Measure what the cheapest SCRFD actually costs in faces

§1 chose scrfd_500m on FLOPs and never measured the recall it gave up.
A dr-ui example now runs several detectors over the same sample of
stored proxies, matches boxes by IoU against the first, buckets the
result by face size, times each, and writes contact sheets of the
disagreements in both directions — because a count of extra faces says
nothing until someone has looked at whether they are faces.

Over 400 proxies from the reference library: 2.5G finds 14% more faces
for 12% more time, 10G a further 12% for 3.1× the time. The extras are
small real faces. The 86 faces only 500M found are a dog a dozen times,
a stop sign, a wheel and the backs of heads. Recorded in faces.md §12.3.

docs/faces.md

@@ -1062,6 +1062,47 @@ profile rather than the pipeline. Any future timing of this subsystem is a relea
 
 Still unmeasured: the same pass on a phone (NFR-RES-2), which does not follow from this one.
 
+### 12.3 SCRFD-2.5G and 10G against 500M · 2026-09-11
+
+§1 chose `500M` on cost; the recall it gives up was never measured. `examples/face_detectors`
+in `dr-ui` runs several detectors over the same 400 proxies, spaced evenly through the reference
+library, matches boxes at IoU ≥ 0.5 against the first, and writes contact sheets of the
+disagreements — because a count of extra faces says nothing until someone has looked at whether
+they are faces. Both size gates off, confidence at the production 0.5, release build, reference
+desktop. Sizes are the box's shorter edge in proxy pixels; the network sees 0.625 of that.
+
+| Detector | File | Mean ms | Faces | <16 | 16–32 | 32–64 | ≥64 |
+|---|---|---|---|---|---|---|---|
+| `scrfd_500m` | 2.5 MB | 157 | 1,490 | 153 | 730 | 399 | 208 |
+| `scrfd_2.5g` | 3.3 MB | 177 | 1,698 | 268 | 801 | 418 | 211 |
+| `scrfd_10g` | 17 MB | 488 | 1,896 | 357 | 886 | 438 | 215 |
+
+| Against `500M` | Both | Candidate only | Baseline only |
+|---|---|---|---|
+| `2.5G` | 1,404 | **294** (242 of them under 32 px) | 86 |
+| `10G` | 1,419 | **477** (411 under 32 px) | 71 |
+
+Two things the sheets settled that the counts cannot:
+
+- **The candidates' extras are faces.** The hundred smallest `2.5G`-only tiles are people —
+  soft, small, a few motion-blurred, and almost none of them anything else. These are the group
+  shots and the figures in the background that §7's table predicted `500M` would lose at 640.
+- **`500M`'s "extras" are mostly not.** Of the 86 faces only `500M` found, the sheet shows the
+  same dog a dozen times, a stop sign, a wheel, two hands, the backs of several heads and one face
+  upside down. The larger models did not miss these; they declined them. So `500M` is paying
+  twice — for the faces it cannot find *and* for the non-faces it embeds, which is exactly the
+  garbage-embedding-bridges-two-clusters failure `DetectOptions::confidence` is set against.
+
+**`2.5G` is the right detector.** 12% more time for 14% more faces and a cleaner set, in a file
+0.8 MB larger; `10G` finds a further 12% for 3.1× the time, which is a desktop-only price and this
+is not a desktop-only feature (NFR-RES-2). It loads in tract with the same fix as `500M`
+(`--input input.1=1,3,640,640`; its outputs are declared dynamic and tract infers them) and
+decodes through the same nine-output path unchanged. Same licence, same `buffalo_m` release page.
+
+What a swap has to deal with: `face_index` is keyed on the *embedder's* `model_id`, so a new
+detector re-queues nothing. The images already indexed under `500M` keep their faces and their
+dogs until something re-detects them — that is a re-index policy question, not a detector one.
