Slice S0380.19: count Elmhurst shower outlets by type (no more hardcoded 1)

Surfaces the lodged shower multiplicity from the Elmhurst Summary §16
on the EPC. Previously `_map_elmhurst_sap_heating` hardcoded:

  electric_shower_count = 1 if has_electric_shower else None
  mixer_shower_count    = 0 if has_electric_shower else None

losing the count for any cert with ≥ 2 outlets. Cert
7800-1501-0922-7127-3563 lodges TWO instantaneous electric showers
("Shower 01" + "Shower 11") but the mapper produced
`electric_shower_count=1`. After this slice:

  electric_shower_count = Σ(s for s in showers if s.outlet_type
                              == "Electric shower")
  mixer_shower_count    = Σ(s for s in showers if s.outlet_type
                              != "Electric shower")

**Cascade SAP effect:** None on cert 7800. Appendix J's eq J16
(`N_ES,per_outlet = N_shower / N_outlets`) and eq J18 (Σ_j E_ES,j)
are symmetric in N_electric_showers when there are no mixer outlets,
so the lodged (64a) kWh and (247a) cost are unchanged. The fix is
correctness-by-construction, not a delta-closer for the negative-band
certs (their +0.69 GBP total-cost gap traces to the gas hot-water
kWh path — separate slice).

**Hand-built fixture updates (5):** the cohort-1 hand-builts at
`domain/sap10_calculator/worksheet/tests/_elmhurst_worksheet_*.py`
previously omitted `electric_shower_count` / `mixer_shower_count`
(implicitly None), which matched the mapper's pre-slice None
sentinel. Updated each to the lodged counts the mapper now surfaces:
  000474: 1 mixer  → (0, 1)
  000477: 1 mixer  → (0, 1)
  000480: 1 mixer  → (0, 1)
  000490: 1 mixer  → (0, 1)
  000516: 1 mixer  → (0, 1)
000487 (already at (1, 0) for an electric-shower lodging) unchanged.

Tests:
- `test_summary_7800_two_electric_showers_count_as_two_not_one` —
  pins the multi-shower mapping for cert 7800 (Summary_000890.pdf).
- 5 hand-built field-parity tests
  (`test_from_elmhurst_site_notes_matches_hand_built_*`) now pass at
  the new integer counts instead of None.

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

Regression baseline: 699 pass + 10 fail (= prior 698 + 10 + 1 new).

Spec refs:
- SAP 10.2 Appendix J §1a — outlet counting drives `N_outlets` used
  in eq J6/J7 (mixer shower water draw) and eq J16/J17/J18 (electric
  shower energy).
- Cert 7800-1501-0922-7127-3563 Summary §16 "Showers" lodgement.

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

backend/documents_parser/tests/test_summary_pdf_mapper_chain.py

@@ -73,6 +73,7 @@ _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)
 _SUMMARY_000910_PDF = _FIXTURES / "Summary_000910.pdf"  # cert 0036 (Flat, party wall U=0)
+_SUMMARY_000890_PDF = _FIXTURES / "Summary_000890.pdf"  # cert 7800 (two electric showers)
 
 # GOV.UK EPB API JSON for cert 001479 — the API-path counterpart of the
 # Summary_001479.pdf fixture. Together they drive the API ≡ Summary
@@ -945,6 +946,28 @@ def test_summary_mapper_raises_on_unmapped_glazing_type_label() -> None:
     assert excinfo.value.value == "Quintuple glazed with helium"
 
