Measured against the instruction-edit models on 2026-07-31: asking a diffusion
model to put a SPECIFIC person's face into a photo does not work by any route.
qwen-image-edit returns the picture essentially unchanged whether asked by
name, by attribute, or by supplying the portrait as a second reference image;
flux-kontext replaces the face with a different generic person. Identity
transfer is a detect/align/blend pipeline, not a better prompt, so it gets its
own interface rather than more Edit options.

imagegen.FaceSwapper is optional and type-asserted, like Editor — a provider
that cannot do this must not have Edit quietly stand in for it.

ListFaces is part of the interface, not a convenience: a caller asked to
change "the man on the right" needs a stable way to NAME one face, and pixel
boxes let it check its own choice. The llamaswap shim orders faces left to
right for exactly that reason (insightface's own order is score-ranked and
unstable between near-identical images), and a malformed box is a protocol
error rather than a zero-filled struct, because a wrong box aims the swap at
the wrong person.

The provider is the first here to POST more than one file, so buildMultipart
gained buildMultipartFiles and now delegates to it — one writer loop, so the
two cannot drift in how they escape names or terminate the body.

index and all are mutually exclusive ON THE WIRE: the shim ignores index under
all=true, and sending both would imply a precedence the caller cannot see.
A JSON body is refused rather than returned as image bytes — the shim answers
JSON on a semantic miss (no face in the source), and handing that back as a
picture would report success while delivering a file that is not one.

@@ -0,0 +55,4 @@
+	Box [4]int
+	// Score is the detector's confidence, 0-1.
+	Score float64
+	// Width and Height are the box dimensions, carried so a caller can pick

@@ -0,0 +62,4 @@
+
+// FaceSwapper is the optional face-transfer surface. Separate interface so
+// existing providers keep compiling; callers type-assert.
+type FaceSwapper interface {

@@ -0,0 +97,4 @@
+	if len(req.Source.Data) == 0 {
+		return nil, fmt.Errorf("%w: face swap requires a source image", llm.ErrUnsupported)
+	}
+	if req.Index != nil && *req.Index < 0 {

@@ -0,0 +130,4 @@
+	if len(raw) == 0 {
+		return nil, &llm.APIError{Provider: m.p.name, Model: m.id, Message: "face swap response contained no image"}
+	}
+	mime := sniffImageMIME(raw)

@@ -0,0 +144,4 @@
+// bytes, not names, but a plausible extension keeps server-side sniffing and
+// request logs honest. base distinguishes the parts of a multi-file form
+// ("target"/"source") so a log line says which one was malformed.
+func imageFilename(mimeType, base string) string {

@@ -0,0 +15,4 @@
+	"gitea.stevedudenhoeffer.com/steve/majordomo/llm"
+)
+
+func swapImg(t *testing.T) imagegen.Image {

@@ -0,0 +162,4 @@
+	if err == nil {
+		t.Fatal("a JSON body was accepted as an image")
+	}
+	var apiErr *llm.APIError