feat(upstream): passthrough all client headers instead of manual header setting

Replace manual header setting (Content-Type, anthropic-version, anthropic-beta)
with full client header passthrough in ForwardUpstream/ForwardUpstreamGemini.
Only authentication headers (Authorization, x-api-key) are overridden with
upstream account credentials. Hop-by-hop headers are excluded.

Add unit tests covering header passthrough, auth override, and hop-by-hop filtering.

backend/internal/service/antigravity_gateway_service.go

@@ -47,6 +47,21 @@ const (
 	googleRPCReasonRateLimitExceeded      = "RATE_LIMIT_EXCEEDED"
 )
 
+// upstreamHopByHopHeaders 透传请求头时需要排除的 hop-by-hop 头
+var upstreamHopByHopHeaders = map[string]bool{
+	"connection":          true,
+	"keep-alive":          true,
+	"proxy-authenticate":  true,
+	"proxy-authorization": true,
+	"proxy-connection":    true,
+	"te":                  true,
+	"trailer":             true,
+	"transfer-encoding":   true,
+	"upgrade":             true,
+	"host":                true,
+	"content-length":      true,
+}
+
 // antigravityPassthroughErrorMessages 透传给客户端的错误消息白名单（小写）
 // 匹配时使用 strings.Contains，无需完全匹配
 var antigravityPassthroughErrorMessages = []string{
@@ -3456,10 +3471,6 @@ func (s *AntigravityGatewayService) ForwardUpstream(ctx context.Context, c *gin.
 	if mappedModel == "" {
 		return nil, s.writeClaudeError(c, http.StatusForbidden, "permission_error", fmt.Sprintf("model %s not in whitelist", claudeReq.Model))
 	}
-	loadModel := mappedModel
-	thinkingEnabled := claudeReq.Thinking != nil && claudeReq.Thinking.Type == "enabled"
-	mappedModel = applyThinkingModelSuffix(mappedModel, thinkingEnabled)
-	quotaScope, _ := resolveAntigravityQuotaScope(originalModel)
 
 	// 代理 URL
 	proxyURL := ""
@@ -3469,98 +3480,38 @@ func (s *AntigravityGatewayService) ForwardUpstream(ctx context.Context, c *gin.
 
 	// 统计模型调用次数
 	if s.cache != nil {
-		_, _ = s.cache.IncrModelCallCount(ctx, account.ID, loadModel)
+		_, _ = s.cache.IncrModelCallCount(ctx, account.ID, mappedModel)
 	}
 
 	apiURL := baseURL + "/antigravity/v1/messages"
 	log.Printf("%s upstream_forward url=%s model=%s", prefix, apiURL, mappedModel)
 
-	// 预检查：模型级限流
-	if remaining := account.GetRateLimitRemainingTimeWithContext(ctx, originalModel); remaining > 0 {
-		if remaining < antigravityRateLimitThreshold {
-			select {
-			case <-ctx.Done():
-				return nil, ctx.Err()
-			case <-time.After(remaining):
-			}
-		} else {
-			return nil, &UpstreamFailoverError{
-				StatusCode:        http.StatusServiceUnavailable,
-				ForceCacheBilling: isStickySession,
-			}
+	// 构建请求：body 原样透传
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, apiURL, bytes.NewReader(body))
+	if err != nil {
+		return nil, s.writeClaudeError(c, http.StatusInternalServerError, "api_error", "Failed to build request")
+	}
+	// 透传客户端所有请求头（排除 hop-by-hop 和认证头）
+	for key, values := range c.Request.Header {
+		if upstreamHopByHopHeaders[strings.ToLower(key)] {
+			continue
+		}
+		for _, v := range values {
+			req.Header.Add(key, v)
 		}
 	}
+	// 覆盖认证头
+	req.Header.Set("Authorization", "Bearer "+apiKey)
+	req.Header.Set("x-api-key", apiKey)
 
-	// 重试循环
-	var resp *http.Response
-	var lastErr error
-	for attempt := 1; attempt <= antigravityMaxRetries; attempt++ {
-		select {
-		case <-ctx.Done():
-			return nil, ctx.Err()
-		default:
-		}
-
-		req, err := http.NewRequestWithContext(ctx, http.MethodPost, apiURL, bytes.NewReader(body))
-		if err != nil {
-			return nil, s.writeClaudeError(c, http.StatusInternalServerError, "api_error", "Failed to build request")
-		}
-		req.Header.Set("Content-Type", "application/json")
-		req.Header.Set("Authorization", "Bearer "+apiKey)
-		req.Header.Set("x-api-key", apiKey)
-
-		// 透传 anthropic headers
-		if v := c.GetHeader("anthropic-version"); v != "" {
-			req.Header.Set("anthropic-version", v)
-		} else {
-			req.Header.Set("anthropic-version", "2023-06-01")
-		}
-		if v := c.GetHeader("anthropic-beta"); v != "" {
-			req.Header.Set("anthropic-beta", v)
-		}
-
-		if c != nil && len(body) > 0 {
-			c.Set(OpsUpstreamRequestBodyKey, string(body))
-		}
-
-		resp, err = s.httpUpstream.Do(req, proxyURL, account.ID, account.Concurrency)
-		if err != nil {
-			lastErr = err
-			if attempt < antigravityMaxRetries {
-				log.Printf("%s status=request_failed retry=%d/%d error=%v", prefix, attempt, antigravityMaxRetries, err)
-				if !sleepAntigravityBackoffWithContext(ctx, attempt) {
-					return nil, ctx.Err()
-				}
-				continue
-			}
-			return nil, s.writeClaudeError(c, http.StatusBadGateway, "upstream_error", "Upstream request failed after retries")
-		}
-
-		// 429/503 重试
-		if resp.StatusCode == http.StatusTooManyRequests || resp.StatusCode == http.StatusServiceUnavailable {
-			respBody, _ := io.ReadAll(io.LimitReader(resp.Body, 2<<20))
-			_ = resp.Body.Close()
-
-			s.handleUpstreamError(ctx, prefix, account, resp.StatusCode, resp.Header, respBody, quotaScope, 0, "", isStickySession)
-
-			if attempt < antigravityMaxRetries {
-				log.Printf("%s status=%d retry=%d/%d body=%s", prefix, resp.StatusCode, attempt, antigravityMaxRetries, truncateForLog(respBody, 200))
-				if !sleepAntigravityBackoffWithContext(ctx, attempt) {
-					return nil, ctx.Err()
-				}
-				continue
-			}
-
-			return nil, &UpstreamFailoverError{
-				StatusCode:        resp.StatusCode,
-				ForceCacheBilling: isStickySession,
-			}
-		}
-
-		break // 成功或非限流错误，跳出重试
+	if c != nil && len(body) > 0 {
+		c.Set(OpsUpstreamRequestBodyKey, string(body))
 	}
-	if resp == nil {
-		return nil, s.writeClaudeError(c, http.StatusBadGateway, "upstream_error", fmt.Sprintf("upstream request failed: %v", lastErr))
+
+	// 单次发送，不重试
+	resp, err := s.httpUpstream.Do(req, proxyURL, account.ID, account.Concurrency)
+	if err != nil {
+		return nil, s.writeClaudeError(c, http.StatusBadGateway, "upstream_error", fmt.Sprintf("Upstream request failed: %v", err))
 	}
 	defer func() { _ = resp.Body.Close() }()
 
@@ -3568,44 +3519,7 @@ func (s *AntigravityGatewayService) ForwardUpstream(ctx context.Context, c *gin.
 	if resp.StatusCode >= 400 {
 		respBody, _ := io.ReadAll(io.LimitReader(resp.Body, 2<<20))
 
