feat: add RPMCache interface and Redis implementation with Lua scripts

backend/internal/repository/rpm_cache.go

+package repository
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/redis/go-redis/v9"
+)
+
+const rpmKeyPrefix = "rpm:"
+
+// Lua scripts use Redis TIME for server-side minute key calculation
+var rpmIncrScript = redis.NewScript(`
+local timeResult = redis.call('TIME')
+local minuteKey = math.floor(tonumber(timeResult[1]) / 60)
+local key = ARGV[1] .. ':' .. minuteKey
+local count = redis.call('INCR', key)
+if count == 1 then
+    redis.call('EXPIRE', key, 120)
+end
+return count
+`)
+
+var rpmGetScript = redis.NewScript(`
+local timeResult = redis.call('TIME')
+local minuteKey = math.floor(tonumber(timeResult[1]) / 60)
+local key = ARGV[1] .. ':' .. minuteKey
+local count = redis.call('GET', key)
+if count == false then
+    return 0
+end
+return tonumber(count)
+`)
+
+type RPMCacheImpl struct {
+	rdb *redis.Client
+}
+
+func NewRPMCache(rdb *redis.Client) *RPMCacheImpl {
+	return &RPMCacheImpl{rdb: rdb}
+}
+
+func rpmKeyBase(accountID int64) string {
+	return fmt.Sprintf("%s%d", rpmKeyPrefix, accountID)
+}
+
+func (c *RPMCacheImpl) IncrementRPM(ctx context.Context, accountID int64) (int, error) {
+	result, err := rpmIncrScript.Run(ctx, c.rdb, nil, rpmKeyBase(accountID)).Int()
+	if err != nil {
+		return 0, fmt.Errorf("rpm increment: %w", err)
+	}
+	return result, nil
+}
+
+func (c *RPMCacheImpl) GetRPM(ctx context.Context, accountID int64) (int, error) {
+	result, err := rpmGetScript.Run(ctx, c.rdb, nil, rpmKeyBase(accountID)).Int()
+	if err != nil {
+		return 0, fmt.Errorf("rpm get: %w", err)
+	}
+	return result, nil
+}
+
+func (c *RPMCacheImpl) GetRPMBatch(ctx context.Context, accountIDs []int64) (map[int64]int, error) {
+	if len(accountIDs) == 0 {
+		return map[int64]int{}, nil
+	}
+
+	pipe := c.rdb.Pipeline()
+	cmds := make(map[int64]*redis.Cmd, len(accountIDs))
+	for _, id := range accountIDs {
+		cmds[id] = rpmGetScript.Run(ctx, pipe, nil, rpmKeyBase(id))
+	}
+
+	_, err := pipe.Exec(ctx)
+	if err != nil && err != redis.Nil {
+		return nil, fmt.Errorf("rpm batch get: %w", err)
+	}
+
+	result := make(map[int64]int, len(accountIDs))
+	for id, cmd := range cmds {
+		if val, err := cmd.Int(); err == nil {
+			result[id] = val
+		} else {
+			result[id] = 0
+		}
+	}
+	return result, nil
+}

backend/internal/service/rpm_cache.go

+package service
+
+import "context"
+
+// RPMCache RPM 计数器缓存接口
+// 用于 Anthropic OAuth/SetupToken 账号的每分钟请求数限制
+type RPMCache interface {
+	// IncrementRPM 原子递增并返回当前分钟的计数
+	// 使用 Redis 服务器时间确定 minute key，避免多实例时钟偏差
+	IncrementRPM(ctx context.Context, accountID int64) (count int, err error)
+
+	// GetRPM 获取当前分钟的 RPM 计数
+	GetRPM(ctx context.Context, accountID int64) (count int, err error)
+
+	// GetRPMBatch 批量获取多个账号的 RPM 计数（使用 Pipeline）
+	GetRPMBatch(ctx context.Context, accountIDs []int64) (map[int64]int, error)
+}