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+# ADR-307: Persistent identity & tracking — privacy-preserving probabilistic tracks
+
+- **Status**: Accepted — initial implementation (ADR-300 phase 2)
+- **Date**: 2026-08-11
+- **Deciders**: ruv
+- **Tags**: tracking, identity, privacy, fusion, worldgraph, phase-2
+
+## Context
+
+This ADR is a child of **ADR-300** and owns primitive #7, *persistent identity
+& tracking*. In the ADR-300 DAG it is a phase-2 primitive sitting on the
+phase-1 spine: it **consumes the ADR-306 ontology** (producing and updating the
+`Track` and `Person` node types defined there), it relies on **ADR-305**
+authenticated identity so that the observations it associates have a verified
+origin, and its outputs are governed `Event`s that ADR-318/ADR-319 can certify
+and witness.
+
+The product need is to reason about *persistent entities* — "person_7 entered
+the kitchen, then the hallway, then the bedroom" — across radios, modalities,
+rooms, and time. The hard constraint is that this must happen **without
+establishing civil identity**. RuView is camera-free (ADR-282), and a
+persistent pseudonymous track must never become, or be joinable to, a real-
+world named individual. This is a privacy property to be enforced *by
+construction*, not a policy footnote.
+
+Substantial scaffolding already exists in
+`v2/crates/wifi-densepose-mat/src/tracking` and must be **reused/extended, not
+rebuilt**:
+
+- `SurvivorTracker`, `TrackedSurvivor`, `TrackId`, `TrackerConfig`,
+  `TrackLifecycle`, and `TrackState` — a multi-target tracker with lifecycle
+  (tentative/active/lost/terminal) and a `TrackId` backed by a UUID
+  (`as_uuid`).
+- `KalmanState` with `predict`/`update`, `position`, `velocity`,
+  `position_uncertainty`, and `mahalanobis_distance_sq` — the motion model and
+  gating distance.
+- `CsiFingerprint`, `DetectionObservation`, `AssociationResult`, and the
+  `can_reidentify`/`matches`/`mark_rescued`/`rescue` re-identification surface —
+  the appearance/fingerprint channel for track continuity.
+
+What is missing is (a) continuity **across radios, modalities, and rooms** (the
+tracker today reasons within a node/room context), (b) a **persistent** entity
+that survives track loss and hand-off between spaces, and (c) an explicit
+**privacy boundary** that guarantees no civil-identity binding.
+
+## Options considered
+
+1. **Per-room independent trackers, no cross-room identity.** Rejected: cannot
+   express "person_7 moved kitchen → hallway → bedroom"; loses the entity at
+   every room boundary.
+2. **Global identity keyed on a strong biometric fingerprint.** Rejected: a
+   fingerprint strong enough to re-identify across long gaps trends toward a
+   civil-identity-grade biometric — exactly what the privacy constraint
+   forbids.
+3. **Probabilistic persistent tracks with bounded, decaying pseudonymous
+   association, built on the existing MAT tracker.** Chosen.
+
+## Decision
+
+Extend `wifi-densepose-mat/tracking` into a **cross-domain persistent track
+layer** that produces ADR-306 `Track`/`Person` nodes.
+
+### 1. Persistent probabilistic entity
+
+- A persistent entity is a pseudonymous `Person` node (ADR-306) with a stable
+  synthetic id (e.g. `person_7`) backed by the existing `TrackId`/UUID. It
+  aggregates one or more `SurvivorTracker` tracks over time and space and holds
+  a **probabilistic** continuity belief — association is never asserted as
+  certain, and every hand-off carries a confidence.
+- Continuity across a track-loss gap reuses the existing re-identification
+  surface (`can_reidentify`, `CsiFingerprint`, `AssociationResult`), extended
+  with a **time- and distance-decayed** association prior so that confidence in
+  "same entity" falls with the size of the gap. Beyond a bounded horizon the
+  association is dropped and a new pseudonym is minted rather than forcing a
+  join — under-linking is the privacy-safe failure mode.
+
+### 2. Cross-radio / cross-modality / cross-room continuity
+
+- Association operates over the ADR-306 ontology graph: `Observes` edges from
+  multiple `Sensor`s and `AdjacentTo`/`Doorway` topology constrain plausible
+  hand-offs (a person can only move between adjacent spaces). The existing
+  `mahalanobis_distance_sq` gating extends to a fused observation across
+  modalities rather than a single node's detections.
+- Fusion here is track-level association; the underlying multi-modality fusion
+  (radar/mmWave per ADR-063, multistatic per ADR-029, and real sensor fusion
+  per ADR-311) supplies the observations. This ADR depends on those for the raw
+  cross-modality evidence and does not re-implement sensor fusion.
+
+### 3. Privacy boundary (by construction)
+
+- **No civil-identity binding.** The persistent id is a synthetic pseudonym
+  with no field, edge, or join key to any name, account, phone, MAC, or other
+  civil identifier. The type carries no such field, so binding is impossible in
+  the schema, not merely discouraged.
+- The `CsiFingerprint` used for re-identification is **bounded and decaying**:
+  it is scoped to short-horizon continuity, is not persisted as a long-term
+  biometric template, and expires. This keeps re-identification useful for
+  "same person across the hallway" while structurally unable to serve "this is
+  the same person who visited last month."
+- Every `Track`/`Person`/`Event` produced carries `SemanticProvenance` and an
+  `EvidenceLevel` (ADR-282), and honors the ADR-277/ADR-280 edge governance and
+  ADR-141 attestation — a pseudonymous track is still governed P-class data.
+  Tracking accuracy is a per-domain claim to be tagged MEASURED/CLAIMED/
+  SYNTHETIC with a reproducer; **this ADR claims no accuracy number.**
+
+## Consequences
+
+- RuView can express persistent, cross-room trajectories for automation and
+  analytics while remaining camera-free and civil-identity-free.
+- The privacy-safe failure mode is **under-linking** (mint a fresh pseudonym
+  when unsure), which will fragment a trajectory across long gaps or sparse
+  coverage. This is a deliberate trade: a fragmented pseudonym is safe, a
+  wrong civil-identity join is not.
+- Extends an existing tracker rather than forking one; single-room single-radio
+  deployments keep the current behavior (one entity = one track).
+- Cross-modality quality depends on ADR-311/ADR-063/ADR-029 landing; until then
+  continuity is WiFi-primary and its limits are stated, not hidden.
+- Being phase 2, this ADR is design intent; it will be revised as the ADR-306
+  ontology and ADR-305 identity spine finalize.
+
+## Validation
+
+- Unit tests (`cargo test -p wifi-densepose-mat`): decayed association prior
+  (confidence falls with gap; drops beyond horizon → new pseudonym);
+  topology-constrained hand-off (no association across non-adjacent spaces);
+  schema check that a `Person`/`Track` carries no civil-identifier field.
+- Integration test against a synthetic multi-room, multi-radio scenario:
+  a scripted walk kitchen → hallway → bedroom yields one persistent pseudonym
+  with per-hand-off confidence, and a deliberately ambiguous crossing produces
+  two pseudonyms rather than a false join.
+- Evidence discipline: any tracking-continuity accuracy is reported only with
+  the ADR-291 leakage-free protocol and an evidence tag; no number is asserted
+  here.
+- Privacy review: confirm no persisted long-term biometric template and no
+  civil-identity join path, as an explicit checklist item before any pilot.