feat(images): 账户开关将生图结果 url 下载回填为 b64_json

部分第三方 GPT-image 上游把 Images 响应里的 b64_json 换成 url，按官方接口实现的
客户端读不到图。账户 extra.images_url_to_b64_json 开启后，OpenAI API Key 的
Images 非流式响应里 b64_json 缺失或为空且 url 非空的项，由网关下载 url 内容并以
base64 回填 b64_json，url 与其余字段原样保留；异步生图任务复用同一路径。

- 下载经账户代理发起，沿用 base_url 的出站 URL 校验策略（validateUpstreamBaseURL
  抽出 validateOutboundURL，nil cfg 按仅格式校验处理），单图上限 20MB 且须为图片
  内容（响应头或字节嗅探）；data: URL 直接取 base64 载荷
- 单项下载失败仅记日志并保留原样；客户端显式 response_format=url 时不回填；
  流式响应不处理
- 创建/编辑账户弹窗在 OpenAI API Key 的 Responses 模式块后新增“生图结果 URL 转
  base64”开关，中英文案；新增 openai_images_b64_backfill_test.go
- 只被 unit 标签测试引用的定价目录测试辅助补上 //go:build unit（admin 包整文件加标签，
  service 包的 newPricingServiceFromModelPricing 搬到 pricing_stub_helpers_unit_test.go），
  消除 golangci-lint 在默认标签下的 unused 报错

backend/internal/service/openai_gateway_request_body.go

@@ -18,24 +18,28 @@ import (
 )
 
 func (s *OpenAIGatewayService) validateUpstreamBaseURL(raw string) (string, error) {
-	if s.cfg != nil && !s.cfg.Security.URLAllowlist.Enabled {
-		normalized, err := urlvalidator.ValidateURLFormat(raw, s.cfg.Security.URLAllowlist.AllowInsecureHTTP)
-		if err != nil {
-			return "", fmt.Errorf("invalid base_url: %w", err)
-		}
-		return normalized, nil
-	}
-	normalized, err := urlvalidator.ValidateHTTPSURL(raw, urlvalidator.ValidationOptions{
-		AllowedHosts:     s.cfg.Security.URLAllowlist.UpstreamHosts,
-		RequireAllowlist: true,
-		AllowPrivate:     s.cfg.Security.URLAllowlist.AllowPrivateHosts,
-	})
+	normalized, err := s.validateOutboundURL(raw)
 	if err != nil {
 		return "", fmt.Errorf("invalid base_url: %w", err)
 	}
 	return normalized, nil
 }
 
+// validateOutboundURL 按 security.url_allowlist 策略校验网关主动连接的出站 URL。
+func (s *OpenAIGatewayService) validateOutboundURL(raw string) (string, error) {
+	if s.cfg == nil {
+		return urlvalidator.ValidateURLFormat(raw, false)
+	}
+	if !s.cfg.Security.URLAllowlist.Enabled {
+		return urlvalidator.ValidateURLFormat(raw, s.cfg.Security.URLAllowlist.AllowInsecureHTTP)
+	}
+	return urlvalidator.ValidateHTTPSURL(raw, urlvalidator.ValidationOptions{
+		AllowedHosts:     s.cfg.Security.URLAllowlist.UpstreamHosts,
+		RequireAllowlist: true,
+		AllowPrivate:     s.cfg.Security.URLAllowlist.AllowPrivateHosts,
+	})
+}
+
 // buildOpenAIResponsesURL 组装 OpenAI Responses 端点。
 // - base 以 /v1 结尾：追加 /responses
 // - base 以其他版本段结尾（如 /v4）：追加 /responses

backend/internal/service/openai_images.go

@@ -722,7 +722,7 @@ func (s *OpenAIGatewayService) forwardOpenAIImagesAPIKey(
 			ImageOutputSizes: imageOutputSizes,
 		}, nil
 	} else {
-		nonStreamUsage, nonStreamCount, nonStreamSizes, err := s.handleOpenAIImagesNonStreamingResponse(resp, c)
+		nonStreamUsage, nonStreamCount, nonStreamSizes, err := s.handleOpenAIImagesNonStreamingResponse(upstreamCtx, resp, c, account, parsed)
 		if err != nil {
 			return nil, err
 		}
@@ -894,11 +894,18 @@ func cloneMultipartHeader(src textproto.MIMEHeader) textproto.MIMEHeader {
 	return dst
 }
 
-func (s *OpenAIGatewayService) handleOpenAIImagesNonStreamingResponse(resp *http.Response, c *gin.Context) (OpenAIUsage, int, []string, error) {
+func (s *OpenAIGatewayService) handleOpenAIImagesNonStreamingResponse(
+	ctx context.Context,
+	resp *http.Response,
+	c *gin.Context,
+	account *Account,
+	parsed *OpenAIImagesRequest,
+) (OpenAIUsage, int, []string, error) {
 	body, err := ReadUpstreamResponseBody(resp.Body, s.cfg, c, openAITooLargeError)
 	if err != nil {
 		return OpenAIUsage{}, 0, nil, err
 	}
+	body = s.backfillOpenAIImagesB64JSON(ctx, account, parsed, body)
 	responseheaders.WriteFilteredHeaders(c.Writer.Header(), resp.Header, s.responseHeaderFilter)
 	contentType := "application/json"
 	if s.cfg != nil && !s.cfg.Security.ResponseHeaders.Enabled {

