User clarified end-of-session: mapper is a thin enum-and-shape
translation; when residuals remain after closing mapper coverage
gaps, the gap is in the **calculator cascade**. This unlocks an
Elmhurst-only fixture path that doesn't need API JSON at all.
The fixture shape mirrors the 6 historical Elmhurst U985 fixtures
(000474, 000477, 000480, 000487, 000490, 000516) at
`domain/sap10_calculator/worksheet/tests/_elmhurst_worksheet_NNNNNN.py`
+ `test_e2e_elmhurst_sap_score.py`:
build_epc() → cert_to_inputs → calculate_sap_from_inputs
↳ every SapResult field pinned at abs=1e-4 against U985 line refs
Any failing pin is definitionally a calculator bug. The user generates
certs in Elmhurst SAP and exports Summary + worksheet ZIPs — no gov.uk
EPB lodgement required.
Extended test case (000565) ready at `sap worksheets/extended test case/`:
- Summary_000565.pdf (input)
- U985-0001-000565.pdf (worksheet ground-truth)
Cert 000565 is a wacky stress-test that exercises 3-4 zero-coverage
cascade paths in one cert: Main + 4 extensions, age mix A through J,
RR on every part with mixed ages, conservatory with fixed heaters,
curtain-wall Ext2 post-2023, mixed wall types (solid brick + stone +
curtain wall), mixed party walls (CU + CF + Unable to determine).
After this cert lands, the user has agreed to generate single-feature
certs (oil only, LPG only, solid fuel only, electric direct only,
multi-main-heating, basement) to surface single-cause calculator gaps.
Handover doc now has implementation outline (mirror
_elmhurst_worksheet_000474.py shape) and a coverage-paths table
showing which targets each fuel-type/config exercises.
Captures the per-cert validation state at HEAD b7fbbcca:
- 5 slices shipped this session: cost cascade β-split (.47), schema
gap closure for real-API battery_capacity (.48), Table 12e
effective-monthly PE factor for PV (.49), §4 seasonal HW for PV β
cascade (.50), UnmappedApiCode strict-raise pattern on API mapper
(.51).
- 769 pass + 0 fail across the full baseline; pyright net-zero on
every touched file.
Crucial finding for the next agent: cohort-2 (38 certs) is chain-
tested at 1e-4 SAP vs worksheet but NOT in test_golden_fixtures.py
— PE/CO2 cascades have NO regression guard. Probed at HEAD:
14/38 cohort-2 certs have non-trivial PE residuals invisible to any
current test, including cert 2102 at +20.4 PE / -0.79 CO2 (single
worst undetected residual in the cohort).
Agreed next slice: add all 38 cohort-2 certs to
test_golden_fixtures.py with current PE/CO2 pinned. Surfaces cert
2102 as the next closure target (worksheet exists under
`sap worksheets/`) and creates PE/CO2 regression guards across the
worksheet-backed cohort.
Open threads ranked by tractability:
- Cert 2102 +20.4 PE — worksheet exists, well-scoped
- PV (233a)+(233b) monthly mystery — documented memory entry; ~0.5
kWh/m² across ASHP cohort
- _api_glazing_transmission strict-raise extension — mechanical
- 8 open-front golden certs (oil + RR) at high residuals — blocked
on worksheets
Fuel-type diversity guidance: heating system breakdown across all
60+ fixtures shows 34 gas, 20 ASHP, 2 oil (both open-front no
worksheets), 0 solid fuel, 0 LPG, 0 electric direct. Closure on
oil + solid fuel + LPG + electric blocked on worksheet availability
— the gov.uk EPB downloads UI returns API JSON only; dr87 worksheets
come from the assessor's tool (typically Elmhurst SAP) export ZIP.
Handover doc at docs/HANDOVER_GOLDEN_COVERAGE.md.
