feat(work_plane gui): overlay inliers used for fit as blue dots on RGB

The fit endpoint now returns fit_points_px (the post-outlier-filter
inliers projected to RGB pixels via Nuwa's RGB intrinsics). The GUI
draws them on the same overlay as the ROI rectangle so the user can
visually verify which depth pixels were fed to fit_plane_svd.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/work_plane.js

@@ -10,6 +10,7 @@ const RGB_REFRESH_MS = 1000;
 let roi = null;            // {u0,v0,u1,v1} in image pixel coords
 let previewPlane = null;   // last response.plane (preview, not saved)
 let previewPoints = null;  // list of [x,y,z] in CV camera frame, meters
+let fitPointsPx = null;    // list of [u,v] pixels of inliers used for the fit
 let savedPlane = null;     // last GET /api/work_plane response.plane
 
 function setChip(text, level) {
@@ -89,6 +90,12 @@ function startRgbLoop() {
   function drawOverlay() {
     const ctx = overlay.getContext('2d');
     ctx.clearRect(0, 0, overlay.width, overlay.height);
+    // Inliers used for the last fit, drawn first so the ROI rectangle stays
+    // on top.
+    if (fitPointsPx && fitPointsPx.length) {
+      ctx.fillStyle = '#4da3ff';
+      for (const [u, v] of fitPointsPx) ctx.fillRect(u, v, 2, 2);
+    }
     if (roi) {
       ctx.strokeStyle = '#9b6dff';
       ctx.lineWidth = 2;
@@ -99,11 +106,15 @@ function startRgbLoop() {
       drawCross(ctx, firstCorner.u, firstCorner.v);
     }
   }
+  // Re-export so doFit can refresh the overlay after a successful fit.
+  window.__wpDrawOverlay = drawOverlay;
 
   viewport.addEventListener('click', (e) => {
     const p = imgPixelFromEvent(e);
     if (firstCorner === null && roi === null) {
-      // First click: place corner A.
+      // First click: place corner A. Drop any stale fit-points overlay so we
+      // don't suggest the new ROI is being analyzed yet.
+      fitPointsPx = null;
       firstCorner = p;
       drawOverlay();
       setChip('punto 1/2 piazzato — clicca il secondo angolo');
@@ -132,6 +143,7 @@ function startRgbLoop() {
     }
     // ROI already set: start a new selection on the next click.
     roi = null;
+    fitPointsPx = null;
     firstCorner = p;
     drawOverlay();
     setRoiInfo();
@@ -277,8 +289,10 @@ async function doFit() {
     if (r.detail) throw new Error(formatDetail(r.detail));
     previewPlane = r.plane;
     previewPoints = r.points_camera;
+    fitPointsPx = r.fit_points_px || null;
     three.setPlane(previewPlane);
     three.setScatter(previewPoints, previewPlane, previewPlane.offset_mm);
+    if (window.__wpDrawOverlay) window.__wpDrawOverlay();
     renderDetails(previewPlane);
     $('wpStateBlock').innerHTML = `<strong>preview</strong> · RMS ${previewPlane.fit_rms_mm.toFixed(1)} mm · n_inliers ${previewPlane.n_inliers} · offset ${previewPlane.offset_mm} mm · <span class="warn">non salvato</span>`;
     setChip('preview pronto', 'ok');