gated propertly

datatypes/epc/domain/mapper.py

@@ -3313,13 +3313,14 @@ def _normalize_sap_schema_16_x(data: Dict[str, Any]) -> Dict[str, Any]:
     # still fail loud — that is correct, the fabric data is insufficient.
     d.setdefault("insulated_door_count", 0)
 
-    # Some 16.x certs (e.g. 16.3 cert 0418-3986-7250-2884-7970) omit
-    # `multiple_glazed_proportion` while still lodging `multiple_glazing_type` —
-    # RdSapSchema17_1 requires it. It is an ML-feature field the SAP-10 calculator
-    # never reads (only `sap10_ml/transform`), so the value is non-load-bearing for
-    # the score; default the modal 100 ("fully" the lodged glazing type) to keep the
-    # cert mappable. Mirrors the `insulated_door_count` default above.
-    d.setdefault("multiple_glazed_proportion", 100)
+    # NB: we deliberately do NOT default `multiple_glazed_proportion` here. A 16.x
+    # cert that omits it (e.g. 16.3 cert 0418-3986-7250-2884-7970) is left to fail
+    # the RdSapSchema17_1 parse and be handled by the cohort skip-and-report path —
+    # synthesising a value (tried `100`) drew the otherwise-unmappable cert into the
+    # EPC-prediction donor pool and tipped near-tie similarity matches, regressing
+    # the frozen-fixture component-accuracy gate (has_hot_water_cylinder 30→29/36,
+    # door_count residual 23→25/36). The field is ML-only (the SAP calc never reads
+    # it), so there is no calc cost to leaving such certs unmapped. See worklist.
 
     # 16.2 lodges glazing in BOTH `multiple_glazing_type` (frequently the "ND"
     # not-defined sentinel) AND the windows[].description. When the numeric field

datatypes/epc/domain/tests/test_from_sap_schema.py

@@ -538,21 +538,20 @@ class TestFromSapSchema16_2:
         assert isinstance(epc, EpcPropertyData)
         assert epc.insulated_door_count == 0
 
-    def test_16_x_missing_multiple_glazed_proportion_still_maps(self) -> None:
-        # Some 16.x certs (e.g. 16.3 cert 0418-3986-7250-2884-7970) lodge
-        # `multiple_glazing_type` but omit `multiple_glazed_proportion`, which
-        # RdSapSchema17_1 requires — previously raised "missing required field
-        # 'multiple_glazed_proportion'", aborting the prediction cohort. The
-        # normaliser defaults the modal 100 so the cert maps. (The field is an
-        # ML-only feature the SAP calculator never reads, and from_rdsap_schema_17_1
-        # does not carry it onto EpcPropertyData — the point here is mappability.)
+    def test_16_x_missing_multiple_glazed_proportion_fails_loud(self) -> None:
+        # A 16.x cert omitting `multiple_glazed_proportion` (e.g. 16.3 cert
+        # 0418-3986-7250-2884-7970) is deliberately NOT defaulted — it fails the
+        # RdSapSchema17_1 parse and is handled by the cohort skip-and-report path.
+        # Synthesising a value drew the otherwise-unmappable cert into the
+        # EPC-prediction donor pool and regressed the component-accuracy gate;
+        # the field is ML-only so there is no calc cost to leaving it unmapped.
         data = load("sap_16_3.json")
         del data["multiple_glazed_proportion"]
-        assert "multiple_glazed_proportion" not in data
 
-        epc = EpcPropertyDataMapper.from_api_response(data)
-
-        assert isinstance(epc, EpcPropertyData)
+        with pytest.raises(
+            ValueError, match="missing required field 'multiple_glazed_proportion'"
+        ):
+            EpcPropertyDataMapper.from_api_response(data)
 
     def test_recorded_co2_as_measurement_dict_is_coerced_not_crashed(self) -> None:
         # Some certs (e.g. 16.x cert 2308-4997-7262-0137-9930) lodge

tests/domain/sap10_calculator/test_real_cert_sap_accuracy.py

@@ -581,6 +581,28 @@ _EXPECTATIONS: Final[tuple[RealCertExpectation, ...]] = (
         cert_num="9978-7098-7226-2633-3994",
         sap_score=75,
     ),
+    # UPRN 10002468137 → cert 0215-2818-7357-9703-2145. RdSAP-Schema-17.1,
+    # all-electric high-heat-retention storage heaters on Economy 7, solid-
+    # brick uninsulated end-terrace. Ground truth is Elmhurst RdSAP10 = 60,
+    # reproduced on identical inputs (summary + full SAP 10.2 worksheet saved
+    # alongside: elmhurst_summary.pdf / elmhurst_worksheet.pdf). The engine
+    # produces 62 — a +2 over-rating localised to OFF-PEAK WATER HEATING:
+    # the worksheet (lines 243-246) prices the 7-hour off-peak immersion at a
+    # Table 13 split (19.36% @ 15.29p high + 80.64% @ 5.5p low), but the engine
+    # prices 100% at the 5.5p low rate, under-costing the bill (£595.68 vs
+    # £629.67) → lower ECF (2.69 vs 2.84) → SAP 62 not 60. (Space heating 100%
+    # off-peak IS correct for storage heaters — the worksheet agrees.) Strict
+    # xfail until the off-peak water-heating rate split is implemented.
+    RealCertExpectation(
+        schema="RdSAP-Schema-17.1",
+        sample="uprn_10002468137",
+        cert_num="0215-2818-7357-9703-2145",
+        sap_score=60,
+        known_bug_xfail=(
+            "off-peak (7-hour) water-heating high/low rate split not applied — "
+            "engine prices 100% at the low rate; see elmhurst_worksheet.pdf (243-246)"
+        ),
+    ),
 )