feat: 网关请求头 wire casing 保持、转发行为开关、调试日志增强及 accept-encoding 恢复

- 新增 header_util.go，通过 setHeaderRaw/getHeaderRaw/addHeaderRaw 绕过
  Go 的 canonical-case 规范化，保持真实 Claude CLI 抓包的请求头大小写
  （如 "x-app" 而非 "X-App"，"X-Stainless-OS" 而非 "X-Stainless-Os"）
- 新增管理后台开关：指纹统一化（默认开启）和 metadata 透传（默认关闭），
  使用 atomic.Value + singleflight 缓存模式，60s TTL
- 调试日志从控制台 body 打印升级为文件级完整快照
  （按真实 wire 顺序输出 headers + 格式化 JSON body + 上下文元数据）
- 恢复 accept-encoding 到白名单，在 http_upstream.go 新增 decompressResponseBody
  处理 gzip/brotli/deflate 解压（Go 显式设置 Accept-Encoding 时不会自动解压）
- OAuth 服务 axios UA 从 1.8.4 更新至 1.13.6
- 测试断言改用 getHeaderRaw 适配 raw header 存储方式

backend/internal/handler/admin/setting_handler.go

@@ -129,6 +129,8 @@ func (h *SettingHandler) GetSettings(c *gin.Context) {
 		MaxClaudeCodeVersion:                 settings.MaxClaudeCodeVersion,
 		AllowUngroupedKeyScheduling:          settings.AllowUngroupedKeyScheduling,
 		BackendModeEnabled:                   settings.BackendModeEnabled,
+		EnableFingerprintUnification:         settings.EnableFingerprintUnification,
+		EnableMetadataPassthrough:            settings.EnableMetadataPassthrough,
 	})
 }
 
@@ -209,6 +211,10 @@ type UpdateSettingsRequest struct {
 
 	// Backend Mode
 	BackendModeEnabled bool `json:"backend_mode_enabled"`
+
+	// Gateway forwarding behavior
+	EnableFingerprintUnification *bool `json:"enable_fingerprint_unification"`
+	EnableMetadataPassthrough    *bool `json:"enable_metadata_passthrough"`
 }
 
 // UpdateSettings 更新系统设置
@@ -601,6 +607,18 @@ func (h *SettingHandler) UpdateSettings(c *gin.Context) {
 			}
 			return previousSettings.OpsMetricsIntervalSeconds
 		}(),
+		EnableFingerprintUnification: func() bool {
+			if req.EnableFingerprintUnification != nil {
+				return *req.EnableFingerprintUnification
+			}
+			return previousSettings.EnableFingerprintUnification
+		}(),
+		EnableMetadataPassthrough: func() bool {
+			if req.EnableMetadataPassthrough != nil {
+				return *req.EnableMetadataPassthrough
+			}
+			return previousSettings.EnableMetadataPassthrough
+		}(),
 	}
 
 	if err := h.settingService.UpdateSettings(c.Request.Context(), settings); err != nil {
@@ -679,6 +697,8 @@ func (h *SettingHandler) UpdateSettings(c *gin.Context) {
 		MaxClaudeCodeVersion:                 updatedSettings.MaxClaudeCodeVersion,
 		AllowUngroupedKeyScheduling:          updatedSettings.AllowUngroupedKeyScheduling,
 		BackendModeEnabled:                   updatedSettings.BackendModeEnabled,
+		EnableFingerprintUnification:         updatedSettings.EnableFingerprintUnification,
+		EnableMetadataPassthrough:            updatedSettings.EnableMetadataPassthrough,
 	})
 }
 
@@ -851,6 +871,12 @@ func diffSettings(before *service.SystemSettings, after *service.SystemSettings,
 	if before.CustomMenuItems != after.CustomMenuItems {
 		changed = append(changed, "custom_menu_items")
 	}
+	if before.EnableFingerprintUnification != after.EnableFingerprintUnification {
+		changed = append(changed, "enable_fingerprint_unification")
+	}
+	if before.EnableMetadataPassthrough != after.EnableMetadataPassthrough {
+		changed = append(changed, "enable_metadata_passthrough")
+	}
 	return changed
 }
 

backend/internal/handler/dto/settings.go

@@ -94,6 +94,10 @@ type SystemSettings struct {
 
 	// Backend Mode
 	BackendModeEnabled bool `json:"backend_mode_enabled"`
+
+	// Gateway forwarding behavior
+	EnableFingerprintUnification bool `json:"enable_fingerprint_unification"`
+	EnableMetadataPassthrough    bool `json:"enable_metadata_passthrough"`
 }
 
 type DefaultSubscriptionSetting struct {

backend/internal/repository/claude_oauth_service.go

@@ -212,7 +212,7 @@ func (s *claudeOAuthService) ExchangeCodeForToken(ctx context.Context, code, cod
 		SetContext(ctx).
 		SetHeader("Accept", "application/json, text/plain, */*").
 		SetHeader("Content-Type", "application/json").
-		SetHeader("User-Agent", "axios/1.8.4").
+		SetHeader("User-Agent", "axios/1.13.6").
 		SetBody(reqBody).
 		SetSuccessResult(&tokenResp).
 		Post(s.tokenURL)
@@ -250,7 +250,7 @@ func (s *claudeOAuthService) RefreshToken(ctx context.Context, refreshToken, pro
 		SetContext(ctx).
 		SetHeader("Accept", "application/json, text/plain, */*").
 		SetHeader("Content-Type", "application/json").
-		SetHeader("User-Agent", "axios/1.8.4").
+		SetHeader("User-Agent", "axios/1.13.6").
 		SetBody(reqBody).
 		SetSuccessResult(&tokenResp).
 		Post(s.tokenURL)

backend/internal/repository/http_upstream.go

 package repository
 
 import (
+	"compress/flate"
+	"compress/gzip"
 	"errors"
 	"fmt"
 	"io"
@@ -13,6 +15,8 @@ import (
 	"sync/atomic"
 	"time"
 
+	"github.com/andybalholm/brotli"
+
 	"github.com/Wei-Shaw/sub2api/internal/config"
 	"github.com/Wei-Shaw/sub2api/internal/pkg/proxyurl"
 	"github.com/Wei-Shaw/sub2api/internal/pkg/proxyutil"
@@ -143,6 +147,9 @@ func (s *httpUpstreamService) Do(req *http.Request, proxyURL string, accountID i
 		return nil, err
 	}
 
+	// 如果上游返回了压缩内容，解压后再交给业务层
+	decompressResponseBody(resp)
+
 	// 包装响应体，在关闭时自动减少计数并更新时间戳
 	// 这确保了流式响应（如 SSE）在完全读取前不会被淘汰
 	resp.Body = wrapTrackedBody(resp.Body, func() {
@@ -218,6 +225,9 @@ func (s *httpUpstreamService) DoWithTLS(req *http.Request, proxyURL string, acco
 
 	slog.Debug("tls_fingerprint_request_success", "account_id", accountID, "status", resp.StatusCode)
 
+	// 如果上游返回了压缩内容，解压后再交给业务层
+	decompressResponseBody(resp)
+
 	// 包装响应体，在关闭时自动减少计数并更新时间戳
 	resp.Body = wrapTrackedBody(resp.Body, func() {
 		atomic.AddInt64(&entry.inFlight, -1)
@@ -884,3 +894,56 @@ func wrapTrackedBody(body io.ReadCloser, onClose func()) io.ReadCloser {
 	}
 	return &trackedBody{ReadCloser: body, onClose: onClose}
 }
+
+// decompressResponseBody 根据 Content-Encoding 解压响应体。
+// 当请求显式设置了 accept-encoding 时，Go 的 Transport 不会自动解压，需要手动处理。
+// 解压成功后会删除 Content-Encoding 和 Content-Length header（长度已不准确）。
+func decompressResponseBody(resp *http.Response) {
+	if resp == nil || resp.Body == nil {
+		return
+	}
+	ce := strings.ToLower(strings.TrimSpace(resp.Header.Get("Content-Encoding")))
+	if ce == "" {
+		return
+	}
+
+	var reader io.Reader
+	switch ce {
+	case "gzip":
+		gr, err := gzip.NewReader(resp.Body)
+		if err != nil {
+			return // 解压失败，保持原样
+		}
+		reader = gr
+	case "br":
+		reader = brotli.NewReader(resp.Body)
+	case "deflate":
+		reader = flate.NewReader(resp.Body)
+	default:
+		return
+	}
+
+	originalBody := resp.Body
+	resp.Body = &decompressedBody{reader: reader, closer: originalBody}
+	resp.Header.Del("Content-Encoding")
+	resp.Header.Del("Content-Length") // 解压后长度不确定
+	resp.ContentLength = -1
+}
+
+// decompressedBody 组合解压 reader 和原始 body 的 close。
+type decompressedBody struct {
+	reader io.Reader
+	closer io.Closer
+}
+
+func (d *decompressedBody) Read(p []byte) (int, error) {
+	return d.reader.Read(p)
+}
+
+func (d *decompressedBody) Close() error {
+	// 如果 reader 本身也是 Closer（如 gzip.Reader），先关闭它
+	if rc, ok := d.reader.(io.Closer); ok {
+		_ = rc.Close()
+	}
+	return d.closer.Close()
+}

backend/internal/server/api_contract_test.go

@@ -540,6 +540,8 @@ func TestAPIContracts(t *testing.T) {
 					"max_claude_code_version": "",
 					"allow_ungrouped_key_scheduling": false,
 					"backend_mode_enabled": false,
+					"enable_fingerprint_unification": true,
+					"enable_metadata_passthrough": false,
 					"custom_menu_items": [],
 					"custom_endpoints": []
 				}

backend/internal/service/domain_constants.go

@@ -235,6 +235,12 @@ const (
 
 	// SettingKeyBackendModeEnabled Backend 模式：禁用用户注册和自助服务，仅管理员可登录
 	SettingKeyBackendModeEnabled = "backend_mode_enabled"
+
+	// Gateway Forwarding Behavior
+	// SettingKeyEnableFingerprintUnification 是否统一 OAuth 账号的 X-Stainless-* 指纹头（默认 true）
+	SettingKeyEnableFingerprintUnification = "enable_fingerprint_unification"
+	// SettingKeyEnableMetadataPassthrough 是否透传客户端原始 metadata.user_id（默认 false）
+	SettingKeyEnableMetadataPassthrough = "enable_metadata_passthrough"
 )
 
 // AdminAPIKeyPrefix is the prefix for admin API keys (distinct from user "sk-" keys).

backend/internal/service/gateway_anthropic_apikey_passthrough_test.go

@@ -175,13 +175,13 @@ func TestGatewayService_AnthropicAPIKeyPassthrough_ForwardStreamPreservesBodyAnd
 
 	require.Equal(t, "claude-3-haiku-20240307", gjson.GetBytes(upstream.lastBody, "model").String(), "透传模式应应用账号级模型映射")
 
-	require.Equal(t, "upstream-anthropic-key", upstream.lastReq.Header.Get("x-api-key"))
-	require.Empty(t, upstream.lastReq.Header.Get("authorization"))
-	require.Empty(t, upstream.lastReq.Header.Get("x-goog-api-key"))
-	require.Empty(t, upstream.lastReq.Header.Get("cookie"))
-	require.Equal(t, "2023-06-01", upstream.lastReq.Header.Get("anthropic-version"))
-	require.Equal(t, "interleaved-thinking-2025-05-14", upstream.lastReq.Header.Get("anthropic-beta"))
-	require.Empty(t, upstream.lastReq.Header.Get("x-stainless-lang"), "API Key 透传不应注入 OAuth 指纹头")
+	require.Equal(t, "upstream-anthropic-key", getHeaderRaw(upstream.lastReq.Header, "x-api-key"))
+	require.Empty(t, getHeaderRaw(upstream.lastReq.Header, "authorization"))
+	require.Empty(t, getHeaderRaw(upstream.lastReq.Header, "x-goog-api-key"))
+	require.Empty(t, getHeaderRaw(upstream.lastReq.Header, "cookie"))
+	require.Equal(t, "2023-06-01", getHeaderRaw(upstream.lastReq.Header, "anthropic-version"))
+	require.Equal(t, "interleaved-thinking-2025-05-14", getHeaderRaw(upstream.lastReq.Header, "anthropic-beta"))
+	require.Empty(t, getHeaderRaw(upstream.lastReq.Header, "x-stainless-lang"), "API Key 透传不应注入 OAuth 指纹头")
 
 	require.Contains(t, rec.Body.String(), `"cached_tokens":7`)
 	require.NotContains(t, rec.Body.String(), `"cache_read_input_tokens":7`, "透传输出不应被网关改写")
@@ -257,9 +257,9 @@ func TestGatewayService_AnthropicAPIKeyPassthrough_ForwardCountTokensPreservesBo
 	require.NoError(t, err)
 
 	require.Equal(t, "claude-3-opus-20240229", gjson.GetBytes(upstream.lastBody, "model").String(), "count_tokens 透传模式应应用账号级模型映射")
-	require.Equal(t, "upstream-anthropic-key", upstream.lastReq.Header.Get("x-api-key"))
-	require.Empty(t, upstream.lastReq.Header.Get("authorization"))
-	require.Empty(t, upstream.lastReq.Header.Get("cookie"))
+	require.Equal(t, "upstream-anthropic-key", getHeaderRaw(upstream.lastReq.Header, "x-api-key"))
+	require.Empty(t, getHeaderRaw(upstream.lastReq.Header, "authorization"))
+	require.Empty(t, getHeaderRaw(upstream.lastReq.Header, "cookie"))
 	require.Equal(t, http.StatusOK, rec.Code)
 	require.JSONEq(t, upstreamRespBody, rec.Body.String())
 	require.Empty(t, rec.Header().Get("Set-Cookie"))
@@ -684,8 +684,8 @@ func TestGatewayService_AnthropicOAuth_NotAffectedByAPIKeyPassthroughToggle(t *t
 
 	req, err := svc.buildUpstreamRequest(context.Background(), c, account, []byte(`{"model":"claude-3-7-sonnet-20250219"}`), "oauth-token", "oauth", "claude-3-7-sonnet-20250219", true, false)
 	require.NoError(t, err)
-	require.Equal(t, "Bearer oauth-token", req.Header.Get("authorization"))
-	require.Contains(t, req.Header.Get("anthropic-beta"), claude.BetaOAuth, "OAuth 链路仍应按原逻辑补齐 oauth beta")
+	require.Equal(t, "Bearer oauth-token", getHeaderRaw(req.Header, "authorization"))
+	require.Contains(t, getHeaderRaw(req.Header, "anthropic-beta"), claude.BetaOAuth, "OAuth 链路仍应按原逻辑补齐 oauth beta")
 }
 
 func TestGatewayService_AnthropicOAuth_ForwardPreservesBillingHeaderSystemBlock(t *testing.T) {
@@ -755,8 +755,8 @@ func TestGatewayService_AnthropicOAuth_ForwardPreservesBillingHeaderSystemBlock(
 			require.NoError(t, err)
 			require.NotNil(t, result)
 			require.NotNil(t, upstream.lastReq)
-			require.Equal(t, "Bearer oauth-token", upstream.lastReq.Header.Get("authorization"))
-			require.Contains(t, upstream.lastReq.Header.Get("anthropic-beta"), claude.BetaOAuth)
+			require.Equal(t, "Bearer oauth-token", getHeaderRaw(upstream.lastReq.Header, "authorization"))
+			require.Contains(t, getHeaderRaw(upstream.lastReq.Header, "anthropic-beta"), claude.BetaOAuth)
 
 			system := gjson.GetBytes(upstream.lastBody, "system")
 			require.True(t, system.Exists())

backend/internal/service/gateway_debug_env_test.go

@@ -2,31 +2,28 @@ package service
 
 import "testing"
 
-func TestDebugGatewayBodyLoggingEnabled(t *testing.T) {
-	t.Run("default disabled", func(t *testing.T) {
-		t.Setenv(debugGatewayBodyEnv, "")
-		if debugGatewayBodyLoggingEnabled() {
-			t.Fatalf("expected debug gateway body logging to be disabled by default")
+func TestParseDebugEnvBool(t *testing.T) {
+	t.Run("empty is false", func(t *testing.T) {
+		if parseDebugEnvBool("") {
+			t.Fatalf("expected false for empty string")
 		}
 	})
 
