fix(cutting): never treat an extent with a nonfinite bound as separated

IsSeparatedFrom promised that NaN bounds are never separated, but a
finite axis could still compare as separated when the other axis held
NaN. Program reading already refuses nonfinite coordinates, so no
public path was affected; the helper now checks every bound and the
margin are finite before comparing, which also covers the empty
extent of an incomplete material snapshot.

OpenNest.Core/Diagnostics/PostVerificationGeometry.cs

@@ -27,11 +27,16 @@ internal static class PostVerificationGeometry
 
         /// <summary>
         /// True only when the extents are farther apart than <paramref name="margin"/> on some axis,
-        /// so nothing inside one can touch or enter the other. NaN bounds are never separated.
+        /// so nothing inside one can touch or enter the other. An extent with any nonfinite bound
+        /// (including the empty one) is never separated.
         /// </summary>
-        internal bool IsSeparatedFrom(Extent other, double margin) =>
-            MaxX + margin < other.MinX || other.MaxX + margin < MinX
-            || MaxY + margin < other.MinY || other.MaxY + margin < MinY;
+        internal bool IsSeparatedFrom(Extent other, double margin) => IsFinite && other.IsFinite
+            && double.IsFinite(margin)
+            && (MaxX + margin < other.MinX || other.MaxX + margin < MinX
+                || MaxY + margin < other.MinY || other.MaxY + margin < MinY);
+
+        private bool IsFinite => double.IsFinite(MinX) && double.IsFinite(MinY)
+            && double.IsFinite(MaxX) && double.IsFinite(MaxY);
     }
 
     internal static void Validate(Vector point)

OpenNest.Tests/CuttingPlanning/NearbyMaterialCheckTests.cs

@@ -145,6 +145,16 @@ public class NearbyMaterialCheckTests
         Assert.Contains("uncertain", result.Reason);
     }
 
+    [Fact]
+    public void ExtentWithANaNBound_IsNeverSeparated()
+    {
+        var partial = new PostVerificationGeometry.Extent(double.NaN, 0, double.NaN, 1);
+        var other = new PostVerificationGeometry.Extent(0, 4, 1, 5);
+
+        Assert.False(partial.IsSeparatedFrom(other, 1e-6));
+        Assert.False(other.IsSeparatedFrom(partial, 1e-6));
+    }
+
     private static Program CleanCircle(double radius)
     {
         var p = new Program();