-		// signature 重试
-		if resp.StatusCode == http.StatusBadRequest && isSignatureRelatedError(respBody) {
-			log.Printf("%s upstream signature error, retrying with thinking stripped", prefix)
-			retryClaudeReq := claudeReq
-			retryClaudeReq.Messages = append([]antigravity.ClaudeMessage(nil), claudeReq.Messages...)
-			if stripped, stripErr := stripThinkingFromClaudeRequest(&retryClaudeReq); stripErr == nil && stripped {
-				retryBody, _ := json.Marshal(&retryClaudeReq)
-				retryReq, err := http.NewRequestWithContext(ctx, http.MethodPost, apiURL, bytes.NewReader(retryBody))
-				if err == nil {
-					retryReq.Header.Set("Content-Type", "application/json")
-					retryReq.Header.Set("Authorization", "Bearer "+apiKey)
-					retryReq.Header.Set("x-api-key", apiKey)
-					retryReq.Header.Set("anthropic-version", "2023-06-01")
-					if v := c.GetHeader("anthropic-beta"); v != "" {
-						retryReq.Header.Set("anthropic-beta", v)
-					}
-					retryResp, retryErr := s.httpUpstream.Do(retryReq, proxyURL, account.ID, account.Concurrency)
-					if retryErr == nil && retryResp != nil && retryResp.StatusCode < 400 {
-						resp = retryResp
-						goto upstreamClaudeSuccess
-					}
-					if retryResp != nil {
-						_ = retryResp.Body.Close()
-					}
-				}
-			}
-		}
-
-		// prompt too long
-		if resp.StatusCode == http.StatusBadRequest && isPromptTooLongError(respBody) {
-			return nil, &PromptTooLongError{
-				StatusCode: resp.StatusCode,
-				RequestID:  resp.Header.Get("x-request-id"),
-				Body:       respBody,
-			}
-		}
-
-		s.handleUpstreamError(ctx, prefix, account, resp.StatusCode, resp.Header, respBody, quotaScope, 0, "", isStickySession)
+		s.handleUpstreamError(ctx, prefix, account, resp.StatusCode, resp.Header, respBody, "", 0, "", isStickySession)
 
 		if s.shouldFailoverUpstreamError(resp.StatusCode) {
 			return nil, &UpstreamFailoverError{StatusCode: resp.StatusCode, ResponseBody: respBody}
@@ -3614,7 +3528,7 @@ func (s *AntigravityGatewayService) ForwardUpstream(ctx context.Context, c *gin.
 		return nil, s.writeMappedClaudeError(c, account, resp.StatusCode, resp.Header.Get("x-request-id"), respBody)
 	}
 
-upstreamClaudeSuccess:
+	// 成功响应
 	requestID := resp.Header.Get("x-request-id")
 	if requestID != "" {
 		c.Header("x-request-id", requestID)
@@ -3674,7 +3588,6 @@ func (s *AntigravityGatewayService) ForwardUpstreamGemini(ctx context.Context, c
 	if len(body) == 0 {
 		return nil, s.writeGoogleError(c, http.StatusBadRequest, "Request body is empty")
 	}
-	quotaScope, _ := resolveAntigravityQuotaScope(originalModel)
 
 	imageSize := s.extractImageSize(body)
 
@@ -3712,143 +3625,52 @@ func (s *AntigravityGatewayService) ForwardUpstreamGemini(ctx context.Context, c
 	}
 
 	// 构建 upstream URL: base_url + /antigravity/v1beta/models/MODEL:ACTION
-	upstreamAction := action
-	if action == "generateContent" && !stream {
-		// 非流式也用 streamGenerateContent，与 OAuth 路径行为一致
-		upstreamAction = action
-	}
-	apiURL := fmt.Sprintf("%s/antigravity/v1beta/models/%s:%s", baseURL, mappedModel, upstreamAction)
-	if stream || upstreamAction == "streamGenerateContent" {
+	apiURL := fmt.Sprintf("%s/antigravity/v1beta/models/%s:%s", baseURL, mappedModel, action)
+	if stream || action == "streamGenerateContent" {
 		apiURL += "?alt=sse"
 	}
 
-	log.Printf("%s upstream_forward_gemini url=%s model=%s action=%s", prefix, apiURL, mappedModel, upstreamAction)
+	log.Printf("%s upstream_forward_gemini url=%s model=%s action=%s", prefix, apiURL, mappedModel, action)
 
-	// 预检查：模型级限流
-	if remaining := account.GetRateLimitRemainingTimeWithContext(ctx, originalModel); remaining > 0 {
-		if remaining < antigravityRateLimitThreshold {
-			select {
-			case <-ctx.Done():
-				return nil, ctx.Err()
-			case <-time.After(remaining):
-			}
-		} else {
-			return nil, &UpstreamFailoverError{
-				StatusCode:        http.StatusServiceUnavailable,
-				ForceCacheBilling: isStickySession,
-			}
+	// 构建请求：body 原样透传
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, apiURL, bytes.NewReader(body))
+	if err != nil {
+		return nil, s.writeGoogleError(c, http.StatusInternalServerError, "Failed to build request")
+	}
+	// 透传客户端所有请求头（排除 hop-by-hop 和认证头）
+	for key, values := range c.Request.Header {
+		if upstreamHopByHopHeaders[strings.ToLower(key)] {
+			continue
+		}
+		for _, v := range values {
+			req.Header.Add(key, v)
 		}
 	}
+	// 覆盖认证头
+	req.Header.Set("Authorization", "Bearer "+apiKey)
 
