A Reducing-CO2 scenario maximises carbon reduction, not SAP 🟥

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

tests/orchestration/test_modelling_goal_objectives.py

@@ -0,0 +1,59 @@
+"""The ModellingOrchestrator aligns the Optimiser's objective with the
+Scenario's goal (ADR-0062): Reducing CO2 emissions maximises the carbon
+reduction the budget buys, Energy Savings maximises the annual bill saving,
+and Increasing EPC keeps its SAP target semantics. End-to-end through
+``run_modelling`` (no database) with the real calculator, against the
+uninsulated solid-brick 001431 dwelling where the SAP-optimal and
+carbon-optimal packages diverge at a £16,000 budget.
+"""
+
+from __future__ import annotations
+
+from datatypes.epc.domain.epc_property_data import EpcPropertyData
+from domain.modelling.measure_type import MeasureType
+from domain.modelling.plan import Plan
+from domain.modelling.scenario import Scenario
+from harness.console import run_modelling
+from tests.domain.modelling._elmhurst_recommendation import (
+    parse_recommendation_summary,
+)
+
+
+def _solid_brick_dwelling() -> EpcPropertyData:
+    return parse_recommendation_summary("solid_brick_ewi_001431_before.pdf")
+
+
+def _scenario(goal: str, *, budget: float) -> Scenario:
+    return Scenario(
+        id=999, goal=goal, goal_value="", budget=budget, is_default=True
+    )
+
+
+def test_reducing_co2_scenario_buys_carbon_not_sap() -> None:
+    # Arrange — at £16,000 the SAP objective buys the wall + floor + £3,200
+    # gas boiler package (~2,069 kg CO2/yr, SAP 72.9). The carbon objective
+    # swaps the boiler for electric storage heaters (~1,098 kg/yr) — a lower
+    # SAP, but ~970 kg/yr less carbon on the low-carbon grid.
+    epc = _solid_brick_dwelling()
+
+    # Act — the same dwelling and budget under each goal.
+    sap_led: Plan = run_modelling(
+        epc,
+        scenario=_scenario("Valuation Improvement", budget=16000.0),
+        print_table=False,
+    )
+    carbon_led: Plan = run_modelling(
+        epc,
+        scenario=_scenario("Reducing CO2 emissions", budget=16000.0),
+        print_table=False,
+    )
+
+    # Assert — the goal changes the outcome in the goal's favour: the carbon
+    # plan cuts materially more CO2 than the SAP plan buys with the same
+    # money, and the gas boiler that wins on SAP-per-£ is rejected.
+    assert (
+        carbon_led.post_retrofit.co2_kg_per_yr
+        < sap_led.post_retrofit.co2_kg_per_yr - 500.0
+    )
+    selected = {measure.measure_type for measure in carbon_led.measures}
+    assert MeasureType.GAS_BOILER_UPGRADE not in selected