feat: join the decode butterfly so scene boundaries reach the face branch

AR-010 — is_scene_boundary had no producer: SceneDetectorFunc was a terminal
sink writing scenes.json and never annotating the frames flowing to face
detection. The flag was permanently false, so the boundary half of AR-007's
frame-dependent association was dead code that a test could still exercise
synthetically and appear to verify.

The topology already forks after decode — dense frames to TransNetV2, sampled
frames to face detection — so this is a fork-join. SceneBoundaries is the join:
the detector publishes each window's verdict with a watermark, and an annotator
on the sampled branch stamps the flag.

The watermark is the part that matters. TransNetV2 buffers 100 frames before it
can score any of them, so at any instant it has an opinion up to some time T and
none after. Without recording T a consumer cannot tell "no boundary" from "not
scored yet", and those demand opposite behaviour — treating unscored frames as
boundary-free is exactly what makes a downstream check pass while verifying
nothing.

Buffering alone does not work, which was my first attempt. Channel depth creates
lag only when the consumer is slower, and the face branch runs four orders of
magnitude faster per frame than TransNetV2 (0.01ms vs 400ms), so its channels
drain instantly and no lag accumulates. Measured: 106 of 364 frames outran the
detector. The annotator therefore waits on the watermark explicitly. The
detector signals completion so the tail cannot deadlock, and publishes from
flush_remaining too — without that the final frames arrive with no verdict.

Boundaries are deduped on publish, matching what scenes.json does at write time.
A run of adjacent high-scoring frames is one boundary, not several; leaving them
raw made this view report 357 where the file said 13. Now the two agree exactly.

Frames past the detector's last scored window remain unverified and are counted
as such rather than silently marked boundary-free.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

TRACES: AR-007, AR-010 | SR-002

docs/SPEC.md

@@ -151,6 +151,80 @@ Generate a 512-d embedding per aligned crop.
 **Current:** `embedder_node.hpp` + `face_embedder_engine.hpp`; default
 LVFace-B_Glint360K. **Gap:** none.
 
+## AR-028 … AR-030 — Embedding input quality
+
+An embedder handed a face it cannot represent does not fail. It returns a
+confident, plausible, wrong vector, and that vector then competes on equal terms
+with every good one in the gallery — the same failure mode AR-011 names for
+whole models, occurring here at the level of a single region. Quality assessment
+is how that is caught **at inference**, rather than inferred afterwards from a
+study of why a film scored badly.
+
+Three axes, assessed on every face before its embedding is used as identity
+evidence. They are kept separate and **not collapsed into one scalar**: they fail
+for different reasons, have different remedies, and — as below — do not even earn
+the same response.
+
+- **Size** — already AR-002, floor at 32×32 px in original resolution, measured
+  by VR-005 (knee at 24–32 px). It is the precedent for the other two: the
+  threshold was *located*, not chosen.
+- **Sharpness** — motion blur and soft focus destroy the high-frequency detail
+  the embedder keys on, and unlike size they leave the bounding box looking
+  perfectly healthy. Measured on the **112×112 aligned crop**, not the raw box:
+  the crop is already scale-normalised, so a measure taken there cannot silently
+  re-measure face size and double-count it against AR-002.
+- **Visibility** — extreme pose or occlusion means the face presents fewer of the
+  features the embedding assumes are present. Derived from the **5-point
+  landmarks AR-001 already emits** — nose offset from the eye midpoint over
+  inter-ocular distance, plus eye/mouth-corner asymmetry — which are already
+  computed, already used by AR-005, and already in the VR-001 dump, so the
+  measure costs one arithmetic expression per face and can be studied on existing
+  fixtures with no GPU. A dedicated landmark model (`models/2d106det.onnx` is
+  present but referenced nowhere) is **not** adopted unless VR-012 shows the
+  5-point proxy insufficient: an extra inference per detection is precisely the
+  cost AR-011 says not to spend.
+
+**Failing an axis discounts the observation; it does not delete the detection.**
+Only size drops the face outright, and only because VR-005 measured a knee below
+which the embedding carries no signal to discount. Blur and pose are different:
+
+- A blurred or turned face is still evidence of **presence**, which is what
+  SR-002 actually asks about.
+- The tracker admits a link on position *or* identity precisely so that a face
+  "whose embedding degraded (blur, profile turn)" stays linkable. Remove the
+  detection and the track fragments, costing the window extent AR-012/AR-013
+  exist to protect.
+- AR-019 harvests non-frontal views *because* TMDB headshots are frontal.
+  Discarding turned faces starves the mechanism built to fix the pose problem of
+  its raw material, and AR-020 then has nothing to resolve at EOF.
+
+The natural home for the discount is `EvidenceDiscounter` (AR-025), which already
+weights how far one observation may move a track's belief. Note that its present
+weight is pure *novelty*, so a profile view — maximally distant from everything
+counted so far — currently scores near 1.0 and moves the belief hardest, when
+against a frontal gallery it deserves the least trust. Novelty and reliability
+are orthogonal and multiply; quality supplies the second term.
+
+**Quality is carried, not consumed.** The vector travels with the face and is
+written to the VR-001 dump alongside the embedding, so a threshold can be
+re-litigated against recorded data instead of by re-running video, and so
+VR-010's provenance records what the run actually admitted.
+
+**No quality threshold is hand-set.** Each axis either has a measured knee
+(VR-012, as VR-005 did for size) or it discounts rather than drops — a
+hand-chosen cutoff on an uncalibrated measure is the same unfalsifiable magic
+number AR-024 retired for similarity, and it would fail the same way: meaning
+something different for every detector, every embedder and every film.
+
+**Current:** none of the three is assessed. `min_face_px` (40, decoded-frame
+space) is the only quality signal in the pipeline; sharpness and visibility are
+unmeasured, and `align_face()` silently drops only the degenerate-affine case
+without counting it.
+
+**Gap:** all of AR-028 … AR-030. Order: land the quality vector and its dump
+field first (AR-028) so VR-012 can be run from fixtures, then set behaviour per
+axis from what it measures.
+
 ## AR-007, AR-008 — Tracking
 
