US base v2: one CPS+ACS+PUF-detail pool; datasets labeled by exact record count (dense = full pool; exact-k L0 selection)

The acceptance rule (stated once, enforced everywhere)

A candidate release ships iff:

1. It beats the incumbent on the frozen comparison register (same targets, both artifacts rescored on it — never each build's own register), and
2. The invariant battery passes — the codified list of everything the loss cannot see: input-mass parity, tail concentration, effective sample size, band delivery, coverage/degeneracy, spine agreement (new here). Every battery entry was purchased with a specific incident; the battery is versioned, machine-checked in one batched pass, and recorded in both manifests.

Nothing else gates a ship. Adjudications and fences are receipts inside rule 2, not extra rules; the per-arm sprawl this epic retires was rule 2 metastasizing across two lineages. Loss is the objective the optimizer games — it can be rule 1 only because rule 2 checks what it can't say.

The design (ratified direction, 2026-07-29)

One base pool, one lineage, every dataset a record count:

1. Two household spines + one detail channel. CPS-ASEC and ACS PUMS as peer household spines; PUF stays a cloned tax-detail channel on household-shaped shells (PUF records are filers — no household structure — so it cannot be a peer spine; today's puf_tax_detail channel is already this).
2. Dense is not a category — it's k = N. The full pool with no selection, calibrated dense_no_l0.
3. Sparse is not a category — it's an exact record count. Releases are labeled by cardinality (…-k57240, …-k250000, …), and the artifact carries exactly that many households, gate-asserted (len(support) == k). "sparse"/"dense" retire as dataset names; future sizes are just new k values.

Exact-k selection (three stages, all seams existing)

• Stage 1 — L0 to the ballpark, keeping probabilities. The hard-concrete gate machinery (populace-calibrate/gates.py) already yields a per-record open-probability π_i; today we threshold it. Instead, stop at π.
• Stage 2 — certainty units + fixed-size πps draw. Records with π_i ≥ π_hi are force-included (certainty units, standard survey practice); the remaining budget k − |certainty| is drawn from the boundary mass with a fixed-size inclusion-probability-proportional design (conditional Poisson / Sampford), seed pinned in the release manifest. Deterministic given (solve state, seed); no per-target knobs anywhere.
• Stage 3 — the existing frozen-support weight refit + full gate battery. Unchanged (calibrate_l0_refit semantics). Cell-coverage gates catch any unlucky boundary draw; a k below the feasibility floor for the target surface fails loudly, never ships thin.

Why now — the measured defects this must clear (the bar, not a hope)

The buildl ACS-multispine staging (#403; 1.61M households, ASEC+ACS) measured three defects that are the acceptance criteria for increment 2:

1. Spine-conditional agreement. Baseline SSI incidence 2.59% (ACS spine) vs 1.85% (ASEC); $10k/$20k delta $821 vs $433 per baseline recipient. NEW GATE: spine-conditional distributions of transferred inputs must agree (declared tolerance) before calibration is attempted.
2. Effective-support collapse. buildl calibration landed ess_fraction 0.003 (≈4,854 effective of 1.6M) with persons-per-household 1.50 (ASEC) vs 2.93 (ACS). A dense arm that is effectively 5k records is worse than an honest exact-k release. Gate on ess and per-spine composition.
3. Baseline SSI overshoot vs SSA on that surface (no SSI target there then; the v9.x register carries the SSA bands now).

The transfer machinery these gates need did not exist in June and does now: donor joint-vector fidelity (#570's construction assertion + bijection), the deterministic mass-conserving tail-transfer stratum (#568), stage-attributable concentration gating (#571), reviewed-exclusion discipline (#564/#574), and arm-fence receipts in both manifests (#577).

