Map RdSAP 20.0.0 certs that omit reduced fields or lodge localised text 🟩

Required->optional defaults (kw_only + data-driven from corpus presence) so
993/1000 certs that omit sap_windows parse, and honest Union[str, DescriptionV1]
typing for description/dwelling_type which the corpus lodges as localised dicts
in ~half the certs. The never-run 20.0.0 mapper path now produces EpcPropertyData;
974/1000 corpus certs map (xpass), up from 7.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

datatypes/epc/domain/mapper.py

@@ -1081,7 +1081,12 @@ class EpcPropertyDataMapper:
             uprn=schema.uprn,
             assessment_type=schema.assessment_type,
             sap_version=schema.sap_version,
-            dwelling_type=schema.dwelling_type,
+            # ADR-0027: 20.0.0 lodges dwelling_type as str OR localised dict.
+            dwelling_type=(
+                schema.dwelling_type
+                if isinstance(schema.dwelling_type, str)
+                else schema.dwelling_type.value
+            ),
             property_type=str(schema.property_type),
             built_form=str(schema.built_form),
             address_line_1=schema.address_line_1,

datatypes/epc/domain/tests/test_from_rdsap_schema.py

@@ -1131,3 +1131,49 @@ class TestApiRoofConstructionCode:
 
         # Assert
         assert result == "Pitched, sloping ceiling"
+
+
+# ---------------------------------------------------------------------------
+# Schema 20.0.0 — Reduced-Field Synthesis (ADR-0027)
+#
+# RdSAP 20.0.0 is a pre-SAP10 reduced-data schema: it records as categories or
+# aggregates the measured fields the calculator needs (a glazed_area *band*, not
+# window m²; bath/shower *room counts*, not bath counts). The mapper synthesises
+# the measured form from the cert alone (no neighbour data). Each test name
+# encodes the synthesis ASSUMPTION it pins, because a pre-SAP10 cert has no
+# same-spec lodged figure to validate against (Validation-Cohort rule).
+# ---------------------------------------------------------------------------
+
+_CORPUS_20_0_0 = os.path.join(
+    os.path.dirname(__file__),
+    "../../../../backend/epc_api/json_samples/RdSAP-Schema-20.0.0/corpus.jsonl",
+)
+
+
+def _load_20_0_0_corpus() -> list[Dict[str, Any]]:
+    if not os.path.exists(_CORPUS_20_0_0):
+        return []
+    with open(_CORPUS_20_0_0) as f:
+        return [json.loads(line) for line in f if line.strip()]
+
+
+class TestRdSap20_0_0ReducedFieldSynthesis:
+
+    def test_cert_omitting_sap_windows_maps_without_missing_required_field(
+        self,
+    ) -> None:
+        # Arrange — 993/1000 corpus certs omit `sap_windows` entirely; the
+        # placeholder schema declared it required, so every one failed to parse.
+        # Required→optional (default []) must let them through.
+        corpus = _load_20_0_0_corpus()
+        if not corpus:
+            pytest.skip("no RdSAP-Schema-20.0.0 corpus harvested")
+        cert = next((c for c in corpus if "sap_windows" not in c), None)
+        if cert is None:
+            pytest.skip("no corpus cert omits sap_windows")
+
+        # Act
+        result = EpcPropertyDataMapper.from_api_response(cert)
+
+        # Assert
+        assert isinstance(result, EpcPropertyData)

datatypes/epc/schema/rdsap_schema_20_0_0.py

@@ -1,20 +1,24 @@
-from dataclasses import dataclass
+from dataclasses import dataclass, field
 from typing import List, Optional, Union
 
-from .common import Measurement
+from .common import DescriptionV1, Measurement
 
 
 @dataclass
 class EnergyElement:
-    # description is a plain string in schema 20.0.0 onwards (no longer a localised object)
-    description: str
+    # ADR-0027: the corpus lodges description as EITHER a plain str OR a
+    # localised {value,language} dict (DescriptionV1) — not str-only as a
+    # one-example placeholder assumed. Union so _coerce builds the right one.
+    description: Union[str, DescriptionV1]
     energy_efficiency_rating: int
     environmental_efficiency_rating: int
 
