fix: omit default OpenAI image partials

Only send partial_images when explicitly configured so Images API streaming requests avoid unsupported parameter errors and extra partial image cost.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: GeorgeXie2333

backend/internal/infra/llm/openai_images.go

@@ -468,13 +468,12 @@ func applyOpenAIImageEditParams(fields map[string]string, model string, options
 
 func applyOpenAIImageEditStreamParams(fields map[string]string, options map[string]interface{}) {
 	value, ok := modelParamIntValue(options, "partial_images")
-	if ok {
-		if value > 0 {
-			fields["partial_images"] = fmt.Sprintf("%d", value)
-		}
+	if !ok {
 		return
 	}
-	fields["partial_images"] = "1"
+	if value >= 0 {
+		fields["partial_images"] = fmt.Sprintf("%d", value)
+	}
 }
 
 func writeOpenAIMultipartFile(writer *multipart.Writer, fieldName string, fileName string, mimeType string, data []byte) error {
@@ -552,13 +551,12 @@ func applyOpenAIImageGenerationParams(payload map[string]interface{}, model stri
 // applyOpenAIImageGenerationStreamParams 只处理流式图片端点支持的增量参数。
 func applyOpenAIImageGenerationStreamParams(payload map[string]interface{}, options map[string]interface{}) {
 	value, ok := modelParamIntValue(options, "partial_images")
-	if ok {
-		if value > 0 {
-			payload["partial_images"] = value
-		}
+	if !ok {
 		return
 	}
-	payload["partial_images"] = 1
+	if value >= 0 {
+		payload["partial_images"] = value
+	}
 }
 
 func openAIImageGenerationModelSupportsStream(model string) bool {

backend/internal/infra/llm/openai_images_test.go

@@ -65,15 +65,18 @@ func TestBuildOpenAIImageGenerationStreamRequestBody(t *testing.T) {
 	}
 }
 
-func TestBuildOpenAIImageGenerationStreamRequestBodyDefaultsPartialImages(t *testing.T) {
+func TestBuildOpenAIImageGenerationStreamRequestBodyOmitsDefaultPartialImages(t *testing.T) {
 	payload, err := buildOpenAIImageGenerationStreamRequestBody("gpt-image-1", GenerateInput{
 		Messages: []Message{{Role: "user", Content: "A clean product render"}},
 	})
 	if err != nil {
 		t.Fatalf("build image stream request body: %v", err)
 	}
-	if payload["partial_images"] != 1 {
-		t.Fatalf("expected default partial_images=1, got %#v", payload)
+	if payload["stream"] != true {
+		t.Fatalf("expected stream request payload, got %#v", payload)
+	}
+	if _, ok := payload["partial_images"]; ok {
+		t.Fatalf("partial_images must only be sent when explicitly configured, got %#v", payload)
 	}
 }