From ffaf89935ba68e7dab3a2c014c83e1fbe7064d13 Mon Sep 17 00:00:00 2001
From: Khalim Conn-Kowlessar <kconnkowlessar@gmail.com>
Date: Thu, 9 Jul 2026 13:13:22 +0000
Subject: [PATCH] =?UTF-8?q?Fabric-first=20phase=202=20re-scores=20candidat?=
 =?UTF-8?q?es=20in=20the=20goal=20objective's=20currency=20=F0=9F=9F=A5?=
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Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
---
 .../test_optimiser_goal_objective.py          | 74 +++++++++++++++++++
 1 file changed, 74 insertions(+)

diff --git a/tests/domain/modelling/test_optimiser_goal_objective.py b/tests/domain/modelling/test_optimiser_goal_objective.py
index 57e3c8240..f64371cc4 100644
--- a/tests/domain/modelling/test_optimiser_goal_objective.py
+++ b/tests/domain/modelling/test_optimiser_goal_objective.py
@@ -26,6 +26,7 @@ from domain.modelling.scoring.package_scorer import Score
 from domain.modelling.simulation import (
     BuildingPartOverlay,
     EpcSimulation,
+    HeatingOverlay,
     VentilationOverlay,
 )
 from tests.domain.sap10_calculator.worksheet._elmhurst_worksheet_000490 import (
@@ -121,3 +122,76 @@ def test_dependency_signals_are_priced_in_the_objective_currency() -> None:
         "mechanical_ventilation",
     }
     assert abs(package.score.co2_kg_per_yr - 480.0) <= 1e-9
+
+
+_IWI_OVERLAY = EpcSimulation(
+    building_parts={
+        BuildingPartIdentifier.MAIN: BuildingPartOverlay(wall_insulation_type=3)
+    }
+)
+_BOILER_OVERLAY = EpcSimulation(heating=HeatingOverlay(sap_main_heating_code=201))
+_ASHP_OVERLAY = EpcSimulation(
+    heating=HeatingOverlay(main_heating_index_number=13000)
+)
+
+
+class _CarbonHeatingScorer:
+    """A stub where the boiler wins on SAP (+10 vs +2) but the heat pump wins
+    on carbon (−50 vs −5 kg/yr): a fabric-first phase 2 that re-scores its
+    candidates in SAP picks the wrong heating for a Reducing-CO2 brief."""
+
+    def score(
+        self, baseline: EpcPropertyData, simulations: Sequence[EpcSimulation]
+    ) -> Score:
+        sap, co2 = 60.0, 500.0
+        for sim in simulations:
+            for part in sim.building_parts.values():
+                if part.wall_insulation_type is not None:
+                    sap += 5.0
+                    co2 -= 10.0
+            if sim.heating is None:
+                continue
+            if sim.heating.sap_main_heating_code is not None:
+                sap += 10.0
+                co2 -= 5.0
+            if sim.heating.main_heating_index_number is not None:
+                sap += 2.0
+                co2 -= 50.0
+        return Score(
+            sap_continuous=sap, co2_kg_per_yr=co2, primary_energy_kwh_per_yr=0.0
+        )
+
+
+def test_fabric_first_phase_two_rescores_in_the_objective_currency() -> None:
+    # Arrange — a fabric-first Reducing-CO2 brief. Phase 1 commits the wall;
+    # phase 2 must choose the heating on its post-fabric *carbon* worth, not
+    # its SAP worth. Signals are supplied in kg CO2 saved (the caller's job).
+    from domain.modelling.optimisation.optimiser import (
+        optimise_package_fabric_first,
+    )
+
+    groups: list[list[ScoredOption]] = [
+        [_scored("internal_wall_insulation", gain=10.0, cost=1000.0, overlay=_IWI_OVERLAY)],
+        [
+            _scored("gas_boiler_upgrade", gain=5.0, cost=2000.0, overlay=_BOILER_OVERLAY),
+            _scored("air_source_heat_pump", gain=50.0, cost=6000.0, overlay=_ASHP_OVERLAY),
+        ],
+    ]
+
+    # Act — no target (goal-aligned briefs have none), generous budget.
+    package: OptimisedPackage = optimise_package_fabric_first(
+        groups=groups,
+        scorer=_CarbonHeatingScorer(),
+        baseline_epc=build_epc(),
+        budget=10000.0,
+        target_sap=None,
+        objective=_carbon_reduction,
+    )
+
+    # Assert — the wall plus the heat pump (−50 kg), not the SAP-favoured
+    # boiler; the truthful package carbon is 500 − 10 − 50 = 440.
+    assert {s.option.measure_type for s in package.selected} == {
+        "internal_wall_insulation",
+        "air_source_heat_pump",
+    }
+    assert abs(package.score.co2_kg_per_yr - 440.0) <= 1e-9