diff --git a/backend/cmd/server/wire_gen.go b/backend/cmd/server/wire_gen.go
index 300cda00..ce898a4a 100644
--- a/backend/cmd/server/wire_gen.go
+++ b/backend/cmd/server/wire_gen.go
@@ -137,7 +137,8 @@ func initializeApplication(buildInfo handler.BuildInfo) (*Application, error) {
 	schedulerOutboxRepository := repository.NewSchedulerOutboxRepository(db)
 	schedulerSnapshotService := service.ProvideSchedulerSnapshotService(schedulerCache, schedulerOutboxRepository, accountRepository, groupRepository, configConfig)
 	antigravityTokenProvider := service.ProvideAntigravityTokenProvider(accountRepository, geminiTokenCache, antigravityOAuthService, oauthRefreshAPI, tempUnschedCache)
-	antigravityGatewayService := service.NewAntigravityGatewayService(accountRepository, gatewayCache, schedulerSnapshotService, antigravityTokenProvider, rateLimitService, httpUpstream, settingService)
+	internal500CounterCache := repository.NewInternal500CounterCache(redisClient)
+	antigravityGatewayService := service.NewAntigravityGatewayService(accountRepository, gatewayCache, schedulerSnapshotService, antigravityTokenProvider, rateLimitService, httpUpstream, settingService, internal500CounterCache)
 	tlsFingerprintProfileRepository := repository.NewTLSFingerprintProfileRepository(client)
 	tlsFingerprintProfileCache := repository.NewTLSFingerprintProfileCache(redisClient)
 	tlsFingerprintProfileService := service.NewTLSFingerprintProfileService(tlsFingerprintProfileRepository, tlsFingerprintProfileCache)
diff --git a/backend/internal/repository/internal500_counter_cache.go b/backend/internal/repository/internal500_counter_cache.go
new file mode 100644
index 00000000..13b0faa8
--- /dev/null
+++ b/backend/internal/repository/internal500_counter_cache.go
@@ -0,0 +1,55 @@
+package repository
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/Wei-Shaw/sub2api/internal/service"
+	"github.com/redis/go-redis/v9"
+)
+
+const (
+	internal500CounterPrefix     = "internal500_count:account:"
+	internal500CounterTTLSeconds = 86400 // 24 小时兜底
+)
+
+// internal500CounterIncrScript 使用 Lua 脚本原子性地增加计数并返回当前值
+// 如果 key 不存在，则创建并设置过期时间
+var internal500CounterIncrScript = redis.NewScript(`
+	local key = KEYS[1]
+	local ttl = tonumber(ARGV[1])
+
+	local count = redis.call('INCR', key)
+	if count == 1 then
+		redis.call('EXPIRE', key, ttl)
+	end
+
+	return count
+`)
+
+type internal500CounterCache struct {
+	rdb *redis.Client
+}
+
+// NewInternal500CounterCache 创建 INTERNAL 500 连续失败计数器缓存实例
+func NewInternal500CounterCache(rdb *redis.Client) service.Internal500CounterCache {
+	return &internal500CounterCache{rdb: rdb}
+}
+
+// IncrementInternal500Count 原子递增计数并返回当前值
+func (c *internal500CounterCache) IncrementInternal500Count(ctx context.Context, accountID int64) (int64, error) {
+	key := fmt.Sprintf("%s%d", internal500CounterPrefix, accountID)
+
+	result, err := internal500CounterIncrScript.Run(ctx, c.rdb, []string{key}, internal500CounterTTLSeconds).Int64()
+	if err != nil {
+		return 0, fmt.Errorf("increment internal500 count: %w", err)
+	}
+
+	return result, nil
+}
+
+// ResetInternal500Count 清零计数器（成功响应时调用）
