feat(work_plane gui): show fit inliers as blue scatter in 3D, drop wrong plane mesh

The 0.4x0.4 PlaneGeometry square was a fixed-size proxy that did not
reflect the actual ROI extent — visually misleading. Replace it with
an explicit blue point cloud of the inliers fed to fit_plane_svd, so
the user can see *exactly* which depth pixels the plane was fit on.

- Backend: fit response now returns fit_points_camera (CV frame) instead
  of the (parallax-shifted) RGB pixel projection.
- Frontend: drop the purple plane mesh; new three.setFitInliers paints
  the inliers in blue. The RGB overlay no longer carries blue dots.

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

web/index.html

@@ -192,7 +192,7 @@
       <div class="canvas-wrap" style="width:min(100%,720px)">
         <canvas id="wp3dCanvas" width="720" height="360" style="display:block;background:#0a0d11;border:1px solid var(--border);border-radius:4px"></canvas>
       </div>
-      <div class="marker-info">vista camera · piano viola · ciano = punti tenuti · rosso = esclusi (sotto piano−offset) · drag = ruota · wheel = zoom</div>
+      <div class="marker-info">vista camera · blu = punti usati per il fit · ciano = scena tenuta · rosso = scena esclusa (sotto piano−offset) · drag = ruota · wheel = zoom</div>
     </div>
     <div>
       <h2>Calibrazione</h2>

web/work_plane.js

@@ -10,7 +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 fitPointsCv = null;    // list of [x,y,z] inliers used for the fit (CV frame)
 let savedPlane = null;     // last GET /api/work_plane response.plane
 
 function setChip(text, level) {
@@ -90,12 +90,6 @@ 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;
@@ -106,15 +100,14 @@ 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. Drop any stale fit-points overlay so we
-      // don't suggest the new ROI is being analyzed yet.
-      fitPointsPx = null;
+      // First click: place corner A. Drop any stale fit-inliers from the 3D
+      // viewer so we don't suggest the new ROI is being analyzed yet.
+      fitPointsCv = null;
+      three.setFitInliers(null);
       firstCorner = p;
       drawOverlay();
       setChip('punto 1/2 piazzato — clicca il secondo angolo');
@@ -143,7 +136,8 @@ function startRgbLoop() {
     }
     // ROI already set: start a new selection on the next click.
     roi = null;
-    fitPointsPx = null;
+    fitPointsCv = null;
+    three.setFitInliers(null);
     firstCorner = p;
     drawOverlay();
     setRoiInfo();
@@ -173,26 +167,19 @@ const three = (function setupThree() {
   controls.target.set(0, 0, 1);
   controls.update();
   scene.add(new THREE.AxesHelper(0.1));
-  const planeMesh = new THREE.Mesh(
-    new THREE.PlaneGeometry(0.4, 0.4),
-    new THREE.MeshBasicMaterial({ color: 0x9b6dff, transparent: true, opacity: 0.3, side: THREE.DoubleSide }),
-  );
-  planeMesh.visible = false;
-  scene.add(planeMesh);
+  // The fitted plane is implied by the blue inlier cloud; no extra mesh is
+  // drawn (the previous PlaneGeometry was a fixed 0.4x0.4 square that did
+  // not reflect the actual ROI extent and was misleading).
   let scatter = null;
+  let fitInliersScatter = null;
 
   function render() { renderer.render(scene, camera); }
   (function loop() { controls.update(); render(); requestAnimationFrame(loop); })();
 
   function setPlane(plane) {
-    if (!plane) { planeMesh.visible = false; return; }
-    const c = plane.centroid;
-    const n = plane.normal;
-    planeMesh.position.set(c[0], c[1], c[2]);
-    // Align plane to its normal.
-    planeMesh.lookAt(c[0] + n[0], c[1] + n[1], c[2] + n[2]);
-    planeMesh.visible = true;
+    if (!plane) return;
     // Move the orbit target onto the plane centroid so rotation feels natural.
+    const c = plane.centroid;
     controls.target.set(c[0], c[1], c[2]);
     controls.update();
   }
@@ -231,7 +218,29 @@ const three = (function setupThree() {
     scene.add(scatter);
   }
 
-  return { setPlane, setScatter };
+  function setFitInliers(pointsCv) {
+    if (fitInliersScatter) {
+      scene.remove(fitInliersScatter);
+      fitInliersScatter.geometry.dispose();
+      fitInliersScatter.material.dispose();
+      fitInliersScatter = null;
+    }
+    if (!pointsCv || pointsCv.length === 0) return;
+    const n = pointsCv.length;
+    const positions = new Float32Array(n * 3);
+    for (let i = 0; i < n; i++) {
+      positions[3 * i]     = pointsCv[i][0];
+      positions[3 * i + 1] = pointsCv[i][1];
+      positions[3 * i + 2] = pointsCv[i][2];
+    }
+    const geom = new THREE.BufferGeometry();
+    geom.setAttribute('position', new THREE.BufferAttribute(positions, 3));
+    const mat = new THREE.PointsMaterial({ color: 0x4da3ff, size: 0.006 });
+    fitInliersScatter = new THREE.Points(geom, mat);
+    scene.add(fitInliersScatter);
+  }
+
+  return { setPlane, setScatter, setFitInliers };
 })();
 
 // ---------------- State + button handlers ----------------
@@ -289,10 +298,10 @@ 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;
+    fitPointsCv = r.fit_points_camera || null;
     three.setPlane(previewPlane);
     three.setScatter(previewPoints, previewPlane, previewPlane.offset_mm);
-    if (window.__wpDrawOverlay) window.__wpDrawOverlay();
+    three.setFitInliers(fitPointsCv);
     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');
@@ -332,8 +341,10 @@ async function doClear() {
     savedPlane = null;
     previewPlane = null;
     previewPoints = null;
+    fitPointsCv = null;
     three.setPlane(null);
     three.setScatter(null);
+    three.setFitInliers(null);
     $('wpStateBlock').innerHTML = '<div class="dim">nessun piano</div>';
     $('wpDetails').textContent = '—';
     setChip('nessun piano');