fix(openai): support streaming image relay and image edit for images API (#4608)

* fix(openai): support streaming image relay

* fix(openai): keep image edit multipart body reusable

* test(openai): cover image stream usage details

* test(openai): cover image edit fallback stream field

* fix(openai): wrap image json fallback as stream

* fix(relay): support OpenAI image streaming

* fix(openai): record image stream upstream error events

* fix(openai): harden image stream relay

* fix(openai): return image JSON errors

* fix(relay): reset stream status per scanner run

* fix(relay): drop upstream credit passthrough

* fix(openai): keep image errors minimal

* fix(openai): keep image error status from response

---------

Co-authored-by: CaIon <i@caion.me>

relay/channel/openai/adaptor.go

@@ -9,6 +9,7 @@ import (
 	"mime/multipart"
 	"net/http"
 	"net/textproto"
+	"net/url"
 	"path/filepath"
 	"strings"
 
@@ -439,10 +440,13 @@ func (a *Adaptor) ConvertImageRequest(c *gin.Context, info *relaycommon.RelayInf
 		// 使用已解析的 multipart 表单，避免重复解析
 		mf := c.Request.MultipartForm
 		if mf == nil {
-			if _, err := c.MultipartForm(); err != nil {
-				return nil, errors.New("failed to parse multipart form")
+			form, err := common.ParseMultipartFormReusable(c)
+			if err != nil {
+				return nil, fmt.Errorf("failed to parse multipart form: %w", err)
 			}
-			mf = c.Request.MultipartForm
+			c.Request.MultipartForm = form
+			c.Request.PostForm = url.Values(form.Value)
+			mf = form
 		}
 
 		// 写入所有非文件字段
@@ -625,7 +629,11 @@ func (a *Adaptor) DoResponse(c *gin.Context, resp *http.Response, info *relaycom
 	case relayconstant.RelayModeAudioTranscription:
 		err, usage = OpenaiSTTHandler(c, resp, info, a.ResponseFormat)
 	case relayconstant.RelayModeImagesGenerations, relayconstant.RelayModeImagesEdits:
-		usage, err = OpenaiHandlerWithUsage(c, info, resp)
+		if info.IsStream {
+			usage, err = OpenaiImageStreamHandler(c, info, resp)
+		} else {
+			usage, err = OpenaiHandlerWithUsage(c, info, resp)
+		}
 	case relayconstant.RelayModeRerank:
 		usage, err = common_handler.RerankHandler(c, info, resp)
 	case relayconstant.RelayModeResponses: