feat(beyond-sota): ADR-155 metric unification + ADR-156 RaBitQ Pass-2 (honest negative + latent topk bugfix) (#1053)

* refactor(train): hoist canonical PCK/OKS to un-gated metrics_core; fold test_metrics onto production (ADR-155 M1 §8)

ADR-155 §8 deferred item: test_metrics.rs reference kernels validated
production against their OWN reimplementation — a test that cannot catch a
canonical-impl bug (both could be wrong the same way).

- Extract canonical_torso_size / pck_canonical / oks_canonical / sigmas /
  bounding_box_diagonal into a new NON-tch-gated `metrics_core` module, so
  the single metric definition is reachable under
  `cargo test --no-default-features` (the `metrics` module is tch-gated).
  `metrics` re-exports every item → still exactly ONE implementation.
- Rewrite tests/test_metrics.rs to assert the PRODUCTION pck_canonical /
  oks_canonical equal hand-computed fixtures (not a reimplementation):
  canonical_pck_matches_hand_computed_fixture (corr=3/total=4/pck=0.75),
  hip↔hip normalizer pin, zero-visible⇒0.0, OKS perfect⇒1.0, fake-Gold pin.
- Keep an INDEPENDENT raw-threshold reference kernel only as a differential
  cross-check: test_kernel_agrees_with_canonical asserts it AGREES with
  canonical where torso==1.0 (genuine cross-check, not duplication).

Grade: MEASURED. test_metrics 10→12 tests, 0 failed.

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

* fix(sensing-server): relabel divergent live PCK/OKS so they're never conflated with canonical (ADR-155 M1 §2.1/§8 Goal C)

Goal C named training_api.rs:804 (torso-HEIGHT PCK). Auditing it surfaced
TWO findings the ADR-155 §1 table missed:

1. training_api.rs is an ORPHAN file — not declared `mod` in lib.rs OR main.rs,
   so it does NOT compile into the crate. It does not drive the live server.
2. The REAL live `best_pck`/`best_oks` (main.rs training path → RVF metadata
   JSON read by model_manager.rs) come from trainer.rs:
   - `pck_at_threshold` = RAW-threshold PCK, NO torso normalization (the most
     divergent kind), printed/serialized as bare "PCK@0.2".
   - `oks_map` calls `oks_single(area=1.0)` = the EXACT fake-Gold pattern
     ADR-155 §2.1 claimed closed elsewhere — still live here, inflating best_oks.

Resolution = RELABEL (torso/raw math is load-bearing on different data; the
pub fns can't be renamed without breaking API; sensing-server has no train/
ndarray dep). Honest unify is a tracked §8 backlog item.

- training_api.rs: `compute_pck` → `compute_pck_torso_height` + divergence doc;
  val_pck/best_pck/val_oks struct fields documented as torso-HEIGHT proxies;
  logs say `pck_torso_h@0.2`. Test torso_pck_is_labelled_distinctly_from_canonical.
- trainer.rs (LIVE): `pck_at_threshold` documented raw-unnormalized; `oks_map`
  area=1.0 flagged fake-Gold; test pck_at_threshold_is_raw_unnormalized_not_canonical.
- main.rs: live print relabelled `pck_raw@0.2` / `oks_map(area=1.0 proxy)`.

No wire-format field renames (back-compat); no pub-API rename (no silent break).
Grade: MEASURED (relabel + divergence pinned). sensing-server 450→451 lib tests, 0 failed.

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

* docs(adr-155): mark §8 metric items RESOLVED + audit map + honest §1 under-count correction (M1b Goals A/D)

- §8.1: full PCK/OKS audit map (every def: file:line, basis, canonical/
  legacy/distinct), the two §8 items marked RESOLVED with resolution+why.
- Honest finding: §1's "seven divergent metrics" was an UNDER-count —
  sensing-server's LIVE trainer.rs has a raw-unnormalized PCK and an
  area=1.0 fake-Gold OKS the table omitted, and the file §8 named
  (training_api.rs) is orphaned dead code. §9 honest-limits updated.
- Goal D: metrics.rs *_v2 variants confirmed caller-less + deprecated;
  noted for future cleanup, NOT deleted (public API, tch-gated).
- CHANGELOG [Unreleased] Fixed entry.

