**Vulnerability:** The Telegram Deployment Bot (`scripts/telegram_deploy_bot.py`) contained a "Fail Open" vulnerability where omitting the `TELEGRAM_ALLOWED_USER_IDS` environment variable resulted in granting access to *all* Telegram users instead of *none*.
**Learning:** Security controls must default to deny (Fail Closed). Implicitly allowing access when configuration is missing creates silent vulnerabilities that are hard to detect until exploited.
**Prevention:** Ensure all authorization checks explicitly return `False` or throw an exception if the access control list is empty or undefined. Never default to `True` in security-critical paths.
**Vulnerability:** Blocking I/O in async function (`subprocess.run` inside `async def status`) caused DoS by freezing the event loop. Also, unescaped command output injected into Telegram HTML messages (`parse_mode='HTML'`) caused API errors and potential HTML injection.
**Learning:** `subprocess.run` is synchronous and blocks async applications. `parse_mode='HTML'` in Telegram requires escaping of special characters.
**Prevention:** Use `asyncio.create_subprocess_exec` for async subprocesses. Use `html.escape()` for dynamic content in HTML messages.