backend/internal/service/openai_images_b64_backfill.go

@@ -0,0 +1,151 @@
+package service
+
+import (
+	"context"
+	"encoding/base64"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"strings"
+	"time"
+
+	"github.com/Wei-Shaw/sub2api/internal/pkg/logger"
+	"github.com/tidwall/gjson"
+	"github.com/tidwall/sjson"
+)
+
+// AccountExtraImagesURLToB64JSON 是账户 extra 中的开关键。开启后，Images 端点的非流式响应里
+// b64_json 缺失或为空但 url 非空的图片项，由网关下载 url 内容并以 base64 回填到 b64_json。
+const AccountExtraImagesURLToB64JSON = "images_url_to_b64_json"
+
+// openAIImageURLDownloadTimeout 是单张图片 url 下载的超时上限。
+const openAIImageURLDownloadTimeout = 60 * time.Second
+
+// ImagesURLToB64JSONEnabled 返回账户是否开启了 url 转 b64_json 回填。
+func ImagesURLToB64JSONEnabled(account *Account) bool {
+	return account != nil && account.getExtraBool(AccountExtraImagesURLToB64JSON)
+}
+
+// backfillOpenAIImagesB64JSON 对 Images 端点的非流式响应做 url 转 b64_json 回填。
+//
+// 只处理 data[i].b64_json 缺失或为空且 url 非空的项；url 字段原样保留。
+// 单项失败仅记日志并保留该项原样，响应整体照常返回。
+// 客户端显式要求 response_format=url 时不做回填。
+func (s *OpenAIGatewayService) backfillOpenAIImagesB64JSON(
+	ctx context.Context,
+	account *Account,
+	parsed *OpenAIImagesRequest,
+	body []byte,
+) []byte {
+	if !ImagesURLToB64JSONEnabled(account) {
+		return body
+	}
+	if parsed != nil && parsed.ResponseFormat == "url" {
+		return body
+	}
+	if len(body) == 0 || !gjson.ValidBytes(body) {
+		return body
+	}
+	items := gjson.GetBytes(body, "data")
+	if !items.IsArray() {
+		return body
+	}
+	for index, item := range items.Array() {
+		if !item.IsObject() {
+			continue
+		}
+		if strings.TrimSpace(item.Get("b64_json").String()) != "" {
+			continue
+		}
+		rawURL := strings.TrimSpace(item.Get("url").String())
+		if rawURL == "" {
+			continue
+		}
+		encoded, err := s.fetchOpenAIImageURLBase64(ctx, account, rawURL)
+		if err != nil {
+			logger.LegacyPrintf(
+				"service.openai_gateway",
+				"[OpenAI] Images b64_json backfill skipped account_id=%d index=%d err=%s",
+				account.ID,
+				index,
+				sanitizeUpstreamErrorMessage(err.Error()),
+			)
+			continue
+		}
+		updated, err := sjson.SetBytes(body, fmt.Sprintf("data.%d.b64_json", index), encoded)
+		if err != nil {
+			logger.LegacyPrintf(
+				"service.openai_gateway",
+				"[OpenAI] Images b64_json backfill skipped account_id=%d index=%d err=%s",
+				account.ID,
+				index,
+				sanitizeUpstreamErrorMessage(err.Error()),
+			)
+			continue
+		}
+		body = updated
+	}
+	return body
+}
+
+// fetchOpenAIImageURLBase64 取得图片 url 内容的标准 base64 编码。
+// data: 形式的 url 直接取其 base64 载荷；其余 url 沿用 base_url 的出站 URL 策略校验后，
+// 经账户代理下载，大小上限与 OAuth 路径的单图下载一致，且必须是图片内容。
+func (s *OpenAIGatewayService) fetchOpenAIImageURLBase64(ctx context.Context, account *Account, rawURL string) (string, error) {
+	if strings.HasPrefix(strings.ToLower(rawURL), "data:") {
+		if encoded := normalizeOpenAIImageBase64(rawURL); encoded != "" {
+			return encoded, nil
+		}
+		return "", errors.New("data url payload is not valid base64")
+	}
+	if s == nil || s.httpUpstream == nil {
+		return "", errors.New("http upstream is not configured")
+	}
+	downloadURL, err := s.validateOutboundURL(rawURL)
+	if err != nil {
+		return "", fmt.Errorf("invalid image url: %w", err)
+	}
+	ctx, cancel := context.WithTimeout(ctx, openAIImageURLDownloadTimeout)
+	defer cancel()
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, downloadURL, nil)
+	if err != nil {
+		return "", fmt.Errorf("build image download request: %w", err)
+	}
+	req.Header.Set("Accept", "image/*,*/*;q=0.8")
+	proxyURL := ""
+	if account.ProxyID != nil && account.Proxy != nil {
+		proxyURL = account.Proxy.URL()
+	}
+	resp, err := s.httpUpstream.Do(req, proxyURL, account.ID, account.Concurrency)
+	if err != nil {
+		return "", fmt.Errorf("download image: %w", err)
+	}
+	defer func() { _ = resp.Body.Close() }()
+	if resp.StatusCode < http.StatusOK || resp.StatusCode >= http.StatusMultipleChoices {
+		return "", fmt.Errorf("download image: unexpected status %d", resp.StatusCode)
+	}
+	data, err := io.ReadAll(io.LimitReader(resp.Body, openAIImageMaxDownloadBytes+1))
+	if err != nil {
+		return "", fmt.Errorf("read image body: %w", err)
+	}
+	if int64(len(data)) > openAIImageMaxDownloadBytes {
+		return "", fmt.Errorf("downloaded image exceeds %d bytes", openAIImageMaxDownloadBytes)
+	}
+	if len(data) == 0 {
+		return "", errors.New("download image: empty body")
+	}
+	if !isImageContent(resp.Header.Get("Content-Type"), data) {
+		return "", errors.New("download image: content is not an image")
+	}
+	return base64.StdEncoding.EncodeToString(data), nil
+}
+
+// isImageContent 由响应头声明或字节嗅探判定内容是否为图片。
+func isImageContent(contentType string, data []byte) bool {
+	declared := strings.ToLower(strings.TrimSpace(strings.Split(contentType, ";")[0]))
+	if strings.HasPrefix(declared, "image/") {
+		return true
+	}
+	return detectedImageContentType(data) != ""
+}

backend/internal/service/openai_images_b64_backfill_test.go

@@ -0,0 +1,311 @@
+package service
+
+import (
+	"bytes"
+	"context"
+	"encoding/base64"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"github.com/Wei-Shaw/sub2api/internal/config"
+	"github.com/gin-gonic/gin"
+	"github.com/stretchr/testify/require"
+	"github.com/tidwall/gjson"
+)
+
+// 8 字节 PNG 魔数足以让字节嗅探判定为 image/png。
+var b64BackfillPNGBytes = []byte{0x89, 'P', 'N', 'G', '\r', '\n', 0x1a, '\n', 0, 0, 0, 0}
+
+func b64BackfillImageResponse(status int, contentType string, payload []byte) *http.Response {
+	header := http.Header{}
+	if contentType != "" {
+		header.Set("Content-Type", contentType)
+	}
+	return &http.Response{
+		StatusCode: status,
+		Header:     header,
+		Body:       io.NopCloser(bytes.NewReader(payload)),
+	}
+}
+
+func b64BackfillAccount(enabled bool) *Account {
+	account := &Account{
+		ID:       7,
+		Name:     "openai-apikey",
+		Platform: PlatformOpenAI,
+		Type:     AccountTypeAPIKey,
+		Credentials: map[string]any{
+			"api_key":  "sk-test",
+			"base_url": "https://relay.example.com/v1",
+		},
+	}
+	if enabled {
+		account.Extra = map[string]any{AccountExtraImagesURLToB64JSON: true}
+	}
+	return account
+}
+
+func TestImagesURLToB64JSONEnabled(t *testing.T) {
+	require.False(t, ImagesURLToB64JSONEnabled(nil))
+	require.False(t, ImagesURLToB64JSONEnabled(&Account{}))
+	require.False(t, ImagesURLToB64JSONEnabled(&Account{Extra: map[string]any{AccountExtraImagesURLToB64JSON: "true"}}))
+	require.False(t, ImagesURLToB64JSONEnabled(&Account{Extra: map[string]any{AccountExtraImagesURLToB64JSON: false}}))
+	require.True(t, ImagesURLToB64JSONEnabled(&Account{Extra: map[string]any{AccountExtraImagesURLToB64JSON: true}}))
+}
+
+func TestBackfillOpenAIImagesB64JSON(t *testing.T) {
+	wantB64 := base64.StdEncoding.EncodeToString(b64BackfillPNGBytes)
+
+	tests := []struct {
+		name          string
+		enabled       bool
+		parsed        *OpenAIImagesRequest
+		body          string
+		upstream      *httpUpstreamRecorder
+		wantB64       []string
+		wantDownloads int
+	}{
+		{
+			name:          "开关关闭时原样返回",
+			enabled:       false,
+			body:          `{"created":1,"data":[{"url":"https://cdn.example.com/a.png"}]}`,
+			upstream:      &httpUpstreamRecorder{resp: b64BackfillImageResponse(http.StatusOK, "image/png", b64BackfillPNGBytes)},
+			wantB64:       []string{""},
+			wantDownloads: 0,
+		},
+		{
+			name:          "缺少 b64_json 且有 url 时下载回填并保留 url",
+			enabled:       true,
+			body:          `{"created":1,"data":[{"url":"https://cdn.example.com/a.png","revised_prompt":"a cat"}]}`,
+			upstream:      &httpUpstreamRecorder{resp: b64BackfillImageResponse(http.StatusOK, "image/png", b64BackfillPNGBytes)},
+			wantB64:       []string{wantB64},
+			wantDownloads: 1,
+		},
+		{
+			name:          "b64_json 为空串时同样回填",
+			enabled:       true,
+			body:          `{"created":1,"data":[{"b64_json":"","url":"https://cdn.example.com/a.png"}]}`,
+			upstream:      &httpUpstreamRecorder{resp: b64BackfillImageResponse(http.StatusOK, "image/png", b64BackfillPNGBytes)},
+			wantB64:       []string{wantB64},
+			wantDownloads: 1,
+		},
+		{
+			name:          "b64_json 已有值时不下载",
+			enabled:       true,
+			body:          `{"created":1,"data":[{"b64_json":"aW1n","url":"https://cdn.example.com/a.png"}]}`,
+			upstream:      &httpUpstreamRecorder{resp: b64BackfillImageResponse(http.StatusOK, "image/png", b64BackfillPNGBytes)},
+			wantB64:       []string{"aW1n"},
+			wantDownloads: 0,
+		},
+		{
+			name:          "多项混合时只回填缺失项",
+			enabled:       true,
+			body:          `{"created":1,"data":[{"b64_json":"aW1n"},{"url":"https://cdn.example.com/b.png"},{"revised_prompt":"none"}]}`,
+			upstream:      &httpUpstreamRecorder{resp: b64BackfillImageResponse(http.StatusOK, "image/png", b64BackfillPNGBytes)},
+			wantB64:       []string{"aW1n", wantB64, ""},
+			wantDownloads: 1,
+		},
+		{
+			name:          "data URL 直接取载荷不下载",
+			enabled:       true,
+			body:          `{"created":1,"data":[{"url":"data:image/png;base64,` + wantB64 + `"}]}`,
+			upstream:      &httpUpstreamRecorder{},
+			wantB64:       []string{wantB64},
+			wantDownloads: 0,
