fix(backend/chat): Use named helper for session_id sanitization to satisfy CodeQL

Replace inline comprehension with _sanitize_session_id() using re.sub
so CodeQL recognizes the path-traversal sanitization barrier.

autogpt_platform/backend/backend/api/features/chat/sdk/service.py

@@ -4,6 +4,7 @@ import asyncio
 import json
 import logging
 import os
+import re
 import uuid
 from collections.abc import AsyncGenerator
 from typing import Any
@@ -45,6 +46,14 @@ config = ChatConfig()
 _background_tasks: set[asyncio.Task[Any]] = set()
 
 
+def _sanitize_session_id(session_id: str) -> str:
+    """Sanitize session_id to prevent path traversal and injection.
+
+    Only allows alphanumeric characters and hyphens, stripping everything else.
+    """
+    return re.sub(r"[^A-Za-z0-9-]", "", session_id)
+
+
 def _cleanup_sdk_tool_results(cwd: str) -> None:
     """Remove SDK tool-result files for a specific session working directory.
 
@@ -239,7 +248,7 @@ async def stream_chat_completion_sdk(
     stream_completed = False
     # Use a session-specific temp dir to avoid cleanup race conditions
     # between concurrent sessions. Sanitize session_id to prevent path traversal.
-    safe_session_id = "".join(c for c in session_id if c.isalnum() or c == "-")
+    safe_session_id = _sanitize_session_id(session_id)
     sdk_cwd = f"/tmp/copilot-{safe_session_id}"
     os.makedirs(sdk_cwd, exist_ok=True)