[BE-48] Startup environment variable validation (Joi schema)

[yusuftomilola]

Overview

The app starts without any warning when required environment variables are missing (e.g. JWT_SECRET, PAYSTACK_SECRET_KEY, DATABASE_HOST). Missing config causes cryptic runtime errors deep in service calls. Joi validation at startup gives an immediate, actionable error listing exactly which variables are absent.

Context

• ConfigModule.forRoot() in backend/src/app.module.ts — supports a validationSchema option from @nestjs/config
• Joi is not currently installed — add it
• backend/.env.example is the reference for required variables

Tasks

• Install joi: npm install joi
• Create backend/src/config/env.validation.ts exporting a Joi ObjectSchema
• Required variables to validate:
  • DB: DATABASE_HOST, DATABASE_PORT (number), DATABASE_NAME, DATABASE_USERNAME, DATABASE_PASSWORD
  • JWT: JWT_SECRET, JWT_EXPIRATION, JWT_REFRESH_SECRET, JWT_REFRESH_EXPIRATION
  • Paystack: PAYSTACK_SECRET_KEY, PAYSTACK_PUBLIC_KEY
  • Cloudinary: CLOUDINARY_CLOUD_NAME, CLOUDINARY_API_KEY, CLOUDINARY_API_SECRET
  • Redis: REDIS_HOST, REDIS_PORT (number)
  • Email: SENDGRID_API_KEY (or SMTP_HOST — whichever is used)
• Pass the schema to ConfigModule.forRoot({ validationSchema, validationOptions: { abortEarly: false } }) so all missing variables are reported at once
• App must refuse to start with a clear error listing each missing variable
• Update backend/.env.example to document every required variable with a description comment

Files to Modify / Create

• New: backend/src/config/env.validation.ts
• backend/src/app.module.ts
• backend/.env.example