This is similar to issue "My backend service cannot read the DATABASE_URL environment variable" (10 days ago).

Problem: Service Variables are not accessible at runtime in Next.js 15.5.12.

What works:

- Railway system variables (RAILWAY_PUBLIC_DOMAIN, etc.) are readable

- Application builds successfully

- NODE_ENV shows as "production"

What doesn't work:

- Custom Service Variables (OPENAI_API_KEY) are completely missing

- process.env.OPENAI_API_KEY returns undefined

Diagnostic output shows all available env vars, but OPENAI_API_KEY is not listed.

Already tried:

1. Removed output: 'standalone' from next.config.js

2. Recreated Service Variables multiple times

3. Verified case sensitivity (OPENAI_API_KEY)

4. Confirmed I'm in correct project and service

I need this resolved for production.