-	// 重试循环
-	var resp *http.Response
-	var lastErr error
-	for attempt := 1; attempt <= antigravityMaxRetries; attempt++ {
-		select {
-		case <-ctx.Done():
-			return nil, ctx.Err()
-		default:
-		}
-
-		req, err := http.NewRequestWithContext(ctx, http.MethodPost, apiURL, bytes.NewReader(body))
-		if err != nil {
-			return nil, s.writeGoogleError(c, http.StatusInternalServerError, "Failed to build request")
-		}
-		req.Header.Set("Content-Type", "application/json")
-		req.Header.Set("Authorization", "Bearer "+apiKey)
-
-		if c != nil && len(body) > 0 {
-			c.Set(OpsUpstreamRequestBodyKey, string(body))
-		}
-
-		resp, err = s.httpUpstream.Do(req, proxyURL, account.ID, account.Concurrency)
-		if err != nil {
-			lastErr = err
-			if attempt < antigravityMaxRetries {
-				log.Printf("%s status=request_failed retry=%d/%d error=%v", prefix, attempt, antigravityMaxRetries, err)
-				if !sleepAntigravityBackoffWithContext(ctx, attempt) {
-					return nil, ctx.Err()
-				}
-				continue
-			}
-			return nil, s.writeGoogleError(c, http.StatusBadGateway, "Upstream request failed after retries")
-		}
-
-		// 429/503 重试
-		if resp.StatusCode == http.StatusTooManyRequests || resp.StatusCode == http.StatusServiceUnavailable {
-			respBody, _ := io.ReadAll(io.LimitReader(resp.Body, 2<<20))
-			_ = resp.Body.Close()
-
-			s.handleUpstreamError(ctx, prefix, account, resp.StatusCode, resp.Header, respBody, quotaScope, 0, "", isStickySession)
-
-			if attempt < antigravityMaxRetries {
-				log.Printf("%s status=%d retry=%d/%d body=%s", prefix, resp.StatusCode, attempt, antigravityMaxRetries, truncateForLog(respBody, 200))
-				if !sleepAntigravityBackoffWithContext(ctx, attempt) {
-					return nil, ctx.Err()
-				}
-				continue
-			}
-
-			return nil, &UpstreamFailoverError{
-				StatusCode:        resp.StatusCode,
-				ForceCacheBilling: isStickySession,
-			}
-		}
-
-		break
+	if c != nil && len(body) > 0 {
+		c.Set(OpsUpstreamRequestBodyKey, string(body))
 	}
-	if resp == nil {
-		return nil, s.writeGoogleError(c, http.StatusBadGateway, fmt.Sprintf("upstream request failed: %v", lastErr))
+
+	// 单次发送，不重试
+	resp, err := s.httpUpstream.Do(req, proxyURL, account.ID, account.Concurrency)
+	if err != nil {
+		return nil, s.writeGoogleError(c, http.StatusBadGateway, fmt.Sprintf("Upstream request failed: %v", err))
 	}
-	defer func() {
-		if resp != nil && resp.Body != nil {
-			_ = resp.Body.Close()
-		}
-	}()
+	defer func() { _ = resp.Body.Close() }()
 
