My first inclination is to break out some parts of HTTP-network-or-cache Fetch into new sections and then grow them.

Specifically -

• bullets 17 and 18 ("If httpRequest's cache mode is neither...", "Otherwise, if httpRequest's cache mode is either...") should be shifted to a new "HTTP Cache Lookup" section, that specifies http://httpwg.org/specs/rfc7234.html#constructing.responses.from.caches algorithmically.
• after bullet 19 ("If response is null, run these substeps..."), insert a new item (or reference to a new section, "HTTP Cache Storage" or similar, along the lines specified in http://httpwg.org/specs/rfc7234.html#response.cacheability.

If that makes sense, I'll start a branch, and probably some tests too.

Question - Is the Streams work largely done? I suspect some of the fine points here are going to need them.