Which project does this relate to?

Start

Describe the bug

Environment variables from .env.development aren't being loaded and merged with .env.

This might be related to #5217.

Your Example Website or App

https://github.com/Benjamin-Lee/tanstack-start-env

Steps to Reproduce the Bug or Issue

1. Clone the repo and install dependencies
2. Run npm run dev or bun run dev (don't run bun --bun run dev since that uses Bun's environment loader)
3. Take a look at localhost:3000

Expected behavior

On localhost, we'd expect to see:

SECRET: foo
EXAMPLE: bar

Screenshots or Videos

Platform

• Router / Start Version: 1.140.0
• OS: macOS
• Browser: N/A
• Browser Version: N/A
• Bundler: vite
• Bundler Version: 7.2.7

Additional context

No response