+func (c *internal500CounterCache) ResetInternal500Count(ctx context.Context, accountID int64) error {
+	key := fmt.Sprintf("%s%d", internal500CounterPrefix, accountID)
+	return c.rdb.Del(ctx, key).Err()
+}
diff --git a/backend/internal/repository/wire.go b/backend/internal/repository/wire.go
index f65f9beb..49d47bf6 100644
--- a/backend/internal/repository/wire.go
+++ b/backend/internal/repository/wire.go
@@ -81,6 +81,7 @@ var ProviderSet = wire.NewSet(
 	NewAPIKeyCache,
 	NewTempUnschedCache,
 	NewTimeoutCounterCache,
+	NewInternal500CounterCache,
 	ProvideConcurrencyCache,
 	ProvideSessionLimitCache,
 	NewRPMCache,
diff --git a/backend/internal/service/antigravity_gateway_service.go b/backend/internal/service/antigravity_gateway_service.go
index aa5d948c..a76e59fb 100644
--- a/backend/internal/service/antigravity_gateway_service.go
+++ b/backend/internal/service/antigravity_gateway_service.go
@@ -614,6 +614,7 @@ func (s *AntigravityGatewayService) antigravityRetryLoop(p antigravityRetryLoopP
 urlFallbackLoop:
 	for urlIdx, baseURL := range availableURLs {
 		usedBaseURL = baseURL
+		allAttemptsInternal500 := true // 追踪本轮所有 attempt 是否全部命中 INTERNAL 500
 		for attempt := 1; attempt <= antigravityMaxRetries; attempt++ {
 			select {
 			case <-p.ctx.Done():
@@ -766,10 +767,19 @@ urlFallbackLoop:
 							logger.LegacyPrintf("service.antigravity_gateway", "%s status=context_canceled_during_backoff", p.prefix)
 							return nil, p.ctx.Err()
 						}
+						// 追踪 INTERNAL 500：非匹配的 attempt 清除标记
+						if !isAntigravityInternalServerError(resp.StatusCode, respBody) {
+							allAttemptsInternal500 = false
+						}
 						continue
 					}
 				}
 
+				// INTERNAL 500 渐进惩罚：3 次重试全部命中特定 500 时递增计数器并惩罚
+				if allAttemptsInternal500 && isAntigravityInternalServerError(resp.StatusCode, respBody) {
+					s.handleInternal500RetryExhausted(p.ctx, p.prefix, p.account)
+				}
+
 				// 其他 4xx 错误或重试用尽，直接返回
 				resp = &http.Response{
 					StatusCode: resp.StatusCode,
@@ -788,6 +798,11 @@ urlFallbackLoop:
 		antigravity.DefaultURLAvailability.MarkSuccess(usedBaseURL)
 	}
 
+	// 成功响应时清零 INTERNAL 500 连续失败计数器（覆盖所有成功路径，含 smart retry）
+	if resp != nil && resp.StatusCode < 400 {
+		s.resetInternal500Counter(p.ctx, p.prefix, p.account.ID)
+	}
+
 	return &antigravityRetryLoopResult{resp: resp}, nil
 }
 
@@ -862,6 +877,7 @@ type AntigravityGatewayService struct {
 	settingService    *SettingService
 	cache             GatewayCache // 用于模型级限流时清除粘性会话绑定
 	schedulerSnapshot *SchedulerSnapshotService
+	internal500Cache  Internal500CounterCache // INTERNAL 500 渐进惩罚计数器
 }
 
 func NewAntigravityGatewayService(
@@ -872,6 +888,7 @@ func NewAntigravityGatewayService(
 	rateLimitService *RateLimitService,
 	httpUpstream HTTPUpstream,
 	settingService *SettingService,
+	internal500Cache Internal500CounterCache,
 ) *AntigravityGatewayService {
 	return &AntigravityGatewayService{
 		accountRepo:       accountRepo,
@@ -881,6 +898,7 @@ func NewAntigravityGatewayService(
 		settingService:    settingService,
 		cache:             cache,
 		schedulerSnapshot: schedulerSnapshot,
+		internal500Cache:  internal500Cache,
 	}
 }
 
diff --git a/backend/internal/service/antigravity_internal500_penalty.go b/backend/internal/service/antigravity_internal500_penalty.go