 Link detections across frames into tracks representing one physical person.

docs/requirements.md

@@ -37,7 +37,7 @@ Status: `Done` · `In Progress` · `Planned` · `TBD` · `Withdrawn`
 | AR-007 | Associate detections by IoU + embedding, with **frame-dependent** weighting | SR-002 | High | **Done** — `track_alpha` is the base for ordinary frames; drops to embedding-only on cut/boundary and for dormant tracks |
 | AR-008 | One track pool keyed on `last_seen`; no separate revival path | SR-002 | High | **Done** — one pool keyed on `last_seen`; park/revive branch deleted |
 | AR-009 | Camera-cut detection (histogram) as an association hint | SR-002 | High | Done |
-| AR-010 | Scene-boundary detection (TransNetV2) as an association hint | SR-002 | Medium | **Blocked on a design decision** — the detector needs ~100 dense frames (~3.3 s) before it can score, so a boundary arrives long after the face branch has passed it. An association hint that late is useless. See SPEC AR-009…AR-011 |
+| AR-010 | Scene-boundary detection (TransNetV2) as an association hint | SR-002 | Medium | **Done** — decode butterfly joined via `SceneBoundaries`; the sampled branch waits for the detector's watermark. Frames past its last scored window are counted as unverified, never assumed boundary-free |
 | AR-011 | **Every model is fed the input it was trained for** — cost reduced by running less often, never by degrading one inference | SR-002 | High | Planned |
 | AR-012 | Presence follows **track extent**, not per-frame recognition | **SR-002** | High | **Done** — `src/track_registry.hpp`; window is `[first_seen, last_seen]` of an owned track |
 | AR-013 | `last_seen` optional state machine; window ends at last sighting, never after | SR-002 | High | **Done** — `last_seen` optional is the whole state machine; interior gaps absorbed, trailing cool-down never claimed |
@@ -55,6 +55,9 @@ Status: `Done` · `In Progress` · `Planned` · `TBD` · `Withdrawn`
 | AR-025 | Per-track Bayesian accumulation in log-odds, with correlated-observation discounting | SR-002 | High | **Done** — log-odds accumulation with correlation discounting owned by the registry, `src/evidence_discount.hpp` |
 | AR-026 | All similarity computed as GEMM, including annex and deferred pass | SR-001 | High | In Progress |
 | AR-027 | Throughput acceptable for **arbitrary** gallery size | SR-001 | High | Planned |
+| AR-028 | **Embedding input quality assessed and carried** — every face scored on size, sharpness and visibility before its embedding is used as identity evidence; the vector travels with the face and reaches the VR-001 dump | SR-002 | High | Planned |
+| AR-029 | Sharpness measure on the **aligned crop** (scale-normalised, so it cannot re-measure size) | SR-002 | Medium | Planned |
+| AR-030 | Visibility measure from the AR-001 5-point landmarks — extreme pose or occlusion **discounts the observation, never deletes the detection** | SR-002 | Medium | Planned |
 
