Write and deploy a Netlify serverless function via netlify.toml functions config, netlify functions:create, and netlify deploy

Documented steps

1. Auth: Requires a Netlify account, netlify login or NETLIFY_AUTH_TOKEN, and (for deploy) a linked or newly created site via the CLI.
2. Install helper types/utilities: npm install @netlify/functions
3. (Optional) Set a custom functions directory in netlify.toml (default is <base>/netlify/functions): [functions] then directory = "my_functions"
4. Scaffold a new function interactively or from a template: netlify functions:create --language typescript --template hello-world
5. Or hand-write a function file directly at netlify/functions/hello.mts using the modern default-export handler: export default async (req: Request, context: Context) => new Response("Hello, world!"); export const config: Config = { path: "/hello" };
6. List functions detected locally to verify naming/format: netlify functions:list
7. Test locally with the full Netlify environment emulated: netlify dev, then trigger it with netlify functions:invoke hello --payload '{"foo":1}'
8. Create a draft (preview) deploy that uploads static files and functions: netlify deploy
9. Ship it live to production: netlify deploy --prod
10. Official docs: https://docs.netlify.com/build/functions/get-started/ ; https://cli.netlify.com/commands/functions/ ; https://docs.netlify.com/build/functions/configuration/ ; https://cli.netlify.com/commands/deploy/