AR: sub-pixel corner refinement, ROI-first detection, anchor coplanarity check

docs/PAGES.md

@@ -101,6 +101,9 @@ ws open  rx active,pong          WebSocket state + recent message types
 scene 11 anchors  ghost recs 2   scene loaded, ghosts held client-side
 60 fps  detect 20Hz@960  fov 58  render rate, detect rate/resolution, camera fov
   REJ:jump                       (only when the solver refused a pose)
+scan roi 4x @1.3x 38kpx          detection mode: 4 crops, each 1.3x the detail
+  subpix 4/4 0.21px              ...of a full scan; corners refined, mean shift
+geom spread 10.4cm (max 16.0)    anchor conditioning — see below
 eng opencv  moving               engine; FROZEN = ghost motion paused
 axis std  cv:ready               engine mode + OpenCV worker state
 markers 3/4 seen [0,4,6] +1dup   solved/raw crests, ids, duplicate decodes
@@ -116,6 +119,31 @@ mirrored axis; a constant ratio means the projection doesn't match the lens (tun
 `localStorage.nbx.hfovDeg`); an intermittent horizontal flip with correct vertical
 is the coplanar ambiguity — stand the tower up.
 
+**Scan line.** `full` means the whole detection frame was decoded; `roi Nx`
+means N crops around the previous frame's crests were decoded instead, each at
+native video resolution. `@1.3x` is how much more detail each crop carries than
+the same patch of a full scan — above 1.0 the crop is the better read. `kpx` is
+pixels actually decoded this tick; compare it against 518k for a full 960x540
+scan. `roi>full` means a crop pass came back short and a full scan ran straight
+after, which is the designed fallback and costs one wasted pass. A full scan
+also runs at least every 600ms regardless, to pick up newly visible crests, so
+`markers ... not in this layout` can lag by up to that long in roi mode.
+
+**Subpix line.** `refined/total` crests whose corners were refined, and the mean
+correction applied, in detection-space pixels. A mean shift around 0.2-0.5px is
+normal and is roughly the quantisation the raw detector leaves behind. `0/4`
+means refinement is rejecting everything: too little contrast, too small a
+crest, or surface texture around the border — it falls back to raw corners, so
+nothing breaks, but tracking is no more precise than before.
+
+**Geom line.** RMS distance of every anchor corner from the best-fit plane
+through all of them. `COPLANAR` means every crest shares a plane, which is the
+condition that makes a mirrored camera pose fit the pixels just as well as the
+true one; the physics gates in `cv-worker.js` will be doing all the work and
+will occasionally be wrong. Stand a crest up — the A3 rig's tower gives ~3.5cm,
+and a single wall-mounted crest at 8cm in a town layout gives ~2.7cm. Both are
+comfortably clear of the 1.5cm threshold.
+
 ## Gotchas worth remembering
 
 **Detection filters against the active scene.** A crest that isn't an anchor in