-	t.Run("enabled with true-like values", func(t *testing.T) {
+	t.Run("true-like values", func(t *testing.T) {
 		for _, value := range []string{"1", "true", "TRUE", "yes", "on"} {
 			t.Run(value, func(t *testing.T) {
-				t.Setenv(debugGatewayBodyEnv, value)
-				if !debugGatewayBodyLoggingEnabled() {
-					t.Fatalf("expected debug gateway body logging to be enabled for %q", value)
+				if !parseDebugEnvBool(value) {
+					t.Fatalf("expected true for %q", value)
 				}
 			})
 		}
 	})
 
-	t.Run("disabled with other values", func(t *testing.T) {
+	t.Run("false-like values", func(t *testing.T) {
 		for _, value := range []string{"0", "false", "off", "debug"} {
 			t.Run(value, func(t *testing.T) {
-				t.Setenv(debugGatewayBodyEnv, value)
-				if debugGatewayBodyLoggingEnabled() {
-					t.Fatalf("expected debug gateway body logging to be disabled for %q", value)
+				if parseDebugEnvBool(value) {
+					t.Fatalf("expected false for %q", value)
 				}
 			})
 		}

backend/internal/service/gateway_service.go

@@ -13,6 +13,7 @@ import (
 	mathrand "math/rand"
 	"net/http"
 	"os"
+	"path/filepath"
 	"regexp"
 	"sort"
 	"strconv"
@@ -366,6 +367,7 @@ var allowedHeaders = map[string]bool{
 	"sec-fetch-mode":                            true,
 	"user-agent":                                true,
 	"content-type":                              true,
+	"accept-encoding":                           true,
 }
 
 // GatewayCache 定义网关服务的缓存操作接口。
@@ -563,6 +565,7 @@ type GatewayService struct {
 	responseHeaderFilter  *responseheaders.CompiledHeaderFilter
 	debugModelRouting     atomic.Bool
 	debugClaudeMimic      atomic.Bool
+	debugGatewayBodyFile  atomic.Pointer[os.File] // non-nil when SUB2API_DEBUG_GATEWAY_BODY is set
 }
 
 // NewGatewayService creates a new GatewayService
@@ -630,6 +633,9 @@ func NewGatewayService(
 	)
 	svc.debugModelRouting.Store(parseDebugEnvBool(os.Getenv("SUB2API_DEBUG_MODEL_ROUTING")))
 	svc.debugClaudeMimic.Store(parseDebugEnvBool(os.Getenv("SUB2API_DEBUG_CLAUDE_MIMIC")))
+	if path := strings.TrimSpace(os.Getenv(debugGatewayBodyEnv)); path != "" {
+		svc.initDebugGatewayBodyFile(path)
+	}
 	return svc
 }
 
@@ -4048,8 +4054,15 @@ func (s *GatewayService) Forward(ctx context.Context, c *gin.Context, account *A
 	reqStream := parsed.Stream
 	originalModel := reqModel
 
-	// === DEBUG: 打印客户端原始请求 body ===
-	debugLogRequestBody("CLIENT_ORIGINAL", body)
+	// === DEBUG: 打印客户端原始请求（headers + body 摘要）===
+	if c != nil {
+		s.debugLogGatewaySnapshot("CLIENT_ORIGINAL", c.Request.Header, body, map[string]string{
+			"account":      fmt.Sprintf("%d(%s)", account.ID, account.Name),
+			"account_type": string(account.Type),
+			"model":        reqModel,
+			"stream":       strconv.FormatBool(reqStream),
+		})
+	}
 
 	isClaudeCode := isClaudeCodeRequest(ctx, c, parsed)
 	shouldMimicClaudeCode := account.IsOAuth() && !isClaudeCode
@@ -4066,9 +4079,13 @@ func (s *GatewayService) Forward(ctx context.Context, c *gin.Context, account *A
 		if s.identityService != nil {
 			fp, err := s.identityService.GetOrCreateFingerprint(ctx, account.ID, c.Request.Header)
 			if err == nil && fp != nil {
-				if metadataUserID := s.buildOAuthMetadataUserID(parsed, account, fp); metadataUserID != "" {
-					normalizeOpts.injectMetadata = true
-					normalizeOpts.metadataUserID = metadataUserID
+				// metadata 透传开启时跳过 metadata 注入
+				_, mimicMPT := s.settingService.GetGatewayForwardingSettings(ctx)
+				if !mimicMPT {
+					if metadataUserID := s.buildOAuthMetadataUserID(parsed, account, fp); metadataUserID != "" {
+						normalizeOpts.injectMetadata = true
+						normalizeOpts.metadataUserID = metadataUserID
+					}
 				}
 			}
 		}
@@ -4840,8 +4857,9 @@ func (s *GatewayService) buildUpstreamRequestAnthropicAPIKeyPassthrough(
 			if !allowedHeaders[lowerKey] {
 				continue
 			}
+			wireKey := resolveWireCasing(key)
 			for _, v := range values {
-				req.Header.Add(key, v)
+				addHeaderRaw(req.Header, wireKey, v)
 			}
 		}
 	}
@@ -4851,13 +4869,13 @@ func (s *GatewayService) buildUpstreamRequestAnthropicAPIKeyPassthrough(
 	req.Header.Del("x-api-key")
 	req.Header.Del("x-goog-api-key")
 	req.Header.Del("cookie")
-	req.Header.Set("x-api-key", token)
+	setHeaderRaw(req.Header, "x-api-key", token)
 
-	if req.Header.Get("content-type") == "" {
-		req.Header.Set("content-type", "application/json")
+	if getHeaderRaw(req.Header, "content-type") == "" {
+		setHeaderRaw(req.Header, "content-type", "application/json")
 	}
-	if req.Header.Get("anthropic-version") == "" {
-		req.Header.Set("anthropic-version", "2023-06-01")
+	if getHeaderRaw(req.Header, "anthropic-version") == "" {
+		setHeaderRaw(req.Header, "anthropic-version", "2023-06-01")
 	}
 
 	return req, nil
@@ -5591,8 +5609,12 @@ func (s *GatewayService) buildUpstreamRequest(ctx context.Context, c *gin.Contex
 		clientHeaders = c.Request.Header
 	}
 
-	// OAuth账号：应用统一指纹
+	// OAuth账号：应用统一指纹和metadata重写（受设置开关控制）
 	var fingerprint *Fingerprint
+	enableFP, enableMPT := true, false
+	if s.settingService != nil {
+		enableFP, enableMPT = s.settingService.GetGatewayForwardingSettings(ctx)
+	}
 	if account.IsOAuth() && s.identityService != nil {
 		// 1. 获取或创建指纹（包含随机生成的ClientID）
 		fp, err := s.identityService.GetOrCreateFingerprint(ctx, account.ID, clientHeaders)
@@ -5600,40 +5622,43 @@ func (s *GatewayService) buildUpstreamRequest(ctx context.Context, c *gin.Contex
 			logger.LegacyPrintf("service.gateway", "Warning: failed to get fingerprint for account %d: %v", account.ID, err)
 			// 失败时降级为透传原始headers
 		} else {
-			fingerprint = fp
+			if enableFP {
+				fingerprint = fp
+			}
 
 			// 2. 重写metadata.user_id（需要指纹中的ClientID和账号的account_uuid）
 			// 如果启用了会话ID伪装，会在重写后替换 session 部分为固定值
-			accountUUID := account.GetExtraString("account_uuid")
-			if accountUUID != "" && fp.ClientID != "" {
-				if newBody, err := s.identityService.RewriteUserIDWithMasking(ctx, body, account, accountUUID, fp.ClientID, fp.UserAgent); err == nil && len(newBody) > 0 {
-					body = newBody
+			// 当 metadata 透传开启时跳过重写
+			if !enableMPT {
+				accountUUID := account.GetExtraString("account_uuid")
+				if accountUUID != "" && fp.ClientID != "" {
+					if newBody, err := s.identityService.RewriteUserIDWithMasking(ctx, body, account, accountUUID, fp.ClientID, fp.UserAgent); err == nil && len(newBody) > 0 {
+						body = newBody
+					}
 				}
 			}
 		}
 	}
 
-	// === DEBUG: 打印转发给上游的 body（metadata 已重写） ===
-	debugLogRequestBody("UPSTREAM_FORWARD", body)
-
 	req, err := http.NewRequestWithContext(ctx, "POST", targetURL, bytes.NewReader(body))
 	if err != nil {
 		return nil, err
 	}
 
-	// 设置认证头
+	// 设置认证头（保持原始大小写）
 	if tokenType == "oauth" {
-		req.Header.Set("authorization", "Bearer "+token)
+		setHeaderRaw(req.Header, "authorization", "Bearer "+token)
 	} else {
-		req.Header.Set("x-api-key", token)
+		setHeaderRaw(req.Header, "x-api-key", token)
 	}
 
-	// 白名单透传headers
+	// 白名单透传headers（恢复真实 wire casing）
 	for key, values := range clientHeaders {
 		lowerKey := strings.ToLower(key)
 		if allowedHeaders[lowerKey] {
+			wireKey := resolveWireCasing(key)
 			for _, v := range values {
-				req.Header.Add(key, v)
+				addHeaderRaw(req.Header, wireKey, v)
 			}
 		}
 	}
@@ -5643,15 +5668,15 @@ func (s *GatewayService) buildUpstreamRequest(ctx context.Context, c *gin.Contex
 		s.identityService.ApplyFingerprint(req, fingerprint)
 	}
 
-	// 确保必要的headers存在
-	if req.Header.Get("content-type") == "" {
-		req.Header.Set("content-type", "application/json")
+	// 确保必要的headers存在（保持原始大小写）
+	if getHeaderRaw(req.Header, "content-type") == "" {
+		setHeaderRaw(req.Header, "content-type", "application/json")
 	}
-	if req.Header.Get("anthropic-version") == "" {
-		req.Header.Set("anthropic-version", "2023-06-01")
+	if getHeaderRaw(req.Header, "anthropic-version") == "" {
+		setHeaderRaw(req.Header, "anthropic-version", "2023-06-01")
 	}
 	if tokenType == "oauth" {
-		applyClaudeOAuthHeaderDefaults(req, reqStream)
+		applyClaudeOAuthHeaderDefaults(req)
 	}
 
 	// Build effective drop set: merge static defaults with dynamic beta policy filter rules
@@ -5667,31 +5692,41 @@ func (s *GatewayService) buildUpstreamRequest(ctx context.Context, c *gin.Contex
 			// - 保留 incoming beta 的同时，确保 OAuth 所需 beta 存在
 			applyClaudeCodeMimicHeaders(req, reqStream)
 
-			incomingBeta := req.Header.Get("anthropic-beta")
+			incomingBeta := getHeaderRaw(req.Header, "anthropic-beta")
 			// Match real Claude CLI traffic (per mitmproxy reports):
 			// messages requests typically use only oauth + interleaved-thinking.
 			// Also drop claude-code beta if a downstream client added it.
 			requiredBetas := []string{claude.BetaOAuth, claude.BetaInterleavedThinking}
-			req.Header.Set("anthropic-beta", mergeAnthropicBetaDropping(requiredBetas, incomingBeta, effectiveDropWithClaudeCodeSet))
+			setHeaderRaw(req.Header, "anthropic-beta", mergeAnthropicBetaDropping(requiredBetas, incomingBeta, effectiveDropWithClaudeCodeSet))
 		} else {
 			// Claude Code 客户端：尽量透传原始 header，仅补齐 oauth beta
-			clientBetaHeader := req.Header.Get("anthropic-beta")
-			req.Header.Set("anthropic-beta", stripBetaTokensWithSet(s.getBetaHeader(modelID, clientBetaHeader), effectiveDropSet))
+			clientBetaHeader := getHeaderRaw(req.Header, "anthropic-beta")
+			setHeaderRaw(req.Header, "anthropic-beta", stripBetaTokensWithSet(s.getBetaHeader(modelID, clientBetaHeader), effectiveDropSet))
 		}
 	} else {
 		// API-key accounts: apply beta policy filter to strip controlled tokens
-		if existingBeta := req.Header.Get("anthropic-beta"); existingBeta != "" {
-			req.Header.Set("anthropic-beta", stripBetaTokensWithSet(existingBeta, effectiveDropSet))
+		if existingBeta := getHeaderRaw(req.Header, "anthropic-beta"); existingBeta != "" {
+			setHeaderRaw(req.Header, "anthropic-beta", stripBetaTokensWithSet(existingBeta, effectiveDropSet))
 		} else if s.cfg != nil && s.cfg.Gateway.InjectBetaForAPIKey {
 			// API-key：仅在请求显式使用 beta 特性且客户端未提供时，按需补齐（默认关闭）
 			if requestNeedsBetaFeatures(body) {
 				if beta := defaultAPIKeyBetaHeader(body); beta != "" {
-					req.Header.Set("anthropic-beta", beta)
+					setHeaderRaw(req.Header, "anthropic-beta", beta)
 				}
 			}
 		}
 	}
 
+	// === DEBUG: 打印上游转发请求（headers + body 摘要），与 CLIENT_ORIGINAL 对比 ===
+	s.debugLogGatewaySnapshot("UPSTREAM_FORWARD", req.Header, body, map[string]string{
+		"url":                 req.URL.String(),
+		"token_type":          tokenType,
+		"mimic_claude_code":   strconv.FormatBool(mimicClaudeCode),
+		"fingerprint_applied": strconv.FormatBool(fingerprint != nil),
+		"enable_fp":           strconv.FormatBool(enableFP),
+		"enable_mpt":          strconv.FormatBool(enableMPT),
+	})
+
 	// Always capture a compact fingerprint line for later error diagnostics.
 	// We only print it when needed (or when the explicit debug flag is enabled).
 	if c != nil && tokenType == "oauth" {
@@ -5771,24 +5806,21 @@ func defaultAPIKeyBetaHeader(body []byte) string {
 	return claude.APIKeyBetaHeader
 }
 
-func applyClaudeOAuthHeaderDefaults(req *http.Request, isStream bool) {
+func applyClaudeOAuthHeaderDefaults(req *http.Request) {
 	if req == nil {
 		return
 	}
-	if req.Header.Get("accept") == "" {
-		req.Header.Set("accept", "application/json")
+	if getHeaderRaw(req.Header, "Accept") == "" {
+		setHeaderRaw(req.Header, "Accept", "application/json")
 	}
 	for key, value := range claude.DefaultHeaders {
 		if value == "" {
 			continue
 		}
-		if req.Header.Get(key) == "" {
-			req.Header.Set(key, value)
+		if getHeaderRaw(req.Header, key) == "" {
+			setHeaderRaw(req.Header, resolveWireCasing(key), value)
 		}
 	}
-	if isStream && req.Header.Get("x-stainless-helper-method") == "" {
-		req.Header.Set("x-stainless-helper-method", "stream")
-	}
 }
 
 func mergeAnthropicBeta(required []string, incoming string) string {
@@ -6083,18 +6115,19 @@ func applyClaudeCodeMimicHeaders(req *http.Request, isStream bool) {
 		return
 	}
 	// Start with the standard defaults (fill missing).
-	applyClaudeOAuthHeaderDefaults(req, isStream)
+	applyClaudeOAuthHeaderDefaults(req)
 	// Then force key headers to match Claude Code fingerprint regardless of what the client sent.
+	// 使用 resolveWireCasing 确保 key 与真实 wire format 一致（如 "x-app" 而非 "X-App"）
 	for key, value := range claude.DefaultHeaders {
 		if value == "" {
 			continue
 		}
-		req.Header.Set(key, value)
+		setHeaderRaw(req.Header, resolveWireCasing(key), value)
 	}
 	// Real Claude CLI uses Accept: application/json (even for streaming).
-	req.Header.Set("accept", "application/json")
+	setHeaderRaw(req.Header, "Accept", "application/json")
 	if isStream {
-		req.Header.Set("x-stainless-helper-method", "stream")
+		setHeaderRaw(req.Header, "x-stainless-helper-method", "stream")
 	}
 }
 
@@ -8197,8 +8230,9 @@ func (s *GatewayService) buildCountTokensRequestAnthropicAPIKeyPassthrough(
 			if !allowedHeaders[lowerKey] {
 				continue
 			}
+			wireKey := resolveWireCasing(key)
 			for _, v := range values {
-				req.Header.Add(key, v)
+				addHeaderRaw(req.Header, wireKey, v)
 			}
 		}
 	}
@@ -8239,15 +8273,23 @@ func (s *GatewayService) buildCountTokensRequest(ctx context.Context, c *gin.Con
 		clientHeaders = c.Request.Header
 	}
 
-	// OAuth 账号：应用统一指纹和重写 userID
+	// OAuth 账号：应用统一指纹和重写 userID（受设置开关控制）
 	// 如果启用了会话ID伪装，会在重写后替换 session 部分为固定值
+	ctEnableFP, ctEnableMPT := true, false
+	if s.settingService != nil {
+		ctEnableFP, ctEnableMPT = s.settingService.GetGatewayForwardingSettings(ctx)
+	}
+	var ctFingerprint *Fingerprint
 	if account.IsOAuth() && s.identityService != nil {
 		fp, err := s.identityService.GetOrCreateFingerprint(ctx, account.ID, clientHeaders)
 		if err == nil {
-			accountUUID := account.GetExtraString("account_uuid")
-			if accountUUID != "" && fp.ClientID != "" {
-				if newBody, err := s.identityService.RewriteUserIDWithMasking(ctx, body, account, accountUUID, fp.ClientID, fp.UserAgent); err == nil && len(newBody) > 0 {
-					body = newBody
+			ctFingerprint = fp
+			if !ctEnableMPT {
+				accountUUID := account.GetExtraString("account_uuid")
+				if accountUUID != "" && fp.ClientID != "" {
+					if newBody, err := s.identityService.RewriteUserIDWithMasking(ctx, body, account, accountUUID, fp.ClientID, fp.UserAgent); err == nil && len(newBody) > 0 {
+						body = newBody
+					}
 				}
 			}
 		}
@@ -8258,40 +8300,38 @@ func (s *GatewayService) buildCountTokensRequest(ctx context.Context, c *gin.Con
 		return nil, err
 	}
 
-	// 设置认证头
+	// 设置认证头（保持原始大小写）
 	if tokenType == "oauth" {
-		req.Header.Set("authorization", "Bearer "+token)
+		setHeaderRaw(req.Header, "authorization", "Bearer "+token)
 	} else {
-		req.Header.Set("x-api-key", token)
+		setHeaderRaw(req.Header, "x-api-key", token)
 	}
 
-	// 白名单透传 headers
+	// 白名单透传 headers（恢复真实 wire casing）
 	for key, values := range clientHeaders {
 		lowerKey := strings.ToLower(key)
 		if allowedHeaders[lowerKey] {
+			wireKey := resolveWireCasing(key)
 			for _, v := range values {
-				req.Header.Add(key, v)
+				addHeaderRaw(req.Header, wireKey, v)
 			}
 		}
 	}
 
-	// OAuth 账号：应用指纹到请求头
-	if account.IsOAuth() && s.identityService != nil {
-		fp, _ := s.identityService.GetOrCreateFingerprint(ctx, account.ID, clientHeaders)
-		if fp != nil {
-			s.identityService.ApplyFingerprint(req, fp)
-		}
+	// OAuth 账号：应用指纹到请求头（受设置开关控制）
+	if ctEnableFP && ctFingerprint != nil {
+		s.identityService.ApplyFingerprint(req, ctFingerprint)
 	}
 
-	// 确保必要的 headers 存在
-	if req.Header.Get("content-type") == "" {
-		req.Header.Set("content-type", "application/json")
+	// 确保必要的 headers 存在（保持原始大小写）
+	if getHeaderRaw(req.Header, "content-type") == "" {
+		setHeaderRaw(req.Header, "content-type", "application/json")
 	}
-	if req.Header.Get("anthropic-version") == "" {
-		req.Header.Set("anthropic-version", "2023-06-01")
+	if getHeaderRaw(req.Header, "anthropic-version") == "" {
+		setHeaderRaw(req.Header, "anthropic-version", "2023-06-01")
 	}
 	if tokenType == "oauth" {
-		applyClaudeOAuthHeaderDefaults(req, false)
+		applyClaudeOAuthHeaderDefaults(req)
 	}
 
 	// Build effective drop set for count_tokens: merge static defaults with dynamic beta policy filter rules
@@ -8302,30 +8342,30 @@ func (s *GatewayService) buildCountTokensRequest(ctx context.Context, c *gin.Con
 		if mimicClaudeCode {
 			applyClaudeCodeMimicHeaders(req, false)
 
-			incomingBeta := req.Header.Get("anthropic-beta")
+			incomingBeta := getHeaderRaw(req.Header, "anthropic-beta")
 			requiredBetas := []string{claude.BetaClaudeCode, claude.BetaOAuth, claude.BetaInterleavedThinking, claude.BetaTokenCounting}
-			req.Header.Set("anthropic-beta", mergeAnthropicBetaDropping(requiredBetas, incomingBeta, ctEffectiveDropSet))
+			setHeaderRaw(req.Header, "anthropic-beta", mergeAnthropicBetaDropping(requiredBetas, incomingBeta, ctEffectiveDropSet))
 		} else {
-			clientBetaHeader := req.Header.Get("anthropic-beta")
+			clientBetaHeader := getHeaderRaw(req.Header, "anthropic-beta")
 			if clientBetaHeader == "" {
-				req.Header.Set("anthropic-beta", claude.CountTokensBetaHeader)
+				setHeaderRaw(req.Header, "anthropic-beta", claude.CountTokensBetaHeader)
 			} else {
 				beta := s.getBetaHeader(modelID, clientBetaHeader)
 				if !strings.Contains(beta, claude.BetaTokenCounting) {
 					beta = beta + "," + claude.BetaTokenCounting
 				}
-				req.Header.Set("anthropic-beta", stripBetaTokensWithSet(beta, ctEffectiveDropSet))
+				setHeaderRaw(req.Header, "anthropic-beta", stripBetaTokensWithSet(beta, ctEffectiveDropSet))
 			}
 		}
 	} else {
 		// API-key accounts: apply beta policy filter to strip controlled tokens
-		if existingBeta := req.Header.Get("anthropic-beta"); existingBeta != "" {
-			req.Header.Set("anthropic-beta", stripBetaTokensWithSet(existingBeta, ctEffectiveDropSet))
+		if existingBeta := getHeaderRaw(req.Header, "anthropic-beta"); existingBeta != "" {
+			setHeaderRaw(req.Header, "anthropic-beta", stripBetaTokensWithSet(existingBeta, ctEffectiveDropSet))
 		} else if s.cfg != nil && s.cfg.Gateway.InjectBetaForAPIKey {
 			// API-key：与 messages 同步的按需 beta 注入（默认关闭）
 			if requestNeedsBetaFeatures(body) {
 				if beta := defaultAPIKeyBetaHeader(body); beta != "" {
-					req.Header.Set("anthropic-beta", beta)
+					setHeaderRaw(req.Header, "anthropic-beta", beta)
 				}
 			}
 		}
@@ -8496,42 +8536,94 @@ func reconcileCachedTokens(usage map[string]any) bool {
 	return true
 }
 
-func debugGatewayBodyLoggingEnabled() bool {
-	raw := strings.TrimSpace(os.Getenv(debugGatewayBodyEnv))
-	if raw == "" {
-		return false
+const debugGatewayBodyDefaultFilename = "gateway_debug.log"
+
+// initDebugGatewayBodyFile 初始化网关调试日志文件。
+//
+//   - "1"/"true" 等布尔值 → 当前目录下 gateway_debug.log
+//   - 已有目录路径        → 该目录下 gateway_debug.log
+//   - 其他               → 视为完整文件路径
+func (s *GatewayService) initDebugGatewayBodyFile(path string) {
+	if parseDebugEnvBool(path) {
+		path = debugGatewayBodyDefaultFilename
 	}
 
-	switch strings.ToLower(raw) {
-	case "1", "true", "yes", "on":
-		return true
-	default:
-		return false
+	// 如果 path 指向一个已存在的目录，自动追加默认文件名
+	if info, err := os.Stat(path); err == nil && info.IsDir() {
+		path = filepath.Join(path, debugGatewayBodyDefaultFilename)
+	}
+
+	// 确保父目录存在
+	if dir := filepath.Dir(path); dir != "." {
+		if err := os.MkdirAll(dir, 0755); err != nil {
+			slog.Error("failed to create gateway debug log directory", "dir", dir, "error", err)
+			return
+		}
+	}
+
+	f, err := os.OpenFile(path, os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0644)
+	if err != nil {
+		slog.Error("failed to open gateway debug log file", "path", path, "error", err)
+		return
 	}
+	s.debugGatewayBodyFile.Store(f)
+	slog.Info("gateway debug logging enabled", "path", path)
 }
 
-// debugLogRequestBody 打印请求 body 用于调试 metadata.user_id 重写。
-// 默认关闭，仅在设置环境变量时启用：
+// debugLogGatewaySnapshot 将网关请求的完整快照（headers + body）写入独立的调试日志文件，
+// 用于对比客户端原始请求和上游转发请求。
+//
+// 启用方式（环境变量）：
 //
-//	SUB2API_DEBUG_GATEWAY_BODY=1
-func debugLogRequestBody(tag string, body []byte) {
-	if !debugGatewayBodyLoggingEnabled() {
+//	SUB2API_DEBUG_GATEWAY_BODY=1                          # 写入 gateway_debug.log
+//	SUB2API_DEBUG_GATEWAY_BODY=/tmp/gateway_debug.log     # 写入指定路径
+//
+// tag: "CLIENT_ORIGINAL" 或 "UPSTREAM_FORWARD"
+func (s *GatewayService) debugLogGatewaySnapshot(tag string, headers http.Header, body []byte, extra map[string]string) {
+	f := s.debugGatewayBodyFile.Load()
+	if f == nil {
 		return
 	}
 
-	if len(body) == 0 {
-		logger.LegacyPrintf("service.gateway", "[DEBUG_%s] body is empty", tag)
-		return
+	var buf strings.Builder
+	ts := time.Now().Format("2006-01-02 15:04:05.000")
+	fmt.Fprintf(&buf, "\n========== [%s] %s ==========\n", ts, tag)
+
+	// 1. context
+	if len(extra) > 0 {
+		fmt.Fprint(&buf, "--- context ---\n")
+		extraKeys := make([]string, 0, len(extra))
+		for k := range extra {
+			extraKeys = append(extraKeys, k)
+		}
+		sort.Strings(extraKeys)
+		for _, k := range extraKeys {
+			fmt.Fprintf(&buf, "  %s: %s\n", k, extra[k])
+		}
+	}
+
+	// 2. headers（按真实 Claude CLI wire 顺序排列，便于与抓包对比；auth 脱敏）
+	fmt.Fprint(&buf, "--- headers ---\n")
+	for _, k := range sortHeadersByWireOrder(headers) {
+		for _, v := range headers[k] {
+			fmt.Fprintf(&buf, "  %s: %s\n", k, safeHeaderValueForLog(k, v))
+		}
 	}
 
-	// 提取 metadata 字段完整打印
-	metadataResult := gjson.GetBytes(body, "metadata")
-	if metadataResult.Exists() {
-		logger.LegacyPrintf("service.gateway", "[DEBUG_%s] metadata = %s", tag, metadataResult.Raw)
+	// 3. body（完整输出，格式化 JSON 便于 diff）
+	fmt.Fprint(&buf, "--- body ---\n")
+	if len(body) == 0 {
+		fmt.Fprint(&buf, "  (empty)\n")
 	} else {
-		logger.LegacyPrintf("service.gateway", "[DEBUG_%s] metadata field not found", tag)
+		var pretty bytes.Buffer
+		if json.Indent(&pretty, body, "  ", "  ") == nil {
+			fmt.Fprintf(&buf, "  %s\n", pretty.Bytes())
+		} else {
+			// JSON 格式化失败时原样输出
+			fmt.Fprintf(&buf, "  %s\n", body)
+		}
 	}
 
-	// 全量打印 body
-	logger.LegacyPrintf("service.gateway", "[DEBUG_%s] body (%d bytes) = %s", tag, len(body), string(body))
+	// 写入文件（调试用，并发写入可能交错但不影响可读性）
+	_, _ = f.WriteString(buf.String())
 }

backend/internal/service/header_util.go

+package service
+
+import (
+	"net/http"
+	"strings"
+)
+
+// headerWireCasing 定义每个白名单 header 在真实 Claude CLI 抓包中的准确大小写。
+// Go 的 HTTP server 解析请求时会将所有 header key 转为 Canonical 形式（如 x-app → X-App），
+// 此 map 用于在转发时恢复到真实的 wire format。
+//
+// 来源：对真实 Claude CLI (claude-cli/2.1.81) 到 api.anthropic.com 的 HTTPS 流量抓包。
+var headerWireCasing = map[string]string{
+	// Title case
+	"accept":     "Accept",
+	"user-agent": "User-Agent",
+
+	// X-Stainless-* 保持 SDK 原始大小写
+	"x-stainless-retry-count":     "X-Stainless-Retry-Count",
+	"x-stainless-timeout":         "X-Stainless-Timeout",
+	"x-stainless-lang":            "X-Stainless-Lang",
+	"x-stainless-package-version": "X-Stainless-Package-Version",
+	"x-stainless-os":              "X-Stainless-OS",
+	"x-stainless-arch":            "X-Stainless-Arch",
+	"x-stainless-runtime":         "X-Stainless-Runtime",
+	"x-stainless-runtime-version": "X-Stainless-Runtime-Version",
+	"x-stainless-helper-method":   "x-stainless-helper-method",
+
+	// Anthropic SDK 自身设置的 header，全小写
+	"anthropic-dangerous-direct-browser-access": "anthropic-dangerous-direct-browser-access",
+	"anthropic-version":                         "anthropic-version",
+	"anthropic-beta":                            "anthropic-beta",
+	"x-app":                                     "x-app",
+	"content-type":                              "content-type",
+	"accept-language":                           "accept-language",
+	"sec-fetch-mode":                            "sec-fetch-mode",
+	"accept-encoding":                           "accept-encoding",
+	"authorization":                             "authorization",
+}
+
+// headerWireOrder 定义真实 Claude CLI 发送 header 的顺序（基于抓包）。
+// 用于 debug log 按此顺序输出，便于与抓包结果直接对比。
+var headerWireOrder = []string{
+	"Accept",
+	"X-Stainless-Retry-Count",
+	"X-Stainless-Timeout",
+	"X-Stainless-Lang",
+	"X-Stainless-Package-Version",
+	"X-Stainless-OS",
+	"X-Stainless-Arch",
+	"X-Stainless-Runtime",
+	"X-Stainless-Runtime-Version",
+	"anthropic-dangerous-direct-browser-access",
+	"anthropic-version",
+	"authorization",
+	"x-app",
+	"User-Agent",
+	"content-type",
+	"anthropic-beta",
+	"accept-language",
+	"sec-fetch-mode",
+	"accept-encoding",
+	"x-stainless-helper-method",
+}
+
+// headerWireOrderSet 用于快速判断某个 key 是否在 headerWireOrder 中（按 lowercase 匹配）。
+var headerWireOrderSet map[string]struct{}
+
+func init() {
+	headerWireOrderSet = make(map[string]struct{}, len(headerWireOrder))
+	for _, k := range headerWireOrder {
+		headerWireOrderSet[strings.ToLower(k)] = struct{}{}
+	}
+}
+
+// resolveWireCasing 将 Go canonical key（如 X-Stainless-Os）映射为真实 wire casing（如 X-Stainless-OS）。
+// 如果 map 中没有对应条目，返回原始 key 不变。
+func resolveWireCasing(key string) string {
+	if wk, ok := headerWireCasing[strings.ToLower(key)]; ok {
+		return wk
+	}
+	return key
+}
+
+// setHeaderRaw sets a header bypassing Go's canonical-case normalization.
+// The key is stored exactly as provided, preserving original casing.
+//
+// It first removes any existing value under the canonical key, the wire casing key,
+// and the exact raw key, preventing duplicates from any source.
+func setHeaderRaw(h http.Header, key, value string) {
+	h.Del(key) // remove canonical form (e.g. "Anthropic-Beta")
+	if wk := resolveWireCasing(key); wk != key {
+		delete(h, wk) // remove wire casing form if different
+	}
+	delete(h, key) // remove exact raw key if it differs from canonical
+	h[key] = []string{value}
+}
+
+// addHeaderRaw appends a header value bypassing Go's canonical-case normalization.
+func addHeaderRaw(h http.Header, key, value string) {
+	h[key] = append(h[key], value)
+}
+
+// getHeaderRaw reads a header value, trying multiple key forms to handle the mismatch
+// between Go canonical keys, wire casing keys, and raw keys:
+//  1. exact key as provided
+//  2. wire casing form (from headerWireCasing)
+//  3. Go canonical form (via http.Header.Get)
+func getHeaderRaw(h http.Header, key string) string {
+	// 1. exact key
+	if vals := h[key]; len(vals) > 0 {
+		return vals[0]
+	}
+	// 2. wire casing (e.g. looking up "Anthropic-Dangerous-Direct-Browser-Access" finds "anthropic-dangerous-direct-browser-access")
+	if wk := resolveWireCasing(key); wk != key {
+		if vals := h[wk]; len(vals) > 0 {
+			return vals[0]
+		}
+	}
+	// 3. canonical fallback
+	return h.Get(key)
+}
+
+// sortHeadersByWireOrder 按照真实 Claude CLI 的 header 顺序返回排序后的 key 列表。
+// 在 headerWireOrder 中定义的 key 按其顺序排列，未定义的 key 追加到末尾。
+func sortHeadersByWireOrder(h http.Header) []string {
+	// 构建 lowercase -> actual map key 的映射
+	present := make(map[string]string, len(h))
+	for k := range h {
+		present[strings.ToLower(k)] = k
+	}
+
+	result := make([]string, 0, len(h))
+	seen := make(map[string]struct{}, len(h))
+
+	// 先按 wire order 输出
+	for _, wk := range headerWireOrder {
+		lk := strings.ToLower(wk)
+		if actual, ok := present[lk]; ok {
+			if _, dup := seen[lk]; !dup {
+				result = append(result, actual)
+				seen[lk] = struct{}{}
+			}
+		}
+	}
+
+	// 再追加不在 wire order 中的 header
+	for k := range h {
+		lk := strings.ToLower(k)
+		if _, ok := seen[lk]; !ok {
+			result = append(result, k)
+			seen[lk] = struct{}{}
+		}
+	}
+
+	return result
+}

