Slice S0380.11: resolve zero-shower lodgings to count=0 (closes cert 2225)

Cert 2225-3062-8205-2856-7204 lodges **zero showers** in its Summary
§1x Baths and Showers block. The Summary mapper at
`mapper.py:3536-3537` predicated the shower-count assignment on
`has_electric_shower`: for cohort certs with no electric shower the
counts collapsed to None — but cert 2225 has no showers at all, and
the cascade's None-handling defaults to 1 mixer shower (over-counting
HW kWh by ~66 against the worksheet (64)/(216) target).

Same disposition the API path received in slice 102f-prep.8 (commit
1d5183c6, "API mapper resolves shower_outlets=None → 0 mixers") —
extending it to the Summary mapper.

Scope-limited fix: zero-shower lodgings resolve to **explicit 0**
counts (not None) so the cascade does not default-assume a mixer.
Non-zero shower lodgings keep their existing convention (None for
non-electric → cascade derives count from `shower_outlets`) so the 5
boiler-cohort hand-built parity tests
(`test_from_elmhurst_site_notes_matches_hand_built_*`) stay GREEN.

Forcing function: cert 2225 first-attempt Summary SAP closes from
Δ -0.3079 to Δ **+0.0441** — within the ±0.07 ASHP-cohort spec floor.

Cohort closure status (5 of 7 ASHP certs now at spec floor):
  cert  Δ vs worksheet  spec floor?
  0380  +0.0594         ✓
  0350  +0.0458         ✓
  2225  +0.0441         ✓  ← this slice
  2636  +0.4873         ✗  (cantilever + alt-wall; next slice)
  3800  +0.0442         ✓
  9285  +0.0502         ✓
  9418  +2.5973         ✗  (Daikin EDLQ05CAV3, distinct PCDB)

Added two tests:
- `test_summary_2225_no_showers_lodged_resolves_to_zero_counts` —
  unit-level pin that no-shower lodgings produce explicit 0 counts.
- `test_summary_2225_full_chain_sap_within_spec_floor_of_worksheet`
  — Layer-4 chain test at ±0.07.

Pyright net-zero on both edited files (mapper.py 32 baseline).

Regression suite: 682 pass + 10 fail (handover baseline 669 + 10 +
13 new GREEN tests across S0380.2..S0380.11). The 5 boiler hand-
built parity tests confirmed still GREEN — the refinement
deliberately preserves their convention by only flipping the zero-
shower case.

Spec refs:
- Slice 102f-prep.8 (commit 1d5183c6) — API-path precedent.
- SAP 10.2 Appendix J — shower energy accounting (electric vs mixer
  routing); mixer showers draw from the HW system and contribute to
  HW kWh; electric showers are §J line 64a (separate energy stream).

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

backend/documents_parser/tests/test_summary_pdf_mapper_chain.py

@@ -62,6 +62,7 @@ _SUMMARY_000899_PDF = _FIXTURES / "Summary_000899.pdf"
 _SUMMARY_000903_PDF = _FIXTURES / "Summary_000903.pdf"
 _SUMMARY_000901_PDF = _FIXTURES / "Summary_000901.pdf"  # cert 3800
 _SUMMARY_000904_PDF = _FIXTURES / "Summary_000904.pdf"  # cert 9285
+_SUMMARY_000900_PDF = _FIXTURES / "Summary_000900.pdf"  # cert 2225
 
 # GOV.UK EPB API JSON for cert 001479 — the API-path counterpart of the
 # Summary_001479.pdf fixture. Together they drive the API ≡ Summary
@@ -713,6 +714,55 @@ def test_summary_0350_full_chain_sap_within_spec_floor_of_worksheet() -> None:
     assert abs(result.sap_score_continuous - worksheet_unrounded_sap) < _ASHP_COHORT_CHAIN_TOLERANCE
 
 
+def test_summary_2225_no_showers_lodged_resolves_to_zero_counts() -> None:
+    # Arrange — cert 2225-3062-8205-2856-7204's Summary §1x Baths and
+    # Showers block lodges 0 baths and ZERO showers (no shower rows at
+    # all). The Summary mapper's existing logic at
+    # `mapper.py:3536-3537` predicates the count assignment on
+    # `has_electric_shower`: when no electric shower is detected the
+    # counts collapse to None — but cert 2225 has no showers at all,
+    # not "non-electric showers". The None values then drive the
+    # cascade's default-1-mixer assumption, over-counting HW kWh.
+    # Same disposition the API path received in slice 102f-prep.8
+    # (commit 1d5183c6: "API mapper resolves shower_outlets=None →
+    # 0 mixers").
+    pages = _summary_pdf_to_textract_style_pages(_SUMMARY_000900_PDF)
+    site_notes = ElmhurstSiteNotesExtractor(pages).extract()
+    # Pre-condition: §1x lodges zero showers (proves the test sees
+    # the same no-showers fixture the cascade does).
+    assert len(site_notes.baths_and_showers.showers) == 0
+
+    # Act
+    epc = EpcPropertyDataMapper.from_elmhurst_site_notes(site_notes)
+
+    # Assert — zero-shower lodgings resolve to explicit 0 counts (not
+    # None) so the cascade does not default-assume a mixer.
+    assert epc.sap_heating.electric_shower_count == 0
+    assert epc.sap_heating.mixer_shower_count == 0
+
+
+def test_summary_2225_full_chain_sap_within_spec_floor_of_worksheet() -> None:
+    # Arrange — cert 2225-3062-8205-2856-7204 (Summary_000900.pdf):
+    # Mitsubishi PUZ-WM50VHA, single-bp single-array PV (3.28 kWp SE),
+    # ZERO showers lodged. Worksheet "SAP value" 88.7921. Slice
+    # S0380.11 closed the zero-shower defaulting bug (None → 0 mixers
+    # for cohort certs that lodge no showers); cert 2225 was the
+    # forcing function. Same disposition the API path received in
+    # slice 102f-prep.8 (commit 1d5183c6).
+    pages = _summary_pdf_to_textract_style_pages(_SUMMARY_000900_PDF)
+    site_notes = ElmhurstSiteNotesExtractor(pages).extract()
+    epc = EpcPropertyDataMapper.from_elmhurst_site_notes(site_notes)
+
+    # Act
+    result = calculate_sap_from_inputs(
+        cert_to_inputs(epc, prices=SAP_10_2_SPEC_PRICES)
+    )
+
+    # Assert — ±0.07 ASHP-cohort spec-floor tolerance.
+    worksheet_unrounded_sap = 88.7921
+    assert abs(result.sap_score_continuous - worksheet_unrounded_sap) < _ASHP_COHORT_CHAIN_TOLERANCE
+
+
 def test_summary_3800_full_chain_sap_within_spec_floor_of_worksheet() -> None:
     # Arrange — cert 3800-8515-0922-3398-3563 (Summary_000901.pdf /
     # dr87-0001-000901.pdf) is the third ASHP cohort cert to close on

datatypes/epc/domain/mapper.py

@@ -3533,8 +3533,24 @@ def _map_elmhurst_sap_heating(survey: ElmhurstSiteNotes) -> SapHeating:
             mh.secondary_heating_sap_code,
         ),
         number_baths=survey.baths_and_showers.number_of_baths,
-        electric_shower_count=1 if has_electric_shower else None,
-        mixer_shower_count=0 if has_electric_shower else None,
+        # 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)
+        ),
     )