+
 ---
 
 ## 13. Order

docs/traceability.md

@@ -9,8 +9,8 @@ Denominators are parsed from [`requirements.md`](requirements.md) at run time, n
 
 | Metric | Value |
 |---|---|
-| Source files scanned | 349 |
-| TRACES tags found | 1367 |
+| Source files scanned | 350 |
+| TRACES tags found | 1368 |
 | Requirements defined | 187 |
 | Requirements covered | 134 |
 | **Coverage** | **71.7%** (134/187) |
@@ -56,7 +56,7 @@ _None._
 | FR-CULL-3 | [`core/dr-gpu/src/focus.rs:154`](../core/dr-gpu/src/focus.rs#L154), [`core/dr-gpu/src/focus.rs:186`](../core/dr-gpu/src/focus.rs#L186), [`core/dr-gpu/src/focus.rs:1`](../core/dr-gpu/src/focus.rs#L1), [`core/dr-gpu/src/focus.rs:317`](../core/dr-gpu/src/focus.rs#L317), [`core/dr-gpu/src/raw_histogram.rs:129`](../core/dr-gpu/src/raw_histogram.rs#L129), [`core/dr-gpu/src/raw_histogram.rs:1`](../core/dr-gpu/src/raw_histogram.rs#L1), [`core/dr-gpu/src/raw_histogram.rs:272`](../core/dr-gpu/src/raw_histogram.rs#L272), [`core/dr-gpu/src/raw_histogram.rs:407`](../core/dr-gpu/src/raw_histogram.rs#L407), [`core/dr-gpu/src/shaders/focus_peak.wgsl:1`](../core/dr-gpu/src/shaders/focus_peak.wgsl#L1), [`core/dr-gpu/src/shaders/raw_histogram.wgsl:1`](../core/dr-gpu/src/shaders/raw_histogram.wgsl#L1), [`ui/dr-ui/src/develop.rs:4094`](../ui/dr-ui/src/develop.rs#L4094), [`ui/dr-ui/src/develop.rs:4107`](../ui/dr-ui/src/develop.rs#L4107), [`ui/dr-ui/src/develop.rs:4152`](../ui/dr-ui/src/develop.rs#L4152), [`ui/dr-ui/src/develop.rs:4163`](../ui/dr-ui/src/develop.rs#L4163), [`ui/dr-ui/src/develop.rs:4169`](../ui/dr-ui/src/develop.rs#L4169), [`ui/dr-ui/src/develop.rs:4186`](../ui/dr-ui/src/develop.rs#L4186), [`ui/dr-ui/src/develop.rs:789`](../ui/dr-ui/src/develop.rs#L789), [`ui/dr-ui/src/develop.rs:809`](../ui/dr-ui/src/develop.rs#L809), [`ui/dr-ui/src/develop.rs:815`](../ui/dr-ui/src/develop.rs#L815), [`ui/dr-ui/src/develop.rs:8432`](../ui/dr-ui/src/develop.rs#L8432), [`ui/dr-ui/src/develop.rs:8496`](../ui/dr-ui/src/develop.rs#L8496), [`ui/dr-ui/src/develop.rs:8519`](../ui/dr-ui/src/develop.rs#L8519), [`ui/dr-ui/src/histogram.rs:1`](../ui/dr-ui/src/histogram.rs#L1), [`ui/dr-ui/src/histogram.rs:208`](../ui/dr-ui/src/histogram.rs#L208), [`ui/dr-ui/src/histogram.rs:228`](../ui/dr-ui/src/histogram.rs#L228), [`ui/dr-ui/src/histogram.rs:272`](../ui/dr-ui/src/histogram.rs#L272), [`ui/dr-ui/src/histogram.rs:544`](../ui/dr-ui/src/histogram.rs#L544), [`ui/dr-ui/src/histogram.rs:565`](../ui/dr-ui/src/histogram.rs#L565), [`ui/dr-ui/src/histogram.rs:593`](../ui/dr-ui/src/histogram.rs#L593), [`ui/dr-ui/src/histogram.rs:621`](../ui/dr-ui/src/histogram.rs#L621), [`ui/dr-ui/src/histogram.rs:658`](../ui/dr-ui/src/histogram.rs#L658), [`ui/dr-ui/src/lib.rs:1760`](../ui/dr-ui/src/lib.rs#L1760), [`ui/dr-ui/src/lib.rs:1857`](../ui/dr-ui/src/lib.rs#L1857), [`ui/dr-ui/src/lib.rs:1966`](../ui/dr-ui/src/lib.rs#L1966), [`ui/dr-ui/src/lib.rs:2007`](../ui/dr-ui/src/lib.rs#L2007), [`ui/dr-ui/src/lib.rs:3416`](../ui/dr-ui/src/lib.rs#L3416), [`ui/dr-ui/src/lib.rs:429`](../ui/dr-ui/src/lib.rs#L429), [`ui/dr-ui/src/peaking.rs:1`](../ui/dr-ui/src/peaking.rs#L1), [`ui/dr-ui/ui/app.slint:1899`](../ui/dr-ui/ui/app.slint#L1899), [`ui/dr-ui/ui/app.slint:2884`](../ui/dr-ui/ui/app.slint#L2884), [`ui/dr-ui/ui/app.slint:79`](../ui/dr-ui/ui/app.slint#L79), [`ui/dr-ui/ui/peaking.slint:1`](../ui/dr-ui/ui/peaking.slint#L1), [`ui/dr-ui/ui/peaking.slint:25`](../ui/dr-ui/ui/peaking.slint#L25), [`ui/dr-ui/ui/peaking.slint:56`](../ui/dr-ui/ui/peaking.slint#L56), [`ui/dr-ui/ui/peaking.slint:91`](../ui/dr-ui/ui/peaking.slint#L91) |
 | FR-CULL-4 | [`core/dr-catalog/src/rating.rs:1`](../core/dr-catalog/src/rating.rs#L1), [`core/dr-pipeline/src/sidecar.rs:139`](../core/dr-pipeline/src/sidecar.rs#L139), [`core/dr-xmp/src/lib.rs:442`](../core/dr-xmp/src/lib.rs#L442), [`ui/dr-ui/src/library.rs:254`](../ui/dr-ui/src/library.rs#L254), [`ui/dr-ui/src/library.rs:500`](../ui/dr-ui/src/library.rs#L500) |
 | FR-CULL-5 | [`core/dr-catalog/src/bursts.rs:1`](../core/dr-catalog/src/bursts.rs#L1), [`core/dr-catalog/src/schema.rs:456`](../core/dr-catalog/src/schema.rs#L456), [`ui/dr-ui/src/bursts.rs:1`](../ui/dr-ui/src/bursts.rs#L1), [`ui/dr-ui/src/library.rs:210`](../ui/dr-ui/src/library.rs#L210), [`ui/dr-ui/src/library.rs:6020`](../ui/dr-ui/src/library.rs#L6020) |
-| FR-CULL-8 | [`core/dr-catalog/src/face_shard.rs:1`](../core/dr-catalog/src/face_shard.rs#L1), [`core/dr-catalog/src/faces.rs:1`](../core/dr-catalog/src/faces.rs#L1), [`core/dr-catalog/src/schema.rs:524`](../core/dr-catalog/src/schema.rs#L524), [`core/dr-catalog/src/schema.rs:646`](../core/dr-catalog/src/schema.rs#L646), [`core/dr-catalog/src/schema.rs:687`](../core/dr-catalog/src/schema.rs#L687), [`core/dr-face/src/align.rs:291`](../core/dr-face/src/align.rs#L291), [`ui/dr-ui/examples/face_native.rs:1`](../ui/dr-ui/examples/face_native.rs#L1), [`ui/dr-ui/src/faces.rs:1`](../ui/