fix(服务): 修复system判定、统计时区与缓存日志

- system 字段存在即视为显式提供，避免 null 触发默认注入
- 日统计分组显式使用应用时区，缺失时从 TZ 回退到 UTC
- 缓存写入队列丢弃日志节流汇总，关键任务同步回退

测试: go test ./internal/service -run TestBillingCacheServiceQueueHighLoad

backend/internal/repository/usage_log_repo.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"database/sql"
 	"fmt"
+	"os"
 	"strings"
 	"time"
 
@@ -536,9 +537,11 @@ func (r *usageLogRepository) GetModelStatsAggregated(ctx context.Context, modelN
 // GetDailyStatsAggregated 使用 SQL 聚合统计用户的每日使用数据
 // 性能优化：使用 GROUP BY 在数据库层按日期分组聚合，避免应用层循环分组统计
 func (r *usageLogRepository) GetDailyStatsAggregated(ctx context.Context, userID int64, startTime, endTime time.Time) (result []map[string]any, err error) {
+	tzName := resolveUsageStatsTimezone()
 	query := `
 		SELECT
-			TO_CHAR(created_at, 'YYYY-MM-DD') as date,
+			-- 使用应用时区分组，避免数据库会话时区导致日边界偏移。
+			TO_CHAR(created_at AT TIME ZONE $4, 'YYYY-MM-DD') as date,
 			COUNT(*) as total_requests,
 			COALESCE(SUM(input_tokens), 0) as total_input_tokens,
 			COALESCE(SUM(output_tokens), 0) as total_output_tokens,
@@ -552,7 +555,7 @@ func (r *usageLogRepository) GetDailyStatsAggregated(ctx context.Context, userID
 		ORDER BY 1
 	`
 
-	rows, err := r.sql.QueryContext(ctx, query, userID, startTime, endTime)
+	rows, err := r.sql.QueryContext(ctx, query, userID, startTime, endTime, tzName)
 	if err != nil {
 		return nil, err
 	}
@@ -607,6 +610,19 @@ func (r *usageLogRepository) GetDailyStatsAggregated(ctx context.Context, userID
 	return result, nil
 }
 
+// resolveUsageStatsTimezone 获取用于 SQL 分组的时区名称。
+// 优先使用应用初始化的时区，其次尝试读取 TZ 环境变量，最后回落为 UTC。
+func resolveUsageStatsTimezone() string {
+	tzName := timezone.Name()
+	if tzName != "" && tzName != "Local" {
+		return tzName
+	}
+	if envTZ := strings.TrimSpace(os.Getenv("TZ")); envTZ != "" {
+		return envTZ
+	}
+	return "UTC"
+}
+
 func (r *usageLogRepository) ListByApiKeyAndTimeRange(ctx context.Context, apiKeyID int64, startTime, endTime time.Time) ([]service.UsageLog, *pagination.PaginationResult, error) {
 	query := "SELECT " + usageLogSelectColumns + " FROM usage_logs WHERE api_key_id = $1 AND created_at >= $2 AND created_at < $3 ORDER BY id DESC"
 	logs, err := r.queryUsageLogs(ctx, query, apiKeyID, startTime, endTime)

backend/internal/service/billing_cache_service.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"log"
 	"sync"
+	"sync/atomic"
 	"time"
 
 	"github.com/Wei-Shaw/sub2api/internal/config"
@@ -49,12 +50,13 @@ const (
 // 新实现使用固定大小的工作池：
 // 1. 预创建 10 个 worker goroutine，避免频繁创建销毁
 // 2. 使用带缓冲的 channel（1000）作为任务队列，平滑写入峰值
-// 3. 非阻塞写入，队列满时丢弃任务（缓存最终一致性可接受）
+// 3. 非阻塞写入，队列满时关键任务同步回退，非关键任务丢弃并告警
 // 4. 统一超时控制，避免慢操作阻塞工作池
 const (
-	cacheWriteWorkerCount = 10              // 工作协程数量
-	cacheWriteBufferSize  = 1000            // 任务队列缓冲大小
-	cacheWriteTimeout     = 2 * time.Second // 单个写入操作超时
+	cacheWriteWorkerCount     = 10              // 工作协程数量
+	cacheWriteBufferSize      = 1000            // 任务队列缓冲大小
+	cacheWriteTimeout         = 2 * time.Second // 单个写入操作超时
+	cacheWriteDropLogInterval = 5 * time.Second // 丢弃日志节流间隔
 )
 
