UK dataset build: full migration from policyengine-uk-data (master epic)

Goal

Migrate the UK dataset build fully from policyengine-uk-data into microcosm, at parity, then archive policyengine-uk-data (the policyengine-us-data precedent). End state: policyengine-uk consumes only microcosm-built datasets — national default, sparse default, and the local variant — calibrated exclusively from chronicle facts.

This epic supersedes #144, which tracked the same goal as a flat backlog.

Architecture invariants

• Frame is the carrier through every stage; calibration is rowwise via the microcosm.calibrate front door.
• Country package = pure JSON specs (build/uk/), executed by shared runtimes; Python in uk_runtime/ migrates toward specs (#159).
• Target values come only from pinned chronicle consumer artifacts; computed targets (uprating, rate×count, splits) are explicit microcosm-side declarations.
• Scope ruling carried from #144 (2026-07-24): the build is based solely on raw microdata, ledger facts, and the rules engine (plus inflation/aging updates) — no inheritance of processed artifacts whose generating code stays behind in uk-data.
• No stage ships degraded: fail-closed plan, closed-world gate entries, evidence_absent over invented passes.
• Every build attempt — including failed rungs and discarded candidates — appends a hash-chained Logbook row (#628), so the migration's intermediate-build history stays reconstructible.
• Never import policyengine_uk_data — port definitions, don't wrap them.

Phases

Workstreams

• A — Unblockers: #663, #630, #609, #654, #636, #666 (UK Logbook adoption), UK CI lane (to be filed)
• B — Facts to chronicle: PolicyEngine/chronicle#133, PolicyEngine/chronicle#134, PolicyEngine/chronicle#135
• C — National targets from facts: #622
• D — National calibration seam: #623, #736
• E — Raw-source ingest + imputations: #145 (children #677–#688 + #723 vintage retarget; E1–E4+E7 landed; vintage decision 2026-08-19: parity vs enhanced_frs_2024_25)
• F — Uprating / multi-year: #148
• G — Local areas (rowwise): #495 (children: #146, #147)
• H — Sparse national default: #355
• I — Release + downstream integration: tracking issue to be filed when the workstream spins up (includes a policyengine-uk child issue for loader consumption)
• J — Decommission: tracking issue to be filed when the workstream spins up

Related, non-blocking: #365, #31, #552/#364/#467, #180, #325, Logbook epics #637/#641 (workstream H publication surface), #661 (diagnostics carry chronicle package IDs — workstream D), naming cleanups #639/#640/#737.

Carried-over uk-data backlog

policyengine-uk-data stayed active after #144's June bookkeeping and accumulates new issues — 5 open as of 2026-08-12: PolicyEngine/policyengine-uk-data#438 (stale public-transfer feed, state pension ≡ £0 → workstream F/#148), PolicyEngine/policyengine-uk-data#448 (Scottish/Welsh council tax +20–30%, WAS owned_land instability → E and C/D), PolicyEngine/policyengine-uk-data#450 (UC deduction attributes imputation → E, new stage), PolicyEngine/policyengine-uk-data#452 (UC caseload ~40% below admin counts → D/E), PolicyEngine/policyengine-uk-data#453 (unsourced mortgage target → B, already a recorded chronicle blocked source). Dispositions live in the roadmap doc's Appendix B; workstream J re-sweeps the live list at decommission time.

Sequencing notes

• C/D deliberately run on the existing certified spine first: prove facts→targets→calibration→gates at parity before any ingest work, then E swaps the spine underneath a fixed harness.
• E (microcosm-side) and wave 3 (chronicle-side) parallelize; G needs both.
• H needs only D + schema-4 verification — the exact-k machinery is country-agnostic.
• The incumbent keeps releasing until I completes; every incumbent refresh widens the parity bar.

Read build/uk/ and uk_runtime/ first, then trace the microcosm.calibrate front door and the certified-spine and gate workflow. Review the pinned chronicle consumer artifacts and Logbook requirements before choosing a phase or workstream. Done means policyengine-uk consumes only microcosm-built national and local datasets at parity, with failed builds recorded and policyengine-uk-data ready for archival.