[bugfix] Normalize tool message content from array to string format (#39899)

Signed-off-by: JaredforReal <w13431838023@gmail.com>

vllm/entrypoints/chat_utils.py

@@ -1550,6 +1550,18 @@ def _parse_chat_message_content(
             parsed_msg = _ToolParser(message)
             if "tool_call_id" in parsed_msg:
                 result_msg["tool_call_id"] = parsed_msg["tool_call_id"]
+            # Normalize tool message content from OpenAI array format to plain
+            # string. Clients like Claude Code / Cursor send tool results as
+            # [{"type": "text", "text": "..."}], but most chat templates only
+            # handle string content for tool messages.
+            msg_content = result_msg.get("content")
+            if isinstance(msg_content, list):
+                texts = [
+                    item.get("text", "")
+                    for item in msg_content
+                    if isinstance(item, dict) and item.get("type") == "text"
+                ]
+                result_msg["content"] = "\n".join(texts) if texts else ""
 
         if "name" in message and isinstance(message["name"], str):
             result_msg["name"] = message["name"]