What is the current behavior?

Three of the tests related to homepage calculation. The are all of the following flavor.

FAIL  tests/rendering/header.js (66.489 s)
  ● header › mobile-only product dropdown links › include github and admin, and emphasize the current product

    expect(received).toBe(expected) // Object.is equality

    Expected: 1
    Received: 0

      72 |
      73 |       const github = $(`#homepages a.active[href="/en/${nonEnterpriseDefaultVersion}/github"]`)
    > 74 |       expect(github.length).toBe(1)
         |                             ^
      75 |       expect(github.text().trim()).toBe('GitHub.com')
      76 |       expect(github.attr('class').includes('active')).toBe(true)
      77 |

      at Object.<anonymous> (tests/rendering/header.js:74:29)

and here is a sample of the HTML being returned from get. As you can see, Windows path separators () are being used indicating that path.join is likely involved. I've not isolated the particular code as yet.

        class=\"position-md-absolute nav-desktop-productDropdown p-md-4 left-md-n4
        top-md-6\" style=\"z-index: 6;\">\r\n \r\n <a
            href=\"/en\\free-pro-team@latest\\github\"\r\n class=\"d-block py-2\r\n
            text-blue-mktg text-underline active\">\r\n GitHub.com\r\n \r\n </a>\r\n
        \r\n <a href=\"/en\\enterprise-server@2.22\\admin\"\r\n class=\"d-block
            py-2\r\n link-gray-dark no-underline\">\r\n Enterprise
            Administrators\r\n \r\n </a>\r\n \r\n <a
            href=\"/en\\free-pro-team@latest\\actions\"\r\n class=\"d-block py-2\r\n
            link-gray-dark no-underline\">\r\n GitHub Actions\r\n \r\n </a>\r\n \r\n
        <a href=\"/en\\free-pro-team@latest\\packages\"\r\n class=\"d-block py-2\r\n

What changes are you suggesting?

Suggest we do an audit of all the places that inject URLs into content or headers and ensure they don't use path.join. In fact, we should make a helper (e.g., safeJoin) that does something like (...segments) => slash(path.join(segments)) and then use that everywhere that has anything to do with web results.

cc @github/docs-engineering , @chiedo