feat: 添加智能sticky会话保持功能

- 新增 sessionHelper.js 实现会话哈希生成，基于Anthropic的prompt caching机制
- 扩展 claudeAccountService.selectAvailableAccount 支持会话绑定
- 更新 claudeRelayService 集成会话保持功能
- 添加 Redis 会话映射存储，支持1小时过期
- 支持故障转移：绑定账户不可用时自动重新选择
- 三级fallback策略：cacheable内容 → system内容 → 第一条消息
- 完全向后兼容，自动启用无需配置

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

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

src/services/claudeAccountService.js

@@ -286,8 +286,8 @@ class ClaudeAccountService {
     }
   }
 
-  // 🎯 智能选择可用账户
-  async selectAvailableAccount() {
+  // 🎯 智能选择可用账户（支持sticky会话）
+  async selectAvailableAccount(sessionHash = null) {
     try {
       const accounts = await redis.getAllClaudeAccounts();
       
@@ -300,6 +300,24 @@ class ClaudeAccountService {
         throw new Error('No active Claude accounts available');
       }
 
+      // 如果有会话哈希，检查是否有已映射的账户
+      if (sessionHash) {
+        const mappedAccountId = await redis.getSessionAccountMapping(sessionHash);
+        if (mappedAccountId) {
+          // 验证映射的账户是否仍然可用
+          const mappedAccount = activeAccounts.find(acc => acc.id === mappedAccountId);
+          if (mappedAccount) {
+            logger.info(`🎯 Using sticky session account: ${mappedAccount.name} (${mappedAccountId}) for session ${sessionHash}`);
+            return mappedAccountId;
+          } else {
+            logger.warn(`⚠️ Mapped account ${mappedAccountId} is no longer available, selecting new account`);
+            // 清理无效的映射
+            await redis.deleteSessionAccountMapping(sessionHash);
+          }
+        }
+      }
+
+      // 如果没有映射或映射无效，选择新账户
       // 优先选择最近刷新过token的账户
       const sortedAccounts = activeAccounts.sort((a, b) => {
         const aLastRefresh = new Date(a.lastRefreshAt || 0).getTime();
@@ -307,7 +325,15 @@ class ClaudeAccountService {
         return bLastRefresh - aLastRefresh;
       });
 
-      return sortedAccounts[0].id;
+      const selectedAccountId = sortedAccounts[0].id;
+      
+      // 如果有会话哈希，建立新的映射
+      if (sessionHash) {
+        await redis.setSessionAccountMapping(sessionHash, selectedAccountId, 3600); // 1小时过期
+        logger.info(`🎯 Created new sticky session mapping: ${sortedAccounts[0].name} (${selectedAccountId}) for session ${sessionHash}`);
+      }
+
+      return selectedAccountId;
     } catch (error) {
       logger.error('❌ Failed to select available account:', error);
       throw error;

src/services/claudeRelayService.js

@@ -2,6 +2,7 @@ const https = require('https');
 const { SocksProxyAgent } = require('socks-proxy-agent');
 const { HttpsProxyAgent } = require('https-proxy-agent');
 const claudeAccountService = require('./claudeAccountService');
+const sessionHelper = require('../utils/sessionHelper');
 const logger = require('../utils/logger');
 const config = require('../../config/config');
 
@@ -16,10 +17,13 @@ class ClaudeRelayService {
   // 🚀 转发请求到Claude API
   async relayRequest(requestBody, apiKeyData) {
     try {
-      // 选择可用的Claude账户
-      const accountId = apiKeyData.claudeAccountId || await claudeAccountService.selectAvailableAccount();
+      // 生成会话哈希用于sticky会话
+      const sessionHash = sessionHelper.generateSessionHash(requestBody);
       
-      logger.info(`📤 Processing API request for key: ${apiKeyData.name || apiKeyData.id}, account: ${accountId}`);
+      // 选择可用的Claude账户（支持sticky会话）
+      const accountId = apiKeyData.claudeAccountId || await claudeAccountService.selectAvailableAccount(sessionHash);
+      
+      logger.info(`📤 Processing API request for key: ${apiKeyData.name || apiKeyData.id}, account: ${accountId}${sessionHash ? `, session: ${sessionHash}` : ''}`);
       
       // 获取有效的访问token
       const accessToken = await claudeAccountService.getValidAccessToken(accountId);
@@ -224,10 +228,13 @@ class ClaudeRelayService {
   // 🌊 处理流式响应（带usage数据捕获）
   async relayStreamRequestWithUsageCapture(requestBody, apiKeyData, responseStream, usageCallback) {
     try {
-      // 选择可用的Claude账户
-      const accountId = apiKeyData.claudeAccountId || await claudeAccountService.selectAvailableAccount();
+      // 生成会话哈希用于sticky会话
+      const sessionHash = sessionHelper.generateSessionHash(requestBody);
       
-      logger.info(`📡 Processing streaming API request with usage capture for key: ${apiKeyData.name || apiKeyData.id}, account: ${accountId}`);
+      // 选择可用的Claude账户（支持sticky会话）
+      const accountId = apiKeyData.claudeAccountId || await claudeAccountService.selectAvailableAccount(sessionHash);
+      
+      logger.info(`📡 Processing streaming API request with usage capture for key: ${apiKeyData.name || apiKeyData.id}, account: ${accountId}${sessionHash ? `, session: ${sessionHash}` : ''}`);
       
       // 获取有效的访问token
       const accessToken = await claudeAccountService.getValidAccessToken(accountId);