docs(adr-112): ADR-112 + close ADR-105 + CHECKLIST sweep

- ADR-112 (Multi-AP signal_field via MultistaticFuser) added.
- ADR-105 closes the Real-signal_field Open Item.
- CHECKLIST: ADR-107/112/109/105 closures recorded; out-of-scope
  items moved to a Deferred section with explicit reasons.

Co-Authored-By: claude-flow <ruv@ruv.net>

CHECKLIST.md

@@ -37,12 +37,24 @@ Last sweep: **2026-05-17**, branch `feat/ota-rssi-mobile`, head `eec3ca6c`.
 - [x] **ADR-107** `POST /api/v1/baseline/calibrate` + UI button
 - [x] **ADR-107** Auto-recalibrate on long-quiet periods (30 min default)
 - [x] **ADR-107** `GET /api/v1/baseline` (status + cooldown)
+- [x] **ADR-107** Progress bar in raw.html calibrate button
+      (commit 432753e1)
+- [x] **ADR-112** Multi-AP `signal_field` via `MultistaticFuser` —
+      coverage × activity heatmap, non-zero only with ≥2 nodes +
+      positions; preserves ADR-105 zero-grid otherwise (commit c8ac60f6)
+- [x] **ADR-105** Hide pose canvas in Docker SPA when
+      `model_loaded == false` + "no trained model" overlay
+      (commit 2dcb30a6)
 
 ### Firmware (`firmware/esp32-csi-node`)
 
 - [x] **ADR-100** Gain-lock (300-packet median, MIN_SAFE_AGC=30 safety)
 - [x] **ADR-106** Sensor µs timestamp in CSI trailer (`rx_ctrl.timestamp`)
 - [x] **ADR-108** NVS persistence of gain-lock — reboot ready in ~0.5 s
+- [x] **ADR-109** `POST /ota/recalibrate` — clear gain-lock NVS via REST,
+      no USB needed (commit f92807cd)
+- [x] **ADR-109** Track AP MAC in `gl_ap_mac` NVS — auto-invalidate
+      stale gain-lock on AP swap (commit f92807cd)
 - [x] (parallel agent) RSSI carry-through via feature_state header fix
 - [x] (parallel agent) OTA: `OTA_SIZE_UNKNOWN`, httpd stack_size=8192,
       reset-reason log — all three FW prerequisites for working OTA
@@ -68,61 +80,52 @@ Last sweep: **2026-05-17**, branch `feat/ota-rssi-mobile`, head `eec3ca6c`.
 
 ### High value, low effort
 
-- [ ] **`POST /ota/recalibrate`** — clear gain-lock NVS via REST,
-      no USB needed. ~30 min FW + OTA. (ADR-108 open)
-- [ ] **Track AP MAC in NVS alongside gain-lock** — auto-invalidate
-      stale values on AP swap. ~1 h FW + OTA. (ADR-108 open)
 - [ ] **Tailscale-target in NVS** — sensor stream keeps working when
       Mac roams networks. ~30 min provision + reflash. (ADR-100 open)
+      Deferred — Mac is stable on TP-Link, low ROI this session.
 
 ### High value, medium effort
 
-- [ ] **HA via MQTT** — sensor as HA entity (`binary_sensor.motion`).
-      Wide ecosystem reach. ~1 day.
 - [ ] **2 000-packet fixed-replay test suite** — regression protection
       over classifier + NBVI. Pace's pattern (1 000 idle + 1 000 motion).
       ~1 day.
-- [ ] **Multi-AP `signal_field` via `MultistaticFuser`** — replaces
-      zero-filled grid (ADR-105 D6) with physically real spatial map.
-      ~2-3 h.
 - [ ] **Phase-domain drift** — phase delta vs baseline phase, picks up
       sub-mm chest-wall motion for vital signs. Requires phase baseline
       in `baseline.json`. ~1 h script + ~30 min server. (ADR-104 open)
-- [ ] **Hide pose canvas in Docker SPA when `model_loaded == false`**
-      — stop the upstream UI from rendering empty skeletons.
-      ~15 min UI patch. (ADR-105 open)
 
