Slice S0380.16: add 'Normal' → cylinder_size=2 (110 L) for cohort 2

Unblocks two 38-cert-cohort certs that previously raised
`UnmappedElmhurstLabel("cylinder_size", 'Normal')` at extraction:
  cert 2536-2525-0600-0788-2292  ws SAP=79.7264
  cert 9421-3045-3205-1646-6200  ws SAP=87.4495

Both Summary §15.1 lodgements read "Cylinder Size: Normal"; both dr87
worksheets lodge line ref (47) "Store volume = 110.0000" L (extracted
from `Hot Water Cylinder → Cylinder Volume 110.00`). RdSAP 10 §10.5
Table 28 documents the "Normal (90-130 litres)" descriptor whose
midpoint is 110 L — the canonical Elmhurst label string in
`datatypes/epc/surveys/elmhurst_site_notes.py` is "Normal (90-130
litres)", and the worksheet's exact 110 L matches the midpoint.

Two-line fix:
  +    "Normal": 2,           in `_ELMHURST_CYLINDER_SIZE_LABEL_TO_SAP10`
  +    2: 110.0,              in `_CYLINDER_SIZE_CODE_TO_LITRES`

The cascade enum 2 is consistent with the existing
`cert_to_inputs.py` docstring's documented (but not-yet-observed)
code 2 → Normal slot, alongside code 3 (Medium / 160 L) and code 4
(Large / 210 L) added in earlier slices.

Slice keeps tight: two mapping unit tests pinning `cylinder_size == 2`
for both certs at extraction. Post-fix the first-attempt cascade
deltas vs worksheet are:
  cert 2536  Δ +0.0244   (was: RAISES)
  cert 9421  Δ +0.0296   (was: RAISES)

Both deltas now sit in the same systematic +0.02..+0.07 small-gap
band as ~12 other first-attempt certs in cohort 2 — chain test +
±0.07 pin would just paper over a known systematic residual that the
user has explicitly asked to drive towards 1e-4, not toward ±0.07.
Following slice will investigate the shared systematic offset and
close cert 2536 / 9421 along with the rest of the +0.04 band on
the chain.

Pyright net-zero per file:
  - datatypes/epc/domain/mapper.py: 32 (baseline 32)
  - domain/sap10_calculator/rdsap/cert_to_inputs.py: 35 (baseline 35)
  - backend/documents_parser/tests/test_summary_pdf_mapper_chain.py: 0

Regression baseline: 691 pass + 10 fail (= prior 689 + 10 + 2 new GREEN).

Spec refs:
- RdSAP 10 §10.5 Table 28 — "Cylinder Volume" Normal band 90-130 L,
  midpoint 110 L (also the canonical Elmhurst label suffix).
- Cert 2536 worksheet `dr87-0001-000889.pdf` line ref (47) = 110.0000.
- Cert 9421 worksheet `dr87-0001-000884.pdf` line ref (47) = 110.0000.

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

backend/documents_parser/tests/test_summary_pdf_mapper_chain.py

@@ -70,6 +70,8 @@ _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
+_SUMMARY_000889_PDF = _FIXTURES / "Summary_000889.pdf"  # cert 2536 (Normal cylinder)
+_SUMMARY_000884_PDF = _FIXTURES / "Summary_000884.pdf"  # cert 9421 (Normal cylinder)
 
 # GOV.UK EPB API JSON for cert 001479 — the API-path counterpart of the
 # Summary_001479.pdf fixture. Together they drive the API ≡ Summary
@@ -876,6 +878,39 @@ def test_all_seven_ashp_cohort_certs_extract_without_unmapped_label_raise() -> N
         EpcPropertyDataMapper.from_elmhurst_site_notes(site_notes)
 
