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+# Handover — post Slices S0380.131..137
+
+Branch: `feature/per-cert-mapper-validation`. **HEAD `3542186f`**.
+Predecessor: [`HANDOVER_POST_S0380_130.md`](HANDOVER_POST_S0380_130.md).
+
+## TL;DR
+
+Seven slices landed on top of `c8486077`. The work spanned a fuel-price
+correction, a strict-raise on missing fuel that surfaced 26 corpus
+variants relying on a silent mains-gas default, a measurement-bug fix
+in the corpus's PE pin, and three slices closing per-cluster cascade
+gaps via SAP 10.2 Table 4a R-dispatch + a canonical electric-fuel
+classifier.
+
+| Slice | Commit | Scope |
+|---|---|---|
+| **S0380.131** | `14eee259` | Heating-oil price 7.64 → 5.44 (empirical, Elmhurst worksheet + cert 0240 back-solve) |
+| **S0380.132** | `0aa40b63` | `MissingMainFuelType` strict-raise on empty `main_fuel_type` (26 corpus variants moved to `_BLOCKED_BY_MISSING_MAIN_FUEL_TYPE`) |
+| **S0380.133** | `0d2d41ab` | Elmhurst §14.0 EES Code → Table 32 fuel code (BAF/BAI/RAM=anthracite, BCC=coal, BDI=dual, BKI=smokeless, BQI=wood chips, RPS=pellets bags, RUN=bulk, RWN=wood logs) — 10 solid-fuel variants unblocked |
+| **S0380.134** | `7530ed3f` | Corpus PE pin compared against `cert_to_demand_inputs` (EPC block) instead of rating mode (rating block has no Total PE row) |
+| **S0380.135** | `829a3318` | Table 4a R-dispatch in `_responsiveness` keyed on `sap_main_heating_code` (solid-fuel codes 151-161, 631-636) |
+| **S0380.136** | `4d004790` | `_is_electric_main` / `_is_electric_water` route via canonical T32-first normaliser (`table_32.is_electric_fuel_code`) — closes solid fuel 6 dual-fuel SAP −11.37 → +1.95 |
+| **S0380.137** | `3542186f` | Table 4a R-dispatch extended to electric storage / UFH / Electricaire / direct-acting / ceiling (codes 401-409, 421-425, 515, 691, 694, 701) |
+
+Extended handover suite at HEAD: **880 pass, 0 fail**.
+
+## What changed
+
+### Spec compliance (Table 4a + Table 32 + spec line 15271)
+
+S0380.135 + S0380.137 implement SAP 10.2 spec line 15271:
+
+> "R = responsiveness of main heating system (Table 4a or Table 4d)"
+
+Pre-slices the cascade only consulted Table 4d (emitter-based) — Table
+4a's per-heating-system R (typically lower than 1.0 for non-modulating
+systems) was silently ignored. The new
+`_RESPONSIVENESS_BY_SAP_CODE` dispatch in
+[`cert_to_inputs.py`](../rdsap/cert_to_inputs.py) overrides the
+Table 4d fallback when the SAP code is in the dict (31 entries
+covering all solid-fuel + electric storage / UFH / direct-acting /
+ceiling codes from Table 4a p.169-170).
+
+S0380.131 corrected `tables/table_32.py` heating oil 7.64 → 5.44
+(empirical, no spec citation possible — RdSAP 10 spec PDF p.95 is
+outlier vs Elmhurst worksheet + gov.uk register back-solve).
+
+### Strict-raise + canonical normalisation pattern
+
+S0380.132 added `MissingMainFuelType(ValueError)` in
+[`exceptions.py`](../exceptions.py). `_main_fuel_code` raises when
+the mapper leaves `main_fuel_type` empty / non-int. This surfaced 26
+of 41 corpus variants relying on the silent mains-gas default.
+
+S0380.136 promoted `table_32._is_electric_code` to public
+`is_electric_fuel_code` and routed `_is_electric_main` /
+`_is_electric_water` through it. Closed an API/Table-32 code-10
+collision (API 10 = electricity, T32 10 = dual fuel) that re-routed
+solid fuel 6's cost through off-peak electric tariff.
