handlers.Params gets an optional Fetcher, marked optional for fx. When
the app provides one, the handlers pass it to the image service, whose
Fetcher option already existed for tests, instead of letting it build
its own from the config. pixad provides none, so production builds its
fetcher from the config exactly as before. A new test builds the
handlers in an fx app that provides no fetcher, as pixad does, and
checks that an image from an allowlisted localhost is refused with 403
by the fetcher the handlers built.
Model: opus-5-5