dr-ui/src/faces.rs#L1), [`ui/dr-ui/src/faces.rs:331`](../ui/dr-ui/src/faces.rs#L331), [`ui/dr-ui/src/faces.rs:347`](../ui/dr-ui/src/faces.rs#L347), [`ui/dr-ui/src/faces.rs:454`](../ui/dr-ui/src/faces.rs#L454), [`ui/dr-ui/src/identity_ui.rs:542`](../ui/dr-ui/src/identity_ui.rs#L542), [`ui/dr-ui/src/lib.rs:1379`](../ui/dr-ui/src/lib.rs#L1379), [`ui/dr-ui/src/library.rs:3293`](../ui/dr-ui/src/library.rs#L3293), [`ui/dr-ui/src/library.rs:3451`](../ui/dr-ui/src/library.rs#L3451), [`ui/dr-ui/src/library.rs:3698`](../ui/dr-ui/src/library.rs#L3698), [`ui/dr-ui/src/library.rs:3864`](../ui/dr-ui/src/library.rs#L3864), [`ui/dr-ui/src/library.rs:3900`](../ui/dr-ui/src/library.rs#L3900), [`ui/dr-ui/src/library.rs:3980`](../ui/dr-ui/src/library.rs#L3980), [`ui/dr-ui/ui/settings.slint:427`](../ui/dr-ui/ui/settings.slint#L427), [`ui/dr-ui/ui/settings.slint:82`](../ui/dr-ui/ui/settings.slint#L82) |
+| FR-CULL-8 | [`core/dr-catalog/src/face_shard.rs:1`](../core/dr-catalog/src/face_shard.rs#L1), [`core/dr-catalog/src/faces.rs:1`](../core/dr-catalog/src/faces.rs#L1), [`core/dr-catalog/src/schema.rs:524`](../core/dr-catalog/src/schema.rs#L524), [`core/dr-catalog/src/schema.rs:646`](../core/dr-catalog/src/schema.rs#L646), [`core/dr-catalog/src/schema.rs:687`](../core/dr-catalog/src/schema.rs#L687), [`core/dr-face/src/align.rs:291`](../core/dr-face/src/align.rs#L291), [`ui/dr-ui/examples/face_detectors.rs:1`](../ui/dr-ui/examples/face_detectors.rs#L1), [`ui/dr-ui/examples/face_native.rs:1`](../ui/dr-ui/examples/face_native.rs#L1), [`ui/dr-ui/src/faces.rs:1`](../ui/dr-ui/src/faces.rs#L1), [`ui/dr-ui/src/faces.rs:331`](../ui/dr-ui/src/faces.rs#L331), [`ui/dr-ui/src/faces.rs:347`](../ui/dr-ui/src/faces.rs#L347), [`ui/dr-ui/src/faces.rs:454`](../ui/dr-ui/src/faces.rs#L454), [`ui/dr-ui/src/identity_ui.rs:542`](../ui/dr-ui/src/identity_ui.rs#L542), [`ui/dr-ui/src/lib.rs:1379`](../ui/dr-ui/src/lib.rs#L1379), [`ui/dr-ui/src/library.rs:3293`](../ui/dr-ui/src/library.rs#L3293), [`ui/dr-ui/src/library.rs:3451`](../ui/dr-ui/src/library.rs#L3451), [`ui/dr-ui/src/library.rs:3698`](../ui/dr-ui/src/library.rs#L3698), [`ui/dr-ui/src/library.rs:3864`](../ui/dr-ui/src/library.rs#L3864), [`ui/dr-ui/src/library.rs:3900`](../ui/dr-ui/src/library.rs#L3900), [`ui/dr-ui/src/library.rs:3980`](../ui/dr-ui/src/library.rs#L3980), [`ui/dr-ui/ui/settings.slint:427`](../ui/dr-ui/ui/settings.slint#L427), [`ui/dr-ui/ui/settings.slint:82`](../ui/dr-ui/ui/settings.slint#L82) |