 // cacheWriteTask 缓存写入任务
@@ -78,6 +80,11 @@ type BillingCacheService struct {
 	cacheWriteChan     chan cacheWriteTask
 	cacheWriteWg       sync.WaitGroup
 	cacheWriteStopOnce sync.Once
+	// 丢弃日志节流计数器（减少高负载下日志噪音）
+	cacheWriteDropFullCount     uint64
+	cacheWriteDropFullLastLog   int64
+	cacheWriteDropClosedCount   uint64
+	cacheWriteDropClosedLastLog int64
 }
 
 // NewBillingCacheService 创建计费缓存服务
@@ -112,16 +119,25 @@ func (s *BillingCacheService) startCacheWriteWorkers() {
 	}
 }
 
-func (s *BillingCacheService) enqueueCacheWrite(task cacheWriteTask) {
+// enqueueCacheWrite 尝试将任务入队，队列满时返回 false（并记录告警）。
+func (s *BillingCacheService) enqueueCacheWrite(task cacheWriteTask) (enqueued bool) {
 	if s.cacheWriteChan == nil {
-		return
+		return false
 	}
 	defer func() {
-		_ = recover()
+		if recovered := recover(); recovered != nil {
+			// 队列已关闭时可能触发 panic，记录后静默失败。
+			s.logCacheWriteDrop(task, "closed")
+			enqueued = false
+		}
 	}()
 	select {
 	case s.cacheWriteChan <- task:
+		return true
 	default:
+		// 队列满时不阻塞主流程，交由调用方决定是否同步回退。
+		s.logCacheWriteDrop(task, "full")
+		return false
 	}
 }
 
@@ -151,6 +167,62 @@ func (s *BillingCacheService) cacheWriteWorker() {
 	}
 }
 
+// cacheWriteKindName 用于日志中的任务类型标识，便于排查丢弃原因。
+func cacheWriteKindName(kind cacheWriteKind) string {
+	switch kind {
+	case cacheWriteSetBalance:
+		return "set_balance"
+	case cacheWriteSetSubscription:
+		return "set_subscription"
+	case cacheWriteUpdateSubscriptionUsage:
+		return "update_subscription_usage"
+	case cacheWriteDeductBalance:
+		return "deduct_balance"
+	default:
+		return "unknown"
+	}
+}
+
+// logCacheWriteDrop 使用节流方式记录丢弃情况，并汇总丢弃数量。
+func (s *BillingCacheService) logCacheWriteDrop(task cacheWriteTask, reason string) {
+	var (
+		countPtr *uint64
+		lastPtr  *int64
+	)
+	switch reason {
+	case "full":
+		countPtr = &s.cacheWriteDropFullCount
+		lastPtr = &s.cacheWriteDropFullLastLog
+	case "closed":
+		countPtr = &s.cacheWriteDropClosedCount
+		lastPtr = &s.cacheWriteDropClosedLastLog
+	default:
+		return
+	}
+
+	atomic.AddUint64(countPtr, 1)
+	now := time.Now().UnixNano()
+	last := atomic.LoadInt64(lastPtr)
+	if now-last < int64(cacheWriteDropLogInterval) {
+		return
+	}
+	if !atomic.CompareAndSwapInt64(lastPtr, last, now) {
+		return
+	}
+	dropped := atomic.SwapUint64(countPtr, 0)
+	if dropped == 0 {
+		return
+	}
+	log.Printf("Warning: cache write queue %s, dropped %d tasks in last %s (latest kind=%s user %d group %d)",
+		reason,
+		dropped,
+		cacheWriteDropLogInterval,
+		cacheWriteKindName(task.kind),
+		task.userID,
+		task.groupID,
+	)
+}
+
 // ============================================
 // 余额缓存方法
 // ============================================
@@ -175,7 +247,7 @@ func (s *BillingCacheService) GetUserBalance(ctx context.Context, userID int64)
 	}
 
 	// 异步建立缓存
-	s.enqueueCacheWrite(cacheWriteTask{
+	_ = s.enqueueCacheWrite(cacheWriteTask{
 		kind:    cacheWriteSetBalance,
 		userID:  userID,
 		balance: balance,
@@ -213,11 +285,22 @@ func (s *BillingCacheService) DeductBalanceCache(ctx context.Context, userID int
 
