refactor: 重构 handleChatCompletions 函数模块化

- 使用策略模式处理不同后端(Claude/OpenAI/Gemini)
- 添加 OpenAI chat/completions 兼容支持

src/services/openaiToClaude.js

@@ -31,10 +31,25 @@ class OpenAIToClaudeConverter {
       stream: openaiRequest.stream || false
     }
 
-    // Claude Code 必需的系统消息
+    // 定义 Claude Code 的默认系统提示词
     const claudeCodeSystemMessage = "You are Claude Code, Anthropic's official CLI for Claude."
 
-    claudeRequest.system = claudeCodeSystemMessage
+    // 如果 OpenAI 请求中包含系统消息,提取并检查
+    const systemMessage = this._extractSystemMessage(openaiRequest.messages)
+    if (systemMessage && systemMessage.includes('You are currently in Xcode')) {
+      // Xcode 系统提示词
+      claudeRequest.system = systemMessage
+      logger.info(
+        `🔍 Xcode request detected, using Xcode system prompt (${systemMessage.length} chars)`
+      )
+      logger.debug(`📋 System prompt preview: ${systemMessage.substring(0, 150)}...`)
+    } else {
+      // 使用 Claude Code 默认系统提示词
+      claudeRequest.system = claudeCodeSystemMessage
+      logger.debug(
+        `📋 Using Claude Code default system prompt${systemMessage ? ' (ignored custom prompt)' : ''}`
+      )
+    }
 
     // 处理停止序列
     if (openaiRequest.stop) {