Inconsistent CSS resolution order between development and production

[GabenGar]

Reproduction

https://github.com/87906913/408919357/tree/main/react-router/invalid-css-resolution-order

Reproduction steps are in the readme.

System Info

System:
    OS: Windows 10
    CPU: (4)
Binaries:
    Node: 22
    npm: 10

Used Package Manager

npm

Expected Behavior

CSS resolves consistently between environments.

Actual Behavior

CSS resolves differently between environments.

[xalechez]

Hey, just a wee bump on this issue. We're currently in the middle of migration, and facing the same issue. Do you have any update?

[GabenGar]

Yeah I would like to know what is the underlying issue at least.
Obviously it's because of different bundlers between environments, esbuild and rollup respectively.
But the symptoms are the same as in the app router of NextJS, but that one is caused by webpack handling "sideEffects" in a specific way. Interesting to note vite in this test works just fine.