 	// 错误响应处理
 	if resp.StatusCode >= 400 {
 		respBody, _ := io.ReadAll(io.LimitReader(resp.Body, 2<<20))
 		contentType := resp.Header.Get("Content-Type")
-		_ = resp.Body.Close()
-		resp.Body = io.NopCloser(bytes.NewReader(respBody))
-
-		// 模型兜底
-		if s.settingService != nil && s.settingService.IsModelFallbackEnabled(ctx) &&
-			isModelNotFoundError(resp.StatusCode, respBody) {
-			fallbackModel := s.settingService.GetFallbackModel(ctx, PlatformAntigravity)
-			if fallbackModel != "" && fallbackModel != mappedModel {
-				log.Printf("[Antigravity-Upstream] Model not found (%s), retrying with fallback model %s (account: %s)", mappedModel, fallbackModel, account.Name)
-				fallbackURL := fmt.Sprintf("%s/antigravity/v1beta/models/%s:%s", baseURL, fallbackModel, upstreamAction)
-				if stream || upstreamAction == "streamGenerateContent" {
-					fallbackURL += "?alt=sse"
-				}
-				fallbackReq, err := http.NewRequestWithContext(ctx, http.MethodPost, fallbackURL, bytes.NewReader(body))
-				if err == nil {
-					fallbackReq.Header.Set("Content-Type", "application/json")
-					fallbackReq.Header.Set("Authorization", "Bearer "+apiKey)
-					fallbackResp, err := s.httpUpstream.Do(fallbackReq, proxyURL, account.ID, account.Concurrency)
-					if err == nil && fallbackResp.StatusCode < 400 {
-						_ = resp.Body.Close()
-						resp = fallbackResp
-					} else if fallbackResp != nil {
-						_ = fallbackResp.Body.Close()
-					}
-				}
-			}
-		}
-
-		// fallback 成功
-		if resp.StatusCode < 400 {
-			goto upstreamGeminiSuccess
-		}
 
 		requestID := resp.Header.Get("x-request-id")
 		if requestID != "" {
 			c.Header("x-request-id", requestID)
 		}
 
-		s.handleUpstreamError(ctx, prefix, account, resp.StatusCode, resp.Header, respBody, quotaScope, 0, "", isStickySession)
+		s.handleUpstreamError(ctx, prefix, account, resp.StatusCode, resp.Header, respBody, "", 0, "", isStickySession)
 		upstreamMsg := strings.TrimSpace(extractAntigravityErrorMessage(respBody))
 		upstreamMsg = sanitizeUpstreamErrorMessage(upstreamMsg)
 		upstreamDetail := s.getUpstreamErrorDetail(respBody)
@@ -3886,7 +3708,7 @@ func (s *AntigravityGatewayService) ForwardUpstreamGemini(ctx context.Context, c
 		return nil, fmt.Errorf("antigravity upstream error: %d", resp.StatusCode)
 	}
 
-upstreamGeminiSuccess:
+	// 成功响应
 	requestID := resp.Header.Get("x-request-id")
 	if requestID != "" {
 		c.Header("x-request-id", requestID)