+		},
+		{
+			name:          "客户端显式要求 url 时不回填",
+			enabled:       true,
+			parsed:        &OpenAIImagesRequest{ResponseFormat: "url"},
+			body:          `{"created":1,"data":[{"url":"https://cdn.example.com/a.png"}]}`,
+			upstream:      &httpUpstreamRecorder{resp: b64BackfillImageResponse(http.StatusOK, "image/png", b64BackfillPNGBytes)},
+			wantB64:       []string{""},
+			wantDownloads: 0,
+		},
+		{
+			name:          "下载非 2xx 时保留原样",
+			enabled:       true,
+			body:          `{"created":1,"data":[{"url":"https://cdn.example.com/a.png"}]}`,
+			upstream:      &httpUpstreamRecorder{resp: b64BackfillImageResponse(http.StatusNotFound, "text/plain", []byte("gone"))},
+			wantB64:       []string{""},
+			wantDownloads: 1,
+		},
+		{
+			name:          "下载内容不是图片时保留原样",
+			enabled:       true,
+			body:          `{"created":1,"data":[{"url":"https://cdn.example.com/a.png"}]}`,
+			upstream:      &httpUpstreamRecorder{resp: b64BackfillImageResponse(http.StatusOK, "text/html", []byte("<html>login required</html>"))},
+			wantB64:       []string{""},
+			wantDownloads: 1,
+		},
+		{
+			name:          "响应头未声明图片类型但字节嗅探为图片时回填",
+			enabled:       true,
+			body:          `{"created":1,"data":[{"url":"https://cdn.example.com/a"}]}`,
+			upstream:      &httpUpstreamRecorder{resp: b64BackfillImageResponse(http.StatusOK, "application/octet-stream", b64BackfillPNGBytes)},
+			wantB64:       []string{wantB64},
+			wantDownloads: 1,
+		},
+		{
+			name:          "非 http(s) 协议的 url 不下载",
+			enabled:       true,
+			body:          `{"created":1,"data":[{"url":"ftp://cdn.example.com/a.png"}]}`,
+			upstream:      &httpUpstreamRecorder{resp: b64BackfillImageResponse(http.StatusOK, "image/png", b64BackfillPNGBytes)},
+			wantB64:       []string{""},
+			wantDownloads: 0,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			svc := &OpenAIGatewayService{cfg: &config.Config{}, httpUpstream: tt.upstream}
+			got := svc.backfillOpenAIImagesB64JSON(context.Background(), b64BackfillAccount(tt.enabled), tt.parsed, []byte(tt.body))
+			require.True(t, gjson.ValidBytes(got))
+			items := gjson.GetBytes(got, "data").Array()
+			require.Len(t, items, len(tt.wantB64))
+			for i, want := range tt.wantB64 {
+				require.Equal(t, want, items[i].Get("b64_json").String(), "data.%d.b64_json", i)
+			}
+			require.Len(t, tt.upstream.requests, tt.wantDownloads)
+			// 除 b64_json 外的字段必须原样保留。
+			original := gjson.Parse(tt.body)
+			original.Get("data").ForEach(func(key, item gjson.Result) bool {
+				item.ForEach(func(field, value gjson.Result) bool {
+					if field.String() == "b64_json" {
+						return true
+					}
+					require.Equal(t, value.Raw, gjson.GetBytes(got, "data."+key.String()+"."+field.String()).Raw)
+					return true
+				})
+				return true
+			})
+			require.Equal(t, original.Get("created").Raw, gjson.GetBytes(got, "created").Raw)
+		})
+	}
+}
+
+func TestBackfillOpenAIImagesB64JSON_DownloadRequestShape(t *testing.T) {
+	upstream := &httpUpstreamRecorder{resp: b64BackfillImageResponse(http.StatusOK, "image/png", b64BackfillPNGBytes)}
+	svc := &OpenAIGatewayService{cfg: &config.Config{}, httpUpstream: upstream}
+	account := b64BackfillAccount(true)
+	proxyID := int64(3)
+	account.ProxyID = &proxyID
+	account.Proxy = &Proxy{Protocol: "http", Host: "127.0.0.1", Port: 7890}
+
+	body := []byte(`{"created":1,"data":[{"url":"https://cdn.example.com/a.png?sig=abc"}]}`)
+	got := svc.backfillOpenAIImagesB64JSON(context.Background(), account, nil, body)
+	require.Equal(t, base64.StdEncoding.EncodeToString(b64BackfillPNGBytes), gjson.GetBytes(got, "data.0.b64_json").String())
+
+	require.Len(t, upstream.requests, 1)
+	req := upstream.requests[0]
+	require.Equal(t, http.MethodGet, req.Method)
+	require.Equal(t, "https://cdn.example.com/a.png?sig=abc", req.URL.String())
+	require.Equal(t, "http://127.0.0.1:7890", upstream.lastProxyURL)
+	_, hasDeadline := req.Context().Deadline()
+	require.True(t, hasDeadline)
+}
+
+func TestBackfillOpenAIImagesB64JSON_NonObjectBodies(t *testing.T) {
+	upstream := &httpUpstreamRecorder{resp: b64BackfillImageResponse(http.StatusOK, "image/png", b64BackfillPNGBytes)}
