redirect , rewrite 만 external url
includeFiles does not work for Next.js or some frameworks
How to read files in Vercel Functions
Learn how to import, read, and store files inside Vercel Functions.
https://vercel.com/guides/how-can-i-use-files-in-serverless-functions
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Vercel.json's "includeFiles" with `pages/api` serverless functions · vercel next.js · Discussion #14807
Lets say i had two files in the root of my next.js project: random.txt and somedir/random2.txt. How could I access those inside of a src/pages/api/function.js file? Whatever I do I can't seem t...
https://github.com/vercel/next.js/discussions/14807
CLI
To allow for interacting with the platform using the terminal or an automated system, Vercel offers a command-line interface called Vercel CLI. If you'd like to interface with the platform programmatically, take a look at the REST API. Vercel CLI provides a set of commands that allow you to deploy and manage your projects.
https://vercel.com/docs/cli#project/headers

Seonglae Cho