fix: validate probabilities for temperature scaling

Author: ooples

src/PredictionModelBuilder.cs

@@ -721,14 +721,41 @@ private static void TryComputeClassificationCalibrationArtifacts(
     private static T FitTemperatureFromProbabilities(Tensor<T> probabilities, Vector<int> labels, int batch, int classes, INumericOperations<T> numOps)
     {
         var eps = numOps.FromDouble(1e-12);
+        var sumTolerance = numOps.FromDouble(1e-3);
         var logits = new Matrix<T>(batch, classes);
         var flat = probabilities.ToVector();
 
         for (int i = 0; i < batch; i++)
         {
+            var sum = numOps.Zero;
             for (int c = 0; c < classes; c++)
             {
                 var p = flat[i * classes + c];
+                if (numOps.LessThan(p, numOps.Zero))
+                {
+                    p = numOps.Zero;
+                }
+                sum = numOps.Add(sum, p);
+            }
+
+            if (numOps.LessThan(sum, eps))
+            {
+                throw new ArgumentException("Temperature scaling requires per-sample probabilities with a positive sum.", nameof(probabilities));
+            }
+
+            var shouldNormalize = numOps.GreaterThan(numOps.Abs(numOps.Subtract(sum, numOps.One)), sumTolerance);
+
+            for (int c = 0; c < classes; c++)
+            {
+                var p = flat[i * classes + c];
+                if (numOps.LessThan(p, numOps.Zero))
+                {
+                    p = numOps.Zero;
+                }
+                if (shouldNormalize)
+                {
+                    p = numOps.Divide(p, sum);
+                }
                 if (numOps.LessThan(p, eps))
                 {
                     p = eps;