Gosh, I'm really down this rabbit hole, huh? :p Anyway, turns out the `vercel dev` command contains a _fork_ of ts-node that doesn't respect the `ts-node` override key in `tsconfig.json`. But it does respect the env var!
So I've now set up `yarn start` to invoke `vercel dev` with the new env, which in turn invokes `yarn dev` to start the create-react-app dev server. Whew! (Probably a better dev experience tbh.)
`yarn build` was crashing on my `build-cached-data` script, because we were trying to run the Typescript file uncompiled!
Now, we run it with `ts-node`, which transparently compiles Typescript files before execution. Phew!
`react-scripts build` made some automated changes to `tsconfig.json` for compatibility with `create-react-app`, and I also added a `ts-node` section to override one of them so we can compile to CommonJS for `ts-node` script execution!
