A Fabric First Scenario spends the budget on the envelope before heating 🟥

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

tests/orchestration/test_modelling_fabric_first.py

@@ -0,0 +1,60 @@
+"""The ModellingOrchestrator honours a Fabric First Scenario: when
+``scenario.fabric_first`` is set, the Optimiser treats the building envelope
+with the full budget before heating / renewables are considered, so a budget
+the plain optimiser would spend on a heating system is spent on fabric
+instead. End-to-end through ``run_modelling`` (no database) with the real
+calculator, against the uninsulated solid-brick 001431 dwelling whose plain
+plan is heating-led.
+"""
+
+from __future__ import annotations
+
+from datatypes.epc.domain.epc_property_data import EpcPropertyData
+from domain.modelling.measure_type import FABRIC_MEASURE_TYPES, 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,
+)
+
+_HEATING_MEASURES: frozenset[MeasureType] = frozenset(
+    {
+        MeasureType.GAS_BOILER_UPGRADE,
+        MeasureType.AIR_SOURCE_HEAT_PUMP,
+        MeasureType.HIGH_HEAT_RETENTION_STORAGE_HEATERS,
+        MeasureType.SOLAR_PV,
+    }
+)
+
+
+def _fabric_first_scenario(*, budget: float) -> Scenario:
+    return Scenario(
+        id=999,
+        goal="Increasing EPC",
+        goal_value="C",
+        budget=budget,
+        is_default=True,
+        fabric_first=True,
+    )
+
+
+def test_fabric_first_scenario_spends_the_budget_on_fabric_before_heating() -> None:
+    # Arrange — uninsulated solid brick: at a £4000 budget the plain optimiser
+    # buys the £3200 gas boiler (the cheapest route toward band C). Fabric
+    # first must commit the envelope work first, after which the boiler no
+    # longer fits the leftover budget.
+    epc: EpcPropertyData = parse_recommendation_summary(
+        "solid_brick_ewi_001431_before.pdf"
+    )
+
+    # Act
+    plan: Plan = run_modelling(
+        epc, scenario=_fabric_first_scenario(budget=4000.0), print_table=False
+    )
+
+    # Assert — the plan is fabric-led: at least one envelope measure, and none
+    # of the budget leaked to a heating system or renewables.
+    selected = {measure.measure_type for measure in plan.measures}
+    assert selected & FABRIC_MEASURE_TYPES
+    assert not selected & _HEATING_MEASURES