The singleton BackendAPIClient was failing with "Cannot send a request, as the client has been closed" error when used after async context manager closed it in linking.py. Changed all client checks from `if not self.client` to `if not self.client or self.client.is_closed` to properly recreate the AsyncClient when needed. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com>