Worked on the resend/react-email repository to address an environment configuration issue affecting email template previews. Focused on CLI development and environment variable management using Node.js and TypeScript, the developer resolved a bug where the preview server previously forced NODE_ENV to 'development', disregarding user settings. By refining the environment variable merge logic, the fix ensures that the preview process now respects the user's intended configuration, aligning development and production environments more closely. This change improves the reliability and predictability of email previews, reducing confusion for developers and QA teams when validating templates and enhancing traceability through explicit commit and PR references.