feat(api): enhance model assignment logic in image handlers

- Updated `buildImagesResponsesRequest` to derive `model` dynamically based on `toolJSON`.
- Adjusted streaming execution to handle dynamic model resolution across multiple contexts.

Closes: #2965

sdk/api/handlers/openai/openai_images_handlers.go

@@ -499,7 +499,17 @@ func (h *OpenAIAPIHandler) imagesEditsFromJSON(c *gin.Context) {
 
 func buildImagesResponsesRequest(prompt string, images []string, toolJSON []byte) []byte {
 	req := []byte(`{"instructions":"","stream":true,"reasoning":{"effort":"medium","summary":"auto"},"parallel_tool_calls":true,"include":["reasoning.encrypted_content"],"model":"","store":false,"tool_choice":{"type":"image_generation"}}`)
-	req, _ = sjson.SetBytes(req, "model", defaultImagesMainModel)
+	mainModel := defaultImagesMainModel
+	if len(toolJSON) > 0 && json.Valid(toolJSON) {
+		toolModel := strings.TrimSpace(gjson.GetBytes(toolJSON, "model").String())
+		if idx := strings.LastIndex(toolModel, "/"); idx > 0 && idx < len(toolModel)-1 {
+			prefix := strings.TrimSpace(toolModel[:idx])
+			if prefix != "" {
+				mainModel = prefix + "/" + defaultImagesMainModel
+			}
+		}
+	}
+	req, _ = sjson.SetBytes(req, "model", mainModel)
 
 	input := []byte(`[{"type":"message","role":"user","content":[{"type":"input_text","text":""}]}]`)
 	input, _ = sjson.SetBytes(input, "0.content.0.text", prompt)
@@ -530,7 +540,11 @@ func (h *OpenAIAPIHandler) collectImagesFromResponses(c *gin.Context, responsesR
 	cliCtx = handlers.WithDisallowFreeAuth(cliCtx)
 	stopKeepAlive := h.StartNonStreamingKeepAlive(c, cliCtx)
 
-	dataChan, upstreamHeaders, errChan := h.ExecuteStreamWithAuthManager(cliCtx, "openai-response", defaultImagesMainModel, responsesReq, "")
+	mainModel := strings.TrimSpace(gjson.GetBytes(responsesReq, "model").String())
+	if mainModel == "" {
+		mainModel = defaultImagesMainModel
+	}
+	dataChan, upstreamHeaders, errChan := h.ExecuteStreamWithAuthManager(cliCtx, "openai-response", mainModel, responsesReq, "")
 
 	out, errMsg := collectImagesFromResponsesStream(cliCtx, dataChan, errChan, responseFormat)
 	stopKeepAlive()
@@ -718,7 +732,11 @@ func (h *OpenAIAPIHandler) streamImagesFromResponses(c *gin.Context, responsesRe
 
 	cliCtx, cliCancel := h.GetContextWithCancel(h, c, context.Background())
 	cliCtx = handlers.WithDisallowFreeAuth(cliCtx)
-	dataChan, upstreamHeaders, errChan := h.ExecuteStreamWithAuthManager(cliCtx, "openai-response", defaultImagesMainModel, responsesReq, "")
+	mainModel := strings.TrimSpace(gjson.GetBytes(responsesReq, "model").String())
+	if mainModel == "" {
+		mainModel = defaultImagesMainModel
+	}
+	dataChan, upstreamHeaders, errChan := h.ExecuteStreamWithAuthManager(cliCtx, "openai-response", mainModel, responsesReq, "")
 
 	setSSEHeaders := func() {
 		c.Header("Content-Type", "text/event-stream")