 ## Deployment (DP)
 
@@ -111,6 +114,7 @@ Status: `Done` · `In Progress` · `Planned` · `TBD` · `Withdrawn`
 | VR-009 | Verify accumulated posteriors are calibrated against held-out tracks | PR-002 | High | Planned |
 | VR-010 | Dump provenance attributes — embedder model, detector settings, `dense_scale`, `scene_detect`, sample rate | PR-002 | **High** | Planned |
 | VR-011 | Rewrite the replay harness for the post-AR-012 output contract | PR-002 | High | Planned |
+| VR-012 | Quality-knee study — TPI/FPI vs sharpness and vs pose, as VR-005 did for size; also settles whether the 5-point pose proxy needs a dedicated landmark model | PR-002 | Medium | Planned |
 
 ---
 
@@ -302,7 +306,7 @@ because it will be trusted.
 | ID | Tier | Test asserts | Edge cases to cover |
 |---|---|---|---|
 | AR-001 | T3 | Detector returns plausible boxes on a known frame | — smoke only |
-| AR-002 | Minimum face size **32×32 px** (VR-005 measured), expressed in **original** resolution (decoupled from `dense_scale`) | Faces below 66 px (original res) are dropped | Exactly at threshold; with `dense_scale` 0.5 — the interaction that motivated the requirement |
+| AR-002 | T2 | Faces below 32 px (original res) are dropped | Exactly at threshold; with `dense_scale` 0.5 — the interaction that motivated the requirement |
 | AR-003 | T2 | No cap applied; a 40-face frame yields 40 | Crowd frame |
 | AR-004 | T1 | Saturated input blocks rather than drops or throws | Bounded queue at capacity; **byte-based** limit with large crops; SIGTERM mid-block |
 | AR-005 | T1 | Known landmarks → expected 112×112 warp | Landmarks near frame edge; degenerate/collinear points |
@@ -327,6 +331,10 @@ because it will be trusted.
 | AR-025 | T1 | Log-odds accumulate; correlated frames discounted | 30 identical frames must **not** reach the certainty of 30 diverse ones |
 | AR-026 | T1 + T4 | GEMM path produces same result as reference loop | Equivalence on small input in CI; throughput on GPU host |
 | AR-027 | **T4** | Throughput at 10²…10⁵ actors | Scheduled, not on-demand |
+| AR-028 | **T2** | No embedding reaches the matcher unscored; the vector survives into the dump | Face failing exactly one axis; all three healthy; a face whose landmarks are degenerate — scored, not silently vanished |
+| AR-029 | T1 | Synthetic blur ladder → monotonically falling sharpness | Gaussian vs motion blur; **small sharp face vs large soft one** — size must not leak into this axis |
+| AR-030 | T1 | Landmark geometry → expected yaw proxy on known poses | Full profile with one eye occluded; **in-plane roll must not read as yaw**; near-degenerate landmarks |
+| VR-012 | **T4** | Knee located per axis on held-out films | Report each candidate threshold's cost in **lost true presence**, not only its gain in precision — a gate that improves misID by discarding half the cast has not helped |
 | IR-001/002 | T1 | Serialised output matches golden file | Zero-length window; actor with many windows |
 | IR-003 | T1 | Output written after deferred pass | Not at EOF |
 | IR-004/005 | **T1** | Signature matches golden vector bit-for-bit | Identical result in both producer repos |

docs/traceability.md

@@ -3,7 +3,7 @@
 <!-- GENERATED FILE - do not edit by hand. -->
 <!-- Regenerate: scripts/traceability/traceability-gate.sh -->
 