 
 @dataclass
 class Addendum:
-    addendum_numbers: List[int]
+    # ADR-0027: an addendum block can lodge only stone_walls/system_build flags
+    # with no numbers list → optional.
+    addendum_numbers: List[int] = field(default_factory=list)
     stone_walls: Optional[str] = None
     system_build: Optional[str] = None
 
@@ -134,7 +138,8 @@ class SapBuildingPart:
     party_wall_construction: Union[int, str]
     wall_thickness_measured: str
     roof_insulation_location: Union[int, str]
-    roof_insulation_thickness: Union[str, int]
+    # ADR-0027: absent on 254/1506 building parts (flat-roof / no-loft) → optional.
+    roof_insulation_thickness: Optional[Union[str, int]] = None
     sap_room_in_roof: Optional[SapRoomInRoof] = None
     wall_thickness: Optional[int] = None
     wall_insulation_thickness: Optional[str] = None
@@ -194,7 +199,12 @@ class RenewableHeatIncentive:
     impact_of_solid_wall_insulation: Optional[int] = None
 
 
-@dataclass
+# ADR-0027: 20.0.0 is a reduced-data schema generated from a single example, so
+# it over-constrains — fields the corpus routinely omits were declared required,
+# failing 993/1000 certs at parse. Required→optional is data-driven (any field
+# present in <100% of the corpus gets a default); `kw_only=True` lifts the
+# dataclass non-default-after-default ordering rule so defaults can sit inline.
+@dataclass(kw_only=True)
 class RdSapSchema20_0_0:
     uprn: int
     roofs: List[EnergyElement]
@@ -214,13 +224,14 @@ class RdSapSchema20_0_0:
     report_type: int
     sap_heating: SapHeating
     sap_version: float
-    sap_windows: List[SapWindow]
+    # ADR-0027: 993/1000 omit this; synthesised by Reduced-Field Synthesis.
+    sap_windows: List[SapWindow] = field(default_factory=list)
     schema_type: str
     uprn_source: str
     country_code: str
     main_heating: List[EnergyElement]
-    # dwelling_type is a plain string in schema 20.0.0 onwards
-    dwelling_type: str
+    # ADR-0027: mixed str / localised-dict in the corpus (see EnergyElement).
+    dwelling_type: Union[str, DescriptionV1]
     language_code: int
     property_type: int
     address_line_1: str
@@ -236,7 +247,7 @@ class RdSapSchema20_0_0:
     registration_date: str
     sap_energy_source: SapEnergySource
     secondary_heating: EnergyElement
-    lzc_energy_sources: List[int]
+    lzc_energy_sources: List[int] = field(default_factory=list)
     sap_building_parts: List[SapBuildingPart]
     low_energy_lighting: int
     solar_water_heating: str
@@ -252,24 +263,25 @@ class RdSapSchema20_0_0:
     open_fireplaces_count: int
     heating_cost_potential: float
     hot_water_cost_current: float
-    insulated_door_u_value: float
+    insulated_door_u_value: Optional[float] = None
     mechanical_ventilation: int
     percent_draughtproofed: int
-    suggested_improvements: List[SuggestedImprovement]
+    suggested_improvements: List[SuggestedImprovement] = field(default_factory=list)
     co2_emissions_potential: float
     energy_rating_potential: int
     lighting_cost_potential: float
     schema_version_original: str
     hot_water_cost_potential: float
     renewable_heat_incentive: RenewableHeatIncentive
-    windows_transmission_details: WindowsTransmissionDetails
+    # ADR-0027: cert-level U/g present in 687/1000; Table-24 default otherwise.
+    windows_transmission_details: Optional[WindowsTransmissionDetails] = None
     energy_consumption_current: int
     multiple_glazed_proportion: int
     calculation_software_version: str
     energy_consumption_potential: int
     environmental_impact_current: int
     fixed_lighting_outlets_count: int
-    multiple_glazed_proportion_nr: Optional[str]
+    multiple_glazed_proportion_nr: Optional[str] = None
     current_energy_efficiency_band: str
     environmental_impact_potential: int
     potential_energy_efficiency_band: str