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CONTEXT.md gains Non-Separated / Separated Conservatory glossary terms; ADR-0036 records the mapper-owned §6.1 split + 1:1 persistence + round-trip contract; the migration note lists the five new epc_property columns for the FE schema repo. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
78 lines
4.4 KiB
Markdown
78 lines
4.4 KiB
Markdown
---
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Status: accepted
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---
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# Non-separated conservatory: mapper-owned §6.1 split, persisted 1:1, with round-trip fidelity as the contract
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Decided in a `/grill-with-docs` session (2026-06-24) while fixing the gov-API
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conservatory path (repro cert 718138, `RdSAP-Schema-19.0`). Extends
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[ADR-0015](0015-mappers-own-cert-normalization.md) (mappers own cert
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normalization) and echoes [ADR-0035](0035-coherent-heating-system-synthesis.md)
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(coherence is a synthesis-time obligation, never a calculator normalisation).
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## Context
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The gov register lodges a **Non-Separated Conservatory** (`conservatory_type = 4`)
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as a glazed "building part" carrying only `{floor_area, room_height,
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double_glazed, glazed_perimeter}` — no construction age band, no wall/roof, no
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floor dimensions. Treated as a generic fabric building part it is **mis-scored**
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(its floor heat-loss is counted as a normal part) and **cannot persist** (the
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`epc_building_part` columns `construction_age_band` / `wall_construction` are
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NOT-NULL). The correct RdSAP treatment folds it into the dwelling under §6.1; a
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**Separated Conservatory** (`type 2/3`) is disregarded under §6.2 and lodges no
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glazed part. See CONTEXT.md for both terms.
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Two placements were available for the §6.1 "split" (detect the glazed part, lift
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it out of the fabric parts, carry it as the dwelling's conservatory):
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- in the **mapper**, producing a normalized `EpcPropertyData` with
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`sap_conservatory` set and the glazed part excluded from `sap_building_parts`
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(the existing 21.0.1 choice, commit `d501535c`);
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- at the **calculator / persistence-reload boundary**, re-deriving the split
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each time the picture is scored.
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The production flow is *map → save → reload-from-DB → score*. The mapper split
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alone is invisible to the scored picture, because the reload (`_compose`) did not
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reconstruct `sap_conservatory` and the glazed part was excluded from the
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persisted `sap_building_parts` — so the conservatory was silently dropped on the
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path that actually scores. This is the same latent gap the 21.0.1 fix carried.
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## Decision
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1. **The §6.1 split lives in the mapper.** It is cert-shape knowledge, not
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physics (ADR-0015). `EpcPropertyData` — `sap_conservatory` populated, glazed
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part excluded from `sap_building_parts` — is the canonical normalized shape.
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We do **not** re-derive the split in the calculator or at reload; a global
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coherence pass over the assembled picture is rejected for the same reason
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ADR-0035 rejected one for heating.
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2. **Persist the conservatory 1:1 on `epc_property`.** `SapConservatory` is a
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single optional value per dwelling, so it is five nullable columns on
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`epc_property` (alongside the existing scalar conservatory flags), not a child
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table. Save writes them; `_compose` rebuilds `SapConservatory` from them. The
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columns are FE/Drizzle-owned — documented in
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`docs/migrations/epc-property-round-trip-fidelity.md`, applied there, never by
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this repo.
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3. **Round-trip fidelity is the contract that makes the split correct.** Because
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the split lives only in the mapper, the *only* thing guaranteeing the scored
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(reloaded) picture matches the mapped one is that `EpcPropertyData` survives
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`save → get` unchanged. We treat that as an enforced invariant: the
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deep-equality round-trip test (Model#1129) gains a non-separated-conservatory
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case, and a structural field-coverage guard fails if any `EpcPropertyData`
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field is neither reconstructed by `_compose` nor on a documented allow-list —
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turning "latent until a fixture exercises it" into an explicit decision.
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## Consequences
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- A future reader sees a conservatory — a "building part" in the source —
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persisted as flat columns on `epc_property` and absent from the dwelling's
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building parts. That is deliberate: it is a §6.1 dwelling attribute, not a
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fabric part.
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- The persistence + guard are schema-version-agnostic, so they close the same
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latent gap for the already-merged 21.0.1 path, not only 19.0.
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- The structural guard documents `sap_roof_windows` and the `solar_hw_collector_*`
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fields as known round-trip gaps (their FE columns are tracked follow-ups), so
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they are visible rather than silently dropped.
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- The per-schema mapper piece (declare the four glazed fields + filter + fold)
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still has to be ported to the remaining gov mappers (17.0/17.1/18.0/20.0.0/
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21.0.0) one validated cert at a time; this ADR covers the shared shape, not
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that rollout.
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