add missing ucl.py and _fixtures.py from slices 2-3

Previous slice commits used -a-style and missed these new files;
imports in transform.py and test_transform.py would dangle on a
fresh checkout. Re-running pytest after this commit covers all four
EpcMlTransform tests cleanly.

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

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

@@ -0,0 +1,80 @@
+"""Test fixtures for EpcMlTransform tests.
+
+`make_minimal_sap10_epc()` constructs a valid EpcPropertyData with the smallest
+sensible defaults for required fields; target values are passed by kwarg so each
+test parametrises only the fields it cares about.
+"""
+
+from datetime import date
+from typing import Optional
+
+from datatypes.epc.domain.epc_property_data import (
+    EpcPropertyData,
+    InstantaneousWwhrs,
+    RenewableHeatIncentive,
+    SapEnergySource,
+    SapHeating,
+)
+
+
+def make_minimal_sap10_epc(
+    *,
+    energy_rating_current: Optional[int] = None,
+    co2_emissions_current: Optional[float] = None,
+    energy_consumption_current: Optional[int] = None,
+    space_heating_kwh: float = 0.0,
+    water_heating_kwh: float = 0.0,
+) -> EpcPropertyData:
+    """Construct a minimal valid SAP10 EpcPropertyData with parametrisable targets."""
+    return EpcPropertyData(
+        dwelling_type="Mid-terrace house",
+        inspection_date=date(2025, 6, 1),
+        tenure="1",
+        transaction_type="1",
+        address_line_1="1 Test Street",
+        postcode="A1 1AA",
+        post_town="Testtown",
+        roofs=[],
+        walls=[],
+        floors=[],
+        main_heating=[],
+        door_count=0,
+        sap_heating=SapHeating(
+            instantaneous_wwhrs=InstantaneousWwhrs(),
+            main_heating_details=[],
+            has_fixed_air_conditioning=False,
+        ),
+        sap_windows=[],
+        sap_energy_source=SapEnergySource(
+            mains_gas=True,
+            meter_type="Single",
+            pv_battery_count=0,
+            wind_turbines_count=0,
+            gas_smart_meter_present=False,
+            is_dwelling_export_capable=False,
+            wind_turbines_terrain_type="Suburban",
+            electricity_smart_meter_present=False,
+        ),
+        sap_building_parts=[],
+        solar_water_heating=False,
+        has_hot_water_cylinder=False,
+        has_fixed_air_conditioning=False,
+        wet_rooms_count=0,
+        extensions_count=0,
+        heated_rooms_count=0,
+        open_chimneys_count=0,
+        habitable_rooms_count=0,
+        insulated_door_count=0,
+        cfl_fixed_lighting_bulbs_count=0,
+        led_fixed_lighting_bulbs_count=0,
+        incandescent_fixed_lighting_bulbs_count=0,
+        total_floor_area_m2=70.0,
+        sap_version=10.2,
+        energy_rating_current=energy_rating_current,
+        co2_emissions_current=co2_emissions_current,
+        energy_consumption_current=energy_consumption_current,
+        renewable_heat_incentive=RenewableHeatIncentive(
+            space_heating_kwh=space_heating_kwh,
+            water_heating_kwh=water_heating_kwh,
+        ),
+    )

packages/domain/src/domain/ml/ucl.py

@@ -0,0 +1,59 @@
+"""UCL per-band correction for Primary Energy Intensity.
+
+Per Few et al. 2023 — "The over-prediction of energy use by EPCs in Great Britain"
+(Energy & Buildings 288, 113024). Table 3 per-band linear correction.
+
+Ported from `backend/ml_models/AnnualBillSavings.adjust_energy_to_metered`. Applied
+to PEUI training labels per ADR-0007, *not* at runtime — the discontinuities at
+EPC band boundaries that arose when this was applied post-prediction are what made
+us fold it into the training labels instead.
+
+Open question §15.14 in the PRD: the paper was calibrated on gas-heated, non-PV
+homes in England and Wales rated under SAP 2012. The current implementation
+extrapolates silently to all properties.
+"""
+
+from typing import Final
+
+from datatypes.epc.domain.epc import Epc
+
+
+_GRADIENTS: Final[dict[Epc, float]] = {
+    Epc.A: -0.10,
+    Epc.B: -0.10,
+    Epc.C: -0.43,
+    Epc.D: -0.52,
+    Epc.E: -0.70,
+    Epc.F: -0.76,
+    Epc.G: -0.76,
+}
+
+_INTERCEPTS: Final[dict[Epc, float]] = {
+    Epc.A: 28.0,
+    Epc.B: 28.0,
+    Epc.C: 97.0,
+    Epc.D: 119.0,
+    Epc.E: 160.0,
+    Epc.F: 157.0,
+    Epc.G: 157.0,
+}
+
+
+def apply_ucl_correction(peui_raw: float, band: Epc) -> float:
+    """Return the metered-equivalent PEUI for an EPC's raw PEUI in a given band.
+
+    The Few et al. correction is one-sided: EPCs over-predict consumption, so the
+    correction only ever subtracts from PEUI. When the linear correction would
+    instead *add* to PEUI for an unusually low-PEUI property in its band, we clamp
+    to zero — leaving PEUI unchanged rather than inflating it.
+    """
+    consumption_difference = _GRADIENTS[band] * peui_raw + _INTERCEPTS[band]
+    if consumption_difference > 0:
+        consumption_difference = 0.0
+    adjusted = peui_raw + consumption_difference
+    if adjusted < 0:
+        raise ValueError(
+            f"UCL-corrected PEUI is negative ({adjusted}) — "
+            f"impossible for raw PEUI {peui_raw} band {band.value}"
+        )
+    return adjusted