docs: handover — golden SAP drive-to-zero priority (2130/7536); 0240 architectural

Add a CURRENT PRIORITY section: of 53 pinned golden certs, 3 have non-zero
SAP residual. 2130 (+0.85 cont) + 7536 (+0.57 cont) are real multi-part-wall
fabric over-predictions (the drive-to-zero targets, possibly one shared
cause). 0240 (-1) is architectural — the lodged 73 needs an unpreserved
2013+ pump; document the cause, do NOT re-pin (user decision).

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

domain/sap10_calculator/docs/HANDOVER_MAPPER_BUGS.md

@@ -6,14 +6,47 @@ state after closing the 0240 investigation and fixing the first of several
 API-mapper/cascade bugs the audit surfaced.
 
 - **Branch:** `feature/per-cert-mapper-validation`
-- **HEAD:** `ee484d9f` (S0380.213). Confirm with `git rev-parse HEAD`.
+- **HEAD:** `b9bbcecb` (docs after S0380.213). Confirm with `git rev-parse HEAD`.
 - **Baseline:** `2386 passed, 1 skipped, 0 failed` (AGENT_GUIDE §4 suite command).
   ALSO run `domain/sap10_ml/tests/` when touching `rdsap_uvalues.py` — 2 PRE-EXISTING
   stone-formula failures there, see Thread 1.
 - **Next slice number:** **S0380.214**.
-- **Open:** Thread 2 *demand* tail only — 9390 ~7% demand over-count (SAP -2, PE 220 vs
-  205) = heat-source-efficiency-default / fabric residual. CO2/PE collision (S0380.212) +
-  standing charge (S0380.213) FIXED. Threads 1 + 3 **CLOSED**.
+
+---
+
+## ★ CURRENT PRIORITY — drive golden-fixture SAP residuals to ZERO
+
+`_EXPECTATIONS` in `test_golden_fixtures.py` holds **53 pinned golden certs**. The suite
+is GREEN. **Only 3 have a non-zero SAP integer residual**, and they split into two kinds:
+
+| cert | lodged | cont SAP | resid | nature |
+|---|---|---|---|---|
+| **2130-1033-4050** | 82 | **83.349** | **+1** | REAL +0.85 over-prediction — multi-part **solid-brick** wall fabric |
+| **7536-3827-0600** | 68 | **69.071** | **+1** | REAL +0.57 over-prediction — multi-bp **D/L/F cavity** wall fabric |
+| **0240-0200-5706** | 73 | **72.462** | **−1** | **ARCHITECTURAL — do NOT chase, do NOT re-pin** (see below) |
+
+**The two real targets are 2130 + 7536.** Both are fabric *over*-predictions on **multi-part
+wall** geometry (a wall with alternative-construction sub-areas / multiple building parts),
+so they may share a single root cause in the §3 per-part wall area/U handling — a fix to
+one could close both. Method: walk the §3 heat-transmission cascade per-part vs the lodged
+register subsystem ratings (the certs are API-only — no worksheet — so the bar is ±0.5 SAP
+vs lodged, but the goal is the integer flip 83→82 / 69→68, i.e. shave ~0.85 / ~0.57 off the
+continuous SAP). If a multi-part-wall U or area is over-counted, that is the lever. The user
+generates Elmhurst worksheets on request — ASK for a simulated case mirroring 2130's wall
+(multi-part solid brick) rather than guess a U-value (the session methodology lesson).
+
+**0240 (−1) is NOT driveable from the JSON and the user has decided NOT to re-pin it —
+document the cause only.** Continuous SAP is 72.462; the true SAP is **72**. The lodged
+**73 requires a "2013 or later" circulation pump (41 kWh)**; 0240's open-data API lodges
+`central_heating_pump_age=0` = **Unknown → 115 kWh**. The encoding was proven across 13
+API+Summary pairs (`0`=Unknown, `2`=2013+). The export did not preserve the pump age that
+produced the lodged 73, so 73 is unreachable without inventing data. Both fabric bugs that
+masked it are now fixed (wall S0380.209 + roof S0380.211 → cont 72.462). **Leave the pin at
+`actual_sap=73, expected_sap_resid=-1`; the notes already record this.** Driving it to zero
+would mean fudging the pump age — don't.
+
+Latent (lower priority): **9390** (community, −2, **unpinned**/retired) ~7% demand
+over-count — see Thread 2.
 
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