Mocks are lost when on test rerun browser mode when using MSW #8410

Describe the bug

Hi 👋🏽

When running tests in browser mode, module mocks work as expected on the first run. However, when rerunning the tests, the mocks are no longer applied — the original module code is used instead, causing test failures.

This looks like the same issue reported in #6633, which had been previously resolved.

Reproduction

Steps:

• Run tests in browser mode
• Confirm mocks work on first run
• Rerun tests (f / a in terminal or save file) — mocks no longer apply

Working reproduction: https://github.com/nizans/vitest-browser-mode-repro-puyhr8hs

https://stackblitz.com/~/github.com/nizans/vitest-browser-mode-repro-puyhr8hs?file=vitest-example/test-extend.ts:L1&initialPath=/__vitest_test__/?sessionId