// ✅ Use satisfies for type checking with inference
const config = {
  apiUrl: 'https://api.example.com',
  timeout: 5000,
} satisfies Config;

// ✅ Discriminated unions for state
type AsyncState<T> = 
  | { status: 'idle' }
  | { status: 'loading' }
  | { status: 'success'; data: T }
  | { status: 'error'; error: Error };

// ❌ Never use any
function processData(data: any) { /* ... */ }

// Unified error hierarchy
class AppError extends Error {
  constructor(
    message: string,
    public readonly code: string,
    public readonly statusCode: number = 500,
    public readonly isOperational: boolean = true,
    public readonly context?: Record<string, unknown>
  ) {
    super(message);
    this.name = this.constructor.name;
  }
}

class NotFoundError extends AppError {
  constructor(resource: string, id: string) {
    super(`${resource} not found: ${id}`, 'NOT_FOUND', 404, true, { resource, id });
  }
}

// Result pattern
type Result<T, E = AppError> = 
  | { success: true; data: T }
  | { success: false; error: E };

// lib/env.server.ts - Server-only (NEVER import in client code)
import { z } from 'zod';

const serverEnvSchema = z.object({
  DATABASE_URL: z.string().url(),
  STRIPE_SECRET_KEY: z.string().startsWith('sk_'),
});

export const serverEnv = serverEnvSchema.parse(process.env);

// lib/env.client.ts - Safe for client bundles
const clientEnvSchema = z.object({
  NEXT_PUBLIC_API_URL: z.string().url(),
});

export const clientEnv = clientEnvSchema.parse({
  NEXT_PUBLIC_API_URL: process.env.NEXT_PUBLIC_API_URL,
});

{
  "compilerOptions": {
    "strict": true,
    "noImplicitAny": true,
    "strictNullChecks": true,
    "noUncheckedIndexedAccess": true,
    "noImplicitReturns": true
  }
}