Add decorator hook for CLR exception error objects

[Copilot]

Enables post-processing of JavaScript error objects created from caught CLR exceptions. Addresses use cases like adding CLR type information, stack traces, or custom context properties to errors.

Changes

• New delegate: ClrExceptionErrorDecoratorDelegate(Engine, ObjectInstance error, Exception clrException) in Options.cs
• Configuration: ClrExceptionErrorDecorator property in Options.InteropOptions, invoked only when ExceptionHandler catches the exception
• Error creation: Throw.FromClrException() centralizes error construction and decorator invocation, used by ClrFunction.CallSlow() and Throw.MeaningfulException()
• Fluent API: DecorateClrExceptionErrors() extension method for configuration

Usage

var engine = new Engine(options =>
{
    options.CatchClrExceptions();
    options.DecorateClrExceptionErrors((engine, error, clrException) =>
    {
        error.Set("clrType", clrException.GetType().FullName);
        error.Set("clrStackTrace", clrException.StackTrace);
    });
});

engine.SetValue("throw", new Action(() => throw new InvalidOperationException("test")));

engine.Execute(@"
    try { throw(); } 
    catch(e) { console.log(e.clrType); }  // System.InvalidOperationException
");

Decorator is called after base error object creation, allowing enrichment without full replacement. No decorator overhead when not configured.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Decorate error object from CLR</issue_title>
<issue_description>We probably need a new option for handling exception enrichening. Now we have the catch CLR exception option but also a way to post-process created exception.

Discussed in #2278

^{Originally posted by kxs-rgamezdiaz February 11, 2026}
Is it possible to add custom properties to the error object that gets caught in js?

Let's say I want to make the following test pass. The idea is to send an "errorCode" property from the CLR.

[TestClass]
public sealed class ScriptEngineExceptionTests
{
    [TestMethod]
    public void ErrorShouldContainProperties()
    {
        Engine engine = new(options =>
        {
            options.CatchClrExceptions();
        });

        engine.SetValue("myClass", new());

        engine.Execute("""
            function main () {
                try {
                    myClass.MethodThatThrows();
                } catch (e) {
                    return JSON.stringify(e);
                }
            }
            """);

        string result = engine.Invoke("main").ToString();

        Assert.AreEqual("{errorCode:'InvalidOperation'}", result);
    }

    public class MyClass()
    {
        public void MethodThatThrows() => throw new InvalidOperationException("This is a test exception.");
    }
}

Right now the Invoke returns an empty object {}.

Thanks!

</issue_description>

<agent_instructions>Think of ways to handle this the way it's sustainable and allows extension. Jint could just create the base exception and let a hook post-process it. Allowing full exception creation might be too much, but analyze.</agent_instructions>

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

• Fixes Decorate error object from CLR #2279

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