Synthesise glazing from the glazed_area band for windowless 18.0 certs 🟥

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

datatypes/epc/domain/tests/test_from_rdsap_schema.py

@@ -1491,3 +1491,37 @@ class TestRdSap18_0ReducedFieldSynthesis:
         assert len(result.sap_windows) == len(lodged)
         total_area = sum(w.window_width * w.window_height for w in result.sap_windows)
         assert total_area == pytest.approx(expected_total)
+
+    def test_band_normal_synthesises_total_glazing_at_0_148_of_floor_area(
+        self,
+    ) -> None:
+        # Arrange — ADR-0028 (inherit-and-validate): 18.0 lodges only a
+        # glazed_area *band* (1 = Normal, 958/1000), not window m². The inherited
+        # 20.0.0 coefficient — synthesised total glazing = 0.148 x total_floor_area
+        # — is reused unchanged; validated against 18.0's own band-4 rich certs
+        # (observed 0.223 ~ 0.148 x 1.51). A band-1 cert with no per-window array.
+        corpus = _load_18_0_corpus()
+        if not corpus:
+            pytest.skip("no RdSAP-Schema-18.0 corpus harvested")
+        cert = next(
+            (
+                c
+                for c in corpus
+                if not c.get("sap_windows") and c.get("glazed_area") == 1
+            ),
+            None,
+        )
+        if cert is None:
+            pytest.skip("no band-1 corpus cert without sap_windows")
+        tfa = float(cert["total_floor_area"])
+
+        # Act
+        result = EpcPropertyDataMapper.from_api_response(cert)
+
+        # Assert — 4 windows (N/E/S/W avg-orientation split), each height 1.0,
+        # total width-sum (= total area, height=1) at 0.148 x TFA.
+        assert len(result.sap_windows) == 4
+        assert all(w.window_height == 1.0 for w in result.sap_windows)
+        assert sorted(w.orientation for w in result.sap_windows) == [1, 3, 5, 7]
+        total_area = sum(w.window_width * w.window_height for w in result.sap_windows)
+        assert total_area == pytest.approx(0.148 * tfa)