Assemble the microcosm-built UK spine: whole-spine parity and swap acceptance #686

Rescoped 2026-08-19 — the parity vintage is FRS 2024-25. Per the vintage decision recorded on #723, the frozen incumbent reference is now enhanced_frs_2024_25 (survey/base 2024, calibration year 2025, the v1.56.x production line), with the parity instruments, record-count identity, and integrity baselines re-frozen at that vintage by #723. Read the vintage-specific lines below accordingly. The certified 2023 H5 keeps exactly one role here: the control build input for swap acceptance. #630 has since been resolved, satisfying that dependency. Sequence: #681/#682 → #723 (retarget) → #684 → this child. The 2023-vintage build itself is deferred to #687.

Workstream E10 of the UK-migration master epic #665; child of #145. The workstream's exit: the microcosm-built spine replaces the certified incumbent H5 in the national build.

Scope

• One driver path running the full ingest+imputation StagePlan at the scale ladder's rungs (smoke/dev/full), every attempt — pass, fail, or abort — landing a Logbook row.
• Whole-spine parity: candidate extraction (extraction-only mode added to tools/build_uk_efrs_parity_reference.py) diffed against the committed 145-column reference — per-column nonzero-share deltas, entity counts satisfying the record-count identity, missing/extra columns through a signed register. Weighted totals across the 131-column licensed register via --emit-weighted-totals on both sides (reference sha-verified; deltas published SDC-safely). New-spine baselines recorded with the weighted-integrity instrument — these become the candidate thresholds for arming uk_input_mass_parity and uk_qrf_tail_concentration.
• Swap acceptance: a control build (certified H5) and a candidate build (microcosm spine at the grain the joint E/D adjudication settles; verify_certified_uk_candidate extended with a second certified identity — never a bypass). tools/compare_uk_h5_payload.py with a --structure-only verdict mode (same surface; values differ only where signed); the full battery in release-candidate posture; macro_realism declared for the assembled spine.
• Signed-differences register (one committed JSON): every intentional deviation — the CGT weight mechanism, the defect fixes, the RNG-stream class, the QRF-implementation class, net-new columns — with id, magnitude evidence, adjudicator, and date. Anything differing that is not in the register is a defect.
• Calibration-seam rehearsal: the rowwise candidate driver consumes the candidate staging H5, calibrates through the front door, and the battery passes there too.

Acceptance

The WS-E epic bar (#145): the microcosm-built spine replaces the certified incumbent H5 in the national build; eFRS parity fixtures beat or match the incumbent on the frozen register with differences signed; determinism covers every stochastic assignment on the live path. Final calibrated sign-off additionally requires WS-D (#623) landed and #630 adjudicated.

Depends on: E2–E9; the joint E/D spine-grain adjudication; #630 for the release-candidate posture.