Confused by "Add an [edit] link for the lead section of a page"

[Artoria2e5]

On English Wikipedia Preferences, I have the gadget "Add an [edit] link for the lead section of a page" installed. That is apparently too much for the userscript: the HTTP 400 error goes

{
    "error": "The article (CIE 1931 color space[edit]) you are trying to request does not exist in english Wikipedia.",
    "success": false,
    "rev_id": null,
    "page_title": "CIE 1931 color space[edit]"
}

Disabling the gadget makes it the text and coloring load.

PS: I'm loading the script in the worst way known to mankind: copy the whole thing and paste it in my Safari console. Hey, it works... ish! (Still bails on TypeError: undefined is not an object (evaluating 'Wikiwho.seqHistBox.offset().left'), clearly my fault.)

PPS: why safari console? because it's the one browser that can't use the wmf extension