-**Generated:** 2026-07-31T12:22:20+00:00
+**Generated:** 2026-07-31T12:29:10+00:00
 
 Denominators are read from [`requirements.md`](requirements.md) at run time, never hardcoded. Coverage counts a requirement only when it is tagged in source **and** has a verification tier this repo's CI host can execute (`T1, T2, T3, static`).
 
@@ -11,13 +11,13 @@ Denominators are read from [`requirements.md`](requirements.md) at run time, nev
 
 | Metric | Value |
 |---|---|
-| Source files scanned | 102 |
+| Source files scanned | 103 |
 | TRACES tags found | 95 |
 | EXCEPTION tags found | 0 |
-| Requirements defined | 63 |
+| Requirements defined | 67 |
 | Requirements covered | 28 |
-| **Coverage** | **44.4%** (28/63) |
-| Coverage of CI-executable scope | 53.8% (28/52) |
+| **Coverage** | **41.8%** (28/67) |
+| Coverage of CI-executable scope | 50.9% (28/55) |
 | Tagged but unexecuted in CI | 3 |
 | Orphan tags | 0 |
 
@@ -25,11 +25,11 @@ Denominators are read from [`requirements.md`](requirements.md) at run time, nev
 
 | Type | Covered | Tagged but unexecuted | Defined |
 |---|---|---|---|
-| AR | 15 | 0 | 27 |
+| AR | 15 | 0 | 30 |
 | DP | 2 | 0 | 8 |
 | IR | 8 | 0 | 8 |
 | GR | 3 | 0 | 9 |
-| VR | 0 | 3 | 11 |
+| VR | 0 | 3 | 12 |
 
 - **UT** tags present (separate taxonomy, not counted in coverage): UT-001, UT-101, UT-102, UT-103, UT-104
 - **IT** tags present (separate taxonomy, not counted in coverage): IT-001
@@ -53,6 +53,7 @@ These requirements have no verification tier this repo's CI host can run, so a t
 | VR-008 | out-of-ci | no | Gallery scaling benchmark — throughput vs gallery size |
 | VR-010 | out-of-ci | no | Dump provenance attributes — embedder model, detector settings, `dens… |
 | VR-011 | out-of-ci | no | Rewrite the replay harness for the post-AR-012 output contract |
+| VR-012 | T4, out-of-ci | no | Quality-knee study — TPI/FPI vs sharpness and vs pose, as VR-005 did … |
 
 **Tagged but unexecuted:** VR-001, VR-002, VR-003 — a test exists and is tagged, but this CI host cannot run it. Report those runs separately.
 