new file mode 100644
index 00000000..747a4d4e
--- /dev/null
+++ b/backend/internal/service/antigravity_internal500_penalty.go
@@ -0,0 +1,97 @@
+package service
+
+import (
+	"context"
+	"fmt"
+	"log/slog"
+	"net/http"
+	"time"
+
+	"github.com/tidwall/gjson"
+)
+
+// INTERNAL 500 渐进惩罚：连续多轮全部返回特定 500 错误时的惩罚时长
+const (
+	internal500PenaltyTier1Duration  = 30 * time.Minute // 第 1 轮：临时不可调度 30 分钟
+	internal500PenaltyTier2Duration  = 2 * time.Hour    // 第 2 轮：临时不可调度 2 小时
+	internal500PenaltyTier3Threshold = 3                // 第 3+ 轮：永久禁用
+)
+
+// isAntigravityInternalServerError 检测特定的 INTERNAL 500 错误
+// 必须同时匹配 error.code==500, error.message=="Internal error encountered.", error.status=="INTERNAL"
+func isAntigravityInternalServerError(statusCode int, body []byte) bool {
+	if statusCode != http.StatusInternalServerError {
+		return false
+	}
+	return gjson.GetBytes(body, "error.code").Int() == 500 &&
+		gjson.GetBytes(body, "error.message").String() == "Internal error encountered." &&
+		gjson.GetBytes(body, "error.status").String() == "INTERNAL"
+}
+
+// applyInternal500Penalty 根据连续 INTERNAL 500 轮次数应用渐进惩罚
+// count=1: temp_unschedulable 10 分钟
+// count=2: temp_unschedulable 10 小时
+// count>=3: SetError 永久禁用
+func (s *AntigravityGatewayService) applyInternal500Penalty(
+	ctx context.Context, prefix string, account *Account, count int64,
+) {
+	switch {
+	case count >= int64(internal500PenaltyTier3Threshold):
+		reason := fmt.Sprintf("INTERNAL 500 consecutive failures: %d rounds", count)
+		if err := s.accountRepo.SetError(ctx, account.ID, reason); err != nil {
+			slog.Error("internal500_set_error_failed", "account_id", account.ID, "error", err)
+			return
+		}
+		slog.Warn("internal500_account_disabled",
+			"account_id", account.ID, "account_name", account.Name, "consecutive_count", count)
+	case count == 2:
+		until := time.Now().Add(internal500PenaltyTier2Duration)
+		reason := fmt.Sprintf("INTERNAL 500 x%d (temp unsched %v)", count, internal500PenaltyTier2Duration)
+		if err := s.accountRepo.SetTempUnschedulable(ctx, account.ID, until, reason); err != nil {
+			slog.Error("internal500_temp_unsched_failed", "account_id", account.ID, "error", err)
+			return
+		}
+		slog.Warn("internal500_temp_unschedulable",
+			"account_id", account.ID, "account_name", account.Name,
+			"duration", internal500PenaltyTier2Duration, "consecutive_count", count)
+	case count == 1:
+		until := time.Now().Add(internal500PenaltyTier1Duration)
+		reason := fmt.Sprintf("INTERNAL 500 x%d (temp unsched %v)", count, internal500PenaltyTier1Duration)
+		if err := s.accountRepo.SetTempUnschedulable(ctx, account.ID, until, reason); err != nil {
+			slog.Error("internal500_temp_unsched_failed", "account_id", account.ID, "error", err)
+			return
+		}
+		slog.Info("internal500_temp_unschedulable",
+			"account_id", account.ID, "account_name", account.Name,
+			"duration", internal500PenaltyTier1Duration, "consecutive_count", count)
+	}
+}
+
+// handleInternal500RetryExhausted 处理 INTERNAL 500 重试耗尽：递增计数器并应用惩罚
+func (s *AntigravityGatewayService) handleInternal500RetryExhausted(
