Impute US humanitarian immigration statuses to cited stocks (H.R.1 channels)

[MaxGhenis]

Fixes #767.

Implements the design proposed in the issue thread, plus one follow-on redesign of the spill controls (Aug 29, "Align immigration controls with Pew methodology") that this description now reflects. The US immigration_status source stage draws humanitarian/temporary-protection statuses to externally cited stocks, so the enacted H.R.1 eligibility channels stop computing ≈$0 on the next build.

What changes

Humanitarian draws (us_runtime/immigration.py). Between the ASEC-UA legal-status indicators and the EAD spill, thirteen seeded draws run — sequential, mutually exclusive, in decreasing order of target precision:

• PAROLED_ONE_YEAR per program origin: OAW Afghans (73,566), U4U Ukrainians (158,000), CHNV Nicaraguans (93,070) and Venezuelans (117,330), with program-specific arrival windows (U4U/CHNV cannot draw from the 2020–21 bin);
• REFUGEE (160k ≈ FY2023+FY2024 OHSS admissions) and ASYLEE (155k ≈ FY2022–24 OHSS grants as revised) from the indicator-documented pool only;
• TPS per country from the CRS RS20844 table (Venezuela 605,015; El Salvador 170,125 with the 2001 continuous-residence cutoff binding at PEINUSYR granularity; Honduras/Nicaragua/Nepal/other-designated likewise);
• DEPORTATION_WITHHELD carries an explicit cited zero (EOIR grants ~2.2k/year and publishes no stock).

Cuba/Haiti-born are excluded everywhere (the CUBAN_HAITIAN_ENTRANT class is the statutorily favorable label H.R.1 preserves — Haiti TPS rides it), as is the DACA statutory cohort; Ukraine/Afghanistan TPS registrants are carried by the parole draw. Residual-pool draws (parole/TPS only) flip ssn_card_type NONE → NON_CITIZEN_VALID_EAD, preserving the NONE ⇔ UNDOCUMENTED gate invariant.

Spill controls re-founded on Pew's universe. Pew's 2025 report supersedes the earlier series with a coherent 2023 pair — 14.0M unauthorized immigrants, 9.7M in the labor force — whose modeled universe deliberately retains DACA, parolees, TPS holders and similar temporary protections (and excludes refugees and granted asylees). The worker/student EAD spills now bind that broad universe rather than the bare residual pool: residual undocumented rows, DACA and residual-cohort Cuban/Haitian rows that keep protected engine labels after an EAD, and the Pew-included humanitarian marks. The worker margin uses measured current labor-force status (A_LFSR, age 16+) restored from the pinned Census ASEC archives by exact PERIDNUM join (checkpoint schema v4) instead of prior-year earnings. The composition gate anchors the same broad universe against 14.0M — identifying residual-derived entrants by the (CUBAN_HAITIAN_ENTRANT, NON_CITIZEN_VALID_EAD) pair, which is exactly the set the spill counts, since indicator-documented entrants carry OTHER_NON_CITIZEN.

Manifest, spec, attestations. Every target lives in source_stages.json with one citation per number (URLs verified live, the DHS OAW/U4U reports by exact byte match); the sources schema gains the required humanitarian_status_stocks block; thirteen _stable_site declarations join the seed protocol with owner-ledger bindings; every closed-world census the fail-closed machinery keeps (site counts, owner links, field universe, pointer claims, inventory digests, envelope digests, coverage evidence) is re-pinned on the merged tree.

Gates & probes. The composition gate bands each category's emitted mass against its cited target (explicit-zero categories must emit zero) and records achieved-vs-target for certification notes. Four release-blocking reform-coverage probes pin the channels end-to-end — restoring the pre-H.R.1 Medicaid list (§71109, 2027), the below-FPL PTC exception (§71302, 2026), the ACA lawful-presence list (§71301, 2027), and the pre-§10108 SNAP list (2026) must each move their budget measure on the export, binding only through immigration_status_str.

Evidence (raw 2024 ASEC, seed 0, merged tree)

category	weighted	ratio to target
PAROLED_ONE_YEAR	372k	0.84 (Ukraine pool saturates; 2020–21 bin excluded for U4U/CHNV)
REFUGEE	129k	0.81
ASYLEE	156k	1.00
TPS	865k	1.01
DACA	371k	— (restored; the earlier draft eroded it)
UNDOCUMENTED	12.90M	—
Pew broad universe	14.71M	1.05× the 14.0M anchor
Pew labor force	9.698M	binds the 9.7M control

CHIP-age humanitarian mass is present (TPS under-19: 118k weighted). test_us_hr1_immigration_channels.py proves each probe's channel on synthetic households against the locked engine (all sign-correct from $0 baselines); nine further tests cover the Pew-universe spill, A_LFSR measurement, entrant retention, and gate inclusion/exclusion. CI was green across the full 23-job tiered matrix at 96c88e6; this push re-runs it on current main.

Deliberately out of scope (filed)

• US: store years_since_us_entry from PEINUSYR (blocked on engine ICHIA option) #776 — store years_since_us_entry (blocked on the engine's CHIPRA-214/ICHIA option).
• Verification/redetermination churn flag surface (option 2 of #767, generalized) #777 — verification/redetermination churn flag surface (the surviving generalization of the issue's option 2).
• Add the CHIP §71109 reform-coverage probe when the engine encodes it (pe-us#9346) #778 — CHIP probe once policyengine-us#9346 lands.

No certified release is touched; the imputation activates in the next build lane, where the smoke gate enforces the four channels permanently.

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