fix(antigravity): add project fallback for standard tier

backend/internal/service/antigravity_gateway_service.go

@@ -90,6 +90,10 @@ const (
 	antigravityFallbackSecondsEnv = "GATEWAY_ANTIGRAVITY_FALLBACK_COOLDOWN_SECONDS"
 )
 
+const antigravityProjectIDFallbackCredentialKey = "antigravity_project_id"
+
+var errAntigravityProjectIDRequired = errors.New("该 standard-tier Antigravity 账号需配置 project_id")
+
 // AntigravityAccountSwitchError 账号切换信号
 // 当账号限流时间超过阈值时，通知上层切换账号
 type AntigravityAccountSwitchError struct {
@@ -1029,6 +1033,22 @@ func (s *AntigravityGatewayService) getMappedModel(account *Account, requestedMo
 	return mapAntigravityModel(account, requestedModel)
 }
 
+func resolveAntigravityProjectID(account *Account) (string, error) {
+	if account == nil {
+		return "", errAntigravityProjectIDRequired
+	}
+	if projectID := strings.TrimSpace(account.GetCredential("project_id")); projectID != "" {
+		return projectID, nil
+	}
+	if projectID := strings.TrimSpace(account.GetCredential(antigravityProjectIDFallbackCredentialKey)); projectID != "" {
+		return projectID, nil
+	}
+	if projectID := strings.TrimSpace(account.GetExtraString(antigravityProjectIDFallbackCredentialKey)); projectID != "" {
+		return projectID, nil
+	}
+	return "", errAntigravityProjectIDRequired
+}
+
 // applyThinkingModelSuffix 根据 thinking 配置调整模型名
 // 当映射结果是 claude-sonnet-4-5 且请求开启了 thinking 时，改为 claude-sonnet-4-5-thinking
 func applyThinkingModelSuffix(mappedModel string, thinkingEnabled bool) string {
@@ -1068,8 +1088,10 @@ func (s *AntigravityGatewayService) TestConnection(ctx context.Context, account
 		return nil, fmt.Errorf("获取 access_token 失败: %w", err)
 	}
 
-	// 获取 project_id（部分账户类型可能没有）
-	projectID := strings.TrimSpace(account.GetCredential("project_id"))
+	projectID, err := resolveAntigravityProjectID(account)
+	if err != nil {
+		return nil, err
+	}
 
 	// 模型映射
 	mappedModel := s.getMappedModel(account, modelID)
@@ -1326,6 +1348,10 @@ func (s *AntigravityGatewayService) wrapV1InternalRequest(projectID, model strin
 	if err := json.Unmarshal(originalBody, &request); err != nil {
 		return nil, fmt.Errorf("解析请求体失败: %w", err)
 	}
+	projectID = strings.TrimSpace(projectID)
+	if projectID == "" {
+		return nil, errAntigravityProjectIDRequired
+	}
 
 	wrapped := map[string]any{
 		"project":     projectID,
@@ -1403,8 +1429,11 @@ func (s *AntigravityGatewayService) Forward(ctx context.Context, c *gin.Context,
 		}
 	}
 
-	// 获取 project_id（部分账户类型可能没有）
-	projectID := strings.TrimSpace(account.GetCredential("project_id"))
+	projectID, err := resolveAntigravityProjectID(account)
+	if err != nil {
+		_ = s.writeClaudeError(c, http.StatusBadRequest, "invalid_request_error", err.Error())
+		return nil, err
+	}
 
 	// 代理 URL
 	proxyURL := ""
@@ -2171,8 +2200,11 @@ func (s *AntigravityGatewayService) ForwardGemini(ctx context.Context, c *gin.Co
 		}
 	}
 
-	// 获取 project_id（部分账户类型可能没有）
-	projectID := strings.TrimSpace(account.GetCredential("project_id"))
+	projectID, err := resolveAntigravityProjectID(account)
+	if err != nil {
+		_ = s.writeGoogleError(c, http.StatusBadRequest, err.Error())
+		return nil, err
+	}
 
