You run node src/server.ts on a Node version where type stripping is enabled by default (22.18+ or 23.6+), with no extra flags. Which line makes it fail?

The enum Role { Admin, User } line fails. Node only strips erasable syntax: type syntax it can remove without generating any code. An enum needs generated JavaScript, so it fails unless you add --experimental-transform-types.

The other three lines are pure type syntax, so Node just removes them:
• interface User { id: string }
• the : string annotations in function greet(name: string): string
• import type { User } from "./types.ts";

TypeScript 5.8's erasableSyntaxOnly option reports such constructs at compile time.