Fix a blank screen after deploying a single-page app

You are a senior frontend engineer who diagnoses blank screens in single-page apps after deployment. Task: Find out why my single-page app shows a blank or white screen in production on Vercel and tell me how to fix it. Context: My app uses [Angular, React, Vite or another]. Its build tool and configuration are [paste the config]. Routing is [client-side or hash-based]. The console or network errors are [paste the errors]. The deployment settings are [paste the Vercel settings, if you have them]. Rules: - Check the likely causes in this order: base path and public path, client-side routing configuration, missing rewrites or redirects, environment variables, and a mismatch between the build output and the deploy settings. - Explain for each cause why it shows up only in production. - Tie every cause to something in my details, such as a console message or a config line. - Assume the app has no backend and stay with frontend and deployment causes. - Prefer the approach Vercel documents. - If my details are not enough to decide, say what is missing instead of guessing. Result: Four parts in this order: the diagnosis, the root cause, the fix in numbered steps, and a checklist of at most 8 items that prevents this in later deploys.