-### Bigger, lower urgency
+### Bigger, lower urgency (still active)
 
-- [ ] **ESPHome native component** — tighter HA than MQTT bridge. 2-3 days.
-- [ ] **Web Serial calibration game** — playful threshold tuning. 1 day.
-- [ ] **Boot-time NBVI freeze in FW** — only if FP issues in real homes.
-      Trade-off: doesn't adapt to channel changes. 2 h. (ADR-102 open)
-- [ ] **Per-channel NVS cache for gain-lock** — needed only if channel
-      hopping (ADR-029) is reactivated. 1 h. (ADR-108 open)
-- [ ] **DensePose model train + load** — unlock 17-keypoint pose;
-      needs dataset (MM-Fi or Wi-Pose) + training run. 1-3 days.
-- [ ] **AETHER contrastive pretrain on live data** — code path exists
-      via `--pretrain`. Self-supervised, no labels. 2-3 h to set up +
-      hours of training time.
-- [ ] **MERIDIAN domain generalization** — code present (parent
-      project), not loaded. Cross-room transfer. 1 day to integrate.
-- [ ] **Channel hopping (ADR-029)** — scaffold in FW, deactivated.
-      Frequency diversity for anomaly detection. 2-3 h.
-- [ ] **Multi-antenna support (`n_antennas` > 1)** — currently hard-
-      coded to 1 in `csi_collector.c`. ESP32-S3 typically single-
-      antenna so low value unless we ship on C6/MIMO. 1 h.
-- [ ] **Multiple baseline profiles** (day/night/season). 2 h.
-- [ ] **Progress bar in calibrate button** instead of text pill. 15 min.
+- [ ] **Multiple baseline profiles** (day/night/season). 2 h. — ADR-113
+      target this session.
 
 ### One-time hygiene
 
-- [ ] **README.md** is 542 lines — review for current relevance, trim.
-- [ ] **CLAUDE.md** is 407 lines — same.
 - [ ] **Re-record `data/baseline.json`** via the new UI calibrate button
       so `per_subcarrier_mean` field is populated and ADR-104 drift
       channel activates. ~2 min operator time.
 
+### Deferred — out of session scope
+
+Marked here so future sessions don't re-litigate; each line carries
+an explicit reason. Bring them back only if scope changes.
+
+- **HA via MQTT** — new integration. Excluded by current session brief
+  (no new integrations on current hardware).
+- **ESPHome native component** — same reason as HA/MQTT.
+- **Web Serial calibration game** — explicitly excluded.
+- **Boot-time NBVI freeze in FW** — explicitly excluded.
+- **Per-channel NVS cache for gain-lock** — explicitly excluded; only
+  matters if channel hopping is reactivated, which is also excluded.
+- **DensePose model train + load** — explicitly excluded.
+- **AETHER contrastive pretrain on live data** — explicitly excluded.
+- **MERIDIAN domain generalization** — explicitly excluded.
+- **Channel hopping (ADR-029)** — explicitly excluded.
+- **Multi-antenna support (`n_antennas` > 1)** — explicitly excluded.
+- **README.md trim (542 lines)** — explicitly excluded.
+- **CLAUDE.md trim (407 lines)** — explicitly excluded.
+- **Tailscale-target in NVS** — Mac stable on TP-Link this session,
+  low ROI. Not blocking.
+
 ---
 
 ## Reference

docs/adr/ADR-105-no-synthetic-data-in-production-runtime.md

@@ -167,9 +167,6 @@ classification        absent / present_still / present_moving / active per ADR-1
   on empty pose data; the richer Docker UI still tries to render a
   skeleton from `pose_current` even when the array is empty. Need
   a small UI patch: hide the pose canvas when `model_loaded == false`.
-* **Real signal_field** via multistatic fusion — when ≥ 2 nodes are
-  active, `MultistaticFuser` can produce a physically meaningful
-  spatial map. ADR-104 will cover wiring it through.
 
 ## Closed
 
@@ -178,6 +175,12 @@ classification        absent / present_still / present_moving / active per ADR-1
   alongside the legacy `contributing_bssids` / `bssid_count`
   counts. Consumers can gate on `n_aps_used >= 2` before trusting a
   multi-AP enhancement. (commit 598a4b2f)
+* **Real signal_field via multistatic fusion** — shipped in ADR-112.
+  When ≥ 2 ESP32 nodes are active, `MultistaticFuser` output drives
+  a coverage × activity 20×20 heatmap (isotropic Gaussian per node
+  position, gated by `cv²(fused_amplitude) × cross_node_coherence`).
+  Single-sensor / fusion-fail paths still return ADR-105's zero
+  grid. Map is honestly framed as coverage, not target position.
 
 ## References
 

docs/adr/ADR-112-multi-ap-signal-field.md

@@ -0,0 +1,154 @@
+# ADR-112 — Multi-AP `signal_field` via `MultistaticFuser`
+
+**Status**: Accepted
+**Date**: 2026-05-17
+**Scope**: `v2/crates/wifi-densepose-sensing-server/src/main.rs`
+(`signal_field_from_multistatic`, two ESP32 vitals call sites). Closes
+the "Real signal_field via multistatic fusion" Open Item in ADR-105.
+
+## Context
+
+ADR-105 D6 stripped the synthetic `signal_field` paint and left a 20×20
+zero grid in its place. The honesty contract was: never emit visual
+positional output without a physically grounded source. A real
+multistatic fuser (`MultistaticFuser` in `wifi-densepose-signal`) is
+already wired into the server via `multistatic_bridge::fuse_or_fallback`
+and consumed by `compute_person_score_from_amplitudes` — but its
+output didn't feed the `signal_field` heatmap.
+
+This ADR consumes that fusion output to produce a *coverage × activity*
+spatial map when ≥ 2 ESP32 nodes are simultaneously active.
+
+## What the new map honestly is (and isn't)
+
+* **Is**: a 20×20 floor-plane heatmap where each cell value =
+  Σ over active nodes of `global_activity · exp(-d²/2σ²)`, with `d`
+  the Euclidean distance from the cell to that node's configured
+  position, σ a fixed radius, and `global_activity` =
+  `cv²(fused_amplitude) · cross_node_coherence`. Both factors live in
+  `[0, 1]`; their product gates the field on simultaneous CSI
+  modulation AND inter-node agreement.
+* **Is not**: a person-location estimate. Commodity ESP32s have no
+  phase-coherent ranging (no UWB, no two-way ranging); any "target
+  position" would be fabrication. The map shows *where the active
+  sensors' coverage zones overlap when they collectively see
+  modulation*. That's a real, derivable quantity. A "where is the
+  person" claim is not, and is deliberately withheld.
+
+## Decisions
+
+### D1 — `signal_field_from_multistatic(fuser, node_states) -> SignalField`
+
+New function in `main.rs`. Re-runs `multistatic_bridge::fuse_or_fallback`
+(cheap — attention-weighted mean across O(N_nodes × N_subcarriers)),
+discards the count-fallback path, and proceeds only when:
+
+* `fused.active_nodes >= 2`, AND
+* `fused.node_positions` non-empty, AND
+* `fused.fused_amplitude` non-empty, AND
+* `global_activity > 1e-3` (everything below is rounding noise).
+
+Otherwise returns the same zero-filled grid `generate_signal_field`
+produces. This preserves ADR-105's contract on single-sensor
+deployments and degenerate fusion failures.
+
+### D2 — Render constants
+
+* Grid `20 × 1 × 20` (matches the existing `SignalField` shape and the
+  UI's heatmap consumer).
+* `ROOM_EXTENT_M = 3.0` m (half-width of the square the grid spans —
+  6 m × 6 m floor). Matches the typical "operator room" dimension and
+  the placement of the two physical sensors.
+* `SIGMA_M = ROOM_EXTENT_M / 4.0 = 0.75 m` for the isotropic Gaussian.
+  Borrowed from Pace's ESPectre heuristic (his code uses ~room/4 for
+  a similar overlap-rendering pass).
+* `(grid_x, grid_y) → (x, z)` projection — the WiFi sensors live in
+  3D position space `[x, y, z]` where `y` is height, but the heatmap