 	// 代理 URL
 	proxyURL := ""

backend/internal/service/antigravity_gateway_service_test.go

@@ -185,6 +185,21 @@ func (s *queuedHTTPUpstreamStub) DoWithTLS(req *http.Request, proxyURL string, a
 	return s.Do(req, proxyURL, accountID, concurrency)
 }
 
+type recordingInternal500CounterCache struct {
+	incrementCalls []int64
+	resetCalls     []int64
+}
+
+func (c *recordingInternal500CounterCache) IncrementInternal500Count(_ context.Context, accountID int64) (int64, error) {
+	c.incrementCalls = append(c.incrementCalls, accountID)
+	return int64(len(c.incrementCalls)), nil
+}
+
+func (c *recordingInternal500CounterCache) ResetInternal500Count(_ context.Context, accountID int64) error {
+	c.resetCalls = append(c.resetCalls, accountID)
+	return nil
+}
+
 type antigravitySettingRepoStub struct{}
 
 func (s *antigravitySettingRepoStub) Get(ctx context.Context, key string) (*Setting, error) {
@@ -215,6 +230,157 @@ func (s *antigravitySettingRepoStub) Delete(ctx context.Context, key string) err
 	panic("unexpected Delete call")
 }
 
+func TestResolveAntigravityProjectID(t *testing.T) {
+	tests := []struct {
+		name    string
+		account *Account
+		want    string
+		wantErr bool
+	}{
+		{
+			name: "uses onboard project_id first",
+			account: &Account{Credentials: map[string]any{
+				"project_id": " onboard-project ",
+				antigravityProjectIDFallbackCredentialKey: " configured-project ",
+			}},
+			want: "onboard-project",
+		},
+		{
+			name: "uses configured credentials fallback",
+			account: &Account{Credentials: map[string]any{
+				antigravityProjectIDFallbackCredentialKey: " configured-project ",
+			}},
+			want: "configured-project",
+		},
+		{
+			name: "uses configured extra fallback",
+			account: &Account{Extra: map[string]any{
+				antigravityProjectIDFallbackCredentialKey: " extra-project ",
+			}},
+			want: "extra-project",
+		},
+		{
+			name:    "missing project",
+			account: &Account{Credentials: map[string]any{}},
+			wantErr: true,
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			got, err := resolveAntigravityProjectID(tc.account)
+			if tc.wantErr {
+				require.ErrorIs(t, err, errAntigravityProjectIDRequired)
+				require.Empty(t, got)
+				return
+			}
+			require.NoError(t, err)
+			require.Equal(t, tc.want, got)
+		})
+	}
+}
+
+func TestAntigravityGatewayService_ForwardGemini_UsesConfiguredProjectFallback(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)
+	c.Request = httptest.NewRequest(http.MethodPost, "/antigravity/v1beta/models/gemini-2.5-flash:streamGenerateContent", bytes.NewReader(body))
+
+	upstreamBody := []byte("data: {\"response\":{\"candidates\":[{\"content\":{\"parts\":[{\"text\":\"ok\"}]},\"finishReason\":\"STOP\"}],\"usageMetadata\":{\"promptTokenCount\":1,\"candidatesTokenCount\":1}}}\n\n")
+	upstream := &queuedHTTPUpstreamStub{
+		responses: []*http.Response{
+			{
+				StatusCode: http.StatusOK,
+				Header:     http.Header{"Content-Type": []string{"text/event-stream"}},
+				Body:       io.NopCloser(bytes.NewReader(upstreamBody)),
+			},
+		},
+	}
+	svc := &AntigravityGatewayService{
+		settingService: NewSettingService(&antigravitySettingRepoStub{}, &config.Config{Gateway: config.GatewayConfig{MaxLineSize: defaultMaxLineSize}}),
+		tokenProvider:  &AntigravityTokenProvider{},
+		httpUpstream:   upstream,
+	}
+
+	account := &Account{
+		ID:          101,
+		Name:        "acc-configured-project",
+		Platform:    PlatformAntigravity,
+		Type:        AccountTypeOAuth,
+		Status:      StatusActive,
+		Concurrency: 1,
+		Credentials: map[string]any{
+			"access_token": "token",
+			antigravityProjectIDFallbackCredentialKey: "configured-project",
+			"model_mapping": map[string]any{
+				"gemini-2.5-flash": "gemini-2.5-flash",
+			},
+		},
+	}
+
+	result, err := svc.ForwardGemini(context.Background(), c, account, "gemini-2.5-flash", "streamGenerateContent", true, body, false)
+	require.NoError(t, err)
+	require.NotNil(t, result)
+	require.Len(t, upstream.requestBodies, 1)
+
+	var wrapped map[string]any
+	require.NoError(t, json.Unmarshal(upstream.requestBodies[0], &wrapped))
+	require.Equal(t, "configured-project", wrapped["project"])
+}
+
+func TestAntigravityGatewayService_ForwardGemini_MissingProjectReturnsLocalError(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)
+	c.Request = httptest.NewRequest(http.MethodPost, "/antigravity/v1beta/models/gemini-2.5-flash:streamGenerateContent", bytes.NewReader(body))
+
+	upstream := &queuedHTTPUpstreamStub{}
+	internal500Cache := &recordingInternal500CounterCache{}
+	svc := &AntigravityGatewayService{
+		tokenProvider:    &AntigravityTokenProvider{},
+		httpUpstream:     upstream,
+		internal500Cache: internal500Cache,
+	}
+
+	account := &Account{
+		ID:          102,
+		Name:        "acc-missing-project",
+		Platform:    PlatformAntigravity,
+		Type:        AccountTypeOAuth,
+		Status:      StatusActive,
+		Concurrency: 1,
+		Credentials: map[string]any{
+			"access_token": "token",
+			"model_mapping": map[string]any{
+				"gemini-2.5-flash": "gemini-2.5-flash",
+			},
+		},
+	}
+
+	result, err := svc.ForwardGemini(context.Background(), c, account, "gemini-2.5-flash", "streamGenerateContent", true, body, false)
+	require.Nil(t, result)
+	require.ErrorIs(t, err, errAntigravityProjectIDRequired)
+	require.Equal(t, http.StatusBadRequest, writer.Code)
+	require.Empty(t, upstream.requestBodies)
+	require.Empty(t, internal500Cache.incrementCalls)
+	require.Contains(t, writer.Body.String(), "project_id")
+	require.NotContains(t, writer.Body.String(), `"project":""`)
+}
+
 func TestAntigravityGatewayService_Forward_PromptTooLong(t *testing.T) {
 	gin.SetMode(gin.TestMode)
 	writer := httptest.NewRecorder()
@@ -255,6 +421,7 @@ func TestAntigravityGatewayService_Forward_PromptTooLong(t *testing.T) {
 		Concurrency: 1,
 		Credentials: map[string]any{
 			"access_token": "token",
+			"project_id":   "proj",
 		},
 	}
 
