fix(elmhurst-extractor): allocate single-glazed alt-wall windows to the alternative wall

The §11 layout parser keys a window's wall Location on the glazing-prefix /
orientation tokens around its data row. An alt-wall window lodges its
"Alternative wall 1" Location wrapped across the lines bracketing the W×H×A
row. For a DOUBLE-glazed alt window the prefix line also carries the glazing
phrase ("Double between 2002   Alternative wall"), so the partition breaks
there and the location survives into the window's pre-data slice. For a
SINGLE-glazed alt window the "Alternative wall" line stands alone with no
glazing-type word, so _partition_after_manuf scanned past it and swallowed
it into the PREVIOUS window's suffix — the window then defaulted to
"External wall" and its opening deducted from the wrong wall.

Fix: treat a standalone wall-location line ("Alternative wall" / "External
wall" / "Party wall") as a window boundary in _partition_after_manuf, so it
attaches to the following window's prefix. Surfaced by simulated case 34
(cert 001431 electric-storage flat): 2 of 4 single-glazed alt-wall windows
were mis-allocated, splitting 2.75/10.78 m² instead of the worksheet's
4.63/8.90 corridor/external opening areas.

Elmhurst-extractor only; API gauge unaffected. Regression gate green (3
pre-existing fails unrelated); worksheet harness 47/47 unchanged. Case 34's
alt-wall opening area now matches the worksheet; the corridor wall net area
is correct (the cert's residual is now isolated to the unheated-corridor
door, a separate slice).

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

backend/documents_parser/elmhurst_extractor.py

@@ -1007,7 +1007,17 @@ class ElmhurstSiteNotesExtractor:
         joined to the data line (no separate prefix line exists), so
         the only signal of window-transition is the orientation tokens
         rotating: orient_suffix(k) → orient_prefix(k+1). Falls through
-        to `next_data_idx` when neither marker is present."""
+        to `next_data_idx` when neither marker is present.
+
+        (c) A standalone wall-location line ("Alternative wall", "External
+        wall", "Party wall") in the gap belongs to the NEXT window's
+        prefix — it is that window's §11 Location cell, wrapped above its
+        W×H×A data row. When the next window is single-glazed its prefix
+        line carries no glazing-type word (branch a never fires), so
+        without this the "Alternative wall" line is swallowed into the
+        current window's suffix and the next window defaults to "External
+        wall" (simulated case 34: 2 of 4 single-glazed alt-wall windows
+        mis-allocated → wrong corridor-wall net area)."""
         scan_start = manuf_idx + 4
         seen_orient = False
         for j in range(scan_start, next_data_idx):
@@ -1015,6 +1025,8 @@ class ElmhurstSiteNotesExtractor:
             first_word = stripped.split(" ", 1)[0]
             if first_word in self._GLAZING_TYPE_PREFIX_WORDS:
                 return j
+            if "wall" in stripped.lower():
+                return j
             if stripped in self._ORIENTATION_TOKENS:
                 if seen_orient:
                     return j

backend/documents_parser/tests/test_summary_pdf_mapper_chain.py

@@ -85,6 +85,11 @@ _SUMMARY_000904_PDF = _FIXTURES / "Summary_000904.pdf"  # cert 9285
 _SUMMARY_000900_PDF = _FIXTURES / "Summary_000900.pdf"  # cert 2225
 _SUMMARY_000898_PDF = _FIXTURES / "Summary_000898.pdf"  # cert 2636
 _SUMMARY_000902_PDF = _FIXTURES / "Summary_000902.pdf"  # cert 9418
+# simulated case 34 (cert 001431 reconfigured as a slimline electric-storage
+# flat with an unheated corridor / sheltered alternative wall + 4 alt-wall
+# windows). Regression net for the flat-roof, sheltered-wall, and §11
+# alt-wall-window-allocation fixes.
+_SUMMARY_CASE34_PDF = _FIXTURES / "Summary_case34_storage_flat.pdf"
 _SUMMARY_000889_PDF = _FIXTURES / "Summary_000889.pdf"  # cert 2536 (Normal cylinder)
 _SUMMARY_000884_PDF = _FIXTURES / "Summary_000884.pdf"  # cert 9421 (Normal cylinder)
 _SUMMARY_000910_PDF = _FIXTURES / "Summary_000910.pdf"  # cert 0036 (Flat, party wall U=0)
@@ -1547,6 +1552,34 @@ def test_summary_mapper_raises_on_unmapped_cylinder_insulation_label() -> None:
     assert excinfo.value.value == "Polyester wool"
 
 
+def test_case34_alt_wall_windows_all_allocated_to_alternative_wall() -> None:
+    # Arrange — simulated case 34 lodges 4 windows on "Alternative wall 1"
+    # (0.70 + 1.75 + 1.18 + 1.00 = 4.63 m²) and 6 on the external wall. The
+    # §11 layout interleaves the wrapped "Alternative wall / 1" Location cell
+    # around each window's data row; for single-glazed alt windows the
+    # location line carries no glazing-type word, so the partition swallowed
+    # it into the previous window's suffix and the window defaulted to
+    # "External wall" — mis-deducting its opening from the wrong wall.
+    from domain.sap10_calculator.worksheet.heat_transmission import (
+        _window_on_alt_wall,  # pyright: ignore[reportPrivateUsage]
+    )
+    pages = _summary_pdf_to_textract_style_pages(_SUMMARY_CASE34_PDF)
+    site_notes = ElmhurstSiteNotesExtractor(pages).extract()
+    epc = EpcPropertyDataMapper.from_elmhurst_site_notes(site_notes)
+
+    # Act
+    alt_area = sum(
+        round(float(w.window_width) * float(w.window_height), 2)
+        for w in (epc.sap_windows or [])
+        if _window_on_alt_wall(w)
+    )
+    alt_count = sum(1 for w in (epc.sap_windows or []) if _window_on_alt_wall(w))
+
+    # Assert — all 4 alt-wall windows recovered (worksheet alt openings 4.63).
+    assert alt_count == 4
+    assert abs(alt_area - 4.63) <= 0.01
+
+
 def test_map_elmhurst_alternative_wall_carries_sheltered_flag() -> None:
     # Arrange — Elmhurst Summary §7 lodges "Alternative Wall N Sheltered
     # Wall: Yes" for a sub-area adjacent to an unheated buffer (e.g. a flat's