fix(antigravity): bill with mapped model and use final model key for rate limiting

- Use mapped model (billingModel) instead of original request model for billing
- Use resolveFinalAntigravityModelKey for 429 rate limit model key,
  ensuring rate limit records match the actual upstream model
- Add regression tests for both fixes

backend/internal/service/antigravity_gateway_service.go

@@ -87,7 +87,6 @@ var (
 )
 
 const (
-	antigravityBillingModelEnv    = "GATEWAY_ANTIGRAVITY_BILL_WITH_MAPPED_MODEL"
 	antigravityForwardBaseURLEnv  = "GATEWAY_ANTIGRAVITY_FORWARD_BASE_URL"
 	antigravityFallbackSecondsEnv = "GATEWAY_ANTIGRAVITY_FALLBACK_COOLDOWN_SECONDS"
 )
@@ -1309,6 +1308,7 @@ func (s *AntigravityGatewayService) Forward(ctx context.Context, c *gin.Context,
 	// 应用 thinking 模式自动后缀：如果 thinking 开启且目标是 claude-sonnet-4-5，自动改为 thinking 版本
 	thinkingEnabled := claudeReq.Thinking != nil && (claudeReq.Thinking.Type == "enabled" || claudeReq.Thinking.Type == "adaptive")
 	mappedModel = applyThinkingModelSuffix(mappedModel, thinkingEnabled)
+	billingModel := mappedModel
 
 	// 获取 access_token
 	if s.tokenProvider == nil {
@@ -1622,7 +1622,7 @@ func (s *AntigravityGatewayService) Forward(ctx context.Context, c *gin.Context,
 	return &ForwardResult{
 		RequestID:        requestID,
 		Usage:            *usage,
-		Model:            originalModel, // 使用原始模型用于计费和日志
+		Model:            billingModel, // 使用映射模型用于计费和日志
 		Stream:           claudeReq.Stream,
 		Duration:         time.Since(startTime),
 		FirstTokenMs:     firstTokenMs,
@@ -1976,6 +1976,7 @@ func (s *AntigravityGatewayService) ForwardGemini(ctx context.Context, c *gin.Co
 	if mappedModel == "" {
 		return nil, s.writeGoogleError(c, http.StatusForbidden, fmt.Sprintf("model %s not in whitelist", originalModel))
 	}
+	billingModel := mappedModel
 
 	// 获取 access_token
 	if s.tokenProvider == nil {
@@ -2205,7 +2206,7 @@ handleSuccess:
 	return &ForwardResult{
 		RequestID:        requestID,
 		Usage:            *usage,
-		Model:            originalModel,
+		Model:            billingModel,
 		Stream:           stream,
 		Duration:         time.Since(startTime),
 		FirstTokenMs:     firstTokenMs,
@@ -2650,7 +2651,16 @@ func (s *AntigravityGatewayService) handleUpstreamError(
 		defaultDur := s.getDefaultRateLimitDuration()
 
 		// 尝试解析模型 key 并设置模型级限流
-		modelKey := resolveAntigravityModelKey(requestedModel)
+		//
+		// 注意：requestedModel 可能是"映射前"的请求模型名（例如 claude-opus-4-6），
+		// 调度与限流判定使用的是 Antigravity 最终模型名（包含映射与 thinking 后缀）。
+		// 因此这里必须写入最终模型 key，确保后续调度能正确避开已限流模型。
+		modelKey := resolveFinalAntigravityModelKey(ctx, account, requestedModel)
+		if strings.TrimSpace(modelKey) == "" {
+			// 极少数情况下无法映射（理论上不应发生：能转发成功说明映射已通过），
+			// 保持旧行为作为兜底，避免完全丢失模型级限流记录。
+			modelKey = resolveAntigravityModelKey(requestedModel)
+		}
 		if modelKey != "" {
 			ra := s.resolveResetTime(resetAt, defaultDur)
 			if err := s.accountRepo.SetModelRateLimit(ctx, account.ID, modelKey, ra); err != nil {
@@ -3889,7 +3899,6 @@ func (s *AntigravityGatewayService) ForwardUpstream(ctx context.Context, c *gin.
 		return nil, fmt.Errorf("missing model")
 	}
 	originalModel := claudeReq.Model
-	billingModel := originalModel
 
 	// 构建上游请求 URL
 	upstreamURL := baseURL + "/v1/messages"
@@ -3942,7 +3951,7 @@ func (s *AntigravityGatewayService) ForwardUpstream(ctx context.Context, c *gin.
 		_, _ = c.Writer.Write(respBody)
 
 		return &ForwardResult{
-			Model: billingModel,
+			Model: originalModel,
 		}, nil
 	}
 