Increments

1. #395 operator ordering — assemble spines first; clone/impute/derive/seed/simulate/calibrate as spine-blind operators downstream. (Existing charter; becomes increment 1 of this epic.)
2. ACS transfer re-run under the #567-era machinery, gated on the #403 defects above (spine-agreement + ess + composition gates).
3. Exact-k selection (stages 1–3 above) from the healthy pool; first ladder: k = N (dense), k ≈ today's 57k contract, and one smaller demo-class k. Spine-aware near-duplicate handling in stage 2 so support composition is not solver noise.
4. Lineage unification: the acs_local overlay (#512) re-bases onto this pool (local = filter/reweight the one national dataset); per-arm adjudication registers re-adjudicate against the unified pool (SSI fences #577, QRF registers, STCG parity #574 all RE-EXAMINED, none carried forward silently).

Non-goals / doctrine carried forward

• No per-target calibration knobs; no loss shaping; gates are never loosened to fit outputs.
• Raw-only doctrine intact: ACS-spine records carry transferred inputs with full provenance; measured frame values untouched.
• Selection is deterministic given the manifest (solve state + pinned seed); the notary/CI split unchanged.
• Release ids state the exact count; nothing labeled "sparse" or "dense" going forward.

Context receipts

• Certified national default today: 57,240 = 35,040 puf_tax_detail clones + 22,200 asec (channel crosstab of the released H5); base pool 352,932 = 184,080 + 168,852 — zero ACS units in either arm; --acs-h5 is input transfer only.
• CD carrying capacity is the motivating example: ~130 households/district on the 57k (47.4% within-10 on the CD surface) vs 65.1% on the full pool.
• Relates: #395 (increment 1), #403 (acceptance bar), #512 (overlay re-base), #567/#577 (dense-arm adjudications to re-examine), #445 (frozen-support discipline), #462/#568/#570/#571 (transfer machinery).

Sequencing: starts after the dense-P3 diagnostic publishes (#567 close-out). Build-Q-scale epic.

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Scope hardening (Max ratified 2026-07-29 evening — this section governs)

1. One suite per country. The separate local-area artifact is RETIRED, not re-based. populace_us_2024_acs_local (and the #512 lane) ends as a product: there is no "local file." Every release of the one pool carries the full geography ladder and geo targets; every file is local — the difference between releases is fidelity, and fidelity is published, not implied by a product name. The k-ladder's scoreboard reports within-tolerance by geography level (national / state / CD) per release, so choosing a k IS choosing a local sample size with its measured consequences in front of you.
2. Record count is the only within-country variation. No sparse/dense, no local/national, no arm names. populace-us-2024-k57240, -k353000, -k5000 — one lineage, one register, one battery, k values.
3. Non-US source tiers (the one extra axis, named by provenance, never by quality). Where a country has a licensed-microdata build and a public-derivable build (UK: FRS-licensed vs the public basis), the tier is named by its spine source license class: proposal populace-uk-2023-frs-k<N> (restricted distribution) and populace-uk-2023-public-k<N>. Rules: the tier token names what the spines are built from, never adjectives ("true", "full"); both tiers run the same register and battery; the public tier's scoreboard shows its fidelity gap to the frs tier as a published number. Tier token per country ratified with that country's onboarding. US ships tierless (single public-safe basis).
4. UK is in scope for the same end state: one UK pool, exact-k ladder, OA-ladder geography on every file, both tiers, same two-line acceptance rule. The UK lineage (June 19 vintage) gets the O/P-era battery and doctrine as part of this epic, not as a separate arc.

Increment 4 is amended accordingly: not "overlay re-base" but overlay retirement — the acs_local consumer surface (policyengine.py named access) migrates to a k-release of the one pool, then the artifact family is closed out with a deprecation note in the bundle manifest.

Start with populace-calibrate/gates.py and the existing calibrate_l0_refit path, then inspect the policyengine.py access named in the scope-hardening section. Trace the machinery referenced in issues #395, #403, and #567–#577 before changing the release flow. Done means the unified exact-k ladder, versioned invariant battery, manifests, and retired local artifact satisfy the stated acceptance rule.