feat: allow passing system prompt to Claude

Add CRS_PASSTHROUGH_SYSTEM_PROMPT to optionally forward OpenAI-format system messages to Claude, improving compatibility with clients that rely on strict system instructions (e.g. MineContext).

.env.example

@@ -131,3 +131,7 @@ DEFAULT_USER_ROLE=user
 USER_SESSION_TIMEOUT=86400000
 MAX_API_KEYS_PER_USER=1
 ALLOW_USER_DELETE_API_KEYS=false
+
+# Pass through incoming OpenAI-format system prompts to Claude.
+# Enable this when using generic OpenAI-compatible clients (e.g. MineContext) that rely on system prompts.
+# CRS_PASSTHROUGH_SYSTEM_PROMPT=true

src/services/openaiToClaude.js

@@ -36,15 +36,28 @@ class OpenAIToClaudeConverter {
 
     // 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
+
+    const passThroughSystemPrompt =
+      String(process.env.CRS_PASSTHROUGH_SYSTEM_PROMPT || '').toLowerCase() === 'true'
+
+    if (
+      systemMessage &&
+      (passThroughSystemPrompt || systemMessage.includes('You are currently in Xcode'))
+    ) {
       claudeRequest.system = systemMessage
+
+      if (systemMessage.includes('You are currently in Xcode')) {
         logger.info(
           `🔍 Xcode request detected, using Xcode system prompt (${systemMessage.length} chars)`
         )
+      } else {
+        logger.info(
+          `🧩 Using caller-provided system prompt (${systemMessage.length} chars) because CRS_PASSTHROUGH_SYSTEM_PROMPT=true`
+        )
+      }
       logger.debug(`📋 System prompt preview: ${systemMessage.substring(0, 150)}...`)
     } else {
-      // 使用 Claude Code 默认系统提示词
+      // 默认行为：兼容 Claude Code（忽略外部 system）
       claudeRequest.system = claudeCodeSystemMessage
       logger.debug(
         `📋 Using Claude Code default system prompt${systemMessage ? ' (ignored custom prompt)' : ''}`