A NetworkError when a transport's reported final URL (HttpResponse.url, fetch's
response.url) is on another origin than the request's: the transport followed a
redirect itself, to a host the caller never checked — with credential headers,
since fetch strips Authorization across origins but not X-API-Key or Cookie.
Undefined when the transport reports no URL or the same origin.
A NetworkError when a transport's reported final URL (
HttpResponse.url, fetch'sresponse.url) is on another origin than the request's: the transport followed a redirect itself, to a host the caller never checked — with credential headers, since fetch strips Authorization across origins but not X-API-Key or Cookie. Undefined when the transport reports no URL or the same origin.