fix: restore OAuth 401 temp-unschedulable for Gemini, update Antigravity tests

The 403 detection PR changed the 401 handler condition from
`account.Type == AccountTypeOAuth` to
`account.Type == AccountTypeOAuth && account.Platform == PlatformOpenAI`,
which accidentally excluded Gemini OAuth from the temp-unschedulable path.

Fix: use `!= PlatformAntigravity` instead, preserving Gemini behavior
while correctly excluding Antigravity (whose 401 is handled by
applyErrorPolicy's temp_unschedulable_rules).

Update tests to reflect Antigravity's new 401 semantics:
- HandleUpstreamError: Antigravity OAuth 401 now uses SetError
- CheckErrorPolicy: Antigravity 401 second hit stays TempUnscheduled
- DB fallback: split into Gemini (escalates) and Antigravity (stays temp)

backend/internal/service/error_policy_test.go

@@ -110,7 +110,9 @@ func TestCheckErrorPolicy(t *testing.T) {
 			expected:   ErrorPolicyTempUnscheduled,
 		},
 		{
-			name: "temp_unschedulable_401_second_hit_upgrades_to_none",
+			// Antigravity 401 不走升级逻辑（由 applyErrorPolicy 的 temp_unschedulable_rules 自行控制），
+			// second hit 仍然返回 TempUnscheduled。
+			name: "temp_unschedulable_401_second_hit_antigravity_stays_temp",
 			account: &Account{
 				ID:                      15,
 				Type:                    AccountTypeOAuth,
@@ -129,7 +131,7 @@ func TestCheckErrorPolicy(t *testing.T) {
 			},
 			statusCode: 401,
 			body:       []byte(`unauthorized`),
-			expected:   ErrorPolicyNone,
+			expected:   ErrorPolicyTempUnscheduled,
 		},
 		{
 			name: "temp_unschedulable_body_miss_returns_none",

backend/internal/service/ratelimit_service.go

@@ -149,9 +149,9 @@ func (s *RateLimitService) HandleUpstreamError(ctx context.Context, account *Acc
 		}
 		// 其他 400 错误（如参数问题）不处理，不禁用账号
 	case 401:
-		// OpenAI OAuth 账号在 401 错误时临时不可调度；其他平台 OAuth 账号保持原有 SetError 行为
-		// （Antigravity 主流程不走此路径，其 401 由 applyErrorPolicy 的 temp_unschedulable_rules 自行控制）
-		if account.Type == AccountTypeOAuth && account.Platform == PlatformOpenAI {
+		// OAuth 账号在 401 错误时临时不可调度（给 token 刷新窗口）；非 OAuth 账号保持原有 SetError 行为。
+		// Antigravity 除外：其 401 由 applyErrorPolicy 的 temp_unschedulable_rules 自行控制。
+		if account.Type == AccountTypeOAuth && account.Platform != PlatformAntigravity {
 			// 1. 失效缓存
 			if s.tokenCacheInvalidator != nil {
 				if err := s.tokenCacheInvalidator.InvalidateToken(ctx, account); err != nil {
@@ -183,7 +183,7 @@ func (s *RateLimitService) HandleUpstreamError(ctx context.Context, account *Acc
 			}
 			shouldDisable = true
 		} else {
-			// 非 OAuth 账号（APIKey）：保持原有 SetError 行为
+			// 非 OAuth / Antigravity OAuth：保持 SetError 行为
 			msg := "Authentication failed (401): invalid or expired credentials"
 			if upstreamMsg != "" {
 				msg = "Authentication failed (401): " + upstreamMsg

backend/internal/service/ratelimit_service_401_db_fallback_test.go

@@ -27,7 +27,40 @@ func (r *dbFallbackRepoStub) GetByID(ctx context.Context, id int64) (*Account, e
 
