Load configuration from the environment and validate it at startup

Configuration such as database URLs, API keys and ports belongs in environment variables, not in code. A missing value should stop the process on boot with a clear message, not fail hours later on the first request that needs it.

1. Read process.env once in a config module.
2. Validate it with a schema.
3. Export a typed object and import that everywhere else.

Node.js can now load a .env file itself, no package needed:

• --env-file=.env loads the file.
• --env-file-if-exists=.env loads it only if present, for local files that may be missing.

--env-file is no longer experimental since Node.js 24.10 and 22.21 (see the command-line docs).

// config.ts
import { z } from 'zod';

const env = z.object({
  NODE_ENV: z.enum(['development', 'test', 'production']),
  PORT: z.coerce.number().default(3000),
  DATABASE_URL: z.url(),
}).parse(process.env);

export default env;
// node --env-file-if-exists=.env src/server.ts