@@ -313,6 +480,7 @@ func TestAntigravityGatewayService_Forward_ModelRateLimitTriggersFailover(t *tes
 		Concurrency: 1,
 		Credentials: map[string]any{
 			"access_token": "token",
+			"project_id":   "proj",
 		},
 		Extra: map[string]any{
 			modelRateLimitsKey: map[string]any{
@@ -369,6 +537,7 @@ func TestAntigravityGatewayService_ForwardGemini_ModelRateLimitTriggersFailover(
 		Concurrency: 1,
 		Credentials: map[string]any{
 			"access_token": "token",
+			"project_id":   "proj",
 		},
 		Extra: map[string]any{
 			modelRateLimitsKey: map[string]any{
@@ -423,6 +592,7 @@ func TestAntigravityGatewayService_Forward_StickySessionForceCacheBilling(t *tes
 		Concurrency: 1,
 		Credentials: map[string]any{
 			"access_token": "token",
+			"project_id":   "proj",
 		},
 		Extra: map[string]any{
 			modelRateLimitsKey: map[string]any{
@@ -478,6 +648,7 @@ func TestAntigravityGatewayService_ForwardGemini_StickySessionForceCacheBilling(
 		Concurrency: 1,
 		Credentials: map[string]any{
 			"access_token": "token",
+			"project_id":   "proj",
 		},
 		Extra: map[string]any{
 			modelRateLimitsKey: map[string]any{
@@ -623,6 +794,7 @@ func TestAntigravityGatewayService_Forward_BillsWithMappedModel(t *testing.T) {
 		Concurrency: 1,
 		Credentials: map[string]any{
 			"access_token": "token",
+			"project_id":   "proj",
 			"model_mapping": map[string]any{
 				"claude-sonnet-4-5": mappedModel,
 			},
@@ -676,6 +848,7 @@ func TestAntigravityGatewayService_ForwardGemini_BillsWithMappedModel(t *testing
 		Concurrency: 1,
 		Credentials: map[string]any{
 			"access_token": "token",
+			"project_id":   "proj",
 			"model_mapping": map[string]any{
 				"gemini-2.5-flash": mappedModel,
 			},
@@ -747,6 +920,7 @@ func TestAntigravityGatewayService_ForwardGemini_RetriesCorruptedThoughtSignatur
 		Concurrency: 1,
 		Credentials: map[string]any{
 			"access_token": "token",
+			"project_id":   "proj",
 			"model_mapping": map[string]any{
 				originalModel: mappedModel,
 			},
@@ -805,6 +979,7 @@ func TestAntigravityGatewayService_ForwardGemini_SignatureRetryPropagatesFailove
 		Concurrency: 1,
 		Credentials: map[string]any{
 			"access_token": "token",
+			"project_id":   "proj",
 			"model_mapping": map[string]any{
 				originalModel: mappedModel,
 			},

