Legacy 2023-vintage build of the microcosm UK spine (deferred)

Workstream E of the UK-migration master epic #665; child of #145. Rescoped 2026-08-19 per the vintage decision on #723: the migration now targets FRS 2024-25 directly, so this issue — formerly "FRS 2024-25 refresh after the 2023 swap" — inverts into the deferred option it displaced.

Scope (if ever activated)

Materialize the 2023 vintage from the microcosm pipeline, only if a concrete consumer needs it (e.g., historical comparability against populace_uk_2023 / the June release):

• Pin the FRS 2023-24 tab set (the original E2/U7 audit already did this).
• Run the ingest StagePlan at the 2023 pins; parity against enhanced_frs_2023_24 @ revision 655dd07e… using the originally frozen 2023 parity instruments (preserved in git history at the pre-#723 pins).
• Battery at the 2023-measured baselines.

Where the old E11 scope went

• Re-pin manifests + release-object discipline + tape-year labeling → #723.
• Period alignment of facts to the calibration year → the contract (#707) and target references (#622).
• Calibration-year materialization mechanism → adjudicated with #688 (thin WS-F slice).
• Retirement of hmrc_income_source_stages.json + its lockstep test → follows once #686 signs off at 2024-25 (the June evidence anchor is superseded by the re-frozen pins, not by this issue).

Not on the August path. No owner. Unscheduled — close outright at decommission (WS-J) if no consumer has claimed it by then.

Do not start this issue unless a concrete consumer requests the 2023 vintage. If activated, read the microcosm pipeline and its ingest StagePlan, then review the original E2/U7 audit, the preserved pre-#723 parity instruments, and the 2023 baselines. Done means the pinned 2023-24 materialization passes parity against enhanced_frs_2023_24 and the battery at the stated baselines.