fix: validate MaxBodyCaptureSizeKb rejects negative values

MaxBodyCaptureSizeKb could previously be set to negative values, which caused incorrect body size calculations and unexpected capture behavior during request/response truncation.

Author: georgidhristov

DebugProbe.AspNetCore.Tests/Configuration/DebugProbeOptionsTests.cs

@@ -87,4 +87,21 @@ public void MaxEntries_negative_throws_InvalidOperationException()
 
         Assert.Contains("MaxEntries", exception.Message);
     }
+
+    [Fact]
+    public void MaxBodyCaptureSizeKb_negative_throws_ArgumentOutOfRangeException()
+    {
+        var options = new DebugProbeOptions();
+
+        Assert.Throws<ArgumentOutOfRangeException>(() => options.MaxBodyCaptureSizeKb = -1);
+    }
+
+    [Fact]
+    public void MaxBodyCaptureSizeKb_zero_is_valid()
+    {
+        var options = new DebugProbeOptions();
+        options.MaxBodyCaptureSizeKb = 0;
+
+        Assert.Equal(0, options.MaxBodyCaptureSizeKb);
+    }
 }

DebugProbe.AspNetCore/Options/DebugProbeOptions.cs

@@ -1,4 +1,4 @@
-namespace DebugProbe.AspNetCore.Options;
+namespace DebugProbe.AspNetCore.Options;
 
 /// <summary>
 /// Configuration options for DebugProbe.
@@ -13,7 +13,18 @@ public class DebugProbeOptions
     /// <summary>
     /// Maximum captured request or response body size in kilobytes.
     /// </summary>
-    public int MaxBodyCaptureSizeKb { get; set; } = 32;
+    private int _maxBodyCaptureSizeKb = 32;
+    public int MaxBodyCaptureSizeKb
+    {
+        get => _maxBodyCaptureSizeKb;
+        set
+        {
+            if (value < 0)
+                throw new ArgumentOutOfRangeException(nameof(MaxBodyCaptureSizeKb),
+                    "MaxBodyCaptureSizeKb must be 0 or greater. Use 0 to disable body capture.");
+            _maxBodyCaptureSizeKb = value;
+        }
+    }
 
     internal int MaxBodyCaptureSizeBytes => MaxBodyCaptureSizeKb * 1024;