Arranging: boxes on everything, handwriting movable, the Eraser's preview, a Circle shape, pixel-exact cues

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

client/js/session.js

@@ -903,7 +903,8 @@ export class Session {
    */
   beginShapeEdit(id) {
     const stroke = this.ownLayer.strokes.get(id);
-    if (!stroke || !stroke.shape || this.shapeEditing) return false;
+    // Any finished stroke of ours: a shape, or handwriting under Arrange (Andy, 2026-10-14).
+    if (!stroke || !stroke.done || this.shapeEditing) return false;
     this.shapeEditing = { id, before: { ...stroke, points: stroke.points.slice() } };
     return true;
   }