feat: cleanup stale concurrency slots on startup

When the service restarts, concurrency slots from the old process
remain in Redis, causing phantom occupancy. On startup, scan all
concurrency sorted sets and remove members with non-current process
prefix, then clear orphaned wait queue counters.

Uses Go-side SCAN to discover keys (compatible with Redis client
prefix hooks in tests), then passes them to a Lua script for
atomic member-level cleanup.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/internal/repository/concurrency_cache.go

@@ -147,17 +147,47 @@ var (
 			return 1
 		`)
 
-	// cleanupExpiredSlotsScript - remove expired slots
-	// KEYS[1] = concurrency:account:{accountID}
-	// ARGV[1] = TTL (seconds)
+	// cleanupExpiredSlotsScript 清理单个账号/用户有序集合中过期槽位
+	// KEYS[1] = 有序集合键
+	// ARGV[1] = TTL（秒）
 	cleanupExpiredSlotsScript = redis.NewScript(`
-			local key = KEYS[1]
-			local ttl = tonumber(ARGV[1])
-			local timeResult = redis.call('TIME')
-			local now = tonumber(timeResult[1])
-			local expireBefore = now - ttl
-			return redis.call('ZREMRANGEBYSCORE', key, '-inf', expireBefore)
-		`)
+		local key = KEYS[1]
+		local ttl = tonumber(ARGV[1])
+		local timeResult = redis.call('TIME')
+		local now = tonumber(timeResult[1])
+		local expireBefore = now - ttl
+		redis.call('ZREMRANGEBYSCORE', key, '-inf', expireBefore)
+		if redis.call('ZCARD', key) == 0 then
+			redis.call('DEL', key)
+		else
+			redis.call('EXPIRE', key, ttl)
+		end
+		return 1
+	`)
+
+	// startupCleanupScript 清理非当前进程前缀的槽位成员。
+	// KEYS 是有序集合键列表，ARGV[1] 是当前进程前缀，ARGV[2] 是槽位 TTL。
+	// 遍历每个 KEYS[i]，移除前缀不匹配的成员，清空后删 key，否则刷新 EXPIRE。
+	startupCleanupScript = redis.NewScript(`
+		local activePrefix = ARGV[1]
+		local slotTTL = tonumber(ARGV[2])
+		local removed = 0
+		for i = 1, #KEYS do
+			local key = KEYS[i]
+			local members = redis.call('ZRANGE', key, 0, -1)
+			for _, member in ipairs(members) do
+				if string.sub(member, 1, string.len(activePrefix)) ~= activePrefix then
+					removed = removed + redis.call('ZREM', key, member)
+				end
+			end
+			if redis.call('ZCARD', key) == 0 then
+				redis.call('DEL', key)
+			else
+				redis.call('EXPIRE', key, slotTTL)
+			end
+		end
+		return removed
+	`)
 )
 
 type concurrencyCache struct {
@@ -463,3 +493,72 @@ func (c *concurrencyCache) CleanupExpiredAccountSlots(ctx context.Context, accou
 	_, err := cleanupExpiredSlotsScript.Run(ctx, c.rdb, []string{key}, c.slotTTLSeconds).Result()
 	return err
 }
+
+func (c *concurrencyCache) CleanupStaleProcessSlots(ctx context.Context, activeRequestPrefix string) error {
+	if activeRequestPrefix == "" {
+		return nil
+	}
+
+	// 1. 清理有序集合中非当前进程前缀的成员
+	slotPatterns := []string{accountSlotKeyPrefix + "*", userSlotKeyPrefix + "*"}
+	for _, pattern := range slotPatterns {
+		if err := c.cleanupSlotsByPattern(ctx, pattern, activeRequestPrefix); err != nil {
+			return err
+		}
+	}
+
+	// 2. 删除所有等待队列计数器（重启后计数器失效）
+	waitPatterns := []string{accountWaitKeyPrefix + "*", waitQueueKeyPrefix + "*"}
+	for _, pattern := range waitPatterns {
+		if err := c.deleteKeysByPattern(ctx, pattern); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+// cleanupSlotsByPattern 扫描匹配 pattern 的有序集合键，批量调用 Lua 脚本清理非当前进程成员。
+func (c *concurrencyCache) cleanupSlotsByPattern(ctx context.Context, pattern, activePrefix string) error {
+	const scanCount = 200
+	var cursor uint64
+	for {
+		keys, nextCursor, err := c.rdb.Scan(ctx, cursor, pattern, scanCount).Result()
+		if err != nil {
+			return fmt.Errorf("scan %s: %w", pattern, err)
+		}
+		if len(keys) > 0 {
+			_, err := startupCleanupScript.Run(ctx, c.rdb, keys, activePrefix, c.slotTTLSeconds).Result()
+			if err != nil {
+				return fmt.Errorf("cleanup slots %s: %w", pattern, err)
+			}
+		}
+		cursor = nextCursor
+		if cursor == 0 {
+			break
+		}
+	}
+	return nil
+}
+
+// deleteKeysByPattern 扫描匹配 pattern 的键并删除。
+func (c *concurrencyCache) deleteKeysByPattern(ctx context.Context, pattern string) error {
+	const scanCount = 200
+	var cursor uint64
+	for {
+		keys, nextCursor, err := c.rdb.Scan(ctx, cursor, pattern, scanCount).Result()
+		if err != nil {
+			return fmt.Errorf("scan %s: %w", pattern, err)
+		}
+		if len(keys) > 0 {
+			if err := c.rdb.Del(ctx, keys...).Err(); err != nil {
+				return fmt.Errorf("del %s: %w", pattern, err)
+			}
+		}
+		cursor = nextCursor
+		if cursor == 0 {
+			break
+		}
+	}
+	return nil
+}