Slice S0380.13: widen cantilever gate to accept "House" descriptive form

Closes cert 2636 to spec floor (Δ +0.5167 → +0.0323) by accepting
both the EPC schema enum-as-string ("0") AND the Elmhurst Summary
mapper's descriptive form ("House") for the cantilever-detection
property-type gate at `heat_transmission.py:768`.

Root cause: slice 102f-prep.9 (commit 06b4ef3d) added cantilever
detection gated on `epc.property_type == _PROPERTY_TYPE_HOUSE` where
`_PROPERTY_TYPE_HOUSE = "0"`. That matches the API mapper's encoding
(schema enum), but the Summary mapper produces "House" (descriptive)
and the hand-built worksheet fixtures also use "House" — so neither
triggers the gate and the cantilever path silently no-ops on the
Summary path. Cert 2636's worksheet (28b) "Exposed floor Main 3.74
× 1.20 = 4.4880" is the cantilever — without surfacing it the
cascade missed 4.488 W/K of floor heat loss.

Three-encoding origins:
- API mapper:        property_type='0'      (schema enum-as-string)
- Summary mapper:    property_type='House'  (descriptive from §1)
- Hand-built fixtures: property_type='House' (legacy convention)

Fix: replace the equality check with a `_is_house()` helper that
accepts the {"0", "House"} frozenset. Centralised so future
property-type sensitive gates can call the same helper.

Forcing function: cert 2636 first-attempt Summary SAP closes from
Δ +0.5167 (after S0380.12 walls fix) to Δ **+0.0323** — within the
±0.07 ASHP-cohort spec floor. `floor_w_per_k` moves from 19.1982
(ground floor only) to 23.6862 (ground 19.20 + cantilever 4.49 =
worksheet (28a) + (28b) exact match).

Cohort closure status (6 of 7 ASHP certs at spec floor):
  cert  Δ vs worksheet  spec floor?
  0380  +0.0594         ✓
  0350  +0.0458         ✓
  2225  +0.0441         ✓
  2636  +0.0323         ✓  ← this slice
  3800  +0.0442         ✓
  9285  +0.0502         ✓
  9418  +2.5973         ✗  (Daikin EDLQ05CAV3 — final cert)

Boiler hand-built parity verified intact: 5 hand-built cohort certs
(000474, 000477, 000480, 000490, 000516) all use property_type=
"House" and now also fire the cantilever gate, but none have
floor1_area > floor0_area + 1m² (the cantilever-area trigger) so
their cascade output is unchanged. Regression suite 683 pass + 10
fail (= handover baseline 669 + 10 + 17 new GREEN tests across
S0380.2..S0380.13).

Pyright net-zero on edited files:
  domain/sap10_calculator/worksheet/heat_transmission.py: 13
    (baseline; no new errors)
  backend/documents_parser/tests/test_summary_pdf_mapper_chain.py: 0

Spec / precedent refs:
- Slice 102f-prep.9 (commit 06b4ef3d) — RdSAP cantilever-exposed-
  floor detection (originally API-only via `property_type=="0"` gate).
- SAP 10.2 Table 20 — U_exposed_floor (age D + no insulation →
  1.20 W/m²K, the cohort's cantilever U-value).
- Cert 2636 worksheet `dr87-0001-000898.pdf` line refs (28a)+(28b)
  sum 23.6862 W/K (exact cascade match after this slice).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/documents_parser/tests/test_summary_pdf_mapper_chain.py

@@ -789,6 +789,33 @@ def test_summary_2225_full_chain_sap_within_spec_floor_of_worksheet() -> None:
     assert abs(result.sap_score_continuous - worksheet_unrounded_sap) < _ASHP_COHORT_CHAIN_TOLERANCE
 
 
+def test_summary_2636_full_chain_sap_within_spec_floor_of_worksheet() -> None:
+    # Arrange — cert 2636-0525-2600-0401-2296 (Summary_000898.pdf):
+    # Mitsubishi PUZ-WM50VHA, mid-terrace house with **alt-wall +
+    # cantilever** — the most complex geometry in the ASHP cohort.
+    # Worksheet "SAP value" lodges 86.2641.
+    #
+    # Closed by two combined slices:
+    #   - S0380.12: alt-wall window-location parser fix (walls W/K
+    #     20.5595 → 20.0240 = worksheet exact).
+    #   - S0380.13: cantilever gate accepts "House" descriptive form
+    #     in addition to the schema enum "0" (allowing the Summary
+    #     mapper's descriptive property_type to trigger the cantilever
+    #     detection that slice 102f-prep.9 added on the API path).
+    pages = _summary_pdf_to_textract_style_pages(_SUMMARY_000898_PDF)
+    site_notes = ElmhurstSiteNotesExtractor(pages).extract()
+    epc = EpcPropertyDataMapper.from_elmhurst_site_notes(site_notes)
+
+    # Act
+    result = calculate_sap_from_inputs(
+        cert_to_inputs(epc, prices=SAP_10_2_SPEC_PRICES)
+    )
+
+    # Assert — ±0.07 ASHP-cohort spec-floor tolerance.
+    worksheet_unrounded_sap = 86.2641
+    assert abs(result.sap_score_continuous - worksheet_unrounded_sap) < _ASHP_COHORT_CHAIN_TOLERANCE
+
+
 def test_summary_3800_full_chain_sap_within_spec_floor_of_worksheet() -> None:
     # Arrange — cert 3800-8515-0922-3398-3563 (Summary_000901.pdf /
     # dr87-0001-000901.pdf) is the third ASHP cohort cert to close on

domain/sap10_calculator/worksheet/heat_transmission.py

@@ -109,10 +109,23 @@ _COS_30_DEG: Final[float] = cos(radians(30.0))
 # BP0: 195%), neither of which the worksheet treats as cantilever.
 _CANTILEVER_MIN_AREA_M2: Final[float] = 1.0
 _CANTILEVER_MAX_RATIO: Final[float] = 0.25
-# EPC API `property_type` strings that flag a dwelling as a house (not
-# flat). Cantilever detection only fires for houses — flats with very
-# small floor=0 areas (stairwell access) would otherwise over-count.
-_PROPERTY_TYPE_HOUSE: Final[str] = "0"
+# `property_type` values that flag a dwelling as a house (not flat).
+# Cantilever detection only fires for houses — flats with very small
+# floor=0 areas (stairwell access) would otherwise over-count.
+# The API mapper produces the EPC schema enum-as-string ("0"), the
+# Elmhurst Summary mapper produces the descriptive form ("House"), and
+# the hand-built worksheet fixtures use the descriptive form too. The
+# canonical check below accepts both so the cantilever path fires
+# uniformly regardless of source-mapper encoding.
+_PROPERTY_TYPES_HOUSE: Final[frozenset[str]] = frozenset({"0", "House"})
+
+
+def _is_house(property_type: Optional[str]) -> bool:
+    """True when `epc.property_type` encodes a house (not flat / maisonette
+    / park home). Tolerant of both the API schema's enum-as-string ("0")
+    and the Summary mapper / hand-built fixture descriptive form
+    ("House")."""
+    return property_type in _PROPERTY_TYPES_HOUSE
 
 
 @dataclass(frozen=True)
@@ -765,7 +778,7 @@ def heat_transmission_from_cert(
         # thermal bridges via its area on (31).
         cantilever_area = (
             _round_half_up(geom.get("cantilever_floor_area_m2", 0.0), _AREA_ROUND_DP)
-            if epc.property_type == _PROPERTY_TYPE_HOUSE
+            if _is_house(epc.property_type)
             else 0.0
         )
         if cantilever_area > 0: