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api-docs/adr/ADR-308-sensor-placement-optimizer.md

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+# ADR-308: Sensor placement optimizer — floorplan + inventory → recommended positions
+
+- **Status**: Accepted — initial implementation (ADR-300 phase 3)
+- **Date**: 2026-08-11
+- **Deciders**: ruv
+- **Tags**: placement, planning, rf-twin, coverage, worldgraph, phase-3
+
+## Context
+
+This ADR is a child of **ADR-300** and owns primitive #8, *sensor placement
+optimizer*. In the ADR-300 DAG it is a phase-3, research-forward primitive that
+sits on top of the fused world state and is tightly coupled to **ADR-315**
+(digital RF twin): the twin provides the propagation simulation this optimizer
+plans against. It reads the **ADR-306** canonical ontology for the physical
+scene and, after install, compares its predictions against ADR-302 observability
+and the ADR-318 capability certificate.
+
+The problem it solves is the single most common cause of a bad RuView
+deployment: sensors placed by guesswork. Whether a room can be reliably sensed
+depends on AP/sensor geometry relative to walls, Fresnel-zone clearance,
+multipath structure, and where people actually move. Today an installer has no
+principled way to answer "where do I put the two nodes I have so the kitchen is
+observable?" — and no way, after install, to know whether reality matched the
+plan. This is a genuine **differentiator**: it turns RuView from "sense
+whatever the given placement happens to allow" into "recommend the placement
+that makes the requested sensing feasible."
+
+Relevant existing assets to build on rather than duplicate:
+
+- The `worldgraph` crate models the physical scene the optimizer plans over:
+  `Room`/`Space` with `bounds_enu`, `Wall { rf_attenuation_db }` (drywall ≈ 3
+  dB, brick ≈ 12 dB), `Doorway`, and `Zone` — enough geometry and coarse RF
+  attenuation to seed a coverage model, plus `Sensor` nodes (ADR-306) for
+  candidate positions.
+- **ADR-315** (RF twin, phase 3) is the propagation/multipath simulator; this
+  optimizer is a *consumer* of the twin, not a second simulator.
+- **ADR-302** (OOD/observability) and **ADR-318** (capability certificate)
+  define what "reliably sense the requested phenomenon" means, so the optimizer
+  can optimize against the same observability metric the runtime later gates on.
+- **ADR-029** (multistatic) and **ADR-063** (mmWave fusion) inform which link
+  geometries are useful for which phenomena.
+
+## Options considered
+
+1. **Static placement guidelines in docs (e.g. "one node per room, opposite
+   the door").** Rejected: ignores the specific floorplan, wall materials, and
+   the actual hardware inventory; gives no uncertainty and no post-install
+   feedback.
+2. **Full electromagnetic solver per site.** Rejected for the default path:
+   too heavy for an installer workflow and overkill relative to the coarse
+   `rf_attenuation_db` scene RuView actually has; reserved as an optional
+   high-fidelity backend inside ADR-315.
+3. **A coverage optimizer that consumes the ADR-315 RF twin over the ADR-306
+   scene, then validates predicted vs. measured observability after install.**
+   Chosen.
+
+## Decision
+
+Define a **placement optimizer** that takes a floor plan (ADR-306 scene) and a
+hardware inventory and recommends sensor positions, then closes the loop after
+install.
+
+### 1. Inputs
+
+- The ADR-306 canonical scene: `Space`/`Zone` bounds, `Wall` segments with
+  `rf_attenuation_db`, `Doorway` topology, and any already-placed `Sensor`
+  nodes.
+- A hardware inventory: the count and type of available radios (ESP32-S3/C6
+  nodes, mmWave, adapters) with their capability envelopes (what each can
+  sense, per ADR-318 / ADR-320 HAL descriptors).
+- A sensing objective: which phenomenon must be observable in which
+  `Space`/`Zone` (presence, vitals, pose), expressed against the ADR-302
+  observability metric.
+
+### 2. Prediction
+
+- For a candidate placement, query the **ADR-315 RF twin** for simulated RF
+  coverage: path loss through `Wall` attenuation, **Fresnel-zone clearance**
+  between link endpoints, and coarse **multipath** structure. From that derive
+  an **expected observability** and an **uncertainty** for each objective in
+  each space — reusing the same observability definition ADR-302 gates on so the
+  plan and the runtime speak one language.
+- Search over candidate positions (the inventory bounds the count; the scene
+  bounds the geometry) to recommend the placement that maximizes objective
+  observability, reporting expected observability **and its uncertainty** per
+  space — never a single confident number for a simulated result.
+
+### 3. Post-install loop
+
+- After install, compare **predicted vs. measured** observability using the
+  ADR-302 runtime observability signal from the freshly enrolled (ADR-305),
+  calibrated (ADR-301) sensors. Where measurement disagrees with prediction,
+  recommend adjustments (move, re-aim, add a node) and feed the residual back
+  to improve the ADR-315 twin's scene parameters (e.g. a wall's effective
+  attenuation).
+
+### Evidence discipline
+
+- Predicted coverage is a **simulation** (evidence level L0 per ADR-282) and is
+  labelled `SYNTHETIC`; it is a *recommendation*, never a sensing claim.
+- The predicted-vs-measured comparison is the only place a `MEASURED` statement
+  appears, and only with a reproducer and real-silicon observability data
+  (CLAUDE.md hardware rule). The optimizer never presents a simulated coverage
+  map as evidence that a room *is* being sensed.
+
+## Consequences
+
+- Installers get a principled, floorplan-specific placement plan and, crucially,
+  a post-install check that says whether reality matched the plan — a
+  differentiating capability over guess-and-check deployment.
+- Quality is bounded by the fidelity of the ADR-315 RF twin and the coarseness
+  of the `worldgraph` scene (2D walls, coarse attenuation). The optimizer
+  reports uncertainty rather than overstating a coarse model; higher fidelity
+  is an ADR-315 concern.
+- Hard dependency on ADR-315 (twin), ADR-302 (observability metric), and
+  ADR-306 (scene); this ADR does not build a simulator or an observability
+  metric of its own.
+- Being phase 3, this is design intent sitting on the fused world state; it is
+  expected to be revised as ADR-315 and the phase-1 spine land.
+- No claim that recommended placement *guarantees* sensing — it maximizes
+  modelled observability subject to inventory and geometry, with explicit
+  uncertainty.
+
+## Validation
+
+- Unit tests: coverage/observability prediction is a deterministic function of
+  scene + placement + twin parameters; Fresnel-zone and wall-attenuation math
+  against known analytic cases; search returns the modelled-optimal placement on
+  small synthetic scenes.
+- Integration test: on a synthetic floorplan with a known-good and a
+  known-bad placement, the optimizer ranks them correctly and reports higher
+  uncertainty for the marginal case.
+- Post-install loop test: injected predicted-vs-measured disagreement produces a
+  sensible adjustment recommendation and a twin-parameter residual.
+- Field validation (deferred, real-silicon): predicted vs. measured
+  observability on an instrumented real site, reported as `MEASURED` with a
+  reproducer. Until then all coverage output is `SYNTHETIC`/L0. No coverage or
+  accuracy number is asserted by this ADR.