feat: 实现基于日费用的智能负载均衡策略

- 新增 sortAccountsByCost() 方法，支持按日费用排序账号
- 修改账号选择逻辑从时间排序改为费用排序
- 添加多层容错机制：单账号失败、全局失败、方法异常
- 费用获取失败的账号设为最低优先级，避免故障传播
- 费用相同时仍按时间排序，保持负载均衡
- 增强日志输出，显示账号费用排名和选中账号费用

🤖 Generated with [Claude Code](https://claude.ai/code)

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

src/services/claudeAccountService.js

@@ -712,12 +712,8 @@ class ClaudeAccountService {
       }
 
       // 如果没有映射或映射无效，选择新账户
-      // 优先选择最久未使用的账户（负载均衡）
-      const sortedAccounts = activeAccounts.sort((a, b) => {
-        const aLastUsed = new Date(a.lastUsedAt || 0).getTime()
-        const bLastUsed = new Date(b.lastUsedAt || 0).getTime()
-        return aLastUsed - bLastUsed // 最久未使用的优先
-      })
+      // 基于日费用选择账户（费用最少的优先）
+      const sortedAccounts = await this.sortAccountsByCost(activeAccounts)
 
       const selectedAccountId = sortedAccounts[0].id
 
@@ -861,12 +857,8 @@ class ClaudeAccountService {
           return aRateLimitedAt - bRateLimitedAt // 最早限流的优先
         })
       } else {
-        // 非限流账户按最后使用时间排序（最久未使用的优先）
-        candidateAccounts = candidateAccounts.sort((a, b) => {
-          const aLastUsed = new Date(a.lastUsedAt || 0).getTime()
-          const bLastUsed = new Date(b.lastUsedAt || 0).getTime()
-          return aLastUsed - bLastUsed // 最久未使用的优先
-        })
+        // 非限流账户按日费用排序（费用最少的优先）
+        candidateAccounts = await this.sortAccountsByCost(candidateAccounts)
       }
 
       if (candidateAccounts.length === 0) {
@@ -883,8 +875,10 @@ class ClaudeAccountService {
         )
       }
 
+      // 显示选择的账号和其日费用
+      const selectedCost = candidateAccounts[0]._dailyCost || 0
       logger.info(
-        `🎯 Selected shared account: ${candidateAccounts[0].name} (${selectedAccountId}) for API key ${apiKeyData.name}`
+        `🎯 Selected shared account: ${candidateAccounts[0].name} (${selectedAccountId}) for API key ${apiKeyData.name} - Daily cost: $${selectedCost.toFixed(4)}`
       )
       return selectedAccountId
     } catch (error) {
@@ -2114,6 +2108,70 @@ class ClaudeAccountService {
       logger.error(`❌ Failed to update session window status for account ${accountId}:`, error)
     }
   }
+
+  // 💰 基于日费用排序账号（费用最少的优先）
+  async sortAccountsByCost(accounts) {
+    try {
+      // 并行获取所有账号的日费用
+      const accountsWithCost = await Promise.all(
+        accounts.map(async (account) => {
+          try {
+            const dailyCost = await redis.getAccountDailyCost(account.id)
+            return {
+              ...account,
+              _dailyCost: dailyCost
+            }
+          } catch (error) {
+            logger.warn(`Failed to get daily cost for account ${account.id}: ${error.message}`)
+            return {
+              ...account,
+              _dailyCost: Number.MAX_SAFE_INTEGER, // 获取费用失败时，设为最高值（最低优先级）
+              _costError: true
+            }
+          }
+        })
+      )
+
+      // 按日费用排序（费用最少的优先）
+      const sortedAccounts = accountsWithCost.sort((a, b) => {
+        // 如果费用相同，按最后使用时间排序（最久未使用的优先）
+        if (Math.abs(a._dailyCost - b._dailyCost) < 0.000001) {
+          const aLastUsed = new Date(a.lastUsedAt || 0).getTime()
+          const bLastUsed = new Date(b.lastUsedAt || 0).getTime()
+          return aLastUsed - bLastUsed
+        }
+        return a._dailyCost - b._dailyCost
+      })
+
+      // 检查是否所有账号的费用获取都失败了
+      const allAccountsHaveErrors = sortedAccounts.every((account) => account._costError)
+
+      if (allAccountsHaveErrors) {
+        logger.warn('⚠️ All accounts failed to get daily cost, falling back to time-based sorting')
+        return accounts.sort((a, b) => {
+          const aLastUsed = new Date(a.lastUsedAt || 0).getTime()
+          const bLastUsed = new Date(b.lastUsedAt || 0).getTime()
+          return aLastUsed - bLastUsed
+        })
+      }
+
+      logger.debug('💰 Account cost ranking:')
+      sortedAccounts.forEach((account, index) => {
+        const costDisplay = account._costError ? 'ERROR' : `$${account._dailyCost.toFixed(4)}`
+        logger.debug(`   ${index + 1}. ${account.name} (${account.id}): ${costDisplay}`)
+      })
+
+      return sortedAccounts
+    } catch (error) {
+      logger.error('❌ Failed to sort accounts by cost:', error)
+      // 回退到原有的按时间排序策略
+      return accounts.sort((a, b) => {
+        const aLastUsed = new Date(a.lastUsedAt || 0).getTime()
+        const bLastUsed = new Date(b.lastUsedAt || 0).getTime()
+        return aLastUsed - bLastUsed
+      })
+    }
+  }
 }
 
 module.exports = new ClaudeAccountService()