Production middlewares will only expose env vars that are statically analyzable, as mentioned here: https://nextjs.org/docs/api-reference/next/server#how-do-i-access-environment-variables
This creates some incompatibility with `next dev` and `next start`, where all `process.env` data is shared and can lead to unexpected behavior in runtime.
This PR fixes it by limiting the data in `process.env` with the inferred env vars from the code usage. I believe the test speaks for itself 🕺
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