+	svc := &OpenAIGatewayService{cfg: &config.Config{}, httpUpstream: upstream}
+	account := b64BackfillAccount(true)
+
+	for _, body := range []string{``, `not json`, `{"created":1}`, `{"created":1,"data":{}}`, `{"created":1,"data":[]}`, `{"created":1,"data":["x"]}`} {
+		got := svc.backfillOpenAIImagesB64JSON(context.Background(), account, nil, []byte(body))
+		require.Equal(t, body, string(got), "body=%q", body)
+	}
+	require.Empty(t, upstream.requests)
+}
+
+func TestOpenAIGatewayServiceForwardImages_APIKeyBackfillsB64JSONFromURL(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	body := []byte(`{"model":"gpt-image-2","prompt":"draw a cat","size":"1024x1024"}`)
+
+	req := httptest.NewRequest(http.MethodPost, "/v1/images/generations", bytes.NewReader(body))
+	req.Header.Set("Content-Type", "application/json")
+	rec := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(rec)
+	c.Request = req
+	c.Set("api_key", &APIKey{ID: 42})
+
+	svc := &OpenAIGatewayService{cfg: &config.Config{}}
+	parsed, err := svc.ParseOpenAIImagesRequest(c, body)
+	require.NoError(t, err)
+
+	upstream := &httpUpstreamRecorder{
+		responses: []*http.Response{
+			{
+				StatusCode: http.StatusOK,
+				Header: http.Header{
+					"Content-Type": []string{"application/json"},
+					"X-Request-Id": []string{"req_img_url"},
+				},
+				Body: io.NopCloser(strings.NewReader(
+					`{"created":1710000000,"data":[{"url":"https://cdn.example.com/cat.png","revised_prompt":"a cat"}],"usage":{"input_tokens":10,"output_tokens":20}}`,
+				)),
+			},
+			b64BackfillImageResponse(http.StatusOK, "image/png", b64BackfillPNGBytes),
+		},
+	}
+	svc.httpUpstream = upstream
+
+	result, err := svc.ForwardImages(context.Background(), c, b64BackfillAccount(true), body, parsed, "")
+	require.NoError(t, err)
+	require.NotNil(t, result)
+	require.Equal(t, 1, result.ImageCount)
+	require.False(t, result.Stream)
+
+	require.Len(t, upstream.requests, 2)
+	require.Equal(t, http.MethodPost, upstream.requests[0].Method)
+	require.Equal(t, "https://relay.example.com/v1/images/generations", upstream.requests[0].URL.String())
+	require.Equal(t, http.MethodGet, upstream.requests[1].Method)
+	require.Equal(t, "https://cdn.example.com/cat.png", upstream.requests[1].URL.String())
+
+	require.Equal(t, http.StatusOK, rec.Code)
+	wantB64 := base64.StdEncoding.EncodeToString(b64BackfillPNGBytes)
+	require.Equal(t, wantB64, gjson.Get(rec.Body.String(), "data.0.b64_json").String())
+	require.Equal(t, "https://cdn.example.com/cat.png", gjson.Get(rec.Body.String(), "data.0.url").String())
+	require.Equal(t, "a cat", gjson.Get(rec.Body.String(), "data.0.revised_prompt").String())
+	require.Equal(t, int64(1710000000), gjson.Get(rec.Body.String(), "created").Int())
+}
+
+func TestOpenAIGatewayServiceForwardImages_APIKeyLeavesURLOnlyResponseWhenDisabled(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	body := []byte(`{"model":"gpt-image-2","prompt":"draw a cat","size":"1024x1024"}`)
+
+	req := httptest.NewRequest(http.MethodPost, "/v1/images/generations", bytes.NewReader(body))
+	req.Header.Set("Content-Type", "application/json")
+	rec := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(rec)
+	c.Request = req
+	c.Set("api_key", &APIKey{ID: 42})
+
+	svc := &OpenAIGatewayService{cfg: &config.Config{}}
+	parsed, err := svc.ParseOpenAIImagesRequest(c, body)
+	require.NoError(t, err)
+
+	upstreamBody := `{"created":1710000000,"data":[{"url":"https://cdn.example.com/cat.png"}]}`
+	upstream := &httpUpstreamRecorder{
+		responses: []*http.Response{
+			{
+				StatusCode: http.StatusOK,
+				Header:     http.Header{"Content-Type": []string{"application/json"}},
+				Body:       io.NopCloser(strings.NewReader(upstreamBody)),
+			},
+			b64BackfillImageResponse(http.StatusOK, "image/png", b64BackfillPNGBytes),
+		},
+	}
+	svc.httpUpstream = upstream
+
+	result, err := svc.ForwardImages(context.Background(), c, b64BackfillAccount(false), body, parsed, "")
+	require.NoError(t, err)
+	require.NotNil(t, result)
+	require.Equal(t, 1, result.ImageCount)
+
+	require.Len(t, upstream.requests, 1)
+	require.Equal(t, http.StatusOK, rec.Code)
+	require.Equal(t, upstreamBody, rec.Body.String())
+}