backend/internal/service/identity_service.go

@@ -174,6 +174,7 @@ func getHeaderOrDefault(headers http.Header, key, defaultValue string) string {
 }
 
 // ApplyFingerprint 将指纹应用到请求头（覆盖原有的x-stainless-*头）
+// 使用 setHeaderRaw 保持原始大小写（如 X-Stainless-OS 而非 X-Stainless-Os）
 func (s *IdentityService) ApplyFingerprint(req *http.Request, fp *Fingerprint) {
 	if fp == nil {
 		return
@@ -181,27 +182,27 @@ func (s *IdentityService) ApplyFingerprint(req *http.Request, fp *Fingerprint) {
 
 	// 设置user-agent
 	if fp.UserAgent != "" {
-		req.Header.Set("user-agent", fp.UserAgent)
+		setHeaderRaw(req.Header, "User-Agent", fp.UserAgent)
 	}
 
-	// 设置x-stainless-*头
+	// 设置x-stainless-*头（保持与 claude.DefaultHeaders 一致的大小写）
 	if fp.StainlessLang != "" {
-		req.Header.Set("X-Stainless-Lang", fp.StainlessLang)
+		setHeaderRaw(req.Header, "X-Stainless-Lang", fp.StainlessLang)
 	}
 	if fp.StainlessPackageVersion != "" {
-		req.Header.Set("X-Stainless-Package-Version", fp.StainlessPackageVersion)
+		setHeaderRaw(req.Header, "X-Stainless-Package-Version", fp.StainlessPackageVersion)
 	}
 	if fp.StainlessOS != "" {
-		req.Header.Set("X-Stainless-OS", fp.StainlessOS)
+		setHeaderRaw(req.Header, "X-Stainless-OS", fp.StainlessOS)
 	}
 	if fp.StainlessArch != "" {
-		req.Header.Set("X-Stainless-Arch", fp.StainlessArch)
+		setHeaderRaw(req.Header, "X-Stainless-Arch", fp.StainlessArch)
 	}
 	if fp.StainlessRuntime != "" {
-		req.Header.Set("X-Stainless-Runtime", fp.StainlessRuntime)
+		setHeaderRaw(req.Header, "X-Stainless-Runtime", fp.StainlessRuntime)
 	}
 	if fp.StainlessRuntimeVersion != "" {
-		req.Header.Set("X-Stainless-Runtime-Version", fp.StainlessRuntimeVersion)
+		setHeaderRaw(req.Header, "X-Stainless-Runtime-Version", fp.StainlessRuntimeVersion)
 	}
 }
 

backend/internal/service/setting_service.go

@@ -79,6 +79,20 @@ const backendModeCacheTTL = 60 * time.Second
 const backendModeErrorTTL = 5 * time.Second
 const backendModeDBTimeout = 5 * time.Second
 
+// cachedGatewayForwardingSettings 缓存网关转发行为设置（进程内缓存，60s TTL）
+type cachedGatewayForwardingSettings struct {
+	fingerprintUnification bool
+	metadataPassthrough    bool
+	expiresAt              int64 // unix nano
+}
+
+var gatewayForwardingCache atomic.Value // *cachedGatewayForwardingSettings
+var gatewayForwardingSF singleflight.Group
+
+const gatewayForwardingCacheTTL = 60 * time.Second
+const gatewayForwardingErrorTTL = 5 * time.Second
+const gatewayForwardingDBTimeout = 5 * time.Second
+
 // DefaultSubscriptionGroupReader validates group references used by default subscriptions.
 type DefaultSubscriptionGroupReader interface {
 	GetByID(ctx context.Context, id int64) (*Group, error)
@@ -510,6 +524,10 @@ func (s *SettingService) UpdateSettings(ctx context.Context, settings *SystemSet
 	// Backend Mode
 	updates[SettingKeyBackendModeEnabled] = strconv.FormatBool(settings.BackendModeEnabled)
 
+	// Gateway forwarding behavior
+	updates[SettingKeyEnableFingerprintUnification] = strconv.FormatBool(settings.EnableFingerprintUnification)
+	updates[SettingKeyEnableMetadataPassthrough] = strconv.FormatBool(settings.EnableMetadataPassthrough)
+
 	err = s.settingRepo.SetMultiple(ctx, updates)
 	if err == nil {
 		// 先使 inflight singleflight 失效，再刷新缓存，缩小旧值覆盖新值的竞态窗口
@@ -524,6 +542,12 @@ func (s *SettingService) UpdateSettings(ctx context.Context, settings *SystemSet
 			value:     settings.BackendModeEnabled,
 			expiresAt: time.Now().Add(backendModeCacheTTL).UnixNano(),
 		})
+		gatewayForwardingSF.Forget("gateway_forwarding")
+		gatewayForwardingCache.Store(&cachedGatewayForwardingSettings{
+			fingerprintUnification: settings.EnableFingerprintUnification,
+			metadataPassthrough:    settings.EnableMetadataPassthrough,
+			expiresAt:              time.Now().Add(gatewayForwardingCacheTTL).UnixNano(),
+		})
 		if s.onUpdate != nil {
 			s.onUpdate() // Invalidate cache after settings update
 		}
@@ -626,6 +650,57 @@ func (s *SettingService) IsBackendModeEnabled(ctx context.Context) bool {
 	return false
 }
 
