Local practice only

• Use only this supplied app on your own computer or an instructor-approved lab machine.
• The server listens on 127.0.0.1 (your computer only). Do not change that address, tunnel it, deploy it or expose it on a school network.
• The failure is simulated. Paths, service names and diagnostic details are fixed fictional strings, not information read from your computer.
• Do not add real credentials, personal data, environment variables or real error stack traces.
• You are learning to prevent diagnostic disclosure, not to probe websites you do not own.
• Only edit config.mjs. The other files provide the local server and display.
• Stop the server with Ctrl+C when finished. Automated checks close their own temporary server.

Disabling this demonstration setting does not make an arbitrary real application production-ready. Production deployments also need appropriate configuration management, access controls, logging and review.