frontend/src/components/account/CreateAccountModal.vue

@@ -3313,6 +3313,37 @@
         </div>
       </div>
 
+      <!-- OpenAI APIKey images: backfill b64_json from url -->
+      <div
+        v-if="form.platform === 'openai' && accountCategory === 'apikey'"
+        class="flex items-center justify-between gap-4 border-t border-gray-200 pt-4 dark:border-dark-600"
+      >
+        <div>
+          <label class="input-label mb-0">{{ t('admin.accounts.openai.imagesUrlToB64Json') }}</label>
+          <p class="mt-1 text-xs text-gray-500 dark:text-gray-400">
+            {{ t('admin.accounts.openai.imagesUrlToB64JsonDesc') }}
+          </p>
+        </div>
+        <button
+          type="button"
+          data-testid="openai-images-url-to-b64-json-toggle"
+          role="switch"
+          :aria-checked="openAIImagesUrlToB64JsonEnabled"
+          @click="openAIImagesUrlToB64JsonEnabled = !openAIImagesUrlToB64JsonEnabled"
+          :class="[
+            'relative inline-flex h-6 w-11 flex-shrink-0 cursor-pointer rounded-full border-2 border-transparent transition-colors duration-200 ease-in-out focus:outline-none focus:ring-2 focus:ring-primary-500 focus:ring-offset-2',
+            openAIImagesUrlToB64JsonEnabled ? 'bg-primary-600' : 'bg-gray-200 dark:bg-dark-600'
+          ]"
+        >
+          <span
+            :class="[
+              'pointer-events-none inline-block h-5 w-5 transform rounded-full bg-white shadow ring-0 transition duration-200 ease-in-out',
+              openAIImagesUrlToB64JsonEnabled ? 'translate-x-5' : 'translate-x-0'
+            ]"
+          />
+        </button>
+      </div>
+
       <div>
         <div class="flex items-center justify-between">
           <div>
@@ -4246,6 +4277,8 @@ const openAILongContextBillingEnabled = ref(false)
 const openAILongContextBillingTouched = ref(false)
 const openAICompactMode = ref<OpenAICompactMode>('auto')
 const openAIResponsesMode = ref<OpenAIResponsesMode>('auto')
+// Images 非流式响应缺 b64_json 时由网关下载 url 回填（仅 OpenAI API Key）。
+const openAIImagesUrlToB64JsonEnabled = ref(false)
 const openAIEndpointCapabilities = ref<OpenAIEndpointCapability[]>(['chat_completions', 'embeddings'])
 const openaiOAuthResponsesWebSocketV2Mode = ref<OpenAIWSMode>(OPENAI_WS_MODE_OFF)
 const openaiAPIKeyResponsesWebSocketV2Mode = ref<OpenAIWSMode>(OPENAI_WS_MODE_OFF)
@@ -4724,6 +4757,7 @@ watch(
     // 避免上一平台的配置行被提交到新平台账号
     headerOverrideEnabled.value = false
     headerOverrideRows.value = []
+    openAIImagesUrlToB64JsonEnabled.value = false
     grokOAuthCustomBaseUrlEnabled.value = false
     grokOAuthBaseUrl.value = ''
     // Reset OAuth states
@@ -5149,6 +5183,7 @@ const resetForm = () => {
   customErrorCodeInput.value = null
   headerOverrideEnabled.value = false
   headerOverrideRows.value = []
+  openAIImagesUrlToB64JsonEnabled.value = false
   grokOAuthCustomBaseUrlEnabled.value = false
   grokOAuthBaseUrl.value = ''
   interceptWarmupRequests.value = false
@@ -5286,6 +5321,11 @@ const buildOpenAIExtra = (base?: Record<string, unknown>): Record<string, unknow
   } else {
     delete extra.openai_responses_mode
   }
+  if (accountCategory.value === 'apikey' && openAIImagesUrlToB64JsonEnabled.value) {
+    extra.images_url_to_b64_json = true
+  } else {
+    delete extra.images_url_to_b64_json
+  }
 