+
+### Mapper extraction extensions
+
+S0380.133 added `main_heating_ees: str` field to
+[`elmhurst_site_notes.py:MainHeating`](../../../datatypes/epc/surveys/elmhurst_site_notes.py)
+and extraction in
+[`elmhurst_extractor.py`](../../../backend/documents_parser/elmhurst_extractor.py),
+plus `_ELMHURST_MAIN_HEATING_EES_TO_FUEL_CODE` dict in
+[`mapper.py`](../../../datatypes/epc/domain/mapper.py) (10 entries
+keyed on 3-letter EES code).
+
+### Corpus test structure
+
+[`test_heating_systems_corpus.py`](../../../backend/documents_parser/tests/test_heating_systems_corpus.py)
+now has three tiers:
+
+1. `_EXPECTATIONS` (25 variants) — full residual-pin grid:
+   SAP / cost / CO2 from `cert_to_inputs` (rating block), PE from
+   `cert_to_demand_inputs` (EPC block).
+2. `_BLOCKED_BY_MISSING_MAIN_FUEL_TYPE` (16 variants) — assert-on-raise
+   tier driving
+   `test_heating_systems_corpus_blocked_variant_raises_missing_main_fuel_type`.
+3. Each variant covered exactly once across the two tiers (41 total).
+
+## Current residual cluster at HEAD `3542186f`
+
+### Solid fuel — 10/10 unblocked, tight cluster
+
+| variant | SAP code | R | ΔSAP | ΔPE |
+|---|---:|---:|---:|---:|
+| solid fuel 2 | 158 | 0.50 | +2.64 | -1211 |
+| solid fuel 3 | 160 | 0.50 | +1.32 | -935 |
+| solid fuel 4 | 633 | 0.50 | +1.59 | +151 |
+| solid fuel 5 | 153 | 0.75 | +1.70 | +160 |
+| solid fuel 6 | 160 | 0.50 | +1.95 | +87 |
+| solid fuel 7 | 160 | 0.50 | +2.04 | +44 |
+| solid fuel 8 | 160 | 0.50 | +1.81 | +88 |
+| solid fuel 9 | 636 | 0.75 | +1.71 | +155 |
+| solid fuel 10 | 634 | 0.50 | +1.75 | +120 |
+| solid fuel 11 | 634 | 0.50 | +1.62 | +171 |
+
+7/10 PE residuals within ±220 kWh. SAP cluster all +1.32 to +2.64.
+solid fuel 2 (-1211 PE) + solid fuel 3 (-935 PE) are the remaining
+outliers — likely Table 4a efficiency variant or kWh-totals issue.
+
+### Electric direct-acting — 6/7 unblocked, +5..+9 SAP cluster open
+
+| variant | SAP code | R | ΔSAP | Δcost | ΔPE |
+|---|---:|---:|---:|---:|---:|
+| electric 1 | 191 | 1.00 | +9.64 | −£222 | +165 |
+| electric 2 | 524 | 1.00 | +5.85 | −£135 | +971 |
+| electric 3 | 401 | 0.00 | +9.43 | −£217 | -1059 |
+| electric 5 | 402 | 0.20 | +6.76 | −£156 | -96 |
+| electric 6 | 404 | 0.40 | +7.82 | −£180 | -494 |
+| electric 7 | 408 | 0.60 | +7.58 | −£175 | -428 |
+| electric 8 | 409 | 0.80 | +5.84 | −£135 | +200 |
+| electric 9 | 421 | 0.00 | +6.77 | −£156 | +154 |
+
+**Shared pattern across all 7:** SAP +5.8..+9.6 with cost −£135..−£222.
+Consistent cost under-count strongly suggests a single Table 12a
+high/low-rate fraction handling bug OR a pumps/fans electric cascade
+gap. Same "one fix many variants" leverage pattern as previous slices.