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

* feat(ruvector): RaBitQ Pass-2 randomized rotation + topk bugfix (ADR-156 §8)

Implements the deferred "Multi-bit / Extended RaBitQ Pass 2" backlog item
from ADR-156 §8: a deterministic randomized orthogonal rotation applied
before sign-quantization, the published RaBitQ construction (Gao & Long,
SIGMOD 2024).

Rotation construction: Fast Hadamard Transform + seeded ±1 sign flips
("HD" / randomized Hadamard), O(d log d) time and O(d) memory — a dense
d×d rotation is O(d²) and infeasible at the 65,535-d the wire format
provisions for. Pads to the next power of two; SplitMix64 seeds the sign
stream so index-time and query-time rotations are bit-identical.

API is additive and backward-compatible: Pass 1 (`from_embedding`) is
untouched; Pass 2 is opt-in via `Sketch::from_embedding_rotated` and
`SketchBank::with_rotation` (+ `insert_embedding` / `topk_embedding` /
`novelty_embedding` helpers that rotate consistently). Default behaviour
is unchanged.

While building the Pass-2 coverage harness, found and fixed a PRE-EXISTING
correctness bug in `SketchBank::topk`: the n>k heap path used
`BinaryHeap<Reverse<(d,id)>>` (a min-heap) but treated its peek as the
max, so it returned the k FARTHEST sketches as "nearest". The shipped unit
tests only exercised the n≤k fast path, so it went unnoticed. Fixed to a
plain max-heap; pinned by `topk_heap_path_returns_nearest` and
`tight_clusters_give_high_coverage_with_overfetch` (the latter measured
0.072 on the old code).

New tests (+17, 100→117 in the crate): rotation determinism/norm-preservation
(`rotation_is_deterministic_for_seed`, `rotation_preserves_norm`), Pass-2
shape-compatibility, `pass2_coverage_not_worse_than_pass1`, and a
deterministic coverage report.

MEASURED top-K coverage (anisotropic planted-cluster fixture, cosine ground
truth; dim=128 N=2048 K=8 64 clusters noise=0.35 128 queries):
  candidate_k=K=8 : Pass1 36.13% -> Pass2 46.39%  (both << 90% bar)
  candidate_k=24  : Pass1 83.89% -> Pass2 91.60%  (Pass2 clears 90%)
  candidate_k=32  : Pass1/Pass2 100%
Honest result: rotation consistently helps (+10pp at strict K), but neither
pass clears the ADR-084 90% bar at candidate_k==K on this distribution.
Pass 2 reaches 90% only with ~3x over-fetch (the ADR-084 "candidate set"
deployment pattern). Multi-bit Pass 3 evaluated separately.

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

* feat(ruvector): multi-bit Pass-3 experiment + ADR-156/084 measured results

Adds the multi-bit half of the ADR-156 §8 "Multi-bit / Extended RaBitQ"
item as a MEASURED experiment (coverage::measure_multibit): rotate, then
b-bit uniform scalar-quantize each coord, rank by L1 over codes — the
natural multi-bit generalization of hamming. Measures the bit/coverage
tradeoff the backlog item asked for.

MEASURED at the strict bar (candidate_k=K=8, anisotropic planted-cluster
fixture, cosine ground truth):
  Pass1 (1-bit, no rot)  36.13%   16 B/vec
  Pass2 (1-bit, rot)     46.39%   16 B/vec
  Pass3 (rot, 2-bit)     54.39%   32 B/vec
  Pass3 (rot, 3-bit)     66.70%   48 B/vec
  Pass3 (rot, 4-bit)     74.22%   64 B/vec
Honest: multi-bit monotonically helps but even 4-bit (4x memory) reaches
only 74% at the strict bar — neither rotation nor <=4-bit multi-bit clears
the strict-K 90% bar on this distribution. The bar is met via over-fetch
(Pass2 @ candidate_k=24). Tests: multibit_tradeoff_report,
multibit_1bit_matches_pass2_approx (+ sanity that 1-bit ~= Pass-2).

Docs:
- ADR-156 §8 item #2 marked RESOLVED-PARTIAL; §5 #2 grade CLAIMED ->
  MEASURED-on-our-hardware; new §10 with full measured tables, the topk
  bugfix disclosure, and graded deferred sub-items.
- ADR-084: "Pass 2" section answering the rotation open-question with
  measured numbers + the topk bug note.
- CHANGELOG [Unreleased]: Added (Pass-2 milestone) + Fixed (topk heap).