   return Object.keys(extra).length > 0 ? extra : undefined
 }

frontend/src/components/account/EditAccountModal.vue

@@ -1821,6 +1821,37 @@
         </div>
       </div>
 
+      <!-- OpenAI APIKey images: backfill b64_json from url -->
+      <div
+        v-if="account?.platform === 'openai' && account?.type === 'apikey'"
+        class="flex items-center justify-between gap-4 border-t border-gray-200 pt-4 dark:border-dark-600"
+      >
+        <div>
+          <label class="input-label mb-0">{{ t('admin.accounts.openai.imagesUrlToB64Json') }}</label>
+          <p class="mt-1 text-xs text-gray-500 dark:text-gray-400">
+            {{ t('admin.accounts.openai.imagesUrlToB64JsonDesc') }}
+          </p>
+        </div>
+        <button
+          type="button"
+          data-testid="openai-images-url-to-b64-json-toggle"
+          role="switch"
+          :aria-checked="openAIImagesUrlToB64JsonEnabled"
+          @click="openAIImagesUrlToB64JsonEnabled = !openAIImagesUrlToB64JsonEnabled"
+          :class="[
+            'relative inline-flex h-6 w-11 flex-shrink-0 cursor-pointer rounded-full border-2 border-transparent transition-colors duration-200 ease-in-out focus:outline-none focus:ring-2 focus:ring-primary-500 focus:ring-offset-2',
+            openAIImagesUrlToB64JsonEnabled ? 'bg-primary-600' : 'bg-gray-200 dark:bg-dark-600'
+          ]"
+        >
+          <span
+            :class="[
+              'pointer-events-none inline-block h-5 w-5 transform rounded-full bg-white shadow ring-0 transition duration-200 ease-in-out',
+              openAIImagesUrlToB64JsonEnabled ? 'translate-x-5' : 'translate-x-0'
+            ]"
+          />
+        </button>
+      </div>
+
       <div
         v-if="account?.type === 'apikey'"
         class="flex items-center justify-between gap-4 border-t border-gray-200 pt-4 dark:border-dark-600"
@@ -3282,6 +3313,8 @@ const openAILongContextBillingEnabled = ref(false)
 const editPlanType = ref<string>('')
 const openAICompactMode = ref<OpenAICompactMode>('auto')
 const openAIResponsesMode = ref<OpenAIResponsesMode>('auto')
+// Images 非流式响应缺 b64_json 时由网关下载 url 回填（仅 OpenAI API Key）。
+const openAIImagesUrlToB64JsonEnabled = ref(false)
 const openAIEndpointCapabilities = ref<OpenAIEndpointCapability[]>(['chat_completions', 'embeddings'])
 const openaiOAuthResponsesWebSocketV2Mode = ref<OpenAIWSMode>(OPENAI_WS_MODE_OFF)
 const openaiAPIKeyResponsesWebSocketV2Mode = ref<OpenAIWSMode>(OPENAI_WS_MODE_OFF)
@@ -3742,6 +3775,7 @@ const syncFormFromAccount = (newAccount: Account | null) => {
 	mixedScheduling.value = extra?.mixed_scheduling === true
 	allowOverages.value = extra?.allow_overages === true
 	upstreamRequestIdHeader.value = readUpstreamRequestIdHeader(extra)
+	openAIImagesUrlToB64JsonEnabled.value = extra?.images_url_to_b64_json === true
 	autoPause5hThreshold.value = typeof extra?.auto_pause_5h_threshold === 'number' ? extra.auto_pause_5h_threshold * 100 : null
 	autoPause7dThreshold.value = typeof extra?.auto_pause_7d_threshold === 'number' ? extra.auto_pause_7d_threshold * 100 : null
 	autoPause5hDisabled.value = extra?.auto_pause_5h_disabled === true
@@ -5214,6 +5248,11 @@ const handleSubmit = async () => {
           delete newExtra.openai_responses_mode
         } else {
           newExtra.openai_responses_mode = openAIResponsesMode.value
+        }
+        if (openAIImagesUrlToB64JsonEnabled.value) {
+          newExtra.images_url_to_b64_json = true
+        } else {
+          delete newExtra.images_url_to_b64_json
         }
 		}
 		if (autoPause5hThreshold.value != null && autoPause5hThreshold.value > 0) {

frontend/src/components/account/__tests__/CreateAccountModal.spec.ts

@@ -268,6 +268,27 @@ describe('CreateAccountModal OpenAI long-context billing', () => {
     expect(createAccountMock.mock.calls[0]?.[0]?.extra?.upstream_request_id_header).toBe('X-Oneapi-Request-Id')
   })
 