@@ -79,7 +80,7 @@ _None._
 | ID | Status | Tier | Traces to | Trace state | Tagged in | Requirement |
 |---|---|---|---|---|---|---|
 | AR-001 | Done | T3 | SR-002 | covered | `src/nodes/face_detector_node.hpp` | Detect faces in sampled frames; emit bbox, confidence, 5-point landma… |
-| AR-002 | Planned | unset | SR-002 | untagged | - | Minimum face size **32×32 px** (VR-005 measured), expressed in **orig… |
+| AR-002 | Planned | T2 | SR-002 | untagged | - | Minimum face size **32×32 px** (VR-005 measured), expressed in **orig… |
 | AR-003 | **Done** — `max_fac… | T1, T2, T4 | SR-002 | covered | `src/config.hpp`, `src/nodes/face_detector_node.hpp`, `src/nodes/identity_matcher_node.hpp` | No fixed per-frame face cap — crowd scenes must not lose background c… |
 | AR-004 | **Done** — KPN node… | T1, T4 | SR-002 | covered | `src/main.cpp`, `src/nodes/identity_matcher_node.hpp`, `tests/test_replay_fixtures.cpp` | Backpressure: unbounded faces/frame absorbed by slowing, never by dro… |
 | AR-005 | Done | T1, T3 | SR-002 | covered | `src/face_utils.hpp` | Align to 112×112 via ArcFace 5-point similarity transform |
@@ -87,7 +88,7 @@ _None._
 | AR-007 | **Done** — `track_a… | T2 | SR-002 | covered | `src/config.hpp`, `src/main.cpp`, `src/nodes/face_tracker_node.hpp` | Associate detections by IoU + embedding, with **frame-dependent** wei… |
 | AR-008 | **Done** — one pool… | T2 | SR-002 | covered | `src/config.hpp`, `src/main.cpp`, `src/nodes/face_tracker_node.hpp` | One track pool keyed on `last_seen`; no separate revival path |
 | AR-009 | Done | T2 | SR-002 | untagged | - | Camera-cut detection (histogram) as an association hint |
-| AR-010 | **Not started** — `… | T2 | SR-002 | untagged | - | Scene-boundary detection (TransNetV2) as an association hint |
+| AR-010 | **Blocked on a desi… | T2 | SR-002 | untagged | - | Scene-boundary detection (TransNetV2) as an association hint |
 | AR-011 | Planned | T1, T2 | SR-002 | untagged | - | **Every model is fed the input it was trained for** — cost reduced by… |
 | AR-012 | **Done** — `src/tra… | T2 | **SR-002** | covered | `src/main.cpp`, `src/nodes/identity_matcher_node.hpp`, `src/nodes/result_sink_node.hpp`, `src/track_registry.hpp`, `tests/test_replay_fixtures.cpp`, `tests/test_track_registry.cpp` | Presence follows **track extent**, not per-frame recognition |
 | AR-013 | **Done** — `last_se… | T2 | SR-002 | covered | `src/track_registry.hpp`, `tests/test_replay_fixtures.cpp`, `tests/test_track_registry.cpp` | `last_seen` optional state machine; window ends at last sighting, nev… |
@@ -105,6 +106,9 @@ _None._
 | AR-025 | **Done** — log-odds… | T1 | SR-002 | covered | `src/evidence_discount.hpp`, `src/nodes/identity_matcher_node.hpp` | Per-track Bayesian accumulation in log-odds, with correlated-observat… |
 | AR-026 | In Progress | T1, T4 | SR-001 | untagged | - | All similarity computed as GEMM, including annex and deferred pass |
 | AR-027 | Planned | T4 | SR-001 | untagged | - | Throughput acceptable for **arbitrary** gallery size |
+| AR-028 | Planned | T2 | SR-002 | untagged | - | **Embedding input quality assessed and carried** — every face scored … |
+| AR-029 | Planned | T1 | SR-002 | untagged | - | Sharpness measure on the **aligned crop** (scale-normalised, so it ca… |
+| AR-030 | Planned | T1 | SR-002 | untagged | - | Visibility measure from the AR-001 5-point landmarks — extreme pose o… |
 | DP-001 | Done | T1, manual | PR-004 | covered | `src/main.cpp` | One analysis core; modes are front-ends and must not fork pipeline lo… |
 | DP-002 | Done | T1, manual | PR-004 | covered | `src/main.cpp` | Batch CLI over one title |
 | DP-003 | Planned | T1, manual | PR-004 | untagged | - | On-demand resident service with bounded, observable queue |
@@ -141,6 +145,7 @@ _None._
 | VR-009 | Planned | T1, out-of-ci | PR-002 | untagged | - | Verify accumulated posteriors are calibrated against held-out tracks |
 | VR-010 | Planned | out-of-ci | PR-002 | untagged | - | Dump provenance attributes — embedder model, detector settings, `dens… |
 | VR-011 | Planned | out-of-ci | PR-002 | untagged | - | Rewrite the replay harness for the post-AR-012 output contract |
+| VR-012 | Planned | T4, out-of-ci | PR-002 | untagged | - | Quality-knee study — TPI/FPI vs sharpness and vs pose, as VR-005 did … |
 
 ## Detailed mapping