 
+def test_summary_2536_normal_cylinder_routes_to_code_2() -> None:
+    # Arrange — cert 2536-2525-0600-0788-2292's Summary §15.1 lodges
+    # "Cylinder Size: Normal". The dr87 worksheet lodges "Cylinder
+    # Volume 110.00" L on line ref (47); the cascade lookup
+    # `_CYLINDER_SIZE_CODE_TO_LITRES` now maps code 2 → 110 L per
+    # RdSAP 10 §10.5 Table 28's Normal (90-130 L) band midpoint.
+    # First cohort cert to exercise the "Normal" cylinder lodging.
+    pages = _summary_pdf_to_textract_style_pages(_SUMMARY_000889_PDF)
+    site_notes = ElmhurstSiteNotesExtractor(pages).extract()
+
+    # Act
+    epc = EpcPropertyDataMapper.from_elmhurst_site_notes(site_notes)
+
+    # Assert
+    assert epc.sap_heating.cylinder_size == 2
+
+
+def test_summary_9421_normal_cylinder_routes_to_code_2() -> None:
+    # Arrange — cert 9421-3045-3205-1646-6200's Summary §15.1 also
+    # lodges "Cylinder Size: Normal" (same 110 L cylinder as cert
+    # 2536). Second cohort cert exercising the "Normal" mapping —
+    # pinned to guard against silent regression of either the mapper
+    # dict entry OR the cascade volume default.
+    pages = _summary_pdf_to_textract_style_pages(_SUMMARY_000884_PDF)
+    site_notes = ElmhurstSiteNotesExtractor(pages).extract()
+
+    # Act
+    epc = EpcPropertyDataMapper.from_elmhurst_site_notes(site_notes)
+
+    # Assert
+    assert epc.sap_heating.cylinder_size == 2
+
+
 def test_summary_9418_large_cylinder_routes_to_code_4() -> None:
     # Arrange — cert 9418-3062-8205-3566-7200's Summary §15.1 lodges
     # "Cylinder Size: Large". The dr87 worksheet lodges "Cylinder

datatypes/epc/domain/mapper.py

@@ -3401,12 +3401,13 @@ class UnmappedElmhurstLabel(ValueError):
 
 # Elmhurst Summary §15.1 "Cylinder Size" labels mapped to the SAP10
 # cascade enum that `domain/sap10_calculator/rdsap/cert_to_inputs.py`
-# `_CYLINDER_SIZE_CODE_TO_LITRES` keys ({3: 160.0, 4: 210.0}). Exercised
-# by the cohort: "Medium" (cert 0380 et al — 160 L) and "Large" (cert
-# 9418 — 210 L). "Small" and "Very Large" labels are deferred until a
-# fixture exercises them — when encountered they raise
-# `UnmappedElmhurstLabel` rather than silently returning None.
+# `_CYLINDER_SIZE_CODE_TO_LITRES` keys. Exercised by the cohort:
+# "Normal" (certs 2536, 9421 — 110 L), "Medium" (cert 0380 et al —
+# 160 L) and "Large" (cert 9418 — 210 L). "Small" and "Very Large"
+# labels are deferred until a fixture exercises them — when encountered
+# they raise `UnmappedElmhurstLabel` rather than silently returning None.
 _ELMHURST_CYLINDER_SIZE_LABEL_TO_SAP10: Dict[str, int] = {
+    "Normal": 2,
     "Medium": 3,
     "Large": 4,
 }

domain/sap10_calculator/rdsap/cert_to_inputs.py

@@ -1869,13 +1869,18 @@ _TABLE_3A_COMBI_LOSS_MAIN_HEATING_CATEGORIES: Final[frozenset[int]] = frozenset(
 # RdSAP 10 §10.5 Table 28: lodged "Cylinder size" descriptors → SAP
 # calculation litres. The Open EPC API encodes the descriptor as an
 # integer per the cohort below (ground-truthed against worksheet (47)
-# line refs in /sap worksheets/Additional data with api/<cert>/dr87-*.pdf):
+# line refs in /sap worksheets/Additional data with api/<cert>/dr87-*.pdf
+# and /sap worksheets/additional with api 2/<cert>/dr87-*.pdf):
 #   code 1 → no cylinder            (gated via `has_hot_water_cylinder`)
+#   code 2 → Normal (110 litres)    (certs 2536, 9421 — worksheet (47)
+#                                    lodges 110.0)
 #   code 3 → Medium (160 litres)    (certs 0350, 0380, 2225, 2636,
 #                                    3800, 9285)
 #   code 4 → Large  (210 litres)    (cert 9418)
-# Codes 2 / 5 / 6 (Normal / Inaccessible / Exact) not yet observed.
-_CYLINDER_SIZE_CODE_TO_LITRES: Final[dict[int, float]] = {3: 160.0, 4: 210.0}
+# Codes 5 / 6 (Inaccessible / Exact) not yet observed.
+_CYLINDER_SIZE_CODE_TO_LITRES: Final[dict[int, float]] = {
+    2: 110.0, 3: 160.0, 4: 210.0
+}
 
 # RdSAP 10 §10.5 code 7-11: cylinder insulation type. Empirical mapping
 # from the ASHP cohort (all 7 certs lodge code 1, worksheet shows