feat(antigravity): 转发与测试支持daily/prod单URL切换

backend/internal/service/antigravity_gateway_service.go

@@ -70,6 +70,7 @@ var antigravityPassthroughErrorMessages = []string{
 
 const (
 	antigravityBillingModelEnv    = "GATEWAY_ANTIGRAVITY_BILL_WITH_MAPPED_MODEL"
+	antigravityForwardBaseURLEnv  = "GATEWAY_ANTIGRAVITY_FORWARD_BASE_URL"
 	antigravityFallbackSecondsEnv = "GATEWAY_ANTIGRAVITY_FALLBACK_COOLDOWN_SECONDS"
 )
 
@@ -131,6 +132,20 @@ type antigravityRetryLoopResult struct {
 	resp *http.Response
 }
 
+// resolveAntigravityForwardBaseURL 解析转发用 base URL。
+// 默认使用 daily（ForwardBaseURLs 的首个地址）；当环境变量为 prod 时使用第二个地址。
+func resolveAntigravityForwardBaseURL() string {
+	baseURLs := antigravity.ForwardBaseURLs()
+	if len(baseURLs) == 0 {
+		return ""
+	}
+	mode := strings.ToLower(strings.TrimSpace(os.Getenv(antigravityForwardBaseURLEnv)))
+	if mode == "prod" && len(baseURLs) > 1 {
+		return baseURLs[1]
+	}
+	return baseURLs[0]
+}
+
 // smartRetryAction 智能重试的处理结果
 type smartRetryAction int
 
@@ -466,10 +481,11 @@ func (s *AntigravityGatewayService) antigravityRetryLoop(p antigravityRetryLoopP
 		}
 	}
 
-	availableURLs := antigravity.DefaultURLAvailability.GetAvailableURLs()
-	if len(availableURLs) == 0 {
-		availableURLs = antigravity.BaseURLs
+	baseURL := resolveAntigravityForwardBaseURL()
+	if baseURL == "" {
+		return nil, errors.New("no antigravity forward base url configured")
 	}
+	availableURLs := []string{baseURL}
 
 	var resp *http.Response
 	var usedBaseURL string
@@ -907,11 +923,11 @@ func (s *AntigravityGatewayService) TestConnection(ctx context.Context, account
 		proxyURL = account.Proxy.URL()
 	}
 
-	// URL fallback 循环
-	availableURLs := antigravity.DefaultURLAvailability.GetAvailableURLs()
-	if len(availableURLs) == 0 {
-		availableURLs = antigravity.BaseURLs // 所有 URL 都不可用时，重试所有
+	baseURL := resolveAntigravityForwardBaseURL()
+	if baseURL == "" {
+		return nil, errors.New("no antigravity forward base url configured")
 	}
+	availableURLs := []string{baseURL}
 
 	var lastErr error
 	for urlIdx, baseURL := range availableURLs {

backend/internal/service/antigravity_rate_limit_test.go

@@ -915,6 +915,22 @@ func TestIsAntigravityAccountSwitchError(t *testing.T) {
 	}
 }
 
+func TestResolveAntigravityForwardBaseURL_DefaultDaily(t *testing.T) {
+	t.Setenv(antigravityForwardBaseURLEnv, "")
+
+	oldBaseURLs := append([]string(nil), antigravity.BaseURLs...)
+	defer func() {
+		antigravity.BaseURLs = oldBaseURLs
+	}()
+
+	prodURL := "https://prod.test"
+	dailyURL := "https://daily.test"
+	antigravity.BaseURLs = []string{dailyURL, prodURL}
+
+	resolved := resolveAntigravityForwardBaseURL()
+	require.Equal(t, dailyURL, resolved)
+}
+
 func TestAntigravityAccountSwitchError_Error(t *testing.T) {
 	err := &AntigravityAccountSwitchError{
 		OriginalAccountID: 789,