frontend/src/components/account/CreateAccountModal.vue

@@ -774,6 +774,18 @@
         </div>
       </div>
 
+      <div v-if="form.platform === 'antigravity' && antigravityAccountType === 'oauth'">
+        <label class="input-label">{{ t('admin.accounts.antigravityProjectIdLabel') }}</label>
+        <input
+          v-model="antigravityProjectId"
+          data-testid="antigravity-project-id-input"
+          type="text"
+          class="input font-mono"
+          :placeholder="t('admin.accounts.antigravityProjectIdPlaceholder')"
+        />
+        <p class="input-hint">{{ t('admin.accounts.antigravityProjectIdHint') }}</p>
+      </div>
+
       <!-- Upstream config (only for Antigravity upstream type) -->
       <div v-if="form.platform === 'antigravity' && antigravityAccountType === 'upstream'" class="space-y-4">
         <div>
@@ -3238,7 +3250,10 @@ import ProxyAdBanner from '@/components/common/ProxyAdBanner.vue'
 import GroupSelector from '@/components/common/GroupSelector.vue'
 import ModelWhitelistSelector from '@/components/account/ModelWhitelistSelector.vue'
 import QuotaLimitCard from '@/components/account/QuotaLimitCard.vue'
-import { applyInterceptWarmup } from '@/components/account/credentialsBuilder'
+import {
+  applyAntigravityProjectID,
+  applyInterceptWarmup
+} from '@/components/account/credentialsBuilder'
 import { formatDateTimeLocalInput, parseDateTimeLocalInput } from '@/utils/format'
 import { createStableObjectKeyResolver } from '@/utils/stableObjectKey'
 import { VERTEX_LOCATION_OPTIONS } from '@/constants/account'
@@ -3440,6 +3455,7 @@ loadQuotaNotifyGlobal()
 const mixedScheduling = ref(false) // For antigravity accounts: enable mixed scheduling
 const allowOverages = ref(false) // For antigravity accounts: enable AI Credits overages
 const antigravityAccountType = ref<'oauth' | 'upstream'>('oauth') // For antigravity: oauth or upstream
+const antigravityProjectId = ref('')
 const upstreamBaseUrl = ref('') // For upstream type: base URL
 const upstreamApiKey = ref('') // For upstream type: API key
 const antigravityModelRestrictionMode = ref<'whitelist' | 'mapping'>('whitelist')
@@ -3813,6 +3829,7 @@ watch(
       antigravityAccountType.value = 'oauth'
     } else {
       allowOverages.value = false
+      antigravityProjectId.value = ''
       antigravityWhitelistModels.value = []
       antigravityModelMappings.value = []
       antigravityModelRestrictionMode.value = 'mapping'
@@ -4271,6 +4288,7 @@ const resetForm = () => {
   customBaseUrl.value = ''
   allowOverages.value = false
   antigravityAccountType.value = 'oauth'
+  antigravityProjectId.value = ''
   upstreamBaseUrl.value = ''
   upstreamApiKey.value = ''
   vertexServiceAccountJson.value = ''
@@ -5133,6 +5151,7 @@ const handleAntigravityValidateRT = async (refreshTokenInput: string) => {
         }
 