backend/internal/service/upstream_header_passthrough_test.go

@@ -0,0 +1,285 @@
+//go:build unit
+
+package service
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/gin-gonic/gin"
+	"github.com/stretchr/testify/require"
+)
+
+// httpUpstreamCapture captures the outgoing *http.Request for assertion.
+type httpUpstreamCapture struct {
+	capturedReq *http.Request
+	resp        *http.Response
+	err         error
+}
+
+func (s *httpUpstreamCapture) Do(req *http.Request, _ string, _ int64, _ int) (*http.Response, error) {
+	s.capturedReq = req
+	return s.resp, s.err
+}
+
+func (s *httpUpstreamCapture) DoWithTLS(req *http.Request, _ string, _ int64, _ int, _ bool) (*http.Response, error) {
+	s.capturedReq = req
+	return s.resp, s.err
+}
+
+func newUpstreamAccount() *Account {
+	return &Account{
+		ID:          100,
+		Name:        "upstream-test",
+		Platform:    PlatformAntigravity,
+		Type:        AccountTypeUpstream,
+		Status:      StatusActive,
+		Concurrency: 1,
+		Credentials: map[string]any{
+			"base_url": "https://upstream.example.com",
+			"api_key":  "sk-upstream-secret",
+		},
+	}
+}
+
+// makeSSEOKResponse builds a minimal SSE response that
+// handleClaudeStreamingResponse / handleGeminiStreamingResponse
+// can consume without error.
+// We return 502 to bypass streaming and hit the error branch instead,
+// which is sufficient for testing header passthrough.
+func makeUpstreamErrorResponse() *http.Response {
+	body := []byte(`{"error":{"message":"test error"}}`)
+	return &http.Response{
+		StatusCode: http.StatusBadGateway,
+		Header:     http.Header{"Content-Type": []string{"application/json"}},
+		Body:       io.NopCloser(bytes.NewReader(body)),
+	}
+}
+
+// --- ForwardUpstream tests ---
+
+func TestForwardUpstream_PassthroughHeaders(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+
+	body, _ := json.Marshal(map[string]any{
+		"model":      "claude-sonnet-4-5",
+		"messages":   []map[string]any{{"role": "user", "content": "hi"}},
+		"max_tokens": 1,
+		"stream":     false,
+	})
+
+	req := httptest.NewRequest(http.MethodPost, "/v1/messages", bytes.NewReader(body))
+	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("anthropic-version", "2024-10-22")
+	req.Header.Set("anthropic-beta", "output-128k-2025-02-19")
+	req.Header.Set("X-Custom-Header", "custom-value")
+	c.Request = req
+
+	stub := &httpUpstreamCapture{resp: makeUpstreamErrorResponse()}
+	svc := &AntigravityGatewayService{
+		tokenProvider: &AntigravityTokenProvider{},
+		httpUpstream:  stub,
+	}
+
+	_, _ = svc.ForwardUpstream(context.Background(), c, newUpstreamAccount(), body, false)
+
+	captured := stub.capturedReq
+	require.NotNil(t, captured, "upstream request should have been made")
+
+	// 客户端 header 应被透传
+	require.Equal(t, "application/json", captured.Header.Get("Content-Type"))
+	require.Equal(t, "2024-10-22", captured.Header.Get("anthropic-version"))
+	require.Equal(t, "output-128k-2025-02-19", captured.Header.Get("anthropic-beta"))
+	require.Equal(t, "custom-value", captured.Header.Get("X-Custom-Header"))
+}
+
+func TestForwardUpstream_OverridesAuthHeaders(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+
+	body, _ := json.Marshal(map[string]any{
+		"model":      "claude-sonnet-4-5",
+		"messages":   []map[string]any{{"role": "user", "content": "hi"}},
+		"max_tokens": 1,
+		"stream":     false,
+	})
+
+	req := httptest.NewRequest(http.MethodPost, "/v1/messages", bytes.NewReader(body))
+	req.Header.Set("Content-Type", "application/json")
+	// 客户端发来的认证头应被覆盖
+	req.Header.Set("Authorization", "Bearer client-token")
+	req.Header.Set("x-api-key", "client-api-key")
+	c.Request = req
+
+	stub := &httpUpstreamCapture{resp: makeUpstreamErrorResponse()}
+	svc := &AntigravityGatewayService{
+		tokenProvider: &AntigravityTokenProvider{},
+		httpUpstream:  stub,
+	}
+
+	_, _ = svc.ForwardUpstream(context.Background(), c, newUpstreamAccount(), body, false)
+
+	captured := stub.capturedReq
+	require.NotNil(t, captured)
+
+	// 认证头应使用上游账号的 api_key，而非客户端的
+	require.Equal(t, "Bearer sk-upstream-secret", captured.Header.Get("Authorization"))
+	require.Equal(t, "sk-upstream-secret", captured.Header.Get("x-api-key"))
+}
+
+func TestForwardUpstream_ExcludesHopByHopHeaders(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+
+	body, _ := json.Marshal(map[string]any{
+		"model":      "claude-sonnet-4-5",
+		"messages":   []map[string]any{{"role": "user", "content": "hi"}},
+		"max_tokens": 1,
+		"stream":     false,
+	})
+
+	req := httptest.NewRequest(http.MethodPost, "/v1/messages", bytes.NewReader(body))
