fix: drop glare holes before the margin and never auto-pick specks

Filtering holes after the margin let -2 mm grow 1 mm specks past the
3 mm cutoff, and could drop real holes shrunk by a positive margin.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/lib/detect.ts

@@ -100,6 +100,7 @@ export function detect(cv: CV, image: RasterImage, params: DetectParams): Shape
     const lab = labels.data32S;
     const m = mask.data;
     for (let i = 0; i < lab.length; i++) m[i] = lab[i] === label ? 255 : 0;
+    fillSmallHoles(cv, mask, params.minHolePx);
     return traceMask(cv, mask, params.marginPx);
   } finally {
     gray.delete();
@@ -134,16 +135,41 @@ function pickComponent(
     }
   }
 
+  // Without a click, specks (dust, grain) must never pass as the piece.
+  const minArea = 0.01 * width * height;
   let best: number | null = null;
   let bestArea = 0;
   for (let label = 1; label < count; label++) {
     const b = box(label);
     if (b.left === 0 || b.top === 0 || b.right === width || b.bottom === height) continue;
     const area = stat(label, cv.CC_STAT_AREA);
-    if (area > bestArea) {
+    if (area >= minArea && area > bestArea) {
       bestArea = area;
       best = label;
     }
   }
   return best;
 }
+
+/** Fill holes under minHolePx in both directions, before the margin can grow them. */
+function fillSmallHoles(cv: CV, mask: Mat, minHolePx: number) {
+  if (minHolePx <= 0) return;
+  const contours = new cv.MatVector();
+  const hierarchy = new cv.Mat();
+  try {
+    cv.findContours(mask, contours, hierarchy, cv.RETR_CCOMP, cv.CHAIN_APPROX_SIMPLE);
+    const h = hierarchy.data32S;
+    for (let i = 0; i < contours.size(); i++) {
+      if (h[i * 4 + 3] === -1) continue;
+      const c = contours.get(i);
+      const rect = cv.boundingRect(c);
+      c.delete();
+      if (rect.width < minHolePx && rect.height < minHolePx) {
+        cv.drawContours(mask, contours, i, new cv.Scalar(255), cv.FILLED);
+      }
+    }
+  } finally {
+    contours.delete();
+    hierarchy.delete();
+  }
+}