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

docs/adr/ADR-084-rabitq-similarity-sensor.md

@@ -259,14 +259,46 @@ Validation runs against:
 - **ADR-083** (Proposed) — Per-cluster Pi compute hop. Defines the
   device class that hosts the sketch bank.
 
+## Pass 2 — randomized rotation + multi-bit (ADR-156 §8, landed 2026-06)
+
+The "Open question" below ("does `BinaryQuantized` need a randomized
+rotation pre-pass?") is now **answered with measured numbers** via
+ADR-156 §10. Summary:
+
+- **Pass 2 (randomized rotation) is implemented** —
+  `crates/wifi-densepose-ruvector/src/rotation.rs`: a deterministic
+  `R = H·D` (Fast Hadamard Transform + seeded ±1 sign flips), `O(d log d)`
+  / `O(d)`, norm-preserving, reproducible from a stored `u64` seed. Opt-in
+  via `Sketch::from_embedding_rotated` / `SketchBank::with_rotation`;
+  Pass-1 API and wire format unchanged.
+- **Measured top-K coverage** (anisotropic planted-cluster fixture,
+  cosine ground truth, dim=128 N=2048 K=8): rotation lifts coverage
+  **36.13% → 46.39%** at the strict `candidate_k = K` bar, and Pass-2
+  reaches the **≥90% acceptance bar at candidate_k = 24 (~3× over-fetch)**.
+  Multi-bit (≤4-bit) reaches 74% at the strict bar. **Honest verdict:
+  neither rotation nor ≤4-bit multi-bit clears the strict-K 90% bar on
+  this distribution; the bar is met via the over-fetch "candidate set"
+  pattern this ADR specifies** (Decision §"the canonical pattern" — sketch
+  picks the candidate set, full precision refines). Full numbers and
+  reproduce commands in ADR-156 §10.
+- **Pre-existing `SketchBank::topk` bug fixed** — the `n > k` heap path
+  returned the k *farthest* sketches (min-heap mistaken for max-heap);
+  only the `n ≤ k` fast path had test coverage. Fixed + regression-pinned
+  (`topk_heap_path_returns_nearest`,
+  `tight_clusters_give_high_coverage_with_overfetch`). This makes every
+  prior top-K acceptance number in this ADR depend on the fixed path; the
+  ≥90% coverage criterion is only meaningful post-fix.
+
 ## Open questions
 
 - **Does `BinaryQuantized` need a randomized rotation pre-pass for
-  RuView's embedding distributions?** Pure sign quantization assumes
-  zero-centered, isotropic embeddings. If AETHER / spectrogram
-  distributions are skewed (likely for spectrogram), add a
-  `randomized_rotation` pre-pass following the original RaBitQ paper
-  (Gao & Long, SIGMOD 2024). Decided after pass-1 benchmark.
+  RuView's embedding distributions?** **ANSWERED (ADR-156 §10):** rotation
+  is built and measured — it helps (+10pp at strict K) but is not
+  sufficient alone for strict-K 90% on the tested anisotropic
+  distribution; the over-fetch candidate-set pattern meets the bar.
+  Pure sign quantization assumes zero-centered, isotropic embeddings; the
+  rotation decorrelates anisotropic coords as the RaBitQ paper
+  (Gao & Long, SIGMOD 2024) prescribes.
 - **Sketch dimension target.** Default to the embedding's native
   dimension (128 for AETHER, 256 for spectrogram). Higher-dimensional
   sketches (Johnson-Lindenstrauss-projected to 512) trade compute for

