A main_fuel override beats a heating archetype's natural-fuel default 🟥

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/repositories/property/test_landlord_override_overlays.py

@@ -7,11 +7,15 @@ that fold onto the lodged EPC — per component, partial, skipping unmapped rows
 from __future__ import annotations
 
 from datatypes.epc.domain.epc_property_data import BuildingPartIdentifier
+from domain.modelling.scoring.overlay_applicator import apply_simulations
 from repositories.property.landlord_override_overlays import overlays_from
 from repositories.property.property_overrides_reader import (
     ResolvedPropertyOverride,
     ResolvedPropertyOverrides,
 )
+from tests.domain.sap10_calculator.worksheet._elmhurst_worksheet_000490 import (
+    build_epc,
+)
 
 
 def test_roof_type_row_produces_a_roof_overlay() -> None:
@@ -143,3 +147,27 @@ def test_unresolvable_rows_are_skipped() -> None:
 
     # Assert
     assert overlays == []
+
+
+def test_main_fuel_override_wins_over_a_heating_archetype_natural_fuel() -> None:
+    # A heating-system override drags a natural fuel (a solid-fuel room heater
+    # defaults to house coal, RdSAP main_fuel 33), but an explicit main_fuel
+    # override must win. apply_simulations is last-wins and the override rows
+    # arrive in arbitrary order, so overlays_from must apply main_fuel AFTER
+    # main_heating_system — otherwise the natural-fuel default clobbers the
+    # explicit fuel (ADR-0041). The rows here are in the order that exposes it.
+    baseline = build_epc()
+    overrides = ResolvedPropertyOverrides(
+        rows=(
+            ResolvedPropertyOverride("main_fuel", 0, "smokeless coal"),
+            ResolvedPropertyOverride(
+                "main_heating_system", 0, "Solid fuel room heater, closed"
+            ),
+        )
+    )
+
+    # Act
+    result = apply_simulations(baseline, overlays_from(overrides))
+
+    # Assert — the explicit fuel (smokeless coal 15) wins over the coal default.
+    assert result.sap_heating.main_heating_details[0].main_fuel_type == 15