+
+### Other cascade-OK variants
+
+| variant | ΔSAP | ΔPE | notes |
+|---|---:|---:|---|
+| ashp | +5.67 | -12 | ✓ PE closed |
+| gshp | +5.16 | -455 | |
+| oil 1 | +2.66 | -1050 | |
+| oil pcdb 1/2 | +0.42 | -84 | ✓ basically closed |
+| oil pcdb 3 | +1.16 | -271 | |
+| pcdb 1 | +6.95 | -3135 | largest open PE |
+
+### Blocked tier (16 variants in `_BLOCKED_BY_MISSING_MAIN_FUEL_TYPE`)
+
+| Category | Variants | SAP code(s) | EES code(s) | Likely fix |
+|---|---|---|---|---|
+| Community heating | 1, 2, 3, 4, 6 | 301-304 | COM (all share) | Derive fuel from §14.1 Community Heating block |
+| Electric storage | 11, 12, 13, 14 | 515, 691, 701 | WEA, REA, OEA | Extend `_ELMHURST_MAIN_HEATING_EES_TO_FUEL_CODE` to electric EES codes |
+| No system | (1) | 699 | NON | Spec assumed electric heaters |
+| Liquid-fuel non-oil | oil 2-6 | Table 4b 126-141 | BFD, BXE, BXF, BZC, B3C | Extend §15.0 fallback / mapper dict for HVO / FAME / B30K / bioethanol |
+| PCDB Bulk LPG | pcdb 3 | (PCDB) | (absent) | Add `"Bulk LPG"` → 2 to `_ELMHURST_MAIN_FUEL_TO_SAP10` |
+
+## Test baseline at HEAD `3542186f`
+
+```bash
+PYTHONPATH=/workspaces/model python -m pytest \
+    backend/documents_parser/tests/test_summary_pdf_mapper_chain.py \
+    backend/documents_parser/tests/test_heating_systems_corpus.py \
+    backend/documents_parser/tests/test_elmhurst_extractor.py \
+    backend/documents_parser/tests/test_elmhurst_end_to_end.py \
+    domain/sap10_calculator/worksheet/tests/test_e2e_elmhurst_sap_score.py \
+    domain/sap10_calculator/worksheet/tests/test_heat_transmission.py \
+    domain/sap10_calculator/worksheet/tests/test_internal_gains.py \
+    domain/sap10_calculator/worksheet/tests/test_solar_gains.py \
+    domain/sap10_calculator/worksheet/tests/test_dimensions.py \
+    domain/sap10_calculator/worksheet/tests/test_rating.py \
+    domain/sap10_calculator/worksheet/tests/test_ventilation.py \
+    domain/sap10_calculator/worksheet/tests/test_appendix_h_solar.py \
+    domain/sap10_calculator/worksheet/tests/test_mev.py \
+    domain/sap10_calculator/rdsap/tests/test_cert_to_inputs.py \
+    domain/sap10_calculator/rdsap/tests/test_golden_fixtures.py \
+    domain/sap10_calculator/tests/test_pcdb_table_322_lookup.py \
+    domain/sap10_calculator/tests/test_pcdb_table_329_lookup.py \
+    domain/sap10_calculator/tests/test_table_12a.py \
+    --no-cov -q
+```
+
+Expected: **880 pass, 0 fail**.
+
+## Memories to load (in order)
+
+```
+project-heating-systems-corpus    # full state at HEAD 3542186f
+feedback-sap-10-2-only-never-10-3 # CRITICAL — never reference SAP 10.3
+feedback-worksheet-not-api-reference
+feedback-spec-citation-in-commits
+feedback-verify-handover-claims
+feedback-zero-error-strict
+feedback-commit-per-slice
+feedback-aaa-test-convention
+feedback-e2e-validation-philosophy
+feedback-abs-diff-over-pytest-approx
+feedback-spec-floor-skepticism
+feedback-golden-residuals-near-zero
+feedback-one-e-minus-4-across-the-board
+reference-unmapped-sap-code       # updated S0380.135 + S0380.137
+reference-unmapped-api-code
+project-oil-price-spec-divergence # S0380.131 detail
+```
+
+## Next-slice candidates (in priority order)
+
+### 1. Electric +5..+9 SAP cluster — highest leverage
+
+7 electric corpus variants share +5.8..+9.6 SAP and −£135..−£222 cost
+under-count. Pattern strongly suggests one shared cascade gap. Likely
+candidates:
+
+- **Table 12a high/low-rate fraction** for electric main heating —
+  the cascade applies tariff splits per `space_heating_high_rate_fraction`,
+  but the worksheet may use a different fraction or skip the split.
+- **Pumps/fans kWh / cost** — cascade reports 130 kWh/yr; worksheet
+  reports 41 kWh/yr. Cascade over-counts by 89 kWh × electric ~13 p/kWh
+  = ~£12 — small, not the dominant cost gap.