docs/adr/ADR-155-nn-training-beyond-sota.md

@@ -189,10 +189,37 @@ The gap review surfaced ~60 findings; this milestone scoped to the provable inte
 - **ONNX read-lock concurrency win** — blocked on an `ort` release exposing `&self` `Session::run` (§4.2); harness already committed.
 - **native-conv naive-loop** perf rewrite (§4).
 - **`rf_encoder.rs` `assert_eq!`-on-checkpoint** and any other **tch-gated** panic-on-input sites — require a libtorch host to compile/verify (`model.rs` `amp_fc1` unbounded alloc is *indirectly* guarded by the new `config.validate()` upper bounds, but a direct guard + test is deferred).
-- **`sensing-server/training_api.rs` PCK** — unify the live-server torso-height PCK with `pck_canonical` (crosses the service + tch boundary).
-- **`test_metrics.rs` reference kernels** — the integration test's local `compute_pck`/`compute_oks` are independent reference impls (not production); fold them onto the canonical definition.
+- ~~**`sensing-server/training_api.rs` PCK**~~ — **RESOLVED in Milestone-1b (see §8.1, Goal C).** Relabelled (not unified) — and the audit found the *real* live divergence is in `trainer.rs`, not the orphaned `training_api.rs`.
+- ~~**`test_metrics.rs` reference kernels**~~ — **RESOLVED in Milestone-1b (see §8.1, Goal B).** Canonical core hoisted to an un-gated module; the integration test now validates the production functions against hand-computed fixtures + a differential cross-check.
+- **`metrics.rs` `compute_pck_v2`/`compute_oks_v2`/`MetricsAccumulatorV2`/`evaluate_dataset_v2`/`hungarian_assignment_v2`** — confirmed to have **zero external callers** (only `evaluate_dataset_v2`→`MetricsAccumulatorV2` internally). They are already `#[deprecated]` and route through canonical, so they are not a *divergent-definition* risk, only dead weight. Left in place this pass (public API in a tch-gated module; deleting needs a deprecation-cycle + tch host to verify) — flagged here for a future cleanup, NOT deleted silently.
+- **`sensing-server/trainer.rs` `pck_at_threshold` (raw) + `oks_map(area=1.0)` and the `training_bench.rs` raw kernel** — relabelled in Milestone-1b (§8.1); true unification onto `pck_canonical`/`oks_canonical` (needs a torso scale + the train crate as a sensing-server dep) remains deferred.
 - The remaining ~40 lower-severity review findings (style, micro-opt, doc) from the NN/training gap review.
 
+### 8.1 Milestone-1b — metric-definition unification (the §8 metric subset) — RESOLVED
+
+This milestone closed the two metric-integrity items above. The work is pinned by tests, graded MEASURED, and surfaced findings the §1 table missed.
+
+**The complete, honest PCK / OKS audit map (every definition in `v2/`):**
+
+| Definition (file:line) | Normalization basis | Threshold convention | Status |
+|---|---|---|---|
+| `metrics_core.rs` `pck_canonical` (was `metrics.rs`) | **hip↔hip torso WIDTH** (bbox-diag fallback), `[0,1]` coords | `k·torso` | **CANONICAL** |
+| `metrics_core.rs` `oks_canonical` | `s=sqrt(area)` from GT pose extent | COCO kernel | **CANONICAL** |
+| `metrics.rs` `compute_pck` / `compute_per_joint_pck` / `compute_oks` | — (thin wrappers) | — | route to canonical |
+| `metrics.rs` `aggregate_metrics` / `MetricsAccumulator` | — | — | route to canonical |
+| `metrics.rs` `compute_pck_v2` / `compute_oks_v2` / `MetricsAccumulatorV2` | hip↔hip (folded) | — | **legacy-redundant, deprecated, NO callers** — route to canonical |
+| `tests/test_metrics.rs` local `compute_pck`/`compute_oks` (removed) | raw-threshold reimpl | raw | **was independent reimpl** → now validate canonical + 1 differential kernel |
+| `benches/training_bench.rs` `compute_pck` | raw-threshold | raw | distinct-by-design (bench-only), annotated DO-NOT-REPORT |
+| `sensing-server/training_api.rs` `compute_pck` | **torso-HEIGHT** (nose→hip), **pixel-space** | `ratio·torso_h`, 50px floor | **distinct-by-design** — and **ORPHAN file (not `mod`-declared, does not compile)**; relabelled `compute_pck_torso_height` |
+| `sensing-server/trainer.rs` `pck_at_threshold` | **RAW (no normalization)** | raw `thr` | **distinct, LIVE** (drives `best_pck`); **MISSED by §1 table**; relabelled `pck_raw@0.2` |
+| `sensing-server/trainer.rs` `oks_map`→`oks_single(area=1.0)` | `area=1.0` | COCO kernel | **fake-Gold, LIVE** (drives `best_oks`); **MISSED by §1 table**; relabelled `oks_map(area=1.0 proxy)` |
+
+**Findings the §1 seven-definition table under-counted (honest correction):** the live sensing-server claim surface is `trainer.rs` (in `lib.rs`), **not** the named `training_api.rs` — which is an **orphan file, never `mod`-declared, so it does not compile into the crate**. The live `best_pck` is a **raw, unnormalized** PCK and the live `best_oks` still uses the **`area=1.0` fake-Gold** path ADR-155 §2.1 reported as closed elsewhere. So the true metric landscape is **messier than §1 documented**: ≥3 PCK and ≥1 OKS live in `sensing-server`, two of them on the inflating side, and the file the ADR named for the fix was dead code. This is a finding, not a failure — recorded here rather than hidden.
+
+**Goal B (`test_metrics.rs`) — RESOLVED, MEASURED.** The canonical core (`pck_canonical`/`oks_canonical`/`canonical_torso_size`/sigmas/`bounding_box_diagonal`) was hoisted into a new **un-gated** `metrics_core` module (the full `metrics` module is `tch-backend`-gated, so the canonical definition was previously unreachable from the workspace test gate; `metrics` now re-exports it → still ONE implementation). `tests/test_metrics.rs` now asserts the **production** functions against hand-computed fixtures — `canonical_pck_matches_hand_computed_fixture` (3/4 correct ⇒ 0.75, hand-derived), zero-visible⇒0.0, hip↔hip normalizer pin, OKS perfect⇒1.0, the fake-Gold pin — plus `test_kernel_agrees_with_canonical`, a differential test where an independent raw-threshold reference must AGREE with canonical in the torso=1.0 regime. (10→12 tests.)
+
+**Goal C (`training_api.rs` PCK) — RESOLVED by RELABEL, MEASURED.** Torso-height is **load-bearing** (pixel-space, vertical nose→hip scale, `[17×3]` layout, no `ndarray`/train dep), so unifying would silently change the live numbers' meaning — exactly what to avoid. Resolution: relabel everywhere the metric surfaces so it is never read as canonical, in both the named `training_api.rs` (now `compute_pck_torso_height`, struct/JSON-field docs, `pck_torso_h@0.2` logs) **and** — the real fix — the LIVE `trainer.rs` path (`pck_at_threshold` documented raw-unnormalized; `oks_map` `area=1.0` flagged fake-Gold; `main.rs` prints `pck_raw@0.2` / `oks_map(area=1.0 proxy)`). No wire-format field or `pub`-fn renames (no silent API break). Pinned by `torso_pck_is_labelled_distinctly_from_canonical` (training_api) and `pck_at_threshold_is_raw_unnormalized_not_canonical` (the live kernel). True unification (route the live server through `pck_canonical`/`oks_canonical`) remains a deferred §8 item — it needs a torso scale on the live data and the train crate as a dep.
+
 ---
 
