Gadfly on #23, blocking, 2/2 agreement — and it is the exact defect this whole line of work has been about: a call that succeeds while handing back the wrong bytes. sniffImageMIME falls back to image/png when detection is inconclusive, and the guard only consulted Content-Type. A response with NO Content-Type therefore skipped the check entirely and was labelled a PNG. The shim answers JSON on a semantic miss (no face found in the source or target), which is precisely the body that would have sailed through as a successful image. The check now validates the BYTES — http.DetectContentType must say image/ — and the reported MIME prefers the server's own label only when that label is itself an image type. Break-checked by restoring the header-only condition, which fails the new test. Also from that review: - index is documented as ignored under all=true, so a negative one is no longer rejected there; it is still rejected when it would actually be sent, and both halves are tested. - initImageFilename (video.go) was imageFilename with the base fixed to "frame" and now delegates to it — two copies of one extension table is how they drift. - DetectedFace carried Width/Height alongside Box, two sources of truth for one fact that can disagree after any transform. Now a Size() method derived from Box. - a dead `apiErr` in the test (declared, then `_ = apiErr`) was an abandoned errors.As check; it is wired up and now asserts callers can classify the error. - swapImg duplicated editInit verbatim; removed. Not taken: adding a FaceSwapProvider/ModelOption surface to match the other optional imagegen capabilities (single-model finding). There are no options to carry yet, and inventing an empty option type to look symmetrical would be API surface with nothing behind it. Worth revisiting when a real knob exists.