+- **Cost factor cascading** — for electric main on 18-hour tariff, the
+  cascade uses 5.50 p/kWh (off-peak low rate). The worksheet uses... need
+  to probe.
+
+Probing one variant (electric 3, the worst at +9.43 SAP / -£217 cost)
+would identify the shared cause. If a single Table 12a / tariff fix
+closes most of the 7, that's a high-value slice.
+
+### 2. Unblock community heating cluster
+
+5 community heating variants all share `EES Code: COM` (no fuel info in
+the EES code). The fuel must be derived from the §14.1 Community
+Heating/Heat Network block which lodges the heat source type (gas
+boiler / CHP / heat pump / etc.). Each maps to a Table 32 heat-network
+code (51-58, 41-49).
+
+Implementation pattern: extend the extractor to capture §14.1 community
+heat source, add a SAP-code-301-304 → community-heating-fuel dispatch
+in the mapper.
+
+### 3. Unblock electric storage variants (11, 12, 13, 14)
+
+4 electric corpus variants blocked because mapper has no fuel. SAP
+codes 515 (Electricaire), 691 (Panel heaters), 701 (Electric ceiling)
+imply electric. Extend `_ELMHURST_MAIN_HEATING_EES_TO_FUEL_CODE`:
+
+| EES | Variant | Fuel |
+|---|---|---|
+| WEA | electric 11 (SAP 515) | 30 (standard electric) |
+| REA | electric 12 (SAP 691) | 30 |
+| OEA | electric 13/14 (SAP 701) | 30 |
+
+Or alternative: gate on `sap_main_heating_code in {191, 401-409, 421-425, 515, 691, 694, 701}` and infer electric — broader pattern.
+
+### 4. solid fuel 2 / 3 PE residuals (-935 to -1211)
+
+After R-dispatch closed 7/10 solid-fuel PE residuals, 2 remain at
+~-1000 PE. Both are anthracite (codes 158, 160). Same fuel and same R
+as other variants that closed. Possible:
+
+- Table 4a efficiency variant (winter/summer split)
+- Secondary heating fraction (Table 11) not applying
+
+### 5. pcdb 1 PE residual −3135
+
+Oil PCDB-listed boiler cert (no SAP code, PCDB index drives lookup).
+Largest open PE residual. Separate cause from R-dispatch.
+
+### 6. Tariff-dependent R promotion
+
+Codes 402/403/405 have R=0.20/0.40 off-peak vs R=0.40/0.60 24-hour
+tariff per Table 4a. Current dict uses off-peak default (corpus is all
+off-peak). If a 24-hour cert ever surfaces, promote
+`_RESPONSIVENESS_BY_SAP_CODE` from `dict[int, float]` to
+`dict[(int, Tariff), float]` lookup.
+
+### 7. Latent strict-raise opportunity
+
+`table_32.is_electric_fuel_code` / `_is_gas_code` silently return False
+for unmapped fuel codes. User raised this in S0380.136 discussion as a
+follow-up forcing-function pattern (same shape as
+`MissingMainFuelType`). Broad blast radius — defer until after the
+visible-residual closures.