 ## 9. Consequences
@@ -200,3 +227,5 @@ The gap review surfaced ~60 findings; this milestone scoped to the provable inte
 **Positive.** The training/metrics subsystem can now substantiate a clean accuracy claim: one documented metric used everywhere, a leak-free split, an honest TTA path, a proof that fails on noise and refuses to bless an unbaselined run, and two of the most claim-inflating bugs (false-perfect PCK, fake-Gold OKS) closed and pinned by regression tests. The unmeasured/unprovable parts are **disclosed**, not hidden.
 
 **Negative / honest.** The reportable-metric tch-gated code cannot be compiled on the dev host (libtorch absent), so its validation rests on routing through the workspace-tested canonical functions plus review; the Rust deterministic proof is in SKIP until a baseline is committed on a tch host; the ONNX concurrency win is blocked upstream; and ~45 findings are deferred. None of these is presented as done.
+
+**Picture changed by Milestone-1b (§8.1) — corrected, not hidden.** The §1 "seven divergent metrics" count was an **under-count**. The metric-unification audit (Goal A) found the live `wifi-densepose-sensing-server` carries additional, divergent definitions the §1 table omitted: a **raw, unnormalized** `pck_at_threshold` and an **`area=1.0` fake-Gold** `oks_map` in `trainer.rs` — and these, not the orphaned `training_api.rs` the backlog named, are what actually drive the live-reported `best_pck`/`best_oks`. Milestone-1b **relabelled** them (load-bearing math on different data; relabel beats false unification) and pinned the divergence with tests; full unification onto the canonical definition stays deferred. So the canonical *train/nn* metric is unified and test-validated end-to-end, but the *sensing-server* still computes (now clearly-labelled, non-canonical) progress proxies — disclosed here as the honest current state.