+	ctx context.Context, prefix string, account *Account,
+) {
+	if s.internal500Cache == nil {
+		return
+	}
+	count, err := s.internal500Cache.IncrementInternal500Count(ctx, account.ID)
+	if err != nil {
+		slog.Error("internal500_counter_increment_failed",
+			"prefix", prefix, "account_id", account.ID, "error", err)
+		return
+	}
+	s.applyInternal500Penalty(ctx, prefix, account, count)
+}
+
+// resetInternal500Counter 成功响应时清零 INTERNAL 500 计数器
+func (s *AntigravityGatewayService) resetInternal500Counter(
+	ctx context.Context, prefix string, accountID int64,
+) {
+	if s.internal500Cache == nil {
+		return
+	}
+	if err := s.internal500Cache.ResetInternal500Count(ctx, accountID); err != nil {
+		slog.Error("internal500_counter_reset_failed",
+			"prefix", prefix, "account_id", accountID, "error", err)
+	}
+}
diff --git a/backend/internal/service/antigravity_internal500_penalty_test.go b/backend/internal/service/antigravity_internal500_penalty_test.go
new file mode 100644
index 00000000..03831839
--- /dev/null
+++ b/backend/internal/service/antigravity_internal500_penalty_test.go
@@ -0,0 +1,321 @@
+//go:build unit
+
+package service
+
+import (
+	"context"
+	"errors"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+)
+
+// --- mock: Internal500CounterCache ---
+
+type mockInternal500Cache struct {
+	incrementCount int64
+	incrementErr   error
+	resetErr       error
+
+	incrementCalls []int64 // 记录 IncrementInternal500Count 被调用时的 accountID
+	resetCalls     []int64 // 记录 ResetInternal500Count 被调用时的 accountID
+}
+
+func (m *mockInternal500Cache) IncrementInternal500Count(_ context.Context, accountID int64) (int64, error) {
+	m.incrementCalls = append(m.incrementCalls, accountID)
+	return m.incrementCount, m.incrementErr
+}
+
+func (m *mockInternal500Cache) ResetInternal500Count(_ context.Context, accountID int64) error {
+	m.resetCalls = append(m.resetCalls, accountID)
+	return m.resetErr
+}
+
+// --- mock: 专用于 internal500 惩罚测试的 AccountRepository ---
+
+type internal500AccountRepoStub struct {
+	AccountRepository // 嵌入接口，未实现的方法会 panic（不应被调用）
+
+	tempUnschedCalls []tempUnschedCall
+	setErrorCalls    []setErrorCall
+}
+
+type tempUnschedCall struct {
+	accountID int64
+	until     time.Time
+	reason    string
+}
+
+type setErrorCall struct {
+	accountID int64
+	reason    string
+}
+
+func (r *internal500AccountRepoStub) SetTempUnschedulable(_ context.Context, id int64, until time.Time, reason string) error {
+	r.tempUnschedCalls = append(r.tempUnschedCalls, tempUnschedCall{accountID: id, until: until, reason: reason})
+	return nil
+}
+
+func (r *internal500AccountRepoStub) SetError(_ context.Context, id int64, errorMsg string) error {
+	r.setErrorCalls = append(r.setErrorCalls, setErrorCall{accountID: id, reason: errorMsg})
+	return nil
+}
+
+// =============================================================================
+// TestIsAntigravityInternalServerError
+// =============================================================================
+
+func TestIsAntigravityInternalServerError(t *testing.T) {
+	t.Run("匹配完整的 INTERNAL 500 body", func(t *testing.T) {
+		body := []byte(`{"error":{"code":500,"message":"Internal error encountered.","status":"INTERNAL"}}`)
