fix(backend/chat): Use normpath+startswith pattern for CodeQL path sanitization

CodeQL doesn't recognize re.sub as a path sanitizer. Switch to the
os.path.normpath + startswith prefix check pattern that CodeQL's
taint model explicitly recognizes as breaking the taint chain.

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

@@ -46,12 +46,20 @@ 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.
+_SDK_CWD_PREFIX = "/tmp/copilot-"
 
-    Only allows alphanumeric characters and hyphens, stripping everything else.
+
+def _make_sdk_cwd(session_id: str) -> str:
+    """Create a safe, session-specific working directory path.
+
+    Sanitizes session_id, then validates the resulting path stays under /tmp/
+    using normpath + startswith (the pattern CodeQL recognises as a sanitizer).
     """
-    return re.sub(r"[^A-Za-z0-9-]", "", session_id)
+    safe_id = re.sub(r"[^A-Za-z0-9-]", "", session_id)
+    cwd = os.path.normpath(f"{_SDK_CWD_PREFIX}{safe_id}")
+    if not cwd.startswith(_SDK_CWD_PREFIX):
+        raise ValueError(f"Session path escaped prefix: {cwd}")
+    return cwd
 
 
 def _cleanup_sdk_tool_results(cwd: str) -> None:
@@ -64,8 +72,13 @@ def _cleanup_sdk_tool_results(cwd: str) -> None:
     import glob as _glob
     import shutil
 
+    # Validate cwd is under the expected prefix (CodeQL sanitizer pattern)
+    normalized = os.path.normpath(cwd)
+    if not normalized.startswith(_SDK_CWD_PREFIX):
+        return
+
     # SDK encodes the cwd path by replacing '/' with '-'
-    encoded_cwd = cwd.replace("/", "-")
+    encoded_cwd = normalized.replace("/", "-")
     project_dir = os.path.expanduser(f"~/.claude/projects/{encoded_cwd}")
     results_glob = os.path.join(project_dir, "tool-results", "*")
 
@@ -76,11 +89,10 @@ def _cleanup_sdk_tool_results(cwd: str) -> None:
             pass
 
     # Also clean up the temp cwd directory itself
-    if cwd.startswith("/tmp/copilot-"):
-        try:
-            shutil.rmtree(cwd, ignore_errors=True)
-        except OSError:
-            pass
+    try:
+        shutil.rmtree(normalized, ignore_errors=True)
+    except OSError:
+        pass
 
 
 async def _compress_conversation_history(
@@ -247,9 +259,8 @@ 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 = _sanitize_session_id(session_id)
-    sdk_cwd = f"/tmp/copilot-{safe_session_id}"
+    # between concurrent sessions.
+    sdk_cwd = _make_sdk_cwd(session_id)
     os.makedirs(sdk_cwd, exist_ok=True)
 
     try: