Route direct image-edit requests through the img2img pipeline

Direct `models/infer` image requests were defaulting to `image.text2image`, which dropped reference inputs and produced unrelated generations. Route image-edit payloads to `image.img2img`, accept canonical `image` URLs during reference resolution, and preserve reference-aware prompt hints.

Constraint: The test server must continue accepting both canonical `image` and legacy alias fields from callers already in circulation
Rejected: Fix only reference URL parsing | direct overrides would still be misrouted as text2image before reference resolution runs
Confidence: high
Scope-risk: narrow
Reversibility: clean
Directive: Any future image-model route inference must inspect input shape before defaulting to text2image
Tested: `env GOCACHE=/tmp/popiartserver-gocache go test ./internal/server -run 'TestInferRouteKeyForModelRecognizesViduAsVideo|TestInferRouteKeyForModelRecognizesImageEditInputs|TestResolveImageToImageReferenceAcceptsCanonicalImageURL|TestGenerateEditedImageRefsUsesSeedreamImagesGenerationsEndpoint'`; deployed to `101.42.99.35` and verified Seedream gateway requests include `image`
Not-tested: Full manual validation against every non-Seedream image-edit provider

internal/server/artifact_upload_test.go

@@ -130,3 +130,42 @@ func TestArtifactUploadCreatesReadableArtifactForSourceArtifactID(t *testing.T)
 		t.Fatal("expected resolved reference content to match uploaded bytes")
 	}
 }
+
+func TestResolveImageToImageReferenceAcceptsCanonicalImageURL(t *testing.T) {
+	cfg := Config{
+		SQLitePath:    filepath.Join(t.TempDir(), "popiart.db"),
+		SkillhubDir:   makeEmptySkillhub(t),
+		SessionSecret: "test-secret",
+	}
+	server, err := NewWithConfig(cfg)
+	if err != nil {
+		t.Fatalf("NewWithConfig: %v", err)
+	}
+
+	imageBytes := tinyPNG(t)
+	refSrv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "image/png")
+		_, _ = w.Write(imageBytes)
+	}))
+	defer refSrv.Close()
+
+	editRef, err := server.resolveImageToImageReference(context.Background(), &job{
+		UserID:      "user_test",
+		UpstreamKey: "sk-upstream",
+		SkillID:     "popiskill-image-img2img-basic-v1",
+	}, map[string]any{
+		"image": refSrv.URL + "/reference.png",
+	})
+	if err != nil {
+		t.Fatalf("resolveImageToImageReference: %v", err)
+	}
+	if editRef.URL != refSrv.URL+"/reference.png" {
+		t.Fatalf("expected resolved URL to match input image, got %q", editRef.URL)
+	}
+	if editRef.ContentType != "image/png" {
+		t.Fatalf("expected image/png, got %q", editRef.ContentType)
+	}
+	if !bytes.Equal(editRef.Content, imageBytes) {
+		t.Fatal("expected resolved canonical image content to match downloaded bytes")
+	}
+}

internal/server/routes_test.go

@@ -31,8 +31,23 @@ func TestInferRouteKeyForModelRecognizesViduAsVideo(t *testing.T) {
 	}
 
 	for modelID, want := range cases {
-		if got := inferRouteKeyForModel(modelID); got != want {
+		if got := inferRouteKeyForModel(modelID, nil); got != want {
 			t.Fatalf("inferRouteKeyForModel(%q) = %q, want %q", modelID, got, want)
 		}
 	}
 }
+
+func TestInferRouteKeyForModelRecognizesImageEditInputs(t *testing.T) {
+	cases := []map[string]any{
+		{"image": "https://example.com/reference.jpg"},
+		{"image_url": "https://example.com/reference.jpg"},
+		{"reference_image_url": "https://example.com/reference.jpg"},
+		{"source_artifact_id": "art_123"},
+	}
+
+	for _, input := range cases {
+		if got := inferRouteKeyForModel("seedream-4-5-251128", input); got != "image.img2img" {
+			t.Fatalf("inferRouteKeyForModel(seedream, %#v) = %q, want image.img2img", input, got)
+		}
+	}
+}

internal/server/server.go

@@ -1046,7 +1046,7 @@ func (s *Server) handleModelsInfer(w http.ResponseWriter, r *http.Request) {
 		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "model_id is required", nil)
 		return
 	}
-	routeKey := inferRouteKeyForModel(req.ModelID)
+	routeKey := inferRouteKeyForModel(req.ModelID, req.Input)
 	record, statusCode, err := s.store.createJob(
 		"",
 		routeKey,
@@ -1334,10 +1334,20 @@ func (s *Server) resolveModelID(routeKey, projectID string) string {
 	}
 }
 
-func inferRouteKeyForModel(modelID string) string {
+func inferRouteKeyForModel(modelID string, input map[string]any) string {
 	if modelType, _ := classifyModelIDFallback(modelID); modelType == "video" {
 		return "video.image2video"
 	}
+	if input != nil {
+		if ref := strings.TrimSpace(stringValue(
+			input["source_artifact_id"],
+			input["image"],
+			input["reference_image_url"],
+			input["image_url"],
+		)); ref != "" {
+			return "image.img2img"
+		}
+	}
 	return "image.text2image"
 }
 
@@ -1371,6 +1381,7 @@ func (s *Server) resolveImageToImageReference(ctx context.Context, record *job,
 	}
 
 	refURL := strings.TrimSpace(stringValue(
+		input["image"],
 		input["reference_image_url"],
 		input["image_url"],
 	))
@@ -1540,7 +1551,7 @@ func buildGenericImageToImagePrompt(input map[string]any, prompt string) string
 	if prompt != "" {
 		parts = append(parts, prompt)
 	}
-	if refURL := strings.TrimSpace(stringValue(input["reference_image_url"], input["image_url"])); refURL != "" {
+	if refURL := strings.TrimSpace(stringValue(input["image"], input["reference_image_url"], input["image_url"])); refURL != "" {
 		parts = append(parts, "preserve the same main subject identity and key visual traits from the reference image")
 	}
 	if aspectRatio := strings.TrimSpace(stringValue(input["aspect_ratio"])); aspectRatio != "" {