Specify face indexing at native resolution, and say what the proxy cost

FR-CULL-8 said detection runs against the thumbnail or proxy tier and
never a full decode, and faces.md §5 said the aligned crop is sampled
from that same proxy. Both are wrong in the same place: they treat
detection and cropping as one resolution problem when they are two, with
opposite answers.

Detection does not care. §4.1 fixes the graph's input at 640x640 and
letterboxes whatever arrives, so a face filling 2% of the frame reaches
the model at 12px whether the buffer handed over is 1024px or 6000px.
Every pixel above the detector's own input is discarded before inference.

The crop cares about nothing else. §5's warp produces the fixed 112x112
ArcFace sees, so source resolution converts directly into whether those
112 pixels were photographed or interpolated. Reading crop_px across the
18,671 faces the proxy-tier implementation stored: 47.3% were upsampled
to reach the embedder, 314 of them by more than 2x, the smallest from 34
source pixels. An upsampled crop does not fail loudly -- it yields a
confident embedding of detail that was never there, and the damage
appears three stages later as clusters that will not separate.

So FR-CULL-8 now specifies four stages with the resolutions named
separately: render native through FR-EXP-9's pipeline, downscale for the
detector, map boxes and landmarks back to native, crop and align from
the native render. The affordability the old rule bought is met instead
by when the pass runs -- background, preempted, resumable -- and the
requirement says plainly what it now costs on a remote library: the
original rather than FR-NC-3's byte range, 412 GB across the reference
library's 19,107 images, so a whole-library pass is a transfer under
FR-NC-6 rather than something that may start on its own.

MIN_CROP_EDGE replaces the MIN_DETECT_EDGE this branch briefly had. Same
number, guarding the quantity that turned out to matter.

faces.md §7b records both measurements, and marks the second as
unexplained rather than dressing it as a finding. Grouped by the buffer
detection ran against, faces per image was 0.078 at 1024 or below and
1.82 at 2048 or better, controlled for file type and size. That gap is
real and reproducible and I cannot account for it, because the letterbox
above says detector input should not matter. M4 is where it gets
settled. The crop measurement does not depend on it.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

ui/dr-ui/src/faces.rs

@@ -50,11 +50,29 @@ pub enum FaceSweepMessage {
     Total(usize),
     /// One image finished, with the faces found in it.
     Indexed { image: ImageId, faces: usize },
+    /// Images the pass gave up on, counted since the last message.
+    ///
+    /// **Progress has to advance on these or it does not advance at all.**
+    /// The count moved only on `Indexed`, so a run where every image failed
+    /// sat at 0/169 from the first tick to the last and then reported
+    /// success: the receiver was told the total, told nothing, and told the
+    /// pass had ended. That is exactly what happened on the reference library
+    /// for a day, and it is why the sweep was thought to be hanging when it
+    /// was in fact finishing in fourteen seconds.
+    ///
+    /// A batch rather than one message per image, because failures come back
+    /// lane-sized and the interesting number is how many. The reason for each
+    /// is logged where it happens.
+    Failed { images: usize },
     /// The pass ended.
     Finished {
         images: usize,
         faces: usize,
         failed: usize,
+        /// Refused for want of a big enough proxy rather than failed; see
+        /// `docs/faces.md` §7c. Counted apart because a library of small
+        /// scans is not a broken network and must not read as one.
+        too_small: usize,
     },
 }
 
@@ -351,6 +369,7 @@ pub fn spawn_store_face_sweep(
                 images: 0,
                 faces: 0,
                 failed: 0,
+                too_small: 0,
             });
         };
 
@@ -508,6 +527,7 @@ pub fn spawn_store_face_sweep(
             images,
             faces: found,
             failed,
+            too_small: 0,
         });
     });