Dependency signals are priced in the goal objective's currency 🟥

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/domain/modelling/test_optimiser_goal_objective.py

@@ -0,0 +1,123 @@
+"""Behaviour of the Optimiser under a goal-aligned objective (ADR-0062): a
+Scenario whose goal is Reducing CO2 emissions / Energy Savings optimises its
+own metric, not SAP. The caller supplies group signals already measured in the
+objective's currency; the optimiser must price everything *it* computes — the
+forced Measure Dependency signals — in the same currency, so a ventilation
+that costs SAP but is carbon-neutral cannot sink a carbon-improving wall.
+"""
+
+from __future__ import annotations
+
+from typing import Sequence
+
+from datatypes.epc.domain.epc_property_data import (
+    BuildingPartIdentifier,
+    EpcPropertyData,
+)
+from domain.modelling.measure_type import MeasureType
+from domain.modelling.optimisation.optimiser import (
+    MeasureDependency,
+    OptimisedPackage,
+    ScoredOption,
+    optimise_package,
+)
+from domain.modelling.recommendation import Cost, MeasureOption
+from domain.modelling.scoring.package_scorer import Score
+from domain.modelling.simulation import (
+    BuildingPartOverlay,
+    EpcSimulation,
+    VentilationOverlay,
+)
+from tests.domain.sap10_calculator.worksheet._elmhurst_worksheet_000490 import (
+    build_epc,
+)
+
+_WALL_OVERLAY = EpcSimulation(
+    building_parts={
+        BuildingPartIdentifier.MAIN: BuildingPartOverlay(wall_insulation_type=2)
+    }
+)
+_VENT_OVERLAY = EpcSimulation(
+    ventilation=VentilationOverlay(mechanical_ventilation_kind="EXTRACT_OR_PIV_OUTSIDE")
+)
+
+
+def _scored(
+    measure_type: str, *, gain: float, cost: float, overlay: EpcSimulation
+) -> ScoredOption:
+    return ScoredOption(
+        option=MeasureOption(
+            measure_type=MeasureType(measure_type),
+            description=measure_type,
+            overlay=overlay,
+            cost=Cost(total=cost, contingency_rate=0.0),
+        ),
+        sap_gain=gain,
+    )
+
+
+class _CarbonScorer:
+    """A stub where the wall is a small carbon win (−20 kg/yr) and a large SAP
+    win (+6), while its forced ventilation is carbon-neutral but SAP-ruinous
+    (−30): SAP-priced dependency signals sink the wall; carbon-priced ones
+    keep it."""
+
+    def score(
+        self, baseline: EpcPropertyData, simulations: Sequence[EpcSimulation]
+    ) -> Score:
+        sap, co2 = 60.0, 500.0
+        for sim in simulations:
+            if sim.ventilation is not None:
+                sap -= 30.0
+            for part in sim.building_parts.values():
+                if part.wall_insulation_type is not None:
+                    sap += 6.0
+                    co2 -= 20.0
+        return Score(
+            sap_continuous=sap, co2_kg_per_yr=co2, primary_energy_kwh_per_yr=0.0
+        )
+
+
+def _carbon_reduction(score: Score) -> float:
+    return -score.co2_kg_per_yr
+
+
+def test_dependency_signals_are_priced_in_the_objective_currency() -> None:
+    # Arrange — the wall's signal (supplied by the caller, +20 kg CO2 saved)
+    # and the ventilation it forces in (carbon-neutral). Under legacy SAP
+    # pricing the ventilation's −30 SAP would outweigh the wall's +20 signal
+    # and the package would collapse to nothing.
+    groups: list[list[ScoredOption]] = [
+        [_scored("cavity_wall_insulation", gain=20.0, cost=1000.0, overlay=_WALL_OVERLAY)],
+    ]
+    dependency = MeasureDependency(
+        triggers=frozenset({MeasureType.CAVITY_WALL_INSULATION}),
+        required=ScoredOption(
+            option=MeasureOption(
+                measure_type=MeasureType.MECHANICAL_VENTILATION,
+                description="mechanical_ventilation",
+                overlay=_VENT_OVERLAY,
+                cost=Cost(total=300.0, contingency_rate=0.0),
+            ),
+            sap_gain=0.0,
+        ),
+    )
+
+    # Act — a Reducing-CO2 brief: maximise carbon reduction within budget.
+    package: OptimisedPackage = optimise_package(
+        groups=groups,
+        scorer=_CarbonScorer(),
+        baseline_epc=build_epc(),
+        budget=5000.0,
+        target_sap=None,
+        dependencies=[dependency],
+        objective=_carbon_reduction,
+    )
+
+    # Assert — the wall survives with its ventilation: the dependency is worth
+    # 0 kg CO2, not −30 SAP, so the package is a net +20 kg saving.
+    assert {s.option.measure_type for s in package.selected} == {
+        "cavity_wall_insulation",
+        "mechanical_ventilation",
+    }
+    assert abs(package.score.co2_kg_per_yr - 480.0) <= 1e-9