 | FR-CULL-9 | [`core/dr-catalog/src/faces.rs:1`](../core/dr-catalog/src/faces.rs#L1), [`core/dr-catalog/src/schema.rs:591`](../core/dr-catalog/src/schema.rs#L591), [`core/dr-catalog/src/schema.rs:687`](../core/dr-catalog/src/schema.rs#L687), [`core/dr-face/src/assign.rs:1`](../core/dr-face/src/assign.rs#L1), [`core/dr-face/src/neighbours.rs:1`](../core/dr-face/src/neighbours.rs#L1), [`core/dr-types/src/settings.rs:117`](../core/dr-types/src/settings.rs#L117), [`ui/dr-ui/src/faces.rs:1`](../ui/dr-ui/src/faces.rs#L1), [`ui/dr-ui/src/faces.rs:454`](../ui/dr-ui/src/faces.rs#L454), [`ui/dr-ui/src/identity_ui.rs:1`](../ui/dr-ui/src/identity_ui.rs#L1), [`ui/dr-ui/src/library.rs:3397`](../ui/dr-ui/src/library.rs#L3397), [`ui/dr-ui/src/library.rs:3980`](../ui/dr-ui/src/library.rs#L3980), [`ui/dr-ui/ui/identity.slint:314`](../ui/dr-ui/ui/identity.slint#L314) |
 | FR-DEV-1 | [`core/dr-pipeline/src/graph.rs:1`](../core/dr-pipeline/src/graph.rs#L1), [`core/dr-pipeline/src/sidecar.rs:1`](../core/dr-pipeline/src/sidecar.rs#L1) |
 | FR-DEV-10 | [`core/dr-gpu/src/mask.rs:1015`](../core/dr-gpu/src/mask.rs#L1015), [`core/dr-gpu/src/mask.rs:1239`](../core/dr-gpu/src/mask.rs#L1239), [`core/dr-gpu/src/mask.rs:1471`](../core/dr-gpu/src/mask.rs#L1471), [`core/dr-gpu/src/mask.rs:421`](../core/dr-gpu/src/mask.rs#L421), [`core/dr-gpu/src/mask.rs:463`](../core/dr-gpu/src/mask.rs#L463), [`core/dr-gpu/src/mask.rs:58`](../core/dr-gpu/src/mask.rs#L58), [`core/dr-gpu/src/mask.rs:60`](../core/dr-gpu/src/mask.rs#L60), [`core/dr-gpu/src/mask.rs:822`](../core/dr-gpu/src/mask.rs#L822), [`core/dr-gpu/src/mask.rs:85`](../core/dr-gpu/src/mask.rs#L85), [`core/dr-gpu/src/mask.rs:901`](../core/dr-gpu/src/mask.rs#L901), [`core/dr-gpu/src/shaders/mask.wgsl:117`](../core/dr-gpu/src/shaders/mask.wgsl#L117), [`core/dr-gpu/src/shaders/mask.wgsl:59`](../core/dr-gpu/src/shaders/mask.wgsl#L59), [`core/dr-gpu/tests/range_masks.rs:119`](../core/dr-gpu/tests/range_masks.rs#L119), [`core/dr-gpu/tests/range_masks.rs:147`](../core/dr-gpu/tests/range_masks.rs#L147), [`core/dr-gpu/tests/range_masks.rs:175`](../core/dr-gpu/tests/range_masks.rs#L175), [`core/dr-gpu/tests/range_masks.rs:1`](../core/dr-gpu/tests/range_masks.rs#L1), [`core/dr-gpu/tests/range_masks.rs:94`](../core/dr-gpu/tests/range_masks.rs#L94), [`core/dr-pipeline/src/mask.rs:125`](../core/dr-pipeline/src/mask.rs#L125), [`core/dr-pipeline/src/mask.rs:2812`](../core