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Adjudicate the UK spine grain at the ingest/calibration seam #688

Description

@juaristi22

Joint adjudication between workstream E (#145) and workstream D (#623) of the UK-migration master epic #665. Needs resolution before the SPI-channel child of WS-E lands its strata declarations, and before the swap-acceptance child.

The mismatch

The two frozen parity instruments (uk/efrs_parity_reference.json, the 131-column input-mass register) were extracted from the incumbent's enhanced_frs_2023_24.h5 — the pre-clone eFRS: 53,508 households carrying national grossing weights. But the national staging build's --input-h5 is the certified populace_uk_2023.h5 — the post-clone artifact: 535,080 households (10 OA clones each, geography-assigned, at a tenth of the weight), and some gate parameters are tuned to that grain (the zero-weight strata caps of 100,000 = 10,000 SPI-synthetic × 10 clones).

WS-E's port naturally reproduces the pre-clone spine — that is what the incumbent's own build produces before its clone-and-assign step, and the only grain where the frozen references compare apples-to-apples. Decided on the WS-E side: the pre-clone spine is E's canonical product and parity runs there.

To adjudicate jointly with WS-D

  1. Staging input contract. Either (a) keep it unchanged and run clone-and-assign (today D-owned tooling) on the microcosm spine before --input-h5 — pipeline order: E spine → clone → staging gates → calibration; or (b) teach the staging build to accept a pre-clone spine and move cloning after staging — E spine → staging gates → clone → calibration. Option (b) is architecturally cleaner (a national staging artifact has no intrinsic need of clones; clones exist for geography) but reorders D's seam and forces re-deriving every gate parameter tuned at the post-clone grain.
  2. Gate parameters. Strata caps, weight-ratio and ESS thresholds, and the input-mass reference identity are re-derived at whichever grain the staging build consumes.
  3. Clone count as a declaration. The 10-clone factor is currently an environment default in the incumbent and a CLI knob in microcosm; wherever cloning ends up, the factor should be a declared build parameter recorded in the release manifest.

Acceptance

A recorded decision (option a or b), the gate-parameter re-derivation plan at the chosen grain, and the swap-acceptance child unblocked.

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