 
+def test_summary_7800_two_electric_showers_count_as_two_not_one() -> None:
+    # Arrange — cert 7800-1501-0922-7127-3563's Summary §16 lodges TWO
+    # instantaneous electric showers ("Shower 01" + "Shower 11", both
+    # `outlet_type='Electric shower'`). Pre-Slice S0380.19 the mapper
+    # hardcoded `electric_shower_count = 1 if has_electric_shower else
+    # None`, losing the multiplicity. Cascade-equivalent on this cert:
+    # Appendix J eq J16 (N_ES,per_outlet = N_shower / N_outlets) and
+    # eq J18 (Σ_j E_ES,j) yield the same (64a) value for 1 vs 2 outlets
+    # when there are no mixer outlets, so the SAP delta is unchanged
+    # — but the lodged multiplicity is now surfaced for any future
+    # cascade consumer that needs it.
+    pages = _summary_pdf_to_textract_style_pages(_SUMMARY_000890_PDF)
+    site_notes = ElmhurstSiteNotesExtractor(pages).extract()
+
+    # Act
+    epc = EpcPropertyDataMapper.from_elmhurst_site_notes(site_notes)
+
+    # Assert — both lodged electric showers surface on the EPC.
+    assert epc.sap_heating.electric_shower_count == 2
+    assert epc.sap_heating.mixer_shower_count == 0
+
+
 def test_summary_0036_flat_unknown_party_wall_routes_to_u_zero() -> None:
     # Arrange — cert 0036-6325-1100-0063-1226 is a "Flat, Mid-Terrace"
     # whose Summary lodges party_wall_type='U Unable to determine'.

datatypes/epc/domain/mapper.py

@@ -3564,12 +3564,19 @@ def _map_elmhurst_sap_heating(survey: ElmhurstSiteNotes) -> SapHeating:
     # Shower-outlet classification: SAP10.2 Appendix J routes electric
     # showers via §J line 64a (their own kWh stream) and treats mixer
     # showers as drawing from the HW system. The Summary PDF lodges
-    # outlet_type as 'Electric shower' or 'Non-electric shower' — set
-    # the explicit counts so the cascade doesn't default mixer=1 on
-    # electric-only dwellings (000487).
-    has_electric_shower = any(
-        s.outlet_type == "Electric shower"
-        for s in survey.baths_and_showers.showers
+    # outlet_type as 'Electric shower' or 'Non-electric shower' — count
+    # each outlet by type so the cascade sees the actual lodged number
+    # (cert 7800-1501-0922-7127-3563 has 2 electric showers; the
+    # previous hardcoded `1 if has_electric_shower else None` lost the
+    # multiplicity, and `None` left the cascade defaulting to mixer=1
+    # on electric-only dwellings).
+    electric_shower_count_from_survey = sum(
+        1 for s in survey.baths_and_showers.showers
+        if s.outlet_type == "Electric shower"
+    )
+    mixer_shower_count_from_survey = sum(
+        1 for s in survey.baths_and_showers.showers
+        if s.outlet_type != "Electric shower"
     )
     # Water heating fuel: Summary §15 "Water Heating Fuel Type" lodges
     # the fuel name as a string ("Mains gas", "Electricity", ...). Map
@@ -3635,24 +3642,12 @@ def _map_elmhurst_sap_heating(survey: ElmhurstSiteNotes) -> SapHeating:
             mh.secondary_heating_sap_code,
         ),
         number_baths=survey.baths_and_showers.number_of_baths,
-        # Zero-shower lodgings resolve to explicit 0 (not None) so the
-        # cascade doesn't default-assume a mixer — same disposition
-        # the API path received in slice 102f-prep.8 ("API mapper
-        # resolves shower_outlets=None → 0 mixers") on cohort cert
-        # 2225. Non-zero shower lodgings keep the hand-built-fixture
-        # convention (None for non-electric → cascade derives count
-        # from `shower_outlets` instead) so the boiler-cohort parity
-        # tests in this file stay GREEN.
-        electric_shower_count=(
-            0
-            if not survey.baths_and_showers.showers
-            else (1 if has_electric_shower else None)
-        ),
-        mixer_shower_count=(
-            0
-            if not survey.baths_and_showers.showers
-            else (0 if has_electric_shower else None)
-        ),
+        # Both counts derived by tallying the lodged shower list. Zero-
+        # shower lodgings resolve to (0, 0) — the API path's slice 102f-
+        # prep.8 disposition for cert 2225. Multi-shower lodgings surface
+        # the lodged multiplicity (cert 7800: 2 electric showers).
+        electric_shower_count=electric_shower_count_from_survey,
+        mixer_shower_count=mixer_shower_count_from_survey,
     )
 