+
+## Spec source quick-reference
+
+All under `domain/sap10_calculator/docs/specs/`:
+
+- **SAP 10.2 full spec**: `sap-10-2-full-specification-2025-03-14.pdf`
+  - **Spec line 15271** (R = responsiveness ... Table 4a or Table 4d)
+  - **Table 4a** (p.163-170) — heating systems with R column
+  - **Table 4b** (p.170-171) — gas / liquid fuel boilers
+  - **Table 4d** (p.170) — heat emitter R
+  - **Table 4e** (p.171-174) — control codes
+  - **Table 9 / 9a / 9b** — heating duration + MIT formulas (where R
+    enters the MIT adjustment)
+  - **Table 12** (p.191) — SAP rating fuel prices (regulated tariff)
+  - **Table 12a** — high/low-rate fraction by system × tariff
+- **RdSAP 10 spec**: `RdSAP 10 Specification 10-06-2025.pdf`
+  - **§19 Table 32** (p.95) — RdSAP10 fuel prices / CO2 / PE
+  - Heating oil price 7.64 in spec but 5.44 empirically (per S0380.131)
+- **BRE technical papers** at `sap10 technical papers/` — no Table 32
+  errata
+- **SAP 10.3** at `sap-10-3-full-specification-2026-01-13.pdf`:
+  **DO NOT reference** (per [[feedback-sap-10-2-only-never-10-3]])
+
+## Workflow per slice
+
+1. Read spec page + identify rule
+2. Probe cascade vs worksheet line-by-line for one variant in the
+   cluster; verify the diagnosis closes the residual via monkey-patch
+3. Write failing AAA test (literal `# Arrange / # Act / # Assert`)
+4. Implement helper / dispatch entry / mapper extension
+5. Verify test passes
+6. Probe full cluster impact + re-pin affected variants
+7. Run extended handover suite (command above)
+8. Pyright net-zero check on touched files (`git stash` → pyright →
+   `git stash pop` → pyright)
+9. Commit with spec citation +
+   `Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>`
+10. Update `project-heating-systems-corpus` + `MEMORY.md` index
+
+## What NOT to do
+
+- **Don't reference SAP 10.3** — track 10.2 deliberately
+- **Don't widen pin tolerances** to make pins pass — re-pin smaller or
+  find the spec gap
+- **Don't re-investigate closed work** (Slices .91..137 all settled)
+- **Don't add new helpers to `domain/sap10_ml/`** — on the deprecation
+  path
+- **Don't conflate the R-dispatch with the cost cluster** — R closes PE
+  (via demand), the +5..+9 SAP residual on electrics is the *cost-side*
+  gap, a separate issue
+- **Don't accept "spec-precision floor" framing** without spec-citation
+  work — verify against worksheet PDF + cross-cert empirical evidence
+
+## User direction at end of session
+
+The conversation flowed:
+1. Started on solid fuel 8 +0.87 ΔSAP — discovered it was a compensating-
+   errors illusion (real CO2 Δ +3525)
+2. User: "could we add an exception in the calculator that an empty
+   fuel type can't be given?" → S0380.132 strict-raise
+3. User: "I'm okay with breaking the tests if that means not debugging
+   silent, incorrect fallbacks"
+4. Suggested SAP-code → fuel derivation → S0380.133 solid-fuel EES
+   dispatch
+5. User asked for audit of remaining patterns → found PE measurement
+   bug + per-cluster issues → S0380.134 (PE pin fix) → S0380.135 (R
+   dispatch solid fuel)
+6. User: "is this another opportunity to raise an exception?" during
+   S0380.136 — answered: this is a *different bug class*
+   (type ambiguity, not missing data); broader raise opportunity exists
+   for `is_electric_fuel_code` / `_is_gas_code` silent-False on
+   unmapped (catalogued as #7 above)
+7. S0380.137 extended R-dispatch to electric
+
+The "find ONE fix that closes MULTIPLE variants" framing is the user's
+preferred approach. Each slice closed 6-10 variants via a single
+table-dispatch or convention-routing change.
+
+Good luck.
diff --git a/domain/sap10_calculator/docs/NEXT_AGENT_PROMPT_POST_S0380_137.md b/domain/sap10_calculator/docs/NEXT_AGENT_PROMPT_POST_S0380_137.md
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+# Next-agent prompt — post S0380.131..137
+
+You are picking up on branch `feature/per-cert-mapper-validation` at
+**HEAD `3542186f`**. The previous session closed seven slices:
+
+| Slice | What it did |
+|---|---|
+| S0380.131 | Heating-oil price 7.64 → 5.44 (empirical, Elmhurst worksheet) |
+| S0380.132 | `MissingMainFuelType` strict-raise; 26 corpus variants moved to blocked tier |
+| S0380.133 | Elmhurst §14.0 EES Code → fuel dispatch (unblocked 10 solid-fuel variants) |
+| S0380.134 | Corpus PE pin compared against `cert_to_demand_inputs` (EPC block) |
+| S0380.135 | SAP 10.2 Table 4a R-dispatch keyed on `sap_main_heating_code` (solid fuel) |
+| S0380.136 | `_is_electric_main` routed via canonical T32-first normaliser (closed solid fuel 6) |
+| S0380.137 | Table 4a R-dispatch extended to electric storage / UFH / Electricaire / ceiling |
+
+Extended handover suite: **880 pass, 0 fail**.
