test(elmhurst): party-ceiling BP window is vertical, not a rooflight 🟥

_is_elmhurst_roof_window mis-routes a vertical window (Location "External
wall") to sap_roof_windows when the building part's roof is a PARTY ceiling
(A "Another dwelling above" / NR "Non-residential space above"). A party
ceiling has no external roof, so it cannot host a rooflight.

Surfaced by simulated case 53 (cert 000565 re-keyed as a mid-floor electric-
storage flat, roof "A Another dwelling above"): its External-wall window
(U 2.00) routed to sap_roof_windows -> window area not deducted from the wall
(wall over-counted ~7 W/K) + priced as a roof window -> our SAP 74.0 vs
Elmhurst worksheet 75. Elmhurst lodges it Type "Window", Location "External
wall".

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

tests/datatypes/epc/domain/test_mapper_roof_window_classification.py

@@ -0,0 +1,89 @@
+"""Mapper boundary: Elmhurst §11 window vs roof window classification.
+
+`_is_elmhurst_roof_window` must NOT route a vertical window (lodged Location
+"External wall") to `sap_roof_windows` when the building part's roof is a
+PARTY ceiling — "A Another dwelling above" / "NR Non-residential space above"
+/ "S Same dwelling above". A party ceiling has no external roof structure, so
+it cannot host a rooflight (RdSAP 10 §3.7.1: a rooflight is glazing in a roof;
+party codes carry no heat-loss roof per `_ELMHURST_PARTY_ROOF_CODES`).
+
+Surfaced by "simulated case 53" (cert 000565 re-keyed as a mid-floor electric-
+storage flat, roof "A Another dwelling above"): its one External-wall window
+(U 2.00) was mis-routed to `sap_roof_windows`, so the window area was never
+deducted from the wall (wall over-counted ~7 W/K) and it was priced as a roof
+window — our SAP 74.0 vs Elmhurst worksheet 75. Elmhurst's own entry lodges it
+Type "Window", Location "External wall".
+"""
+
+from datatypes.epc.surveys.elmhurst_site_notes import (
+    RoofDetails,
+    Window as ElmhurstWindow,
+)
+from datatypes.epc.surveys.elmhurst_site_notes import ElmhurstSiteNotes
+from datatypes.epc.domain.mapper import (
+    _is_elmhurst_roof_window,  # pyright: ignore[reportPrivateUsage]
+)
+
+
+def _external_wall_window(*, glazing: str, u_value: float) -> ElmhurstWindow:
+    return ElmhurstWindow(
+        width_m=15.14,
+        height_m=1.0,
+        area_m2=15.14,
+        glazing_type=glazing,
+        frame_factor=0.7,
+        building_part="Main",
+        location="External wall",
+        orientation="North",
+        data_source="Manufacturer",
+        u_value=u_value,
+        g_value=0.72,
+        draught_proofed=True,
+        permanent_shutters="None",
+        frame_type="PVC",
+    )
+
+
+def _survey_with_main_roof(roof_type: str) -> ElmhurstSiteNotes:
+    """Partial `ElmhurstSiteNotes` carrying only what the roof-window
+    classifier reads: `roof`, `room_in_roof`, `extensions`."""
+    survey = object.__new__(ElmhurstSiteNotes)
+    survey.roof = RoofDetails(
+        roof_type=roof_type, insulation="", u_value_known=False
+    )
+    survey.room_in_roof = None
+    survey.extensions = []
+    return survey
+
+
+def test_external_wall_window_on_party_ceiling_is_vertical() -> None:
+    # Arrange — mid-floor flat: Main BP roof is "Another dwelling above"
+    # (party ceiling, no external roof). Window lodged on External wall.
+    window = _external_wall_window(
+        glazing="Double between 2002 and 2021", u_value=2.0
+    )
+    survey = _survey_with_main_roof("A Another dwelling above")
+
+    # Act / Assert — vertical, not a rooflight.
+    assert _is_elmhurst_roof_window(window, survey) is False
+
+
+def test_external_wall_window_under_non_residential_space_is_vertical() -> None:
+    window = _external_wall_window(
+        glazing="Double between 2002 and 2021", u_value=2.0
+    )
+    survey = _survey_with_main_roof("NR Non-residential space above")
+
+    assert _is_elmhurst_roof_window(window, survey) is False
+
+
+def test_roof_of_room_location_still_classified_as_rooflight() -> None:
+    # Guard: an explicit "Roof of Room" location stays a rooflight
+    # (unaffected by the party-ceiling fix).
+    window = _external_wall_window(
+        glazing="Double between 2002 and 2021", u_value=2.0
+    )
+    window.location = "Roof of Room"
+    survey = _survey_with_main_roof("A Another dwelling above")
+
+    assert _is_elmhurst_roof_window(window, survey) is True