Multiple Content-Disposition response headers

Content-Disposition (RFC 6266) is not defined as a list-based field, so a server is not supposed to send it more than once (RFC 9110 section 5.3), and RFC 6266 says nothing about how a recipient should combine repeated field lines. Servers send them anyway.

These tests are .tentative because that is unspecified. They assert the Fetch header list model: both field lines are kept, they are combined with , when read back, and the response is not a network error. The same assertions run over HTTP/1.1 and HTTP/2 so that differences between protocol versions within one implementation are visible.

The “is not a network error” and “are combined” assertions are separate because an implementation may load the response while exposing only one field line.

See https://bugzilla.mozilla.org/show_bug.cgi?id=1982182 and https://github.com/whatwg/fetch/issues/1156 for context.