         const credentials = antigravityOAuth.buildCredentials(tokenInfo)
+        applyAntigravityProjectID(credentials, antigravityProjectId.value, 'create')
         
         // Generate account name with index for batch
         const accountName = refreshTokens.length > 1 ? `${form.name} #${i + 1}` : form.name
@@ -5249,6 +5268,7 @@ const handleAntigravityExchange = async (authCode: string) => {
 		if (!tokenInfo) return
 
 		const credentials = antigravityOAuth.buildCredentials(tokenInfo)
+		applyAntigravityProjectID(credentials, antigravityProjectId.value, 'create')
 		applyInterceptWarmup(credentials, interceptWarmupRequests.value, 'create')
 		// Antigravity 只使用映射模式
 		const antigravityModelMapping = buildModelMappingObject(

frontend/src/components/account/EditAccountModal.vue

@@ -1000,6 +1000,21 @@
         </div>
       </div>
 
+      <div
+        v-if="account.platform === 'antigravity' && account.type === 'oauth'"
+        class="border-t border-gray-200 pt-4 dark:border-dark-600"
+      >
+        <label class="input-label">{{ t('admin.accounts.antigravityProjectIdLabel') }}</label>
+        <input
+          v-model="antigravityProjectId"
+          data-testid="antigravity-project-id-input"
+          type="text"
+          class="input font-mono"
+          :placeholder="t('admin.accounts.antigravityProjectIdPlaceholder')"
+        />
+        <p class="input-hint">{{ t('admin.accounts.antigravityProjectIdHint') }}</p>
+      </div>
+
       <!-- Antigravity model restriction (applies to all antigravity types) -->
       <!-- Antigravity 只支持模型映射模式，不支持白名单模式 -->
       <div v-if="account.platform === 'antigravity'" class="border-t border-gray-200 pt-4 dark:border-dark-600">
@@ -2398,7 +2413,10 @@ import ProxyAdBanner from '@/components/common/ProxyAdBanner.vue'
 import GroupSelector from '@/components/common/GroupSelector.vue'
 import ModelWhitelistSelector from '@/components/account/ModelWhitelistSelector.vue'
 import QuotaLimitCard from '@/components/account/QuotaLimitCard.vue'
-import { applyInterceptWarmup } from '@/components/account/credentialsBuilder'
+import {
+  applyAntigravityProjectID,
+  applyInterceptWarmup
+} from '@/components/account/credentialsBuilder'
 import { formatDateTime, formatDateTimeLocalInput, parseDateTimeLocalInput } from '@/utils/format'
 import { createStableObjectKeyResolver } from '@/utils/stableObjectKey'
 import { VERTEX_LOCATION_OPTIONS } from '@/constants/account'
@@ -2531,6 +2549,7 @@ const autoPause5hDisabled = ref(false)
 const autoPause7dDisabled = ref(false)
 const mixedScheduling = ref(false) // For antigravity accounts: enable mixed scheduling
 const allowOverages = ref(false) // For antigravity accounts: enable AI Credits overages
+const antigravityProjectId = ref('')
 const antigravityModelRestrictionMode = ref<'whitelist' | 'mapping'>('whitelist')
 const antigravityWhitelistModels = ref<string[]>([])
 const antigravityModelMappings = ref<ModelMapping[]>([])
@@ -2940,6 +2959,12 @@ const syncFormFromAccount = (newAccount: Account | null) => {
   editVertexProjectId.value = ''
   editVertexClientEmail.value = ''
   editVertexLocation.value = 'us-central1'
+  antigravityProjectId.value =
+    newAccount.platform === 'antigravity' &&
+    newAccount.type === 'oauth' &&
+    typeof credentials?.antigravity_project_id === 'string'
+      ? credentials.antigravity_project_id.trim()
+      : ''
 