+  it('omits images_url_to_b64_json from extra by default', async () => {
+    await submitApiKeyAccount('openai')
+
+    expect(createAccountMock).toHaveBeenCalledTimes(1)
+    expect(createAccountMock.mock.calls[0]?.[0]?.extra).not.toHaveProperty('images_url_to_b64_json')
+  })
+
+  it('sends images_url_to_b64_json in extra when the toggle is enabled', async () => {
+    const wrapper = mountModal()
+    await selectButtonByText(wrapper, 'OpenAI')
+    await selectButtonByText(wrapper, 'API Key')
+    await wrapper.get('form#create-account-form input[type="text"]').setValue('openai account')
+    await wrapper.get('form#create-account-form input[type="password"]').setValue('test-api-key')
+    await wrapper.get('[data-testid="openai-images-url-to-b64-json-toggle"]').trigger('click')
+    await wrapper.get('form#create-account-form').trigger('submit.prevent')
+    await flushPromises()
+
+    expect(createAccountMock).toHaveBeenCalledTimes(1)
+    expect(createAccountMock.mock.calls[0]?.[0]?.extra?.images_url_to_b64_json).toBe(true)
+  })
+
   it('persists upstream model metadata after creating an account from preview', async () => {
     const wrapper = mountModal()
     await selectButtonByText(wrapper, 'OpenAI')

frontend/src/components/account/__tests__/EditAccountModal.spec.ts

@@ -718,6 +718,42 @@ describe('EditAccountModal', () => {
     expect(updateAccountMock.mock.calls[0]?.[1]?.extra).not.toHaveProperty('upstream_request_id_header')
   })
 
+  it('writes images_url_to_b64_json into extra when toggled on', async () => {
+    const account = buildAccount()
+    updateAccountMock.mockReset()
+    checkMixedChannelRiskMock.mockReset()
+    checkMixedChannelRiskMock.mockResolvedValue({ has_risk: false })
+    updateAccountMock.mockResolvedValue(account)
+
+    const wrapper = mountModal(account)
+    const toggle = wrapper.get('[data-testid="openai-images-url-to-b64-json-toggle"]')
+    expect(toggle.attributes('aria-checked')).toBe('false')
+    await toggle.trigger('click')
+    await wrapper.get('form#edit-account-form').trigger('submit.prevent')
+
+    expect(updateAccountMock).toHaveBeenCalledTimes(1)
+    expect(updateAccountMock.mock.calls[0]?.[1]?.extra?.images_url_to_b64_json).toBe(true)
+  })
+
+  it('removes images_url_to_b64_json from extra when toggled off', async () => {
+    const account = buildAccount()
+    account.extra = { images_url_to_b64_json: true }
+    updateAccountMock.mockReset()
+    checkMixedChannelRiskMock.mockReset()
+    checkMixedChannelRiskMock.mockResolvedValue({ has_risk: false })
+    updateAccountMock.mockResolvedValue(account)
+
+    const wrapper = mountModal(account)
+    const toggle = wrapper.get('[data-testid="openai-images-url-to-b64-json-toggle"]')
+    expect(toggle.attributes('aria-checked')).toBe('true')
+    await toggle.trigger('click')
+    await wrapper.get('form#edit-account-form').trigger('submit.prevent')
+
+    expect(updateAccountMock).toHaveBeenCalledTimes(1)
+    expect(updateAccountMock.mock.calls[0]?.[1]?.extra).toBeDefined()
+    expect(updateAccountMock.mock.calls[0]?.[1]?.extra).not.toHaveProperty('images_url_to_b64_json')
+  })
+
   it('hides the Codex namespace flatten toggle for non-OAuth OpenAI accounts', async () => {
     const account = buildAccount()
     const wrapper = mountModal(account)

frontend/src/i18n/locales/en/admin/accounts.ts

@@ -611,6 +611,9 @@ export default {
         responsesModeForceChatCompletions: 'Force Chat Completions',
         responsesModeTextDisabledHint:
           'Not applicable when the Responses / Chat Completions endpoint is not enabled.',
+        imagesUrlToB64Json: 'Image result URL to base64',
+        imagesUrlToB64JsonDesc:
+          'Only applies to non-streaming Images responses of OpenAI API Key accounts. When an upstream image item has a url but no b64_json, the gateway downloads the url and fills b64_json with its base64 content (url is kept) for clients built on the official API; the response is returned unchanged if the download fails.',
         endpointCapabilities: 'Endpoint capabilities',
         endpointCapabilitiesDesc:
           'Used by account routing. The text endpoint follows the Responses API support setting above and is shown as Responses, Chat Completions, or auto mode; Embeddings independently controls /v1/embeddings.',

frontend/src/i18n/locales/zh/admin/accounts.ts

@@ -692,6 +692,9 @@ export default {
         responsesModeForceResponses: '强制 Responses',
         responsesModeForceChatCompletions: '强制 Chat Completions',
         responsesModeTextDisabledHint: '未启用 Responses / Chat Completions 端点时，此设置不适用。',
+        imagesUrlToB64Json: '生图结果 URL 转 base64',
+        imagesUrlToB64JsonDesc:
+          '仅对 OpenAI API Key 的 Images 非流式响应生效。上游返回的图片缺少 b64_json 但带 url 时，网关下载该 url 并以 base64 回填 b64_json（url 保留），兼容按官方接口实现的客户端；下载失败则原样返回。',
         endpointCapabilities: '端点能力',
         endpointCapabilitiesDesc:
           '用于调度筛选。文本端点会跟随上方 Responses API 支持显示为 Responses、Chat Completions 或自动模式；Embeddings 独立控制 /v1/embeddings。',