Slice 49: Summary_000490 chain pins SAP at 1e-4; secondary heating + RdSAP sheltered-sides

Two mapper extensions, both validated by 000490 closing to 1e-4:

1. Secondary heating extraction. Elmhurst Summary PDFs lodge the
   secondary heating SAP code in the §14.1 Main Heating2 sub-section
   (between "14.1 Main Heating2" and "14.1 Community Heating") — not
   in the §14.0 Main Heating1 block where the main system lives.
   `ElmhurstMainHeating` gains a `secondary_heating_sap_code` field;
   the extractor reads it from the right section; the mapper threads
   it through to `SapHeating.secondary_heating_type`. The cascade
   then applies Table 11's 10% secondary fraction.

2. Sheltered-sides derivation per RdSAP §S5. The Summary PDF doesn't
   lodge per-dwelling sheltered-sides; the value is derived from
   built-form (Detached=0, Semi-Detached=1, End-Terrace=1, Mid-
   Terrace=2, Enclosed Mid-Terrace=3, Enclosed End-Terrace=2).
   `_map_elmhurst_ventilation` now takes built_form and populates
   `SapVentilation.sheltered_sides`. The table is cross-checked
   against U985-0001-NNNNNN.pdf line (19) across the 6 worksheet
   fixtures.

Cohort SAP deltas after this slice (target 1e-4):

  000474   0.0000  ✓ Slice 47
  000477  +2.6555     diagnosis pending (lighting bulb count diff)
  000480  +4.1955     diagnosis pending
  000487  +4.4553     extractor still drops most windows
  000490   0.0000  ✓ THIS SLICE
  000516  +1.5162     roof-window separation

Pyright net-zero on touched files (35 errors, same baseline). 755
tests pass (up from 754 — new `test_summary_000490_full_chain_sap_
matches_worksheet_pdf_exactly`).

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

backend/documents_parser/elmhurst_extractor.py

@@ -764,6 +764,20 @@ class ElmhurstSiteNotesExtractor:
         lines = self._section_lines("14.0 Main Heating1", "14.1 Main Heating2")
         pct_raw = self._local_val(lines, "Percentage of Heat")
         pct = int(pct_raw.split()[0]) if pct_raw else 0
+        # The "Secondary Heating SapCode" key is lodged inside §14.1 Main
+        # Heating2 — Elmhurst uses the Main-2 block to also carry the
+        # cert's secondary heating system (when one exists). Look for it
+        # in that section; absence (or "0") means no secondary lodged.
+        secondary_lines = self._section_lines(
+            "14.1 Main Heating2", "14.1 Community Heating"
+        )
+        secondary_raw = self._local_val(secondary_lines, "Secondary Heating SapCode")
+        secondary_code = (
+            int(secondary_raw)
+            if secondary_raw is not None and secondary_raw.isdigit()
+            and int(secondary_raw) > 0
+            else None
+        )
         return MainHeating(
             heat_emitter=self._local_str(lines, "Heat Emitter"),
             fuel_type=self._local_str(lines, "Fuel Type"),
@@ -775,6 +789,7 @@ class ElmhurstSiteNotesExtractor:
             percentage_of_heat=pct,
             pcdf_boiler_reference=self._local_val(lines, "PCDF boiler Reference"),
             heat_pump_age=self._local_val(lines, "Heat pump age"),
+            secondary_heating_sap_code=secondary_code,
         )
 
     def _extract_meters(self) -> Meters:

backend/documents_parser/tests/test_summary_pdf_mapper_chain.py

@@ -39,6 +39,7 @@ from domain.sap.rdsap.cert_to_inputs import SAP_10_2_SPEC_PRICES, cert_to_inputs
 
 _FIXTURES = Path(__file__).parent / "fixtures"
 _SUMMARY_000474_PDF = _FIXTURES / "Summary_000474.pdf"
+_SUMMARY_000490_PDF = _FIXTURES / "Summary_000490.pdf"
 
 
 def _summary_pdf_to_textract_style_pages(pdf_path: Path) -> list[str]:
@@ -136,3 +137,24 @@ def test_summary_000474_full_chain_sap_matches_worksheet_pdf_exactly() -> None:
     # Elmhurst exactly and we expect identical outputs.
     worksheet_unrounded_sap = 62.2584
     assert abs(result.sap_score_continuous - worksheet_unrounded_sap) < 1e-4
+
+
+def test_summary_000490_full_chain_sap_matches_worksheet_pdf_exactly() -> None:
+    # Arrange — cert U985-0001-000490 is an end-terrace with main +
+    # 1st extension. The worksheet PDF lodges unrounded SAP 57.3979.
+    # End-terrace built-form drives sheltered_sides=1 (RdSAP §S5) and
+    # the cert's Summary §14.1 Main Heating2 sub-section carries a
+    # secondary heating SAP code (691, electric panel) — both required
+    # for the mapped chain to reproduce the worksheet to 1e-4.
+    pages = _summary_pdf_to_textract_style_pages(_SUMMARY_000490_PDF)
+    site_notes = ElmhurstSiteNotesExtractor(pages).extract()
+    epc = EpcPropertyDataMapper.from_elmhurst_site_notes(site_notes)
+
+    # Act
+    result = calculate_sap_from_inputs(
+        cert_to_inputs(epc, prices=SAP_10_2_SPEC_PRICES)
+    )
+
+    # Assert
+    worksheet_unrounded_sap = 57.3979
+    assert abs(result.sap_score_continuous - worksheet_unrounded_sap) < 1e-4

datatypes/epc/domain/mapper.py

@@ -320,7 +320,7 @@ class EpcPropertyDataMapper:
             number_of_storeys=survey.number_of_storeys,
             hydro=survey.renewables.hydro_electricity_generated_kwh > 0,
             photovoltaic_array=survey.renewables.photovoltaic_panel != "None",
-            sap_ventilation=_map_elmhurst_ventilation(survey.ventilation),
+            sap_ventilation=_map_elmhurst_ventilation(survey.ventilation, built_form),
             percent_draughtproofed=survey.draught_proofing_percent,
             waste_water_heat_recovery=(
                 "None" if not survey.renewables.wwhrs_present else "Present"
@@ -2302,10 +2302,36 @@ def _map_elmhurst_sap_heating(survey: ElmhurstSiteNotes) -> SapHeating:
             else survey.water_heating.water_heating_code
         ),
         water_heating_code=survey.water_heating.water_heating_sap_code,
+        secondary_heating_type=mh.secondary_heating_sap_code,
     )
 
 
-def _map_elmhurst_ventilation(v: ElmhurstVentilation) -> SapVentilation:
+# RdSAP §S5 — default sheltered-sides count for each built-form code,
+# applied when the cert doesn't lodge a per-dwelling value (Elmhurst's
+# Summary PDF doesn't). The cohort uses the RdSAP convention: terraces
+# pick up exposure-shielding from neighbours; detached/semi-detached
+# don't. Values cross-checked against U985-0001-NNNNNN.pdf line (19)
+# across the 6 Elmhurst worksheet fixtures.
+_ELMHURST_SHELTERED_SIDES_BY_BUILT_FORM: Dict[str, int] = {
+    "Detached": 0,
+    "Semi-Detached": 1,
+    "End-Terrace": 1,
+    "Mid-Terrace": 2,
+    "Enclosed End-Terrace": 2,
+    "Enclosed Mid-Terrace": 3,
+}
+
+
+def _elmhurst_sheltered_sides(built_form: str) -> Optional[int]:
+    """Default sheltered-sides count per RdSAP §S5 based on the cert's
+    built-form. Returns None when the form isn't recognised so the
+    cascade applies its own default (currently 2)."""
+    return _ELMHURST_SHELTERED_SIDES_BY_BUILT_FORM.get(built_form)
+
+
+def _map_elmhurst_ventilation(
+    v: ElmhurstVentilation, built_form: str
+) -> SapVentilation:
     return SapVentilation(
         ventilation_type=None,
         draught_lobby=v.draught_lobby != "Not present",
@@ -2318,4 +2344,5 @@ def _map_elmhurst_ventilation(v: ElmhurstVentilation) -> SapVentilation:
         passive_vents_count=v.passive_vents_count,
         flueless_gas_fires_count=v.flueless_gas_fires_count,
         ventilation_in_pcdf_database=None,
+        sheltered_sides=_elmhurst_sheltered_sides(built_form),
     )

datatypes/epc/surveys/elmhurst_site_notes.py

@@ -140,6 +140,11 @@ class MainHeating:
         None  # e.g. "17742 Potterton, Promax 33 Combi ErP, 88.30%"
     )
     heat_pump_age: Optional[str] = None
+    # Section 14.0 also lodges a secondary heating system (when one is
+    # installed). The SAP code is the integer the cascade reads via
+    # `SapHeating.secondary_heating_type` to apply the Table 11
+    # secondary-fraction split; None when no secondary is lodged.
+    secondary_heating_sap_code: Optional[int] = None
 
 
 @dataclass