Restore the SSI countable-resource asset columns via the SCF-wealth stage (#368 Deliverable 2)

[MaxGhenis]

populace #368 Deliverable 2 — restore the SSI countable-resource asset columns

Deliverable 1 (#369) shipped the hard input-coverage gate + SSI reform-coverage smoke, both RED by design on today's asset-less artifacts. This finishes Deliverable 2: it restores bank_account_assets / stock_assets / bond_assets so ssi_countable_resources derives again and the SSI resource-limit reform class scores nonzero — turning both #368 gates green.

What was missing

The scf_wealth stage (packages/populace-build/src/populace/build/us_runtime/scf_wealth.py) was implemented and unit-tested but never invoked by the release builder — the imports and the --scf-summary-extract CLI arg were wired, but with_us_scf_wealth_inputs was not called anywhere. This wires it into base_frame construction (after the SNAP discretionary-exemption stage, before the ACA source outputs), following the established with_us_*_inputs → us_*_signal_gate → raise-on-fail pattern, so the three asset inputs reach export_frame → the input-coverage gate (line 6353) and the reform-coverage smoke (line 6484) both pass.

SCF fetch: fixed HTTP 403 + sha-pinned

fetch_scf_2022_summary_extract failed outright — Federal Reserve econres returns HTTP 403 to urllib's default user-agent. It now sends a browser UA and pins/verifies the SHA-256 of both the zip and the extracted rscfp2022.dta (the build_us_block_ladder_artifact._sha256 provenance convention): a cache hit is reused only when its digest matches, a drifted cache is re-fetched, a mismatched download raises. Digests verified against the Federal Reserve download 2026-07-09:

• scfp2022s.zip → 3bb4d890ae2463ff6039ec7692e375f544dd98a55a37ca2cb2340354b9cc9d80
• rscfp2022.dta → 6b8dd2d935a76ed225ddebc80fb2db22a467f0c80d9a1acaa67b4584aa4bafd1

Acceptance probe — the SSI reform binds again

Imputed the three columns onto the Build H dense frame (_buildh-runtime/.../dense/artifacts/populace_us_2024.h5, 337,704 households / 865,046 persons) via the real stage (with_us_scf_wealth_inputs, seed 0), wrote a release H5, and scored the reforms with policyengine-us 1.764.6 (the Build H engine; dense-native SSI is identical on 1.764.6 and the #356 reference's 1.752.2). Reference class = dense-native f0af251 verified from #356 (TY2026): baseline 8.05M / $63.6B, 42.5% nonzero on assets, $10k/$20k = +$1.60B / +499k, no-limit = +$16.05B / +3.23M.

measure (2026)	before (no assets)	after SCF restore	#356 dense-native ref
ssi_countable_resources nonzero share	0.0%	40.3%	42.5%
SSI baseline	$65.51B / 8.502M	$38.30B / 4.742M	$63.6B / 8.05M
$10k/$20k limit Δ	+$0.00B / +0	+$9.66B / +1.365M	+$1.60B / +499k
no-limit (remove test) Δ	+$0.00B / +0	+$27.22B / +3.761M	+$16.05B / +3.23M

Before restore, ssi_countable_resources is exactly $0 for every record and both reforms score +$0.00B — the #368 failure, probe-reproduced. After restore, countable resources carry signal and the reforms bind: +$9.66B at $10k/$20k clears the $1B reform-coverage floor ~9.7×, so the smoke gate passes. 2024 is consistent (+$9.23B / +$25.90B).

Plausible but above the dense-native magnitude — diagnosed (two documented factors, neither a stage bug)

The reform binds with the right sign and order of magnitude (no-limit +$27.22B is within ~1.7× of the +$16.05B reference), but the $10k/$20k delta runs above +$1.60B and the restored baseline (4.742M) sits below 8.05M. Two compounding causes, both already flagged on #356:

1. Post-hoc overlay without an SSI-target refit. The probe imputes assets onto a frame whose weights were already calibrated with no assets (the SSI caseload was absorbed by the weight solve). Sparse-57k certified release drops SSI asset input columns; SSI resource-test reforms score $0 on bundle 4.18.8 #356 records that populace asset overlays land at baseline 3.0–4.0M / $10k-$20k +$9–26B — this probe's 4.742M / +$9.66B sits squarely in that band, corroborating the imputation is behaving correctly rather than buggily. The stage itself runs in-build, before calibration (the correct location), so a full certified rebuild re-solves the weights with assets present; Sparse-57k certified release drops SSI asset input columns; SSI resource-test reforms score $0 on bundle 4.18.8 #356 notes the restore "must ship with an SSI-target refit."
2. SCF-only vs the retired SIPP+SCF blend. Confirmed from the retired source (policyengine_us_data/utils/asset_imputation.py): the retired pipeline draws these three leaves from a 50/50 SIPP+SCF blend (FINANCIAL_ASSET_SOURCE_SCF_PROBABILITY = 0.5); SIPP supplies the realistic low liquid-asset mass at the bottom. This stage ships the SCF draw only, assigning more liquid wealth to the SSI-marginal population.

The nonzero incidence already matches the reference (40.3% vs 42.5%); the gap is amount + calibration, not the grain. The module docstring records this precisely, and the prior draft's fabricated "the SSI baseline is preserved (verified on the Build H dense frame)" claim is replaced with the measured result. Aligning the magnitude — SIPP blend + SSI-target refit in a full rebuild — is the #356 follow-up.

Tests

• test_us_scf_wealth.py (20 tests): manifest, donor load, sentinel/race mapping, head-carry, determinism, frame integration, signal gate, sha-pinned fetch.
• test_us_fiscal_refresh_builder.py::test_main_writes_diagnostics_...: the full-pipeline main() test now monkeypatches the scf stage consistently with the other stages.
• Full populace-build suite (~1,096 tests) green at PE-US 1.764.6; ruff check . clean (also fixed an unsorted scf export block the salvage left in us_runtime/__init__.py, which would have failed CI lint).

No changelog fragment: populace carries no changelog mechanism (no changelog.d/, no towncrier config), consistent with #369.

Refs #368. Reference and root cause verified against #356 and the retired asset_imputation.py.

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