slice 4: total_floor_area_m2 feature

First feature column lands on the transform: schema() advertises
total_floor_area_m2 as a non-nullable float; to_row() emits the value
from EpcPropertyData.total_floor_area_m2 alongside the six targets.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

packages/domain/src/domain/ml/tests/test_transform.py

@@ -31,7 +31,6 @@ def test_transform_advertises_version_and_target_columns() -> None:
         column = schema.target_columns[target_name]
         assert isinstance(column, ColumnSpec)
         assert column.dtype is expected_dtype
-    assert schema.feature_columns == {}
 
 
 def test_to_row_extracts_targets_from_epc_property_data() -> None:
@@ -90,3 +89,31 @@ def test_to_row_clamps_ucl_correction_when_band_b_would_increase_peui() -> None:
     # Band B: gradient=-0.10, intercept=28 → cd = -0.10*232 + 28 = +4.8 → clamp to 0
     # adjusted = 232 + 0 = 232.0
     assert row["peui_ucl"] == 232.0
+
+
+def test_schema_advertises_total_floor_area_m2_feature() -> None:
+    # Arrange
+    transform = EpcMlTransform()
+
+    # Act
+    schema = transform.schema()
+
+    # Assert
+    assert "total_floor_area_m2" in schema.feature_columns
+    column = schema.feature_columns["total_floor_area_m2"]
+    assert isinstance(column, ColumnSpec)
+    assert column.dtype is float
+    assert column.nullable is False
+
+
+def test_to_row_extracts_total_floor_area_m2() -> None:
+    # Arrange
+    epc = make_minimal_sap10_epc(energy_rating_current=82)
+    transform = EpcMlTransform()
+
+    # Act
+    row = transform.to_row(epc)
+
+    # Assert
+    # make_minimal_sap10_epc sets total_floor_area_m2=70.0 by default
+    assert row["total_floor_area_m2"] == 70.0

packages/domain/src/domain/ml/transform.py

@@ -18,6 +18,15 @@ from domain.ml.schema import ColumnSpec, TransformSchema
 from domain.ml.ucl import apply_ucl_correction
 
 
+_FEATURE_COLUMNS: dict[str, ColumnSpec] = {
+    "total_floor_area_m2": ColumnSpec(
+        dtype=float,
+        nullable=False,
+        description="Total floor area in square metres, from `total_floor_area`.",
+    ),
+}
+
+
 _TARGET_COLUMNS: dict[str, ColumnSpec] = {
     "sap_score": ColumnSpec(
         dtype=int,
@@ -79,7 +88,7 @@ class EpcMlTransform:
         """
         return TransformSchema(
             transform_version=self.VERSION,
-            feature_columns={},
+            feature_columns=dict(_FEATURE_COLUMNS),
             target_columns=dict(_TARGET_COLUMNS),
         )
 
@@ -90,6 +99,9 @@ class EpcMlTransform:
         """
         rhi = epc.renewable_heat_incentive
         return {
+            # Features
+            "total_floor_area_m2": epc.total_floor_area_m2,
+            # Targets
             "sap_score": epc.energy_rating_current,
             "co2_emissions": epc.co2_emissions_current,
             "peui_raw": epc.energy_consumption_current,