'TypeError: Cannot add property 3, object is not extensible' when using vitest@3.0.0 with sveltekit

[johnal95]

Describe the bug

I came across this issue when upgrading vitest from 3.0.0-beta.4 to vitest 3.0.0 on a sveltekit project, where it seems the configuration fails to be resolved:

TypeError: Cannot add property 3, object is not extensible
    at Array.push (<anonymous>)
    ...

(minimal reproduction repo linked as part of this issue)

Reproduction

https://github.com/johnal95/vitest-with-sveltekit-plugin.git

System Info

System:
  OS: macOS 15.2
  CPU: (12) arm64 Apple M3 Pro
  Memory: 119.56 MB / 36.00 GB
  Shell: 5.9 - /bin/zsh
Binaries:
  Node: 22.12.0
  npm: 10.9.0
  pnpm: 9.15.4
npmPackages:
  vite: 6.0.7 => 6.0.7 
  vitest: 3.0.0 => 3.0.0

Used Package Manager

pnpm

Validations

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• Read the Contributing Guidelines.
• Read the docs.
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• The provided reproduction is a minimal reproducible example of the bug.

[andy0130tw]

Same here: https://github.com/qbane/sveltekit-template/actions/runs/12814716650/job/35731787371

[dominikg]

minimal reproduction: https://stackblitz.com/edit/vitejs-vite-ya6cn6ih?file=vite.config.js&terminal=test

seems to be caused by a frozen resolve.conditions object.