   // Load mixed scheduling setting (only for antigravity accounts)
   mixedScheduling.value = false
@@ -3930,6 +3955,9 @@ const handleSubmit = async () => {
       const currentCredentials = (updatePayload.credentials as Record<string, unknown>) ||
         ((props.account.credentials as Record<string, unknown>) || {})
       const newCredentials: Record<string, unknown> = { ...currentCredentials }
+      if (props.account.type === 'oauth') {
+        applyAntigravityProjectID(newCredentials, antigravityProjectId.value, 'edit')
+      }
 
       // 移除旧字段
       delete newCredentials.model_whitelist

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

@@ -167,6 +167,31 @@ function buildVertexAccount() {
   } as any
 }
 
+function buildAntigravityAccount(projectId = 'configured-project') {
+  return {
+    id: 3,
+    name: 'Antigravity OAuth',
+    notes: '',
+    platform: 'antigravity',
+    type: 'oauth',
+    credentials: {
+      antigravity_project_id: projectId,
+      model_mapping: {
+        'gemini-2.5-flash': 'gemini-2.5-flash'
+      }
+    },
+    extra: {},
+    proxy_id: null,
+    concurrency: 1,
+    priority: 1,
+    rate_multiplier: 1,
+    status: 'active',
+    group_ids: [],
+    expires_at: null,
+    auto_pause_on_expired: false
+  } as any
+}
+
 function mountModal(account = buildAccount()) {
   return mount(EditAccountModal, {
     props: {
@@ -579,4 +604,43 @@ describe('EditAccountModal', () => {
 
     expect(updateAccountMock).not.toHaveBeenCalled()
   })
+
+  it('loads and submits Antigravity configured project fallback', async () => {
+    const account = buildAntigravityAccount('configured-project')
+    updateAccountMock.mockReset()
+    checkMixedChannelRiskMock.mockReset()
+    checkMixedChannelRiskMock.mockResolvedValue({ has_risk: false })
+    updateAccountMock.mockResolvedValue(account)
+
+    const wrapper = mountModal(account)
+    const input = wrapper.get<HTMLInputElement>('[data-testid="antigravity-project-id-input"]')
+    expect(input.element.value).toBe('configured-project')
+
+    await input.setValue('  updated-project  ')
+    await wrapper.get('form#edit-account-form').trigger('submit.prevent')
+
+    expect(updateAccountMock).toHaveBeenCalledTimes(1)
+    expect(updateAccountMock.mock.calls[0]?.[1]?.credentials?.antigravity_project_id).toBe(
+      'updated-project'
+    )
+  })
+
+  it('clears Antigravity configured project fallback when input is empty', async () => {
+    const account = buildAntigravityAccount('configured-project')
+    updateAccountMock.mockReset()
+    checkMixedChannelRiskMock.mockReset()
+    checkMixedChannelRiskMock.mockResolvedValue({ has_risk: false })
+    updateAccountMock.mockResolvedValue(account)
+
+    const wrapper = mountModal(account)
+    const input = wrapper.get<HTMLInputElement>('[data-testid="antigravity-project-id-input"]')
+
+    await input.setValue('')
+    await wrapper.get('form#edit-account-form').trigger('submit.prevent')
+
+    expect(updateAccountMock).toHaveBeenCalledTimes(1)
+    expect(updateAccountMock.mock.calls[0]?.[1]?.credentials).not.toHaveProperty(
+      'antigravity_project_id'
+    )
+  })
 })

