Slice S0380.24: SAP code 631 → house coal secondary fuel — closes cert 2102 -15.81 → +5e-5

Per SAP 10.2 spec page 165 Table 4a Category 10 (Room heaters), the
600-range secondary-heating SAP codes split by fuel:
  601-613: Gas (mains gas / LPG / biogas) — column A is mains gas.
  621-625: Liquid fuel room heaters (oil / bioethanol).
  631-634: Solid fuel room heaters (open fire, closed room heater
           with/without boiler) — house coal is the modal default.
  691-699: Electric room heaters.

`_elmhurst_secondary_fuel_from_sap_code` previously mapped the entire
601-630 range to mains gas (API code 26). Two bugs:
  1. Codes 621-625 are oil heaters, not gas. (Cohort hasn't surfaced
     an oil-secondary cert yet — deferred until a fixture exercises.)
  2. Codes 631-634 are solid fuel, not gas, and weren't in the range
     at all. Cascade fell through to the secondary-fuel-None default
     (standard electricity at 13.19 p/kWh), over-charging cert 2102's
     "Open fire in grate" secondary by ~£340/yr.

Narrow the gas range to 601-613 (per the spec) and add 631-634 → API
fuel code 11 (Coal in `_ELMHURST_MAIN_FUEL_TO_SAP10`) → Table 32
direct lookup returns 3.67 p/kWh (house coal), matching worksheet
(242) "Space heating - secondary 3585.2401 × 3.6700 = 131.58".

Cohort-2 outcome (38 certs, Summary path):
  exact (<1e-4): 20 → **21**  (+1: cert 2102 -15.81 → +5e-5)
  ±5+:           1 → **0**    (last big-gap closed)

Cert 2102 verified end-to-end:
  - secondary_heating_type=631 → secondary_fuel_type=11 → 3.67 p/kWh
  - Cascade SAP 63.8732 vs worksheet 63.8732 (delta +5e-5)
  - Cascade total fuel cost £787.03 = worksheet £787.03 exactly

Pyright net-zero on both touched files (mapper.py 32→32, test 0→0).

Tests: 703 → 704 pass (+1 new SAP-code-631 secondary-fuel routing
test), 10 expected fails unchanged.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/documents_parser/tests/test_summary_pdf_mapper_chain.py

@@ -313,6 +313,33 @@ def test_summary_001479_secondary_heating_routes_mains_gas_fuel() -> None:
     assert epc.sap_heating.secondary_fuel_type == 26
 
 
+def test_summary_2102_secondary_heating_routes_house_coal_for_open_fire() -> None:
+    # Arrange — cohort-2 cert 2102-3018-0205-7886-5204 §14.1 lodges
+    # "Secondary Heating Code: SAP code 631" — "Open fire in grate"
+    # per SAP 10.2 Table 4a Category 10 (Room heaters), solid fuel
+    # column. Without the per-code routing the cascade defaults to
+    # standard electricity at 13.19 p/kWh and over-charges secondary
+    # heating by ~£340/yr, pushing SAP -15.81 below the worksheet's
+    # 63.87. Worksheet line (242) "Space heating - secondary 3585.24
+    # × 3.6700 = 131.58" confirms house-coal pricing (Table 32 fuel
+    # code 11 = 3.67 p/kWh).
+    cert_dir = Path(
+        "sap worksheets/additional with api 2/2102-3018-0205-7886-5204"
+    )
+    summary_pdf = next(cert_dir.glob("Summary_*.pdf"))
+    pages = _summary_pdf_to_textract_style_pages(summary_pdf)
+    site_notes = ElmhurstSiteNotesExtractor(pages).extract()
+
+    # Act
+    epc = EpcPropertyDataMapper.from_elmhurst_site_notes(site_notes)
+
+    # Assert
+    assert epc.sap_heating.secondary_heating_type == 631
+    # 11 = "Coal" in `_ELMHURST_MAIN_FUEL_TO_SAP10` → Table 32 lookup
+    # returns 3.67 p/kWh (house coal).
+    assert epc.sap_heating.secondary_fuel_type == 11
+
+
 def test_summary_9501_flat_has_no_built_form_in_summary_pdf() -> None:
     # Arrange — cert 9501 (Summary_000784.pdf) is a flat. The Elmhurst
     # Summary's §1.0 "Property type" section lodges the built-form

datatypes/epc/domain/mapper.py

@@ -3350,14 +3350,31 @@ def _elmhurst_secondary_fuel_from_sap_code(
     fitting live effect gas fire") but not the fuel int separately; the
     cascade's `_secondary_fuel_cost_gbp_per_kwh` defaults to standard
     electricity when `secondary_fuel_type` is None — correct for the
-    portable-electric default but wrong for cert 001479's mains-gas fire.
-    Returns 26 (mains gas) for SAP codes in the 600-630 range; None for
-    other codes (cascade default fires, matching cohort 000490 SAP code
-    691 electric panel)."""
+    portable-electric default but wrong for fuel-fired room heaters.
+
+    SAP 10.2 Table 4a Category 10 ("Room heaters") code blocks:
+      601-613: Gas (mains gas / LPG / biogas) — column A is mains gas;
+               column B for LPG. Cohort default is mains gas
+               (`_ELMHURST_MAIN_FUEL_TO_SAP10["Mains gas"] = 26`).
+      621-625: Liquid fuel room heaters (oil / bioethanol). Cohort
+               not yet exercised; deferred until a fixture surfaces.
+      631-634: Solid fuel room heaters (open fire, closed room
+               heater with/without boiler). House coal is the modal
+               default per Table 12 secondary rate (3.67 p/kWh).
+      691-699: Electric room heaters. Cascade default (None) routes
+               to standard electricity (13.19 p/kWh).
+
+    Cohort cert 2102-3018-0205-7886-5204 surfaces the 631 ("Open fire
+    in grate") path — pre-slice the cascade defaulted to electricity
+    at 13.19 p/kWh, over-charging secondary by ~£340/yr and pushing
+    SAP -15.81 below the worksheet's 63.87.
+    """
     if sap_code is None:
         return None
-    if 601 <= sap_code <= 630:
+    if 601 <= sap_code <= 613:
         return 26  # Mains gas, matching `_ELMHURST_MAIN_FUEL_TO_SAP10`
+    if 631 <= sap_code <= 634:
+        return 11  # House coal (Coal in `_ELMHURST_MAIN_FUEL_TO_SAP10`)
     return None