+		require.True(t, isAntigravityInternalServerError(500, body))
+	})
+
+	t.Run("statusCode 不是 500", func(t *testing.T) {
+		body := []byte(`{"error":{"code":500,"message":"Internal error encountered.","status":"INTERNAL"}}`)
+		require.False(t, isAntigravityInternalServerError(429, body))
+		require.False(t, isAntigravityInternalServerError(503, body))
+		require.False(t, isAntigravityInternalServerError(200, body))
+	})
+
+	t.Run("body 中 message 不匹配", func(t *testing.T) {
+		body := []byte(`{"error":{"code":500,"message":"Some other error","status":"INTERNAL"}}`)
+		require.False(t, isAntigravityInternalServerError(500, body))
+	})
+
+	t.Run("body 中 status 不匹配", func(t *testing.T) {
+		body := []byte(`{"error":{"code":500,"message":"Internal error encountered.","status":"UNAVAILABLE"}}`)
+		require.False(t, isAntigravityInternalServerError(500, body))
+	})
+
+	t.Run("body 中 code 不匹配", func(t *testing.T) {
+		body := []byte(`{"error":{"code":503,"message":"Internal error encountered.","status":"INTERNAL"}}`)
+		require.False(t, isAntigravityInternalServerError(500, body))
+	})
+
+	t.Run("空 body", func(t *testing.T) {
+		require.False(t, isAntigravityInternalServerError(500, []byte{}))
+		require.False(t, isAntigravityInternalServerError(500, nil))
+	})
+
+	t.Run("其他 500 错误格式（纯文本）", func(t *testing.T) {
+		body := []byte(`Internal Server Error`)
+		require.False(t, isAntigravityInternalServerError(500, body))
+	})
+
+	t.Run("其他 500 错误格式（不同 JSON 结构）", func(t *testing.T) {
+		body := []byte(`{"message":"Internal Server Error","statusCode":500}`)
+		require.False(t, isAntigravityInternalServerError(500, body))
+	})
+}
+
+// =============================================================================
+// TestApplyInternal500Penalty
+// =============================================================================
+
+func TestApplyInternal500Penalty(t *testing.T) {
+	t.Run("count=1 → SetTempUnschedulable 10 分钟", func(t *testing.T) {
+		repo := &internal500AccountRepoStub{}
+		svc := &AntigravityGatewayService{accountRepo: repo}
+		account := &Account{ID: 1, Name: "acc-1"}
+
+		before := time.Now()
+		svc.applyInternal500Penalty(context.Background(), "[test]", account, 1)
+		after := time.Now()
+
+		require.Len(t, repo.tempUnschedCalls, 1)
+		require.Empty(t, repo.setErrorCalls)
+
+		call := repo.tempUnschedCalls[0]
+		require.Equal(t, int64(1), call.accountID)
+		require.Contains(t, call.reason, "INTERNAL 500")
+		// until 应在 [before+10m, after+10m] 范围内
+		require.True(t, call.until.After(before.Add(internal500PenaltyTier1Duration).Add(-time.Second)))
+		require.True(t, call.until.Before(after.Add(internal500PenaltyTier1Duration).Add(time.Second)))
+	})
+
+	t.Run("count=2 → SetTempUnschedulable 10 小时", func(t *testing.T) {
+		repo := &internal500AccountRepoStub{}
+		svc := &AntigravityGatewayService{accountRepo: repo}
+		account := &Account{ID: 2, Name: "acc-2"}
+
+		before := time.Now()
+		svc.applyInternal500Penalty(context.Background(), "[test]", account, 2)
+		after := time.Now()
+
+		require.Len(t, repo.tempUnschedCalls, 1)
+		require.Empty(t, repo.setErrorCalls)
+
+		call := repo.tempUnschedCalls[0]