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

@@ -1,5 +1,9 @@
 import { describe, it, expect } from 'vitest'
-import { applyInterceptWarmup } from '../credentialsBuilder'
+import {
+  ANTIGRAVITY_PROJECT_ID_CREDENTIAL_KEY,
+  applyAntigravityProjectID,
+  applyInterceptWarmup
+} from '../credentialsBuilder'
 
 describe('applyInterceptWarmup', () => {
   it('create + enabled=true: should set intercept_warmup_requests to true', () => {
@@ -44,3 +48,37 @@ describe('applyInterceptWarmup', () => {
     expect('intercept_warmup_requests' in creds).toBe(false)
   })
 })
+
+describe('applyAntigravityProjectID', () => {
+  it('create + project id: trims and stores configured project fallback', () => {
+    const creds: Record<string, unknown> = { access_token: 'tok' }
+    applyAntigravityProjectID(creds, '  configured-project  ', 'create')
+    expect(creds[ANTIGRAVITY_PROJECT_ID_CREDENTIAL_KEY]).toBe('configured-project')
+  })
+
+  it('create + empty project id: should not add the field', () => {
+    const creds: Record<string, unknown> = { access_token: 'tok' }
+    applyAntigravityProjectID(creds, '   ', 'create')
+    expect(ANTIGRAVITY_PROJECT_ID_CREDENTIAL_KEY in creds).toBe(false)
+  })
+
+  it('edit + empty project id: deletes existing fallback', () => {
+    const creds: Record<string, unknown> = {
+      access_token: 'tok',
+      [ANTIGRAVITY_PROJECT_ID_CREDENTIAL_KEY]: 'old-project'
+    }
+    applyAntigravityProjectID(creds, '', 'edit')
+    expect(ANTIGRAVITY_PROJECT_ID_CREDENTIAL_KEY in creds).toBe(false)
+  })
+
+  it('does not affect onboard project_id or other credentials', () => {
+    const creds: Record<string, unknown> = {
+      project_id: 'onboard-project',
+      model_mapping: { 'gemini-*': 'gemini-2.5-flash' }
+    }
+    applyAntigravityProjectID(creds, 'configured-project', 'edit')
+    expect(creds.project_id).toBe('onboard-project')
+    expect(creds.model_mapping).toEqual({ 'gemini-*': 'gemini-2.5-flash' })
+    expect(creds[ANTIGRAVITY_PROJECT_ID_CREDENTIAL_KEY]).toBe('configured-project')
+  })
+})

frontend/src/components/account/credentialsBuilder.ts

@@ -9,3 +9,18 @@ export function applyInterceptWarmup(
     delete credentials.intercept_warmup_requests
   }
 }
+
+export const ANTIGRAVITY_PROJECT_ID_CREDENTIAL_KEY = 'antigravity_project_id'
+
+export function applyAntigravityProjectID(
+  credentials: Record<string, unknown>,
+  projectId: string,
+  mode: 'create' | 'edit'
+): void {
+  const trimmed = projectId.trim()
+  if (trimmed) {
+    credentials[ANTIGRAVITY_PROJECT_ID_CREDENTIAL_KEY] = trimmed
+  } else if (mode === 'edit') {
+    delete credentials[ANTIGRAVITY_PROJECT_ID_CREDENTIAL_KEY]
+  }
+}

frontend/src/i18n/locales/en.ts

@@ -3139,6 +3139,10 @@ export default {
         upstream: 'Upstream',
         upstreamDesc: 'Connect via Base URL + API Key'
       },
+      antigravityProjectIdLabel: 'GCP Project ID (optional)',
+      antigravityProjectIdPlaceholder: 'your-gcp-project-id',
+      antigravityProjectIdHint:
+        'Antigravity standard-tier accounts that do not receive an automatic project_id need a user-owned GCP project.',
       status: {
         active: 'Active',
         inactive: 'Inactive',

frontend/src/i18n/locales/zh.ts

@@ -3329,6 +3329,10 @@ export default {
         api_key: 'API Key',
         cookie: 'Cookie'
       },
+      antigravityProjectIdLabel: 'GCP Project ID（可选）',
+      antigravityProjectIdPlaceholder: 'your-gcp-project-id',
+      antigravityProjectIdHint:
+        'standard-tier 且未自动返回 project_id 的 Antigravity 账号需要填写用户自带 GCP project。',
       status: {
         active: '正常',
         inactive: '停用',