/dr-pipeline/src/mask.rs#L2812), [`core/dr-pipeline/src/mask.rs:2825`](../core/dr-pipeline/src/mask.rs#L2825), [`core/dr-pipeline/src/mask.rs:2844`](../core/dr-pipeline/src/mask.rs#L2844), [`core/dr-pipeline/src/mask.rs:2858`](../core/dr-pipeline/src/mask.rs#L2858), [`core/dr-pipeline/src/mask.rs:2868`](../core/dr-pipeline/src/mask.rs#L2868), [`core/dr-pipeline/src/mask.rs:709`](../core/dr-pipeline/src/mask.rs#L709), [`core/dr-pipeline/src/mask.rs:748`](../core/dr-pipeline/src/mask.rs#L748), [`core/dr-pipeline/src/mask.rs:808`](../core/dr-pipeline/src/mask.rs#L808), [`core/dr-pipeline/src/mask.rs:827`](../core/dr-pipeline/src/mask.rs#L827), [`core/dr-pipeline/src/mask.rs:851`](../core/dr-pipeline/src/mask.rs#L851), [`core/dr-pipeline/src/mask.rs:863`](../core/dr-pipeline/src/mask.rs#L863), [`core/dr-pipeline/src/mask.rs:875`](../core/dr-pipeline/src/mask.rs#L875), [`core/dr-pipeline/src/sidecar.rs:1224`](../core/dr-pipeline/src/sidecar.rs#L1224), [`core/dr-pipeline/src/sidecar.rs:1403`](../core/dr-pipeline/src/sidecar.rs#L1403), [`core/dr-pipeline/src/sidecar.rs:1490`](../core/dr-pipeline/src/sidecar.rs#L1490), [`core/dr-pipeline/src/sidecar.rs:1591`](../core/dr-pipeline/src/sidecar.rs#L1591), [`core/dr-pipeline/src/sidecar.rs:1798`](../core/dr-pipeline/src/sidecar.rs#L1798), [`core/dr-pipeline/tests/mask_sidecar.rs:1157`](../core/dr-pipeline/tests/mask_sidecar.rs#L1157), [`core/dr-pipeline/tests/mask_sidecar.rs:1186`](../core/dr-pipeline/tests/mask_sidecar.rs#L1186), [`core/dr-pipeline/tests/mask_sidecar.rs:1204`](../core/dr-pipeline/tests/mask_sidecar.rs#L1204), [`core/dr-pipeline/tests/mask_sidecar.rs:1234`](../core/dr-pipeline/tests/mask_sidecar.rs#L1234), [`ui/dr-ui/src/develop.rs:2294`](../ui/dr-ui/src/develop.rs#L2294), [`ui/dr-ui/src/develop.rs:3614`](../ui/dr-ui/src/develop.rs#L3614), [`ui/dr-ui/src/develop.rs:3641`](../ui/dr-ui/src/develop.rs#L3641), [`ui/dr-ui/src/develop.rs:3673`](../ui/dr-ui/src/develop.rs#L3673), [`ui/dr-ui/src/develop.rs:3697`](../ui/dr-ui/src/develop.rs#L3697), [`ui/dr-ui/src/develop.rs:3703`](../ui/dr-ui/src/develop.rs#L3703), [`ui/dr-ui/src/develop.rs:3710`](../ui/dr-ui/src/develop.rs#L3710), [`ui/dr-ui/src/develop.rs:3730`](../ui/dr-ui/src/develop.rs#L3730), [`ui/dr-ui/src/labels.rs:60`](../ui/dr-ui/src/labels.rs#L60), [`ui/dr-ui/src/masks_ui.rs:1102`](../ui/dr-ui/src/masks_ui.rs#L1102), [`ui/dr-ui/src/masks_ui.rs:719`](../ui/dr-ui/src/masks_ui.rs#L719) |