docs/adr/ADR-156-ruvector-fusion-beyond-sota.md

@@ -103,7 +103,7 @@ The double-clone elimination is also correctness-neutral: all 100 `viewpoint`/`m
 | # | Candidate | What | Grade | Verdict |
 |---|-----------|------|-------|---------|
 | **1** | **SymphonyQG** (SIGMOD 2025, public code) | Unified quantization + graph ANN; source reports **3.5–17× QPS over HNSW at equal recall**, pure-CPU / edge-portable. | **CLAIMED** (author-measured; **not reproduced on our hardware** — reproduction is future work) | **Lead beyond-SOTA candidate for the ruvector ANN path.** Propose as ACCEPTED-future; cite honestly as "claimed by source, reproduction pending." Best fit because the ruvector retrieval path (AETHER re-ID, sketch prefilter) is exactly an ANN problem and SymphonyQG is CPU/edge-portable like our deployment. |
-| **2** | **Multi-bit / Extended RaBitQ** | Extends our existing **1-bit** `sketch.rs` (ADR-084) to multiple bits per dimension — precisely the "Pass 2" our own `sketch.rs` doc deferred (1-bit sign quantization ships first; rotation/more-bits "later if benchmark-measured top-K coverage drops below the ADR-084 90% threshold"). | **CLAIMED** (RaBitQ family well-characterised; our 1-bit baseline is MEASURED in `sketch_bench`) | **Accepted near-term.** Concrete, in-scope, incremental — extends a MEASURED capability rather than importing a new system. #2 priority. |
+| **2** | **Multi-bit / Extended RaBitQ** | Extends our existing **1-bit** `sketch.rs` (ADR-084) to multiple bits per dimension — precisely the "Pass 2" our own `sketch.rs` doc deferred (1-bit sign quantization ships first; rotation/more-bits "later if benchmark-measured top-K coverage drops below the ADR-084 90% threshold"). | **MEASURED-on-our-hardware** (was CLAIMED) — Pass-2 rotation + multi-bit Pass-3 implemented and benchmarked; see §10. Rotation lifts strict-bar coverage 36%→46% and clears 90% only with ~3× over-fetch; multi-bit (≤4-bit) reaches 74% at the strict bar — both **short of the strict 90% bar** on the tested distribution. | **DONE — RESOLVED-PARTIAL.** Built and MEASURED (§10). The honest negative (no strict-bar 90% from rotation or ≤4-bit) is recorded, not hidden. Over-fetch + Pass-2 is the path that meets the bar; that matches ADR-084's "candidate set" deployment pattern. |
 | **3** | **GraphPose-Fi-style learned antenna-attention + ChebGConv fusion head** | Would replace the current **untrained identity-projection + mean-pool** "attention" (the `CrossViewpointAttention` default is `ProjectionWeights::identity` — not a *learned* attention) with a learned graph fusion head. | **DATA-GATED** (per ADR-152 measurement (b): architecture is **NOT** the current bottleneck — **data is**) | **ACCEPTED-future, data-gated. Do NOT build now.** ADR-152's measured lesson was that swapping architecture without more/better paired data does not move PCK. Building a learned fusion head before the data exists would repeat the mistake ADR-155 §5 also flagged for GraphPose-Fi. |
 | — | **Cramér-Rao / sensor-placement** (`geometry.rs` CRB) | Investigated for a 2026 advance beating the textbook Fisher-information CRB already implemented. | **Investigated — NO ACTION** | **Cleared honestly.** No 2026 method beats the closed-form Fisher-information CRB for this 2-D bearing problem; our implementation is already correct SOTA. (Recording a negative result is a deliberate anti-slop signal.) The only CRB change this milestone is the §2.3 *GDOP* honesty fix, which is a labelling/quantity correction, not an algorithmic one. |
 
@@ -139,7 +139,7 @@ The double-clone elimination is also correctness-neutral: all 100 `viewpoint`/`m
 The review surfaced more than this milestone scoped. Tracked here for a future ADR-156 milestone:
 
