Source generator: CancellationToken declared before a params array on a non-generic test does not receive the test token #7147

Summary

On a non-generic test method, a CancellationToken parameter declared before a trailing params array does not receive the test's cancellation token in source-generated mode. Reflection mode injects it correctly, so the two modes disagree.

Repro

public class TokenBeforeParams
{
    [Test]
    [Arguments]
    public async Task M(int count = 42, CancellationToken token = default, params int[] values)
    {
        await Assert.That(token.CanBeCanceled).IsTrue();
    }
}

• --reflection: passes.
• Source-generated: fails. The generated invoker treats token as a data parameter and passes default(CancellationToken) (on main the token was simply omitted, with the same result).

Found while working on #7122 (verified on its branch by adding the assertion above to tests/TUnit.TestProject/Bugs/_7122/OmittedOptionalOverloadTests.cs, Optional_Before_Params_With_Token).

Where

TestMetadataGenerator.GetLeadingCancellationTokenIndex and its comment state a non-trailing token is "only reachable for generic methods"; for non-generic methods the token apparently stays in parametersFromArgs. Reflection mode (ReflectionTestMetadata, ~line 112) inserts the token at its declared index for any method.

Expected

Both modes pass the test's cancellation token to a CancellationToken parameter wherever it is declared (or an analyzer rejects non-trailing tokens consistently).