Predict ventilation kind from the cohort mode 🟥

Prediction never synthesises ventilation — it keeps the size-template's
sap_ventilation, so a predicted dwelling in an MEV/MVHR neighbourhood is scored
+ displayed as natural (predicted property 721167 follow-up). Mode the
mechanical_ventilation_kind across the cohort like glazing.

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

tests/domain/epc_prediction/test_epc_prediction.py

@@ -17,6 +17,7 @@ from datatypes.epc.domain.epc_property_data import (
     SapEnergySource,
     SapFloorDimension,
     SapHeating,
+    SapVentilation,
     SapWindow,
 )
 from domain.geospatial.coordinates import Coordinates
@@ -54,6 +55,7 @@ def _epc(
     meter_type: str = "2",
     main_heating_label: str = "Boiler and radiators, mains gas",
     main_heating_controls_label: Optional[str] = None,
+    mechanical_ventilation_kind: Optional[str] = None,
 ) -> EpcPropertyData:
     epc: EpcPropertyData = object.__new__(EpcPropertyData)
     epc.property_type = "2"
@@ -108,6 +110,10 @@ def _epc(
     )
     epc.has_hot_water_cylinder = has_hot_water_cylinder
     epc.solar_water_heating = solar_water_heating
+    epc.sap_ventilation = SapVentilation(
+        mechanical_ventilation_kind=mechanical_ventilation_kind,
+        sheltered_sides=1,
+    )
     energy: SapEnergySource = object.__new__(SapEnergySource)
     energy.meter_type = meter_type
     epc.sap_energy_source = energy
@@ -557,6 +563,31 @@ def test_heating_is_a_coherent_donor_not_the_structural_template() -> None:
     assert predicted.has_hot_water_cylinder is True
 
 
+def test_ventilation_kind_follows_the_cohort_mode() -> None:
+    # Mechanical ventilation (MEV/MVHR) is a new-build / retrofit feature that
+    # clusters by era and street — like glazing — so the predicted ventilation
+    # kind takes the recency/geo-weighted cohort mode, not the size-template's.
+    # The size-closest template here is natural (None); the cohort is
+    # predominantly MVHR, so the prediction must reflect the MVHR neighbourhood
+    # rather than leave the template's empty ventilation (predicted property
+    # 721167 follow-up). Natural-vent cohorts mode to None and stay natural.
+    cohort = _cohort(
+        _epc(mechanical_ventilation_kind=None),  # template (size tie → first)
+        _epc(mechanical_ventilation_kind="MVHR"),
+        _epc(mechanical_ventilation_kind="MVHR"),
+        _epc(mechanical_ventilation_kind="MVHR"),
+    )
+
+    # Act
+    predicted: EpcPropertyData = EpcPrediction().predict(
+        PredictionTarget(postcode="LS6 1AA", property_type="2"), cohort
+    )
+
+    # Assert — the predicted kind is the cohort's MVHR mode, not the template's None.
+    assert predicted.sap_ventilation is not None
+    assert predicted.sap_ventilation.mechanical_ventilation_kind == "MVHR"
+
+
 def test_glazing_follows_the_recency_weighted_cohort_mode() -> None:
     # Arrange — an old majority single-glazed (type 1, 2015) and a recent
     # minority double-glazed (type 3, 2025). Glazing is retrofitted over time