P5.2: SapResult.intermediate exposes heat transmission group

Seven fabric W/K components from `inputs.heat_transmission` populated on
`intermediate`: walls, roof, floor, party_walls, windows, doors,
thermal_bridging. Handover §11 / §5 (sap-spec sweep).

132 SAP tests pass.

packages/domain/src/domain/sap/calculator.py

@@ -332,10 +332,18 @@ def calculate_sap_from_inputs(inputs: CalculatorInputs) -> SapResult:
     )
     primary_energy_per_m2 = primary_energy_kwh / tfa if tfa > 0 else 0.0
 
+    ht = inputs.heat_transmission
     intermediate: dict[str, float] = {
         "tfa_m2": inputs.dimensions.total_floor_area_m2,
         "volume_m3": inputs.dimensions.volume_m3,
         "storey_count": float(inputs.dimensions.storey_count),
+        "walls_w_per_k": ht.walls_w_per_k,
+        "roof_w_per_k": ht.roof_w_per_k,
+        "floor_w_per_k": ht.floor_w_per_k,
+        "party_walls_w_per_k": ht.party_walls_w_per_k,
+        "windows_w_per_k": ht.windows_w_per_k,
+        "doors_w_per_k": ht.doors_w_per_k,
+        "thermal_bridging_w_per_k": ht.thermal_bridging_w_per_k,
     }
 
     return SapResult(

packages/domain/src/domain/sap/tests/test_calculator.py

@@ -139,6 +139,26 @@ def test_calculate_exposes_dimensions_intermediates() -> None:
     assert result.intermediate["storey_count"] == float(inputs.dimensions.storey_count)
 
 
+def test_calculate_exposes_heat_transmission_intermediates() -> None:
+    # Arrange — P5 trace mode: the 7 fabric W/K components must surface on
+    # `intermediate` so section-§5 sweep slices can diff per-component
+    # against BRE worked examples.
+    inputs = _baseline_inputs()
+
+    # Act
+    result = calculate_sap_from_inputs(inputs)
+
+    # Assert
+    ht = inputs.heat_transmission
+    assert result.intermediate["walls_w_per_k"] == ht.walls_w_per_k
+    assert result.intermediate["roof_w_per_k"] == ht.roof_w_per_k
+    assert result.intermediate["floor_w_per_k"] == ht.floor_w_per_k
+    assert result.intermediate["party_walls_w_per_k"] == ht.party_walls_w_per_k
+    assert result.intermediate["windows_w_per_k"] == ht.windows_w_per_k
+    assert result.intermediate["doors_w_per_k"] == ht.doors_w_per_k
+    assert result.intermediate["thermal_bridging_w_per_k"] == ht.thermal_bridging_w_per_k
+
+
 def test_higher_main_heating_efficiency_reduces_fuel_use() -> None:
     # Arrange — Direction check: doubling the boiler efficiency must halve
     # the main-heating fuel kWh, holding everything else constant.