feat: enforce Delaunay vertices at inset boundary corners + update geometry to v2.0 with arcs

- Add explicit corner vertices of the inset boundary (w_frame offset) to Delaunay point set
- This guarantees no triangle can cross a boundary corner
- Updated test_data geometry files to v2.0 format with typed segments
- Sandbox 2 now has proper arc curves (4 arc segments) from extract_sandbox
- Preserved holes from v1.0 geometry
- Boundary vertices also enforced on keepout boundaries

tools/adaptive-isogrid/src/brain/triangulation.py

@@ -154,29 +154,55 @@ def _add_boundary_vertices(points, geometry, params, keepout_union):
     
     This ensures triangles conform to boundaries rather than just being
     clipped. Points are spaced at approximately s_min along boundaries.
+    
+    KEY: Enforce explicit vertices at every corner of the inset boundary.
+    This guarantees no triangle can cross a corner — the Delaunay triangulation
+    is forced to use these corner points as vertices.
     """
     s_min = params['s_min']
     w_frame = params.get('w_frame', 8.0)
 
     new_pts = list(points)
 
-    # Add points along inset outer boundary (frame inner edge)
     plate_poly = Polygon(geometry['outer_boundary'])
     inner_frame = plate_poly.buffer(-w_frame)
-    if not inner_frame.is_empty and inner_frame.geom_type == 'Polygon':
-        ring = inner_frame.exterior
-        length = ring.length
-        n_pts = max(int(length / s_min), 4)
-        for i in range(n_pts):
-            frac = i / n_pts
-            pt = ring.interpolate(frac, normalized=True)
-            new_pts.append([pt.x, pt.y])
+    if not inner_frame.is_empty:
+        # Handle MultiPolygon from buffer on complex shapes
+        if inner_frame.geom_type == 'MultiPolygon':
+            inner_polys = list(inner_frame.geoms)
+        else:
+            inner_polys = [inner_frame]
+
+        for inner_poly in inner_polys:
+            ring = inner_poly.exterior
+
+            # 1) ENFORCE corner vertices: add every vertex of the inset boundary
+            #    These are the actual corner points — critical for preventing crossovers
+            coords = list(ring.coords)[:-1]  # skip closing duplicate
+            for cx, cy in coords:
+                new_pts.append([cx, cy])
+
+            # 2) Add evenly spaced points along edges for density
+            length = ring.length
+            n_pts = max(int(length / s_min), 4)
+            for i in range(n_pts):
+                frac = i / n_pts
+                pt = ring.interpolate(frac, normalized=True)
+                new_pts.append([pt.x, pt.y])
+
+            # Also add inner ring vertices (for any holes in the inset boundary)
+            for interior in inner_poly.interiors:
+                for cx, cy in list(interior.coords)[:-1]:
+                    new_pts.append([cx, cy])
 
     # Add points along hole keepout boundaries
     if not keepout_union.is_empty:
         geoms = [keepout_union] if keepout_union.geom_type == 'Polygon' else list(keepout_union.geoms)
         for geom in geoms:
             ring = geom.exterior
+            # Enforce corner vertices on keepout boundaries too
+            for cx, cy in list(ring.coords)[:-1]:
+                new_pts.append([cx, cy])
             length = ring.length
             n_pts = max(int(length / (s_min * 0.7)), 6)
             for i in range(n_pts):