 func TestCheckErrorPolicy_401_DBFallback_Escalates(t *testing.T) {
 	// Scenario: cache account has empty TempUnschedulableReason (cache miss),
-	// but DB account has a previous 401 record → should escalate to ErrorPolicyNone.
+	// but DB account has a previous 401 record.
+	// Non-Antigravity: should escalate to ErrorPolicyNone (second 401 = permanent error).
+	// Antigravity: skips escalation logic (401 handled by applyErrorPolicy rules).
+	t.Run("gemini_escalates", func(t *testing.T) {
+		repo := &dbFallbackRepoStub{
+			dbAccount: &Account{
+				ID:                      20,
+				TempUnschedulableReason: `{"status_code":401,"until_unix":1735689600}`,
+			},
+		}
+		svc := NewRateLimitService(repo, nil, &config.Config{}, nil, nil)
+
+		account := &Account{
+			ID:                      20,
+			Type:                    AccountTypeOAuth,
+			Platform:                PlatformGemini,
+			TempUnschedulableReason: "",
+			Credentials: map[string]any{
+				"temp_unschedulable_enabled": true,
+				"temp_unschedulable_rules": []any{
+					map[string]any{
+						"error_code":       float64(401),
+						"keywords":         []any{"unauthorized"},
+						"duration_minutes": float64(10),
+					},
+				},
+			},
+		}
+
+		result := svc.CheckErrorPolicy(context.Background(), account, http.StatusUnauthorized, []byte(`unauthorized`))
+		require.Equal(t, ErrorPolicyNone, result, "gemini 401 with DB fallback showing previous 401 should escalate")
+	})
+
+	t.Run("antigravity_stays_temp", func(t *testing.T) {
 		repo := &dbFallbackRepoStub{
 			dbAccount: &Account{
 				ID:                      20,
@@ -40,7 +73,7 @@ func TestCheckErrorPolicy_401_DBFallback_Escalates(t *testing.T) {
 			ID:                      20,
 			Type:                    AccountTypeOAuth,
 			Platform:                PlatformAntigravity,
-		TempUnschedulableReason: "", // cache miss — reason is empty
+			TempUnschedulableReason: "",
 			Credentials: map[string]any{
 				"temp_unschedulable_enabled": true,
 				"temp_unschedulable_rules": []any{
@@ -54,7 +87,8 @@ func TestCheckErrorPolicy_401_DBFallback_Escalates(t *testing.T) {
 		}
 
 		result := svc.CheckErrorPolicy(context.Background(), account, http.StatusUnauthorized, []byte(`unauthorized`))
-	require.Equal(t, ErrorPolicyNone, result, "401 with DB fallback showing previous 401 should escalate to ErrorPolicyNone")
+		require.Equal(t, ErrorPolicyTempUnscheduled, result, "antigravity 401 skips escalation, stays temp-unscheduled")
+	})
 }
 
 func TestCheckErrorPolicy_401_DBFallback_NoDBRecord_FirstHit(t *testing.T) {

backend/internal/service/ratelimit_service_401_test.go

@@ -42,23 +42,14 @@ func (r *tokenCacheInvalidatorRecorder) InvalidateToken(ctx context.Context, acc
 }
 
 func TestRateLimitService_HandleUpstreamError_OAuth401SetsTempUnschedulable(t *testing.T) {
-	tests := []struct {
-		name     string
-		platform string
-	}{
-		{name: "gemini", platform: PlatformGemini},
-		{name: "antigravity", platform: PlatformAntigravity},
-	}
-
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
+	t.Run("gemini", func(t *testing.T) {
 		repo := &rateLimitAccountRepoStub{}
 		invalidator := &tokenCacheInvalidatorRecorder{}
 		service := NewRateLimitService(repo, nil, &config.Config{}, nil, nil)
 		service.SetTokenCacheInvalidator(invalidator)
 		account := &Account{
 			ID:       100,
-				Platform: tt.platform,
+			Platform: PlatformGemini,
 			Type:     AccountTypeOAuth,
 			Credentials: map[string]any{
 				"temp_unschedulable_enabled": true,
@@ -80,7 +71,27 @@ func TestRateLimitService_HandleUpstreamError_OAuth401SetsTempUnschedulable(t *t
 		require.Equal(t, 1, repo.tempCalls)
 		require.Len(t, invalidator.accounts, 1)
 	})
+
+	t.Run("antigravity_401_uses_SetError", func(t *testing.T) {
+		// Antigravity 401 由 applyErrorPolicy 的 temp_unschedulable_rules 控制，
+		// HandleUpstreamError 中走 SetError 路径。
+		repo := &rateLimitAccountRepoStub{}
+		invalidator := &tokenCacheInvalidatorRecorder{}
+		service := NewRateLimitService(repo, nil, &config.Config{}, nil, nil)
+		service.SetTokenCacheInvalidator(invalidator)
+		account := &Account{
+			ID:       100,
+			Platform: PlatformAntigravity,
+			Type:     AccountTypeOAuth,
 		}
+
+		shouldDisable := service.HandleUpstreamError(context.Background(), account, 401, http.Header{}, []byte("unauthorized"))
+
+		require.True(t, shouldDisable)
+		require.Equal(t, 1, repo.setErrorCalls)
+		require.Equal(t, 0, repo.tempCalls)
+		require.Empty(t, invalidator.accounts)
+	})
 }
 
 func TestRateLimitService_HandleUpstreamError_OAuth401InvalidatorError(t *testing.T) {