 

domain/sap10_calculator/worksheet/tests/_elmhurst_worksheet_000474.py

@@ -221,6 +221,12 @@ def build_epc() -> EpcPropertyData:
     epc.sap_heating.shower_outlets = ShowerOutlets(
         shower_outlet=ShowerOutlet(shower_outlet_type="Non-electric shower"),
     )
+    # Slice S0380.19: Elmhurst mapper now counts shower outlets by
+    # type (electric vs mixer) instead of the previous hardcoded
+    # 0/1/None sentinels. Cohort cert 000474 lodges 1 non-electric
+    # (mixer) outlet → electric=0, mixer=1.
+    epc.sap_heating.electric_shower_count = 0
+    epc.sap_heating.mixer_shower_count = 1
     # Summary §14 "Heat pump age: Unknown" — surfaced by the Elmhurst
     # mapper as the str dual-encoding that internal_gains.py reads.
     # `make_main_heating_detail` doesn't expose the str kwarg, so set

domain/sap10_calculator/worksheet/tests/_elmhurst_worksheet_000477.py

@@ -188,6 +188,9 @@ def build_epc() -> EpcPropertyData:
     epc.sap_heating.shower_outlets = ShowerOutlets(
         shower_outlet=ShowerOutlet(shower_outlet_type="Non-electric shower"),
     )
+    # Slice S0380.19: counted shower outlets (was: None/None sentinels).
+    epc.sap_heating.electric_shower_count = 0
+    epc.sap_heating.mixer_shower_count = 1
     # Summary §14 "Heat pump age: Unknown" — surfaced by the Elmhurst
     # mapper as the str dual-encoding that internal_gains.py reads.
     # `make_main_heating_detail` doesn't expose the str kwarg, so set

domain/sap10_calculator/worksheet/tests/_elmhurst_worksheet_000480.py

@@ -238,6 +238,9 @@ def build_epc() -> EpcPropertyData:
     epc.sap_heating.shower_outlets = ShowerOutlets(
         shower_outlet=ShowerOutlet(shower_outlet_type="Non-electric shower"),
     )
+    # Slice S0380.19: counted shower outlets (was: None/None sentinels).
+    epc.sap_heating.electric_shower_count = 0
+    epc.sap_heating.mixer_shower_count = 1
     # Summary §14 "Heat pump age: Unknown" — surfaced by the Elmhurst
     # mapper as the str dual-encoding that internal_gains.py reads.
     epc.sap_heating.main_heating_details[0].central_heating_pump_age_str = "Unknown"

domain/sap10_calculator/worksheet/tests/_elmhurst_worksheet_000490.py

@@ -190,6 +190,9 @@ def build_epc() -> EpcPropertyData:
     epc.sap_heating.shower_outlets = ShowerOutlets(
         shower_outlet=ShowerOutlet(shower_outlet_type="Non-electric shower"),
     )
+    # Slice S0380.19: counted shower outlets (was: None/None sentinels).
+    epc.sap_heating.electric_shower_count = 0
+    epc.sap_heating.mixer_shower_count = 1
     epc.sap_heating.main_heating_details[0].central_heating_pump_age_str = "Unknown"
     return epc
 

domain/sap10_calculator/worksheet/tests/_elmhurst_worksheet_000516.py

@@ -214,6 +214,9 @@ def build_epc() -> EpcPropertyData:
     epc.sap_heating.shower_outlets = ShowerOutlets(
         shower_outlet=ShowerOutlet(shower_outlet_type="Non-electric shower"),
     )
+    # Slice S0380.19: counted shower outlets (was: None/None sentinels).
+    epc.sap_heating.electric_shower_count = 0
+    epc.sap_heating.mixer_shower_count = 1
     epc.sap_heating.main_heating_details[0].central_heating_pump_age_str = "Unknown"
     return epc