@@ -3983,7 +3992,7 @@ func (s *AntigravityGatewayService) ForwardUpstream(ctx context.Context, c *gin.
 	logger.LegacyPrintf("service.antigravity_gateway", "%s status=success duration_ms=%d", prefix, duration.Milliseconds())
 
 	return &ForwardResult{
-		Model:            billingModel,
+		Model:            originalModel,
 		Stream:           claudeReq.Stream,
 		Duration:         duration,
 		FirstTokenMs:     firstTokenMs,

backend/internal/service/antigravity_gateway_service_test.go

@@ -134,6 +134,36 @@ func (s *httpUpstreamStub) DoWithTLS(_ *http.Request, _ string, _ int64, _ int,
 	return s.resp, s.err
 }
 
+type antigravitySettingRepoStub struct{}
+
+func (s *antigravitySettingRepoStub) Get(ctx context.Context, key string) (*Setting, error) {
+	panic("unexpected Get call")
+}
+
+func (s *antigravitySettingRepoStub) GetValue(ctx context.Context, key string) (string, error) {
+	return "", ErrSettingNotFound
+}
+
+func (s *antigravitySettingRepoStub) Set(ctx context.Context, key, value string) error {
+	panic("unexpected Set call")
+}
+
+func (s *antigravitySettingRepoStub) GetMultiple(ctx context.Context, keys []string) (map[string]string, error) {
+	panic("unexpected GetMultiple call")
+}
+
+func (s *antigravitySettingRepoStub) SetMultiple(ctx context.Context, settings map[string]string) error {
+	panic("unexpected SetMultiple call")
+}
+
+func (s *antigravitySettingRepoStub) GetAll(ctx context.Context) (map[string]string, error) {
+	panic("unexpected GetAll call")
+}
+
+func (s *antigravitySettingRepoStub) Delete(ctx context.Context, key string) error {
+	panic("unexpected Delete call")
+}
+
 func TestAntigravityGatewayService_Forward_PromptTooLong(t *testing.T) {
 	gin.SetMode(gin.TestMode)
 	writer := httptest.NewRecorder()
@@ -160,8 +190,9 @@ func TestAntigravityGatewayService_Forward_PromptTooLong(t *testing.T) {
 	}
 
 	svc := &AntigravityGatewayService{
-		tokenProvider: &AntigravityTokenProvider{},
+		settingService: NewSettingService(&antigravitySettingRepoStub{}, &config.Config{Gateway: config.GatewayConfig{MaxLineSize: defaultMaxLineSize}}),
-		httpUpstream:  &httpUpstreamStub{resp: resp},
+		tokenProvider:  &AntigravityTokenProvider{},
+		httpUpstream:   &httpUpstreamStub{resp: resp},
 	}
 
 	account := &Account{
@@ -418,6 +449,113 @@ func TestAntigravityGatewayService_ForwardGemini_StickySessionForceCacheBilling(
 	require.True(t, failoverErr.ForceCacheBilling, "ForceCacheBilling should be true for sticky session switch")
 }
 