 // QueueDeductBalance 异步扣减余额缓存
 func (s *BillingCacheService) QueueDeductBalance(userID int64, amount float64) {
-	s.enqueueCacheWrite(cacheWriteTask{
+	if s.cache == nil {
+		return
+	}
+	// 队列满时同步回退，避免关键扣减被静默丢弃。
+	if s.enqueueCacheWrite(cacheWriteTask{
 		kind:   cacheWriteDeductBalance,
 		userID: userID,
 		amount: amount,
-	})
+	}) {
+		return
+	}
+	ctx, cancel := context.WithTimeout(context.Background(), cacheWriteTimeout)
+	defer cancel()
+	if err := s.DeductBalanceCache(ctx, userID, amount); err != nil {
+		log.Printf("Warning: deduct balance cache fallback failed for user %d: %v", userID, err)
+	}
 }
 
 // InvalidateUserBalance 失效用户余额缓存
@@ -255,7 +338,7 @@ func (s *BillingCacheService) GetSubscriptionStatus(ctx context.Context, userID,
 	}
 
 	// 异步建立缓存
-	s.enqueueCacheWrite(cacheWriteTask{
+	_ = s.enqueueCacheWrite(cacheWriteTask{
 		kind:             cacheWriteSetSubscription,
 		userID:           userID,
 		groupID:          groupID,
@@ -324,12 +407,23 @@ func (s *BillingCacheService) UpdateSubscriptionUsage(ctx context.Context, userI
 
 // QueueUpdateSubscriptionUsage 异步更新订阅用量缓存
 func (s *BillingCacheService) QueueUpdateSubscriptionUsage(userID, groupID int64, costUSD float64) {
-	s.enqueueCacheWrite(cacheWriteTask{
+	if s.cache == nil {
+		return
+	}
+	// 队列满时同步回退，确保订阅用量及时更新。
+	if s.enqueueCacheWrite(cacheWriteTask{
 		kind:    cacheWriteUpdateSubscriptionUsage,
 		userID:  userID,
 		groupID: groupID,
 		amount:  costUSD,
-	})
+	}) {
+		return
+	}
+	ctx, cancel := context.WithTimeout(context.Background(), cacheWriteTimeout)
+	defer cancel()
+	if err := s.UpdateSubscriptionUsage(ctx, userID, groupID, costUSD); err != nil {
+		log.Printf("Warning: update subscription cache fallback failed for user %d group %d: %v", userID, groupID, err)
+	}
 }
 
 // InvalidateSubscription 失效指定订阅缓存

backend/internal/service/gateway_request.go

@@ -24,7 +24,7 @@ type ParsedRequest struct {
 	MetadataUserID string // metadata.user_id（用于会话亲和）
 	System         any    // system 字段内容
 	Messages       []any  // messages 数组
-	HasSystem      bool   // 是否包含 system 字段
+	HasSystem      bool   // 是否包含 system 字段（包含 null 也视为显式传入）
 }
 
 // ParseGatewayRequest 解析网关请求体并返回结构化结果
@@ -58,7 +58,9 @@ func ParseGatewayRequest(body []byte) (*ParsedRequest, error) {
 			parsed.MetadataUserID = userID
 		}
 	}
-	if system, ok := req["system"]; ok && system != nil {
+	// system 字段只要存在就视为显式提供（即使为 null），
+	// 以避免客户端传 null 时被默认 system 误注入。
+	if system, ok := req["system"]; ok {
 		parsed.HasSystem = true
 		parsed.System = system
 	}

backend/internal/service/gateway_request_test.go

@@ -22,7 +22,9 @@ func TestParseGatewayRequest_SystemNull(t *testing.T) {
 	body := []byte(`{"model":"claude-3","system":null}`)
 	parsed, err := ParseGatewayRequest(body)
 	require.NoError(t, err)
-	require.False(t, parsed.HasSystem)
+	// 显式传入 system:null 也应视为“字段已存在”，避免默认 system 被注入。
+	require.True(t, parsed.HasSystem)
+	require.Nil(t, parsed.System)
 }
 
 func TestParseGatewayRequest_InvalidModelType(t *testing.T) {