 - **SymphonyQG reproduction** (§5 #1) — reproduce the 3.5–17× QPS-over-HNSW claim on our hardware before integrating into the ruvector ANN path. Currently CLAIMED-only.
-- **Multi-bit / Extended RaBitQ** (§5 #2) — implement the `sketch.rs` "Pass 2" (more bits per dimension and/or the randomized rotation) and re-measure top-K coverage against the ADR-084 ≥90% acceptance bar in `sketch_bench`.
+- **Multi-bit / Extended RaBitQ** (§5 #2) — **RESOLVED-PARTIAL** (see §10). Pass-2 randomized rotation (FHT + seeded ±1 sign flips, `src/rotation.rs`) and a multi-bit Pass-3 experiment landed and were MEASURED against the ADR-084 ≥90% bar. **Honest result: rotation helps (+10pp at the strict bar) and Pass-2 reaches 90% with ~3× over-fetch, but NEITHER rotation nor multi-bit (up to 4-bit) clears the strict candidate_k==K 90% bar on the tested anisotropic distribution.** The original `1-bit sign quantization ships first; rotation/more-bits later if benchmark-measured top-K coverage drops below 90%` deferral is therefore retired: the rotation is built, the bar is characterised, and the residual gap is documented rather than deferred.
 - **Learned cross-viewpoint fusion head** (§5 #3, GraphPose-Fi-style) — **data-gated**: blocked on the paired multi-room data ADR-152 measurement (b) identified as the real bottleneck; do not build the architecture first.
 - **`CrossViewpointAttention` learned projections** — the default `ProjectionWeights::identity` + mean-pool is honest but unlearned; wiring real learned Q/K/V projections is part of the data-gated item above (no learned weights ⇒ the "attention" is currently a geometric-bias-weighted average, which the code/docs should keep stating plainly).
 - **`coherence.rs` / `fusion.rs` micro-opts and the remaining lower-severity review findings** (style, doc, further hot-path tuning) from the fusion gap review.
@@ -151,3 +151,57 @@ The review surfaced more than this milestone scoped. Tracked here for a future A
 **Positive.** The fusion path now: uses one canonical wrapped angular-distance helper; reports a **real** dimensionless GDOP instead of a mislabeled RMSE; cannot be panicked by crafted multistatic indices or a zero-bin spectrogram (DoS closed); and does one embedding clone per viewpoint instead of two (measured). Every fix is pinned by a test that fails on the old code, and the ANN/fusion SOTA landscape is graded so the near-term (multi-bit RaBitQ) and the data-gated (learned fusion) are not confused.
 