+		require.Equal(t, int64(2), call.accountID)
+		require.Contains(t, call.reason, "INTERNAL 500")
+		require.True(t, call.until.After(before.Add(internal500PenaltyTier2Duration).Add(-time.Second)))
+		require.True(t, call.until.Before(after.Add(internal500PenaltyTier2Duration).Add(time.Second)))
+	})
+
+	t.Run("count=3 → SetError 永久禁用", func(t *testing.T) {
+		repo := &internal500AccountRepoStub{}
+		svc := &AntigravityGatewayService{accountRepo: repo}
+		account := &Account{ID: 3, Name: "acc-3"}
+
+		svc.applyInternal500Penalty(context.Background(), "[test]", account, 3)
+
+		require.Empty(t, repo.tempUnschedCalls)
+		require.Len(t, repo.setErrorCalls, 1)
+
+		call := repo.setErrorCalls[0]
+		require.Equal(t, int64(3), call.accountID)
+		require.Contains(t, call.reason, "INTERNAL 500 consecutive failures: 3")
+	})
+
+	t.Run("count=5 → SetError 永久禁用（>=3 都走永久禁用）", func(t *testing.T) {
+		repo := &internal500AccountRepoStub{}
+		svc := &AntigravityGatewayService{accountRepo: repo}
+		account := &Account{ID: 5, Name: "acc-5"}
+
+		svc.applyInternal500Penalty(context.Background(), "[test]", account, 5)
+
+		require.Empty(t, repo.tempUnschedCalls)
+		require.Len(t, repo.setErrorCalls, 1)
+
+		call := repo.setErrorCalls[0]
+		require.Equal(t, int64(5), call.accountID)
+		require.Contains(t, call.reason, "INTERNAL 500 consecutive failures: 5")
+	})
+
+	t.Run("count=0 → 不调用任何方法", func(t *testing.T) {
+		repo := &internal500AccountRepoStub{}
+		svc := &AntigravityGatewayService{accountRepo: repo}
+		account := &Account{ID: 10, Name: "acc-10"}
+
+		svc.applyInternal500Penalty(context.Background(), "[test]", account, 0)
+
+		require.Empty(t, repo.tempUnschedCalls)
+		require.Empty(t, repo.setErrorCalls)
+	})
+}
+
+// =============================================================================
+// TestHandleInternal500RetryExhausted
+// =============================================================================
+
+func TestHandleInternal500RetryExhausted(t *testing.T) {
+	t.Run("internal500Cache 为 nil → 不 panic，不调用任何方法", func(t *testing.T) {
+		repo := &internal500AccountRepoStub{}
+		svc := &AntigravityGatewayService{
+			accountRepo:      repo,
+			internal500Cache: nil,
+		}
+		account := &Account{ID: 1, Name: "acc-1"}
+
+		// 不应 panic
+		require.NotPanics(t, func() {
+			svc.handleInternal500RetryExhausted(context.Background(), "[test]", account)
+		})
+		require.Empty(t, repo.tempUnschedCalls)
+		require.Empty(t, repo.setErrorCalls)
+	})
+
+	t.Run("IncrementInternal500Count 返回 error → 不调用惩罚方法", func(t *testing.T) {
+		repo := &internal500AccountRepoStub{}
+		cache := &mockInternal500Cache{
+			incrementErr: errors.New("redis connection error"),
+		}
+		svc := &AntigravityGatewayService{
+			accountRepo:      repo,
+			internal500Cache: cache,
+		}
+		account := &Account{ID: 2, Name: "acc-2"}
+
+		svc.handleInternal500RetryExhausted(context.Background(), "[test]", account)
+
+		require.Len(t, cache.incrementCalls, 1)
+		require.Equal(t, int64(2), cache.incrementCalls[0])
+		require.Empty(t, repo.tempUnschedCalls)
+		require.Empty(t, repo.setErrorCalls)
+	})
+
+	t.Run("IncrementInternal500Count 返回 count=1 → 触发 tier1 惩罚", func(t *testing.T) {
