyholder recode
• ESI premium reproducing the eCPS reference fixture exactly, plus non-owner / no-employer-contribution / staging-drop / MEPS-prior-constant checks
• Export-config wiring: SAFE membership, no aliasing, legacy person entity, G9 constant False, all four REQUIRED by the contract

tests/data_sources/  →  23 passed
new file              →  14 passed
ruff check            →  All checks passed!

End-to-end on the real 146,133-record 2023 CPS: 3,889 unmarried partners; 39,838 ESI policyholders; 36,033 nonzero ESI premiums (mean ≈ $12,025, capped at the $21,207 family total) — all real, non-degenerate, mirroring eCPS.

Pre-existing microunit/pe-us import failures in this environment are unchanged by this branch (verified: identical pass/fail counts on origin/main).

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