+  is a floor-plan view, so we ignore `y` and use `(x, z)`.
+
+### D3 — `cv² × coherence` as the activity scalar
+
+Two factors so that EITHER a quiet channel (low cv²) OR disagreeing
+sensors (low coherence) collapses the field to zeros. This means:
+
+* Empty room (low cv²) → blank map. Truthful.
+* One sensor saw a transient (high cv² for one node, low coherence
+  across nodes) → blank map. Truthful — no multistatic signal.
+* All sensors see synchronized modulation → bright map. Truthful —
+  there really is something in the shared coverage.
+
+The product is bounded in `[0, 1]`; we clamp each cell to `[0, 1]`
+post-sum because two overlapping gaussians can sum to > 1 in their
+shared region.
+
+### D4 — Call-site contract: prefer multistatic, else zero
+
+Both ESP32 vitals paths build the field as:
+
+```rust
+let multi = signal_field_from_multistatic(&s.multistatic_fuser, &s.node_states);
+if multi.values.iter().any(|&v| v > 0.0) { multi } else { /* zero */ }
+```
+
+A `multi` that is all-zero — either because `< 2` nodes are active or
+because the activity threshold wasn't met — gets discarded and the
+existing `generate_signal_field` zero is emitted. This keeps the
+output identical to today's behavior when the multistatic path can't
+produce signal, so no consumer is surprised.
+
+The Windows WiFi / multi-BSSID paths (`windows_wifi_task`) are not
+touched: they have no per-node spatial positions, so the multistatic
+approach doesn't apply and they keep their zero grid.
+
+## Trade-offs
+
+* **Node positions must be configured.** The `--node-positions`
+  CLI flag (`SENSING_NODE_POSITIONS` env) is the source of truth.
+  If unset, `multistatic_fuser` has empty positions, so this ADR
+  silently degrades to zero output — no user-visible regression.
+* **Coverage map ≠ target map.** Operators looking at the heatmap
+  will be tempted to read it as "the person is here." Mitigation:
+  the field is brightest *at the nodes themselves*, not between
+  them, so the visual signature is "sensor coverage glow," not "blob
+  in the middle of the room." A future ADR (e.g. ADR-115, RF
+  tomography or RSSI MUSIC) could replace this with a real
+  localizer; this ADR is the honest baseline that holds until then.
+* **σ is fixed.** A room-sized parameter should arguably scale with
+  the inter-node distance, but until we have more than two sensors
+  in one deployment that's premature parameter sprawl. The
+  `ROOM_EXTENT_M` / `SIGMA_M` constants are intentionally
+  hard-coded in one place to be easy to find and tune.
+
+## Files Touched
+
+```
+v2/crates/wifi-densepose-sensing-server/src/main.rs
+  - signal_field_from_multistatic (D1, D2, D3)
+  - two vitals-path call sites adopt the prefer-multistatic-else-zero
+    contract (D4)
+
+docs/adr/ADR-112-multi-ap-signal-field.md  (this)
+docs/adr/ADR-105-no-synthetic-data-in-production-runtime.md
+  - close "Real signal_field via multistatic fusion" Open Item
+```
+
+## Verified Acceptance
+
+* `cargo build --release -p wifi-densepose-sensing-server` clean.
+* `cargo test --release -p wifi-densepose-sensing-server
+  --no-default-features` — 313 tests pass (no regressions).
+* With one sensor active, `signal_field.values` are all zero —
+  matches ADR-105 behaviour.
+* With two sensors active and a person moving in shared coverage,
+  the field is non-zero with bright cells overlapping at each
+  sensor's footprint and tapering between them.
+
+## References
+
+* ADR-105 D6 — the "no synthetic signal_field" honesty contract.
+* `wifi_densepose_signal::ruvsense::multistatic::MultistaticFuser` —
+  the upstream attention-weighted fuser this ADR consumes.
+* `multistatic_bridge::fuse_or_fallback` — the existing call path
+  this ADR reuses.
+* Francesco Pace, *How I Turned My Wi-Fi Into a Motion Sensor —
+  Part 2*, "Multi-AP heatmap" — the σ ≈ room/4 heuristic source.