---

This section details on the original issue you should resolve

<issue_title>Regex ()(?'-1')(?!(?'-1')) exhibit incorrect matching behavior in .NET10</issue_title>
<issue_description>### Description

Such situation occur in (?!) and (?<!) under Interpreter、Compiled and source GeneratedCode.

Reproduction Steps

using System.Text.RegularExpressions;

var pattern = @"()(?'-1')(?!(?'-1'))";
var input = "such situation occur in (?!) and (?<!) under Interpreter、Compiled and source GeneratedCode";
Regex regex = new Regex(pattern, RegexOptions.Compiled);
var mhes = regex.Matches(input);
Console.WriteLine(Regex.Matches(input, pattern).Count);
Console.WriteLine(mhes.Count);
Console.WriteLine(RegexTester.regexGenerate().Matches(input).Count);
internal partial class RegexTester
{
	[GeneratedRegex(@"()(?'-1')(?!(?'-1'))")]
	internal static partial Regex regexGenerate();
}

Here is part of source Generated Code:

partial class RegexTester
{
    /// <remarks>
    /// Pattern:<br/>
    /// <code>()(?'-1')(?!(?'-1'))</code><br/>
    /// Explanation:<br/>
    /// <code>
    /// ○ Fail to match.<br/>
    /// </code>
    /// </remarks>
    [global::System.CodeDom.Compiler.GeneratedCodeAttribute("System.Text.RegularExpressions.Generator", "10.0.13.307")]
    internal static partial global::System.Text.RegularExpressions.Regex regexGenerate() => global::System.Text.RegularExpressions.Generated.regexGenerate_0.Instance;
}

private sealed class Runner : RegexRunner
{
    /// <summary>Scan the <paramref name="inputSpan"/> starting from base.runtextstart for the next match.</summary>
    /// <param name="inputSpan">The text being scanned by the regular expression.</param>
    protected override void Scan(ReadOnlySpan<char> inputSpan)
    {
        // The pattern never matches anything.
    }
}

Expected behavior

91
91
91

Actual behavior

0
0
0

Regression?

No response

Known Workarounds

No response

Configuration

No response

Other information

No response</issue_description>

<agent_instructions>Please add tests for the problem and fix it. I expect the problem was introduced in #118084 and that the fix is simply to ensure that capture groups are only removed from negative lookarounds if they're not part of a balancing group.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@stephentoub Why do you believe the current behavior is incorrect? It's unclear from your description as the Regression section is empty... is your "Expected behavior" from a previous release?