Resolve a party-ceiling roof marker to the party-ceiling member 🟥

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

domain/epc/property_overrides/roof_party_ceiling_guard.py

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+from __future__ import annotations
+
+from typing import Optional
+
+from domain.epc.property_overrides.roof_type import RoofType
+
+
+def roof_party_ceiling_guard(description: str) -> Optional[RoofType]:
+    """Deterministically resolve a party-ceiling roof description to its RoofType.
+
+    A building part whose top boundary is another (or the same) dwelling / premises
+    above has ~0 heat loss (RdSAP 10 Table 18: "There is no heat loss through the
+    roof of a building part that has the same dwelling or another dwelling above"),
+    so it must resolve to a party-ceiling `RoofType` member — which the roof
+    Simulation Overlay leaves as no overlay, keeping the lodged EPC — and never to
+    an external `Pitched` / `Flat` roof.
+
+    Recognises the party-ceiling markers regardless of a trailing insulation token
+    (``: 100mm`` / ``: unknown``) or spacing/case, and returns ``None`` for anything
+    that is not a party-ceiling marker so the LLM classifier still handles it
+    (#1376).
+    """
+    raise NotImplementedError

tests/domain/epc/test_roof_party_ceiling_guard.py

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+from __future__ import annotations
+
+from domain.epc.property_overrides.roof_type import RoofType
+from domain.epc.property_overrides.roof_party_ceiling_guard import (
+    roof_party_ceiling_guard,
+)
+
+
+def test_party_ceiling_marker_with_a_trailing_depth_resolves_to_the_party_ceiling_member() -> None:
+    # Arrange — the bug: a party ceiling ("another dwelling above") carrying a
+    # trailing loft depth the LLM misreads as an external pitched roof.
+    description = "another dwelling above: 100mm"
+
+    # Act
+    result = roof_party_ceiling_guard(description)
+
+    # Assert — it is a party ceiling (~0 heat loss), not a Pitched roof.
+    assert result is RoofType.ADJACENT_ANOTHER_DWELLING_ABOVE