+
+## Read these first
+
+In order, before any tool call:
+
+1. [`HANDOVER_POST_S0380_137.md`](HANDOVER_POST_S0380_137.md) — full
+   state at HEAD `3542186f`, all 25 unblocked + 16 blocked variants,
+   per-cluster residuals, ranked next-slice candidates.
+2. [`HANDOVER_POST_S0380_130.md`](HANDOVER_POST_S0380_130.md) — prior
+   state at HEAD `c8486077` (for context on the corpus + S0380.131
+   plan that landed this session).
+
+## Load these memories before starting
+
+```
+project-heating-systems-corpus    # corpus state at HEAD 3542186f
+feedback-sap-10-2-only-never-10-3 # CRITICAL — never reference SAP 10.3
+feedback-worksheet-not-api-reference
+feedback-spec-citation-in-commits
+feedback-verify-handover-claims
+feedback-zero-error-strict
+feedback-commit-per-slice
+feedback-aaa-test-convention
+feedback-e2e-validation-philosophy
+feedback-abs-diff-over-pytest-approx
+feedback-spec-floor-skepticism
+feedback-golden-residuals-near-zero
+feedback-one-e-minus-4-across-the-board
+reference-unmapped-sap-code       # updated this session
+reference-unmapped-api-code
+project-oil-price-spec-divergence # S0380.131 detail
+```
+
+## Verify baseline first
+
+```bash
+PYTHONPATH=/workspaces/model python -m pytest \
+    backend/documents_parser/tests/test_summary_pdf_mapper_chain.py \
+    backend/documents_parser/tests/test_heating_systems_corpus.py \
+    backend/documents_parser/tests/test_elmhurst_extractor.py \
+    backend/documents_parser/tests/test_elmhurst_end_to_end.py \
+    domain/sap10_calculator/worksheet/tests/test_e2e_elmhurst_sap_score.py \
+    domain/sap10_calculator/worksheet/tests/test_heat_transmission.py \
+    domain/sap10_calculator/worksheet/tests/test_internal_gains.py \
+    domain/sap10_calculator/worksheet/tests/test_solar_gains.py \
+    domain/sap10_calculator/worksheet/tests/test_dimensions.py \
+    domain/sap10_calculator/worksheet/tests/test_rating.py \
+    domain/sap10_calculator/worksheet/tests/test_ventilation.py \
+    domain/sap10_calculator/worksheet/tests/test_appendix_h_solar.py \
+    domain/sap10_calculator/worksheet/tests/test_mev.py \
+    domain/sap10_calculator/rdsap/tests/test_cert_to_inputs.py \
+    domain/sap10_calculator/rdsap/tests/test_golden_fixtures.py \
+    domain/sap10_calculator/tests/test_pcdb_table_322_lookup.py \
+    domain/sap10_calculator/tests/test_pcdb_table_329_lookup.py \
+    domain/sap10_calculator/tests/test_table_12a.py \
+    --no-cov -q
+```
+
+Expected: **880 pass, 0 fail**.
+
+## Recommended next slice — electric +5..+9 SAP cluster
+
+**The signal:** all 7 cascade-OK electric corpus variants share a
+remarkably consistent pattern:
+
+| variant | SAP | Δcost   | ΔPE  |
+|---|---:|---:|---:|
+| electric 1 (191) | +9.64 | −£222 | +165  |
+| electric 2 (524) | +5.85 | −£135 | +971  |
+| electric 3 (401) | +9.43 | −£217 | -1059 |
+| electric 5 (402) | +6.76 | −£156 | -96   |
+| electric 6 (404) | +7.82 | −£180 | -494  |
+| electric 7 (408) | +7.58 | −£175 | -428  |
+| electric 8 (409) | +5.84 | −£135 | +200  |
+| electric 9 (421) | +6.77 | −£156 | +154  |
+
+All 7 carry SAP +5.8..+9.6 with cost under-count −£135..−£222 (cascade
+under-counts cost → over-counts SAP). The cost under-count is too
+uniform to be 7 separate causes — strongly suggests one shared cascade
+gap in electric main heating cost computation.
+
+**Most likely candidates** (in order):
+
+1. **Table 12a high/low-rate fraction** for electric main heating on
+   18-hour tariff (all corpus variants lodge `meter_type: 18 Hour`).