+// GetGatewayForwardingSettings returns cached gateway forwarding settings.
+// Uses in-process atomic.Value cache with 60s TTL, zero-lock hot path.
+// Returns (fingerprintUnification, metadataPassthrough).
+func (s *SettingService) GetGatewayForwardingSettings(ctx context.Context) (fingerprintUnification, metadataPassthrough bool) {
+	if cached, ok := gatewayForwardingCache.Load().(*cachedGatewayForwardingSettings); ok && cached != nil {
+		if time.Now().UnixNano() < cached.expiresAt {
+			return cached.fingerprintUnification, cached.metadataPassthrough
+		}
+	}
+	type gwfResult struct {
+		fp, mp bool
+	}
+	val, _, _ := gatewayForwardingSF.Do("gateway_forwarding", func() (any, error) {
+		if cached, ok := gatewayForwardingCache.Load().(*cachedGatewayForwardingSettings); ok && cached != nil {
+			if time.Now().UnixNano() < cached.expiresAt {
+				return gwfResult{cached.fingerprintUnification, cached.metadataPassthrough}, nil
+			}
+		}
+		dbCtx, cancel := context.WithTimeout(context.WithoutCancel(ctx), gatewayForwardingDBTimeout)
+		defer cancel()
+		values, err := s.settingRepo.GetMultiple(dbCtx, []string{
+			SettingKeyEnableFingerprintUnification,
+			SettingKeyEnableMetadataPassthrough,
+		})
+		if err != nil {
+			slog.Warn("failed to get gateway forwarding settings", "error", err)
+			gatewayForwardingCache.Store(&cachedGatewayForwardingSettings{
+				fingerprintUnification: true,
+				metadataPassthrough:    false,
+				expiresAt:              time.Now().Add(gatewayForwardingErrorTTL).UnixNano(),
+			})
+			return gwfResult{true, false}, nil
+		}
+		fp := true
+		if v, ok := values[SettingKeyEnableFingerprintUnification]; ok && v != "" {
+			fp = v == "true"
+		}
+		mp := values[SettingKeyEnableMetadataPassthrough] == "true"
+		gatewayForwardingCache.Store(&cachedGatewayForwardingSettings{
+			fingerprintUnification: fp,
+			metadataPassthrough:    mp,
+			expiresAt:              time.Now().Add(gatewayForwardingCacheTTL).UnixNano(),
+		})
+		return gwfResult{fp, mp}, nil
+	})
+	if r, ok := val.(gwfResult); ok {
+		return r.fp, r.mp
+	}
+	return true, false // fail-open defaults
+}
+
 // IsEmailVerifyEnabled 检查是否开启邮件验证
 func (s *SettingService) IsEmailVerifyEnabled(ctx context.Context) bool {
 	value, err := s.settingRepo.GetValue(ctx, SettingKeyEmailVerifyEnabled)
@@ -923,6 +998,14 @@ func (s *SettingService) parseSettings(settings map[string]string) *SystemSettin
 	// 分组隔离
 	result.AllowUngroupedKeyScheduling = settings[SettingKeyAllowUngroupedKeyScheduling] == "true"
 
+	// Gateway forwarding behavior (defaults: fingerprint=true, metadata_passthrough=false)
+	if v, ok := settings[SettingKeyEnableFingerprintUnification]; ok && v != "" {
+		result.EnableFingerprintUnification = v == "true"
+	} else {
+		result.EnableFingerprintUnification = true // default: enabled (current behavior)
+	}
+	result.EnableMetadataPassthrough = settings[SettingKeyEnableMetadataPassthrough] == "true"
+
 	return result
 }
 

backend/internal/service/settings_view.go

@@ -75,6 +75,10 @@ type SystemSettings struct {
 
 	// Backend 模式：禁用用户注册和自助服务，仅管理员可登录
 	BackendModeEnabled bool
+
+	// Gateway forwarding behavior
+	EnableFingerprintUnification bool // 是否统一 OAuth 账号的指纹头（默认 true）
+	EnableMetadataPassthrough    bool // 是否透传客户端原始 metadata（默认 false）
 }
 
 type DefaultSubscriptionSetting struct {

frontend/src/api/admin/settings.ts

@@ -86,6 +86,10 @@ export interface SystemSettings {
 
   // 分组隔离
   allow_ungrouped_key_scheduling: boolean
+
+  // Gateway forwarding behavior
+  enable_fingerprint_unification: boolean
+  enable_metadata_passthrough: boolean
 }
 
 export interface UpdateSettingsRequest {
@@ -142,6 +146,8 @@ export interface UpdateSettingsRequest {
   min_claude_code_version?: string
   max_claude_code_version?: string
   allow_ungrouped_key_scheduling?: boolean
+  enable_fingerprint_unification?: boolean
+  enable_metadata_passthrough?: boolean
 }
 
 /**

frontend/src/i18n/locales/en.ts

@@ -4171,6 +4171,14 @@ export default {
         allowUngroupedKey: 'Allow Ungrouped Key Scheduling',
         allowUngroupedKeyHint: 'When disabled, API Keys not assigned to any group cannot make requests (403 Forbidden). Keep disabled to ensure all Keys belong to a specific group.'
       },
+      gatewayForwarding: {
+        title: 'Request Forwarding',
+        description: 'Control how requests are forwarded to upstream OAuth accounts',
+        fingerprintUnification: 'Fingerprint Unification',
+        fingerprintUnificationHint: 'Unify X-Stainless-* headers across users sharing the same OAuth account. Disabling passes through each client\'s original headers.',
+        metadataPassthrough: 'Metadata Passthrough',
+        metadataPassthroughHint: 'Pass through client\'s original metadata.user_id without rewriting. May improve upstream cache hit rates.',
+      },
       site: {
         title: 'Site Settings',
         description: 'Customize site branding',

frontend/src/i18n/locales/zh.ts

@@ -4334,6 +4334,14 @@ export default {
         allowUngroupedKey: '允许未分组 Key 调度',
         allowUngroupedKeyHint: '关闭后，未分配到任何分组的 API Key 将无法发起请求（返回 403）。建议保持关闭以确保所有 Key 都归属明确的分组。'
       },
+      gatewayForwarding: {
+        title: '请求转发行为',
+        description: '控制请求转发到上游 OAuth 账号时的行为',
+        fingerprintUnification: '指纹统一化',
+        fingerprintUnificationHint: '统一共享同一 OAuth 账号的用户的 X-Stainless-* 请求头。关闭后透传客户端原始请求头。',
+        metadataPassthrough: 'Metadata 透传',
+        metadataPassthroughHint: '透传客户端原始 metadata.user_id，不进行重写。可能提高上游缓存命中率。',
+      },
       site: {
         title: '站点设置',
         description: '自定义站点品牌',

frontend/src/views/admin/SettingsView.vue

@@ -1171,6 +1171,45 @@
             </div>
           </div>
         </div>
+
+        <!-- Gateway Forwarding Behavior -->
+        <div class="card">
+          <div class="border-b border-gray-100 px-6 py-4 dark:border-dark-700">
+            <h2 class="text-lg font-semibold text-gray-900 dark:text-white">
+              {{ t('admin.settings.gatewayForwarding.title') }}
+            </h2>
+            <p class="mt-1 text-sm text-gray-500 dark:text-gray-400">
+              {{ t('admin.settings.gatewayForwarding.description') }}
+            </p>
+          </div>
+          <div class="space-y-5 p-6">
+            <!-- Fingerprint Unification -->
+            <div class="flex items-center justify-between">
+              <div>
+                <label class="text-sm font-medium text-gray-700 dark:text-gray-300">
+                  {{ t('admin.settings.gatewayForwarding.fingerprintUnification') }}
+                </label>
+                <p class="mt-0.5 text-xs text-gray-500 dark:text-gray-400">
+                  {{ t('admin.settings.gatewayForwarding.fingerprintUnificationHint') }}
+                </p>
+              </div>
+              <Toggle v-model="form.enable_fingerprint_unification" />
+            </div>
+
+            <!-- Metadata Passthrough -->
+            <div class="flex items-center justify-between">
+              <div>
+                <label class="text-sm font-medium text-gray-700 dark:text-gray-300">
+                  {{ t('admin.settings.gatewayForwarding.metadataPassthrough') }}
+                </label>
+                <p class="mt-0.5 text-xs text-gray-500 dark:text-gray-400">
+                  {{ t('admin.settings.gatewayForwarding.metadataPassthroughHint') }}
+                </p>
+              </div>
+              <Toggle v-model="form.enable_metadata_passthrough" />
+            </div>
+          </div>
+        </div>
         </div><!-- /Tab: Gateway — Claude Code, Scheduling -->
 
         <!-- Tab: General -->
@@ -2066,7 +2105,10 @@ const form = reactive<SettingsForm>({
   min_claude_code_version: '',
   max_claude_code_version: '',
   // 分组隔离
-  allow_ungrouped_key_scheduling: false
+  allow_ungrouped_key_scheduling: false,
+  // Gateway forwarding behavior
+  enable_fingerprint_unification: true,
+  enable_metadata_passthrough: false
 })
 
 const defaultSubscriptionGroupOptions = computed<DefaultSubscriptionGroupOption[]>(() =>
@@ -2373,7 +2415,9 @@ async function saveSettings() {
       identity_patch_prompt: form.identity_patch_prompt,
       min_claude_code_version: form.min_claude_code_version,
       max_claude_code_version: form.max_claude_code_version,
-      allow_ungrouped_key_scheduling: form.allow_ungrouped_key_scheduling
+      allow_ungrouped_key_scheduling: form.allow_ungrouped_key_scheduling,
+      enable_fingerprint_unification: form.enable_fingerprint_unification,
+      enable_metadata_passthrough: form.enable_metadata_passthrough
     }
     const updated = await adminAPI.settings.updateSettings(payload)
     Object.assign(form, updated)