// ✅ Preferred: Validate at entry point
function validateEnvironment() {
  const required = ['AWS_REGION', 'PROJECT_ID', 'ENVIRONMENT'];
  const missing = required.filter(key => !process.env[key]);
  
  if (missing.length > 0) {
    throw new Error(`Missing required environment variables: ${missing.join(', ')}`);
  }
}

// At script/app entry point
validateEnvironment();
// Now proceed with business logic

// shared/env-loader.ts
export function loadAndValidateEnv() {
  const required = ['AWS_REGION', 'PROJECT_ID', 'ENVIRONMENT'];
  const missing = required.filter(key => !process.env[key]);
  
  if (missing.length > 0) {
    throw new Error(`Missing: ${missing.join(', ')}`);
  }
  
  return {
    awsRegion: process.env.AWS_REGION!,
    projectId: process.env.PROJECT_ID!,
    environment: process.env.ENVIRONMENT!
  };
}

// Usage in scripts/handlers
const config = loadAndValidateEnv();
// All env vars validated, proceed with business logic

// core/env-manager.ts
export class EnvironmentManager extends BaseManager {
  loadEnv(stage: string): Record<string, string> {
    this.log(`Loading environment for ${stage}`);
    
    // Validate required variables
    const required = ['AWS_REGION', 'PROJECT_ID'];
    const missing = required.filter(key => !process.env[key]);
    
    if (missing.length > 0) {
      throw new Error(`Missing: ${missing.join(', ')}`);
    }
    
    return process.env;
  }
}