Maybe it's painfully obvious?

I'm trying to add a redirect to an existing site. Uses Page Routing.

Ideally, from root, anything matching ^/\d{1,5} (non-empty path, beginning with 1 to 5 digits) should be redirected to a given, existing path.

I have read https://nextjs.org/docs/pages/api-reference/next-config-js/redirects multiple times.

I made sure to explicitly set trailingSlashes value. I've also removed any other redirects, removed all rewrites, and turned off any existing middleware.

Here's a relevant portion of my config:

{
  trailingSlash: false,
  async redirects() {
    return [
      {
        source: `/(\\d+)`,
        destination: 'https://www.example.com/',
        permanent: true,
        locale: false, // Avoid `/{lang}/...` prefixes from i18n.
        basePath: false, // Destination will not receive prefix.
      },
      {
        source: `/:versionId(\\d+)/:slug`,
        destination: '/some/valid/path',
        permanent: true,
        locale: false,
      },
      // Invalid case: bare Regex is invalid redirect (app won't start):
      // {
      //   source: `/\\d+`,
      //   destination: '/some/valid/path',
      //   permanent: true,
      //   locale: false,
      // },
      {
        source: `/(\\d{1,5})`,
        destination: '/some/valid/path',
        permanent: true,
        locale: false,
      },
      {
        source: `/:slug(\\d+)`,
        destination: '/some/valid/path',
        permanent: true,
        locale: false,
      },
      {
        source: `/fake/:slug(\\d+)`,
        destination: '/some/valid/path',
        permanent: true,
        locale: false,
      },
    ];
  }
}

None of these, even /fake/123 receive a redirect response.

Testing via curl, with curl -I -X GET http://localhost:3000/123, etc. Always receiving a 404.

Any ideas how to best debug this? E.g., how to test matchers, etc?