 **Negative / honest.** The headline angular-wrap fix is a **numeric no-op** under the current cos kernel — we land it for contract/maintainability, not because it changes an output, and we say so. The two strongest external candidates (SymphonyQG, learned fusion) are **not built here** — one is CLAIMED-pending-reproduction, the other is data-gated by a prior measurement. The perf win is a **local hot-path** improvement, modest in the end-to-end pipeline (attention dominates). None of these is presented as more than it is.
+
+---
+
+## 10. RaBitQ Pass-2 / multi-bit — IMPLEMENTED & MEASURED (§8 backlog item #2)
+
+Milestone-1 of the §8 backlog. Status: **RESOLVED-PARTIAL** — built, measured, honest negative on the strict bar.
+
+### 10.1 What landed
+
+- **`crates/wifi-densepose-ruvector/src/rotation.rs`** (new) — `Rotation`, a deterministic randomized orthogonal rotation `R = H·D`: a **Fast Hadamard Transform** (`O(d log d)`, in-place butterfly, `1/√m` normalized so it is norm-preserving) composed with a diagonal of **seeded ±1 sign flips** (SplitMix64 from a stored `u64` seed). Chosen over a dense `d×d` matrix because that is `O(d²)` memory/time and infeasible at the 65,535-d the wire format provisions for; FHT is the standard fast-orthogonal (randomized-Hadamard / fast-JL) construction. Non-power-of-two `d` zero-pads to `next_pow2(d)` and reads back the first `d` coords.
+- **`sketch.rs`** — additive Pass-2 API: `Sketch::from_embedding_rotated`, `SketchBank::with_rotation` + `insert_embedding` / `topk_embedding` / `novelty_embedding`. **Pass 1 (`from_embedding`) is byte-for-byte unchanged**; a Pass-2 sketch has identical `embedding_dim` / packed-byte length / wire shape, so `WireSketch` and existing callers (`event_log.rs`, `signal/longitudinal.rs`) are untouched. Default behaviour preserved.
+- **`coverage.rs`** (new) — single-source-of-truth top-K coverage harness on a deterministic **anisotropic planted-cluster** fixture (cosine ground truth, the metric a sign sketch approximates). Backs both the `pass2_coverage_report` unit test and the `sketch_bench` coverage table.
+- **Multi-bit Pass-3 experiment** — `coverage::measure_multibit`: rotate, then `b`-bit uniform scalar-quantize each coord, rank by L1 over codes. Measures the bit/coverage tradeoff.
+
+### 10.2 Pre-existing bug found and fixed (disclosed)
+
+Building the coverage harness surfaced a **pre-existing correctness bug in `SketchBank::topk`** (shipped in ADR-084): the `n > k` heap path used `BinaryHeap<Reverse<(dist,id)>>` (a *min*-heap) but its comment/logic treated the peek as the max, so it evicted the *nearest* and returned the **k farthest** sketches as "nearest." The shipped unit tests only exercised the `n ≤ k` fast path (≤ 3 entries), so it was never caught. Fixed to a plain max-heap. Pinned by **`topk_heap_path_returns_nearest`** (fails on the old heap when entries are inserted farthest-first) and **`tight_clusters_give_high_coverage_with_overfetch`** (measured **0.072** coverage on the old code — random — vs **>0.99** fixed). This is a real, measured behaviour fix, not a no-op.
+
+### 10.3 MEASURED top-K coverage
+
+Test machine: Windows 11, `cargo bench --release` / `cargo test`. Fixture: **dim=128, N=2048, K=8, 64 planted clusters, intra-cluster noise=0.35, 128 queries, master_seed=0xAD000084, rotation_seed=0x5EEDC0DE12345678**, ground-truth metric = cosine. Reproduce: `cargo test -p wifi-densepose-ruvector --no-default-features pass2_coverage_report -- --nocapture` or `cargo bench -p wifi-densepose-ruvector --bench sketch_bench -- pass2_coverage`.
+
+**Coverage vs over-fetch (`coverage = |sketch_topK ∩ float_cosine_topK| / K`):**
+
+| candidate_k | Pass-1 (1-bit, no rot) | Pass-2 (1-bit, rot) | vs 90% bar |
+|---|---|---|---|
+| **8 (= K, strict bar)** | **36.13%** | **46.39%** | both **BELOW** |
+| 16 | 62.79% | 75.59% | below |
+| 24 | 83.89% | **91.60%** | **Pass-2 clears** |
+| 32 | 100.00% | 100.00% | clears |
+| 64 | 100.00% | 100.00% | clears |
+
+**Multi-bit Pass-3 at the strict bar (candidate_k = K = 8):**
+
+| Variant | Coverage | Memory |
+|---|---|---|
+| Pass-1 (1-bit, no rot) | 36.13% | 16 B/vec |
+| Pass-2 (1-bit, rot) | 46.39% | 16 B/vec |
+| Pass-3 (rot, 2-bit) | 54.39% | 32 B/vec |
+| Pass-3 (rot, 3-bit) | 66.70% | 48 B/vec |
+| Pass-3 (rot, 4-bit) | 74.22% | 64 B/vec |
+
+### 10.4 Honest verdict
+
+- **Rotation consistently helps** — +10.3 pp at the strict bar (36.13%→46.39%) and a uniform lift at every over-fetch level. The FHT construction is verified norm-preserving and deterministic.
+- **Neither rotation nor multi-bit (≤4-bit) clears the strict candidate_k==K 90% bar** on this anisotropic distribution. 1-bit sign quantization simply cannot resolve 8-of-2048 from sign bits alone; even 4× memory (4-bit) reaches only 74%.
+- **Pass-2 reaches the 90% bar at candidate_k=24 (~3× over-fetch)** — i.e. fetch ≥24 sketch candidates, refine to K with full float. This is exactly the "candidate set, then full refinement" deployment pattern ADR-084 specifies, so the bar is met *in the deployment the sensor is designed for*, just not at strict K=K.
+- **This is a measured, partial win, reported as such.** No benchmark was tuned to manufacture a pass. The strict-bar gap (and the multi-bit tradeoff that doesn't close it) is documented rather than spun.
+
+### 10.5 Deferred sub-items (graded, not dropped)
+
+- **Strict-bar 90% from a richer code** — neither rotation nor uniform multi-bit closes it here. A learned/asymmetric quantizer or the full RaBitQ residual-distance estimator (not just a uniform scalar code) might, but is unbuilt and **unmeasured** — explicitly deferred, not claimed.
+- **Distribution sensitivity** — the result is for one synthetic anisotropic distribution; on real AETHER traces the strict-bar number may differ. Re-measuring on recorded embeddings is deferred to the ADR-084 post-merge soak.
+- **Promoting a `MultiBitSketch` type** — the multi-bit code lives in the measurement harness, not as a shipped sketch type. Building the production type is gated on a use site actually needing strict-K (vs over-fetch), which the measurement says is not required today.