Regression in 4.1.0: (method) decorators not accepted in class defined in test files

Describe the bug

(clean version of https://github.com/vitest-dev/vitest/issues/9873, sorry for the mess)

I'm trying to test a method decorator, copying example from TypeScript documentation (inside a test file, the actual case is too test that decorator by defining a class with a method using it).

function loggedMethod(originalMethod: any, _context: any) {
  function replacementMethod(this: any, ...args: any[]) {
    console.log("LOG: Entering method.");
    const result = originalMethod.call(this, ...args);
    console.log("LOG: Exiting method.");
    return result;
  }

  return replacementMethod;
}

class Person {
  name: string;
  constructor(name: string) {
    this.name = name;
  }

  @loggedMethod
  greet() {
    console.log(`Hello, my name is ${this.name}.`);
  }
}

With 4.0.18, this worked fine. With 4.1.0, I get error

FAIL  packages/alfa-cache/test/cache.spec.ts [ packages/alfa-cache/test/cache.spec.ts ]
SyntaxError: Invalid or unexpected token

When commenting out the @loggedMethod line, the tests run fine.

I guess the "unexpected token" is the @ symbol. Couldn't find anything obvious in the changelog that this should now break, so I guess it is a regression (and also, the error message is pretty bad, not giving at least the line where the problem is).

Reproduction

https://github.com/Jym77/vitest-decorator

The Vitest 4.0.18 workflow runs fine.
The Vitest 4.1.0 workflow fails with the "unexpected token" error. The test-no-decorator file passes, but the test-decorator one doesn't. The only difference between them being the inclusion of the decorator (in a class that is not even used, so likely a parsing error?)

System Info

System:
    OS: Linux 6.6 Ubuntu 24.04.4 LTS 24.04.4 LTS (Noble Numbat)
    CPU: (8) x64 11th Gen Intel(R) Core(TM) i7-1165G7 @ 2.80GHz
    Memory: 14.54 GB / 15.48 GB
    Container: Yes
    Shell: 5.2.21 - /bin/bash
  Binaries:
    Node: 24.14.0 - /home/jym/.nvm/versions/node/v24.14.0/bin/node
    Yarn: 4.13.0 - /home/jym/.nvm/versions/node/v24.14.0/bin/yarn
    npm: 11.9.0 - /home/jym/.nvm/versions/node/v24.14.0/bin/npm
  npmPackages:
    @vitest/coverage-v8: ^4.1.0 => 4.1.0
    vitest: ^4.1.0 => 4.1.0


(node project, not using any browser)

Used Package Manager

yarn

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion or join our Discord Chat Server.
• The provided reproduction is a minimal reproducible example of the bug.

Start with the reproduction's test-decorator and test-no-decorator files, comparing their behavior under Vitest 4.0.18 and 4.1.0. Trace how the test file containing the method decorator is parsed or transformed, then verify that the decorator test passes under 4.1.0 while the existing no-decorator test remains passing.