+		repo := &internal500AccountRepoStub{}
+		cache := &mockInternal500Cache{
+			incrementCount: 1,
+		}
+		svc := &AntigravityGatewayService{
+			accountRepo:      repo,
+			internal500Cache: cache,
+		}
+		account := &Account{ID: 3, Name: "acc-3"}
+
+		svc.handleInternal500RetryExhausted(context.Background(), "[test]", account)
+
+		require.Len(t, cache.incrementCalls, 1)
+		require.Equal(t, int64(3), cache.incrementCalls[0])
+		// tier1: SetTempUnschedulable
+		require.Len(t, repo.tempUnschedCalls, 1)
+		require.Equal(t, int64(3), repo.tempUnschedCalls[0].accountID)
+		require.Empty(t, repo.setErrorCalls)
+	})
+
+	t.Run("IncrementInternal500Count 返回 count=3 → 触发 tier3 永久禁用", func(t *testing.T) {
+		repo := &internal500AccountRepoStub{}
+		cache := &mockInternal500Cache{
+			incrementCount: 3,
+		}
+		svc := &AntigravityGatewayService{
+			accountRepo:      repo,
+			internal500Cache: cache,
+		}
+		account := &Account{ID: 4, Name: "acc-4"}
+
+		svc.handleInternal500RetryExhausted(context.Background(), "[test]", account)
+
+		require.Len(t, cache.incrementCalls, 1)
+		require.Empty(t, repo.tempUnschedCalls)
+		require.Len(t, repo.setErrorCalls, 1)
+		require.Equal(t, int64(4), repo.setErrorCalls[0].accountID)
+	})
+}
+
+// =============================================================================
+// TestResetInternal500Counter
+// =============================================================================
+
+func TestResetInternal500Counter(t *testing.T) {
+	t.Run("internal500Cache 为 nil → 不 panic", func(t *testing.T) {
+		svc := &AntigravityGatewayService{
+			internal500Cache: nil,
+		}
+
+		require.NotPanics(t, func() {
+			svc.resetInternal500Counter(context.Background(), "[test]", 1)
+		})
+	})
+
+	t.Run("ResetInternal500Count 返回 error → 不 panic（仅日志）", func(t *testing.T) {
+		cache := &mockInternal500Cache{
+			resetErr: errors.New("redis timeout"),
+		}
+		svc := &AntigravityGatewayService{
+			internal500Cache: cache,
+		}
+
+		require.NotPanics(t, func() {
+			svc.resetInternal500Counter(context.Background(), "[test]", 42)
+		})
+		require.Len(t, cache.resetCalls, 1)
+		require.Equal(t, int64(42), cache.resetCalls[0])
+	})
+
+	t.Run("正常调用 → 调用 ResetInternal500Count", func(t *testing.T) {
+		cache := &mockInternal500Cache{}
+		svc := &AntigravityGatewayService{
+			internal500Cache: cache,
+		}
+
+		svc.resetInternal500Counter(context.Background(), "[test]", 99)
+
+		require.Len(t, cache.resetCalls, 1)
+		require.Equal(t, int64(99), cache.resetCalls[0])
+	})
+}
diff --git a/backend/internal/service/internal500_counter.go b/backend/internal/service/internal500_counter.go
new file mode 100644
index 00000000..0f0bc50c
--- /dev/null
+++ b/backend/internal/service/internal500_counter.go
@@ -0,0 +1,11 @@
+package service
+
+import "context"
+
+// Internal500CounterCache 追踪 Antigravity 账号连续 INTERNAL 500 失败轮数
+type Internal500CounterCache interface {
+	// IncrementInternal500Count 原子递增计数并返回当前值
+	IncrementInternal500Count(ctx context.Context, accountID int64) (int64, error)
+	// ResetInternal500Count 清零计数器（成功响应时调用）
+	ResetInternal500Count(ctx context.Context, accountID int64) error
+}