Extract the PasHub community heat-source label 🟥

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

backend/documents_parser/tests/test_extractor.py

@@ -706,6 +706,43 @@ class TestRenewablesPvArrays:
         assert renewables.pv_arrays is None
 
 
+class TestMainHeatingCommunityHeatSource:
+    """A community-heating dwelling lodges its heat source under "Heating
+    System (Other):" (e.g. "Community heating - boilers only", verbatim from
+    accuracy fixture deal 507644414148). Dropped, the mapper cannot lodge the
+    Table 4a heat-network SAP code and the dwelling is priced as an ordinary
+    boiler (issue #1590 follow-up).
+    """
+
+    def test_heat_source_label_is_captured(self) -> None:
+        # Arrange — fixture 1's heating section with the community block
+        # spliced in after its "Fuel:" lodgement.
+        lines = load_text_fixture()
+        idx = lines.index("Fuel:")
+        spliced = (
+            lines[: idx + 2]
+            + ["Heating System (Other):", "Community heating - boilers only"]
+            + lines[idx + 2 :]
+        )
+
+        # Act
+        mh = PasHubRdSapSiteNotesExtractor(
+            spliced
+        ).extract_heating_and_hot_water().main_heating
+
+        # Assert
+        assert mh.community_heat_source == "Community heating - boilers only"
+
+    def test_absent_label_stays_blank(self) -> None:
+        # Arrange / Act — fixture 1 as lodged (no community block).
+        mh = PasHubRdSapSiteNotesExtractor(
+            load_text_fixture()
+        ).extract_heating_and_hot_water().main_heating
+
+        # Assert
+        assert mh.community_heat_source == ""
+
+
 class TestRoofSpaceRoomInRoof:
     """"Are there rooms in the roof? Yes" lodges an RdSAP §3.10 detailed RIR
     block (age, floor area, gables/slopes/common walls/flat ceiling as