fix: validate MaxEntries to prevent infinite loop in DebugEntryStore

Added DebugProbeOptionsValidator that validates MaxEntries >= 1
during startup. If the value is invalid, an InvalidOperationException
is thrown immediately with a clear error message.

Author: georgidhristov

DebugProbe.AspNetCore.Tests/Configuration/DebugProbeOptionsTests.cs

@@ -60,4 +60,31 @@ public void Custom_options_are_registered_and_used()
         Assert.Equal("***", options.RedactionText);
         Assert.NotNull(store.Environment);
     }
+    [Fact]
+    public void MaxEntries_zero_throws_InvalidOperationException()
+    {
+        var services = new ServiceCollection();
+
+        var exception = Assert.Throws<InvalidOperationException>(() =>
+            services.AddDebugProbe(options =>
+            {
+                options.MaxEntries = 0;
+            }));
+
+        Assert.Contains("MaxEntries", exception.Message);
+    }
+
+    [Fact]
+    public void MaxEntries_negative_throws_InvalidOperationException()
+    {
+        var services = new ServiceCollection();
+
+        var exception = Assert.Throws<InvalidOperationException>(() =>
+            services.AddDebugProbe(options =>
+            {
+                options.MaxEntries = -1;
+            }));
+
+        Assert.Contains("MaxEntries", exception.Message);
+    }
 }

DebugProbe.AspNetCore/Extensions/DebugProbeExtensions.cs

@@ -36,6 +36,11 @@ public static IServiceCollection AddDebugProbe(this IServiceCollection services,
 
         configure?.Invoke(options);
 
+        var validator = new DebugProbeOptionsValidator();
+        var result = validator.Validate(null, options);
+        if (result.Failed)
+            throw new InvalidOperationException(result.FailureMessage);
+
         services.AddSingleton(options);
 
         services.AddSingleton<DebugEntryStore>();

DebugProbe.AspNetCore/Options/DebugProbeOptionsValidator.cs

@@ -0,0 +1,22 @@
+using Microsoft.Extensions.Options;
+
+namespace DebugProbe.AspNetCore.Options;
+
+internal sealed class DebugProbeOptionsValidator
+    : IValidateOptions<DebugProbeOptions>
+{
+    public ValidateOptionsResult Validate(
+        string? name,
+        DebugProbeOptions options)
+    {
+        if (options.MaxEntries < 1)
+        {
+            return ValidateOptionsResult.Fail(
+                $"DebugProbe configuration is invalid. " +
+                $"MaxEntries must be greater than or equal to 1. " +
+                $"Provided value: {options.MaxEntries}.");
+        }
+
+        return ValidateOptionsResult.Success;
+    }
+}