+// TestAntigravityGatewayService_Forward_BillsWithMappedModel
+// 验证：Antigravity Claude 转发返回的计费模型使用映射后的模型
+func TestAntigravityGatewayService_Forward_BillsWithMappedModel(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	writer := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(writer)
+
+	body, err := json.Marshal(map[string]any{
+		"model": "claude-sonnet-4-5",
+		"messages": []map[string]any{
+			{"role": "user", "content": "hello"},
+		},
+		"max_tokens": 16,
+		"stream":     true,
+	})
+	require.NoError(t, err)
+
+	req := httptest.NewRequest(http.MethodPost, "/v1/messages", bytes.NewReader(body))
+	c.Request = req
+
+	upstreamBody := []byte("data: {\"response\":{\"candidates\":[{\"content\":{\"parts\":[{\"text\":\"ok\"}]},\"finishReason\":\"STOP\"}],\"usageMetadata\":{\"promptTokenCount\":8,\"candidatesTokenCount\":3}}}\n\n")
+	resp := &http.Response{
+		StatusCode: http.StatusOK,
+		Header:     http.Header{"X-Request-Id": []string{"req-bill-1"}},
+		Body:       io.NopCloser(bytes.NewReader(upstreamBody)),
+	}
+
+	svc := &AntigravityGatewayService{
+		settingService: NewSettingService(&antigravitySettingRepoStub{}, &config.Config{Gateway: config.GatewayConfig{MaxLineSize: defaultMaxLineSize}}),
+		tokenProvider:  &AntigravityTokenProvider{},
+		httpUpstream:   &httpUpstreamStub{resp: resp},
+	}
+
+	const mappedModel = "gemini-3-pro-high"
+	account := &Account{
+		ID:          5,
+		Name:        "acc-forward-billing",
+		Platform:    PlatformAntigravity,
+		Type:        AccountTypeOAuth,
+		Status:      StatusActive,
+		Concurrency: 1,
+		Credentials: map[string]any{
+			"access_token": "token",
+			"model_mapping": map[string]any{
+				"claude-sonnet-4-5": mappedModel,
+			},
+		},
+	}
+
+	result, err := svc.Forward(context.Background(), c, account, body, false)
+	require.NoError(t, err)
+	require.NotNil(t, result)
+	require.Equal(t, mappedModel, result.Model)
+}
+
+// TestAntigravityGatewayService_ForwardGemini_BillsWithMappedModel
+// 验证：Antigravity Gemini 转发返回的计费模型使用映射后的模型
+func TestAntigravityGatewayService_ForwardGemini_BillsWithMappedModel(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	writer := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(writer)
+
+	body, err := json.Marshal(map[string]any{
+		"contents": []map[string]any{
+			{"role": "user", "parts": []map[string]any{{"text": "hello"}}},
+		},
+	})
+	require.NoError(t, err)
+
+	req := httptest.NewRequest(http.MethodPost, "/v1beta/models/gemini-2.5-flash:generateContent", bytes.NewReader(body))
+	c.Request = req
+
+	upstreamBody := []byte("data: {\"response\":{\"candidates\":[{\"content\":{\"parts\":[{\"text\":\"ok\"}]},\"finishReason\":\"STOP\"}],\"usageMetadata\":{\"promptTokenCount\":8,\"candidatesTokenCount\":3}}}\n\n")
+	resp := &http.Response{
+		StatusCode: http.StatusOK,
+		Header:     http.Header{"X-Request-Id": []string{"req-bill-2"}},
+		Body:       io.NopCloser(bytes.NewReader(upstreamBody)),
+	}
+
+	svc := &AntigravityGatewayService{
+		settingService: NewSettingService(&antigravitySettingRepoStub{}, &config.Config{Gateway: config.GatewayConfig{MaxLineSize: defaultMaxLineSize}}),
+		tokenProvider:  &AntigravityTokenProvider{},
+		httpUpstream:   &httpUpstreamStub{resp: resp},
+	}
+
+	const mappedModel = "gemini-3-pro-high"
+	account := &Account{
+		ID:          6,
+		Name:        "acc-gemini-billing",
+		Platform:    PlatformAntigravity,
+		Type:        AccountTypeOAuth,
+		Status:      StatusActive,
+		Concurrency: 1,
+		Credentials: map[string]any{
+			"access_token": "token",
+			"model_mapping": map[string]any{
+				"gemini-2.5-flash": mappedModel,
+			},
+		},
+	}
+
+	result, err := svc.ForwardGemini(context.Background(), c, account, "gemini-2.5-flash", "generateContent", true, body, false)
+	require.NoError(t, err)
+	require.NotNil(t, result)
+	require.Equal(t, mappedModel, result.Model)
+}
+
 // TestStreamUpstreamResponse_UsageAndFirstToken
 // 验证：usage 字段可被累积/覆盖更新，并且能记录首 token 时间
 func TestStreamUpstreamResponse_UsageAndFirstToken(t *testing.T) {

backend/internal/service/antigravity_rate_limit_test.go

@@ -197,6 +197,22 @@ func TestHandleUpstreamError_429_NonModelRateLimit(t *testing.T) {
 	require.Equal(t, "claude-sonnet-4-5", repo.modelRateLimitCalls[0].modelKey)
 }
 
+// TestHandleUpstreamError_429_NonModelRateLimit_UsesMappedModelKey 测试 429 非模型限流场景
+// 验证：requestedModel 会被映射到 Antigravity 最终模型（例如 claude-opus-4-6 -> claude-opus-4-6-thinking）
+func TestHandleUpstreamError_429_NonModelRateLimit_UsesMappedModelKey(t *testing.T) {
+	repo := &stubAntigravityAccountRepo{}
+	svc := &AntigravityGatewayService{accountRepo: repo}
+	account := &Account{ID: 20, Name: "acc-20", Platform: PlatformAntigravity}
+
+	body := buildGeminiRateLimitBody("5s")
+
+	result := svc.handleUpstreamError(context.Background(), "[test]", account, http.StatusTooManyRequests, http.Header{}, body, "claude-opus-4-6", 0, "", false)
+
+	require.Nil(t, result)
+	require.Len(t, repo.modelRateLimitCalls, 1)
+	require.Equal(t, "claude-opus-4-6-thinking", repo.modelRateLimitCalls[0].modelKey)
+}
+
 // TestHandleUpstreamError_503_ModelCapacityExhausted 测试 503 模型容量不足场景
 // MODEL_CAPACITY_EXHAUSTED 时应等待重试，不切换账号
 func TestHandleUpstreamError_503_ModelCapacityExhausted(t *testing.T) {