In web-platform-tests/wpt#27837 (comment) @mfalken suggested that synthetic responses should receive validation similar to network responses. A simple example I can think of would be:

e.respondWith(new Response("...", { headers: [["content-length":"1"],["content-length":"2"]] }))

I tend to think this should be fine and we just ignore the content-length header as it's pointless for synthetic responses. Am I missing something here?

(I'm going to merge that PR as it matches the specification as written, but I figured I should at least file a follow-up.)