+   Cascade applies the tariff split per
+   `space_heating_high_rate_fraction(system, tariff)` — worksheet may
+   use a different split or skip the split.
+2. **Pumps/fans cascade** — cascade reports 130 kWh/yr, worksheet
+   reports 41 kWh/yr (+89 kWh × ~13 p/kWh = ~£12). Small, won't
+   close £150-£220 cost gap alone.
+3. **Cost factor selection** — cascade picks 5.50 p/kWh (18-hour low
+   rate) for electric main on off-peak; worksheet may apply a different
+   blended rate.
+
+**Slice plan:**
+
+1. Probe `electric 3` (worst at +9.43 SAP / -£217 cost / -1059 PE):
+   dump `inputs.space_heating_fuel_cost_gbp_per_kwh`, cascade
+   `fuel_cost.main_1_*` fields, worksheet block 11a (255) breakdown.
+2. Compare cascade cost components vs worksheet line refs (240/245/
+   246/249/250/251/255) to localise the gap.
+3. Identify the spec rule (Table 12a section + page).
+4. Write failing AAA test for the specific cost-component fix.
+5. Implement; verify cluster closure across all 7 electric variants
+   (electric 1/2/3/5/6/7/8/9).
+6. Re-pin affected variants; run extended handover suite + pyright
+   net-zero; commit.
+
+## Alternative next-slice candidates
+
+If the electric cost cluster diagnosis turns out heterogeneous (not
+one shared cause), pivot to:
+
+| # | Candidate | Variants closed | Notes |
+|---|---|---|---|
+| 2 | Community heating unblocking | 5 | Derive fuel from §14.1 Community Heating block (heat-network codes 41-58) |
+| 3 | Electric storage unblocking (WEA/REA/OEA) | 4 | Extend EES dict (electric 11/12/13/14 currently RAISE) |
+| 4 | solid fuel 2/3 PE residuals -935/-1211 | 2 | Both anthracite SAP 158/160; same R + fuel as variants that closed |
+| 5 | pcdb 1 PE -3135 | 1 | Oil PCDB-listed cert, largest open PE |
+| 6 | Tariff-dependent R promotion (402/403/405) | 0 | No 24-hour cert in corpus; defer until one surfaces |
+| 7 | `is_electric_fuel_code` / `_is_gas_code` strict-raise on unmapped | latent | User flagged in S0380.136 discussion |
+
+See `HANDOVER_POST_S0380_137.md` for full detail on each.
+
+## Standard slice workflow
+
+1. Read spec page + identify rule
+2. Probe cascade vs worksheet for one cluster variant; monkey-patch
+   to verify the fix closes
+3. Write failing AAA test (literal `# Arrange / # Act / # Assert`)
+4. Implement helper / dispatch entry / mapper extension
+5. Probe full cluster + re-pin affected variants
+6. Run extended handover suite + pyright net-zero
+   (`git stash` → pyright → `git stash pop` → pyright)
+7. Commit with spec citation +
+   `Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>`
+8. Update `project-heating-systems-corpus` + `MEMORY.md` index
+
+## What NOT to do
+
+- **Don't reference SAP 10.3** ([[feedback-sap-10-2-only-never-10-3]])
+- **Don't widen pin tolerances** to make pins pass — re-pin smaller or
+  find the spec gap
+- **Don't re-investigate closed work** — Slices .91..137 all settled
+- **Don't add new helpers to `domain/sap10_ml/`** — on deprecation path
+- **Don't conflate R-dispatch (PE-side) with the +5..+9 SAP cluster
+  (cost-side)** — R closes PE via demand calc; the cost-side cluster
+  is a separate Table 12a / tariff issue
+- **Don't accept "spec-precision floor" framing** without spec-citation
+  verification
+
+## User context
+
+The user's framing all session: **"find ONE fix that closes MULTIPLE
+variants at the same time, rather than per-variant chasing."** Each
+of the seven slices closed 6-10 variants via a single table-dispatch
+or convention-routing change. The electric +5..+9 cluster is the next
+high-leverage opportunity matching this pattern.
+
+The user is also explicitly OK with breaking tests if it surfaces
+silent fallbacks. Don't patch around silent defaults — make them
+loud.
+
+Good luck.