+	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("Connection", "keep-alive")
+	req.Header.Set("Keep-Alive", "timeout=5")
+	req.Header.Set("Transfer-Encoding", "chunked")
+	req.Header.Set("Upgrade", "websocket")
+	req.Header.Set("Te", "trailers")
+	c.Request = req
+
+	stub := &httpUpstreamCapture{resp: makeUpstreamErrorResponse()}
+	svc := &AntigravityGatewayService{
+		tokenProvider: &AntigravityTokenProvider{},
+		httpUpstream:  stub,
+	}
+
+	_, _ = svc.ForwardUpstream(context.Background(), c, newUpstreamAccount(), body, false)
+
+	captured := stub.capturedReq
+	require.NotNil(t, captured)
+
+	// hop-by-hop header 不应出现
+	require.Empty(t, captured.Header.Get("Connection"))
+	require.Empty(t, captured.Header.Get("Keep-Alive"))
+	require.Empty(t, captured.Header.Get("Transfer-Encoding"))
+	require.Empty(t, captured.Header.Get("Upgrade"))
+	require.Empty(t, captured.Header.Get("Te"))
+
+	// 但普通 header 应保留
+	require.Equal(t, "application/json", captured.Header.Get("Content-Type"))
+}
+
+// --- ForwardUpstreamGemini tests ---
+
+func TestForwardUpstreamGemini_PassthroughHeaders(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+
+	body, _ := json.Marshal(map[string]any{
+		"contents": []map[string]any{
+			{"role": "user", "parts": []map[string]any{{"text": "hi"}}},
+		},
+	})
+
+	req := httptest.NewRequest(http.MethodPost, "/v1beta/models/gemini-2.5-flash:generateContent", bytes.NewReader(body))
+	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("X-Custom-Gemini", "gemini-value")
+	req.Header.Set("X-Request-Id", "req-abc-123")
+	c.Request = req
+
+	stub := &httpUpstreamCapture{resp: makeUpstreamErrorResponse()}
+	svc := &AntigravityGatewayService{
+		tokenProvider: &AntigravityTokenProvider{},
+		httpUpstream:  stub,
+	}
+
+	_, _ = svc.ForwardUpstreamGemini(context.Background(), c, newUpstreamAccount(), "gemini-2.5-flash", "generateContent", false, body, false)
+
+	captured := stub.capturedReq
+	require.NotNil(t, captured, "upstream request should have been made")
+
+	// 客户端 header 应被透传
+	require.Equal(t, "application/json", captured.Header.Get("Content-Type"))
+	require.Equal(t, "gemini-value", captured.Header.Get("X-Custom-Gemini"))
+	require.Equal(t, "req-abc-123", captured.Header.Get("X-Request-Id"))
+}
+
+func TestForwardUpstreamGemini_OverridesAuthHeaders(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+
+	body, _ := json.Marshal(map[string]any{
+		"contents": []map[string]any{
+			{"role": "user", "parts": []map[string]any{{"text": "hi"}}},
+		},
+	})
+
+	req := httptest.NewRequest(http.MethodPost, "/v1beta/models/gemini-2.5-flash:generateContent", bytes.NewReader(body))
+	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("Authorization", "Bearer client-gemini-token")
+	c.Request = req
+
+	stub := &httpUpstreamCapture{resp: makeUpstreamErrorResponse()}
+	svc := &AntigravityGatewayService{
+		tokenProvider: &AntigravityTokenProvider{},
+		httpUpstream:  stub,
+	}
+
+	_, _ = svc.ForwardUpstreamGemini(context.Background(), c, newUpstreamAccount(), "gemini-2.5-flash", "generateContent", false, body, false)
+
+	captured := stub.capturedReq
+	require.NotNil(t, captured)
+
+	// 认证头应使用上游账号的 api_key
+	require.Equal(t, "Bearer sk-upstream-secret", captured.Header.Get("Authorization"))
+}
+
+func TestForwardUpstreamGemini_ExcludesHopByHopHeaders(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+
+	body, _ := json.Marshal(map[string]any{
+		"contents": []map[string]any{
+			{"role": "user", "parts": []map[string]any{{"text": "hi"}}},
+		},
+	})
+
+	req := httptest.NewRequest(http.MethodPost, "/v1beta/models/gemini-2.5-flash:generateContent", bytes.NewReader(body))
+	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("Connection", "keep-alive")
+	req.Header.Set("Proxy-Authorization", "Basic dXNlcjpwYXNz")
+	req.Header.Set("Host", "evil.example.com")
+	c.Request = req
+
+	stub := &httpUpstreamCapture{resp: makeUpstreamErrorResponse()}
+	svc := &AntigravityGatewayService{
+		tokenProvider: &AntigravityTokenProvider{},
+		httpUpstream:  stub,
+	}
+
+	_, _ = svc.ForwardUpstreamGemini(context.Background(), c, newUpstreamAccount(), "gemini-2.5-flash", "generateContent", false, body, false)
+
+	captured := stub.capturedReq
+	require.NotNil(t, captured)
+
+	// hop-by-hop header 不应出现
+	require.Empty(t, captured.Header.Get("Connection"))
+	require.Empty(t, captured.Header.Get("Proxy-Authorization"))
+	// Host header 在 Go http.Request 中特殊处理，但我们的黑名单应阻止透传
+	require.Empty(t, captured.Header.Values("Host"))
+
+	// 普通 header 应保留
+	require.Equal(t, "application/json", captured.Header.Get("Content-Type"))
+}