feat(baseline): sap_code_to_fuel normalizes via the calculator's own helper

The fuel codes the calculator now puts on SapResult are its own codes — raw
gov-API enums or already-Table-32, depending on the source mapper (ADR-0015).
sap_code_to_fuel now runs the code through table_32.to_table_32_code
(promoted from private _to_table_32_code) — T32-first, then API-translate,
the SAME normalization the calculator's pricing/CO2 helpers use — before the
Table-32 -> Fuel dispatch, so the bill's carrier matches what the calculator
billed (incl. the API/T32 collision codes, e.g. 20 = wood-logs not heat-net).

Falls back to the raw code for billing fuels the price table omits (the 41-58
heat-network range), which resolve to HEAT_NETWORK -> UnpricedFuel — stricter
than, and intentionally divergent from, the calculator's lossy
default-to-mains-gas for an unpriced code (ADR-0014 §5).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

domain/property_baseline/sap_fuel.py

@@ -4,13 +4,13 @@ from typing import Final
 
 from domain.fuel_rates.fuel import Fuel
 from domain.sap10_calculator.exceptions import UnmappedSapCode
+from domain.sap10_calculator.tables.table_32 import to_table_32_code
 
-# SAP 10.2 / Table 32 fuel code -> canonical billing Fuel (ADR-0014). Bounded to
-# the ~47 Table 32 fuel codes (the keys of `table_12.UNIT_PRICE_P_PER_KWH`) — the
-# carrier, NOT the PCDB product, so a thousand PCDB heat pumps all share one code.
-# Input is a normalised Table 32 fuel code (the calculator sets `main_fuel_type`
-# to Table 32 codes); an unmapped code raises `UnmappedSapCode` rather than
-# guessing — a bounded, self-surfacing backlog [[reference-unmapped-sap-code]].
+# Table 32 fuel code -> canonical billing Fuel (ADR-0014). Bounded to the ~47
+# Table 32 fuel codes (the keys of `UNIT_PRICE_P_PER_KWH`) — the carrier, NOT the
+# PCDB product, so a thousand PCDB heat pumps all share one code. An unmapped code
+# raises `UnmappedSapCode` rather than guessing — a bounded, self-surfacing
+# backlog [[reference-unmapped-sap-code]].
 _CODE_TO_FUEL: Final[dict[int, Fuel]] = {
     **dict.fromkeys([1, 7], Fuel.MAINS_GAS),  # mains gas, grid biogas
     **dict.fromkeys([2, 3, 5, 9], Fuel.LPG),
@@ -29,13 +29,26 @@ _CODE_TO_FUEL: Final[dict[int, Fuel]] = {
 
 
 def sap_code_to_fuel(code: int) -> Fuel:
-    """Map a SAP 10.2 / Table 32 fuel code to its canonical billing Fuel.
+    """Map one of the calculator's per-end-use fuel codes to its billing Fuel.
+
+    The code may be a raw gov-API `main_fuel_type` enum or an already-Table-32
+    code depending on the source mapper (until [[adr-0015]] normalizes the cert),
+    so it is first run through the calculator's own ``to_table_32_code`` —
+    T32-first, then API-translate — the **same** normalization the calculator's
+    pricing/CO2 helpers use, so the bill's carrier matches what the calculator
+    billed. The normalized Table-32 code is then dispatched to a billing Fuel.
 
     Raises ``UnmappedSapCode`` on a code with no single billing carrier — e.g.
     dual fuel (10) or the grid-export codes (36/60), which are not an end use's
     input fuel.
     """
-    fuel = _CODE_TO_FUEL.get(code)
+    # Normalize to a Table-32 code; fall back to the raw code for billing fuels
+    # the price table does not carry (the 41-58 heat-network range — `to_table_32_
+    # code` returns None there, but they still resolve to HEAT_NETWORK and so to
+    # UnpricedFuel, which is stricter — and correct — than the calculator's
+    # lossy default-to-mains-gas for an unpriced code).
+    normalized = to_table_32_code(code)
+    fuel = _CODE_TO_FUEL.get(normalized if normalized is not None else code)
     if fuel is None:
         raise UnmappedSapCode("fuel_code", code)
     return fuel

domain/sap10_calculator/tables/table_32.py

@@ -194,7 +194,7 @@ _OFF_PEAK_STANDING_CODE: Final[dict[Tariff, int]] = {
 }
 
 
-def _to_table_32_code(fuel_code: Optional[int]) -> Optional[int]:
+def to_table_32_code(fuel_code: Optional[int]) -> Optional[int]:
     """Normalise a fuel code (Table 32 or API enum) to its Table 32 form."""
     if fuel_code is None:
         return None
@@ -204,7 +204,7 @@ def _to_table_32_code(fuel_code: Optional[int]) -> Optional[int]:
 
 
 def _is_gas_code(fuel_code: Optional[int]) -> bool:
-    code = _to_table_32_code(fuel_code)
+    code = to_table_32_code(fuel_code)
     return code is not None and code in _GAS_FUEL_CODES
 
 
@@ -219,9 +219,9 @@ def is_electric_fuel_code(fuel_code: Optional[int]) -> bool:
     silently mis-classifies as electric. The S0380.135 EES-code →
     Table 32 mapper lookups set `main_fuel_type` to Table 32 codes
     (BDI → 10 = dual fuel), so the literal-set checks fail loudly here
-    unless normalised through `_to_table_32_code` first.
+    unless normalised through `to_table_32_code` first.
     """
-    code = _to_table_32_code(fuel_code)
+    code = to_table_32_code(fuel_code)
     return code is not None and code in _ELECTRIC_FUEL_CODES
 
 
@@ -235,7 +235,7 @@ def is_liquid_fuel_code(fuel_code: Optional[int]) -> bool:
     LPG is treated as GAS by Table 4f (separate "Gas boiler" row,
     45 kWh/yr) — `is_liquid_fuel_code` returns False for LPG codes.
     """
-    code = _to_table_32_code(fuel_code)
+    code = to_table_32_code(fuel_code)
     return code is not None and code in _LIQUID_FUEL_CODES
 
 

tests/domain/property_baseline/test_sap_fuel.py

@@ -35,6 +35,22 @@ def test_table_32_codes_map_to_their_billing_fuel(code: int, fuel: Fuel) -> None
     assert sap_code_to_fuel(code) == fuel
 
 
+@pytest.mark.parametrize(
+    ("api_code", "fuel"),
+    [
+        (26, Fuel.MAINS_GAS),  # gov-API mains-gas enum -> Table 32 code 1
+        (0, Fuel.ELECTRICITY),  # API "electricity" -> Table 32 code 30
+        (25, Fuel.HEAT_NETWORK),  # API community heat -> Table 32 code 41
+        (14, Fuel.COAL),  # API house coal -> Table 32 code 11
+    ],
+)
+def test_raw_api_fuel_codes_normalize_before_mapping(api_code: int, fuel: Fuel) -> None:
+    # Arrange — the calculator may carry a raw gov-API fuel code (not yet a Table
+    # 32 code); sap_code_to_fuel normalizes via the calculator's own helper first.
+    # Act / Assert
+    assert sap_code_to_fuel(api_code) == fuel
+
+
 def test_an_unmapped_code_raises_rather_than_guessing() -> None:
     # Arrange — code 10 (dual fuel) has no single billing fuel.
     # Act / Assert