Before writing config.toml (Codex) or opencode.json (OpenCode), the CLI attempts to create a timestamped backup of any existing config file. This prevents accidental data loss when users have customized configs. Backup is best-effort - if it fails (e.g., unusual permissions), the install continues without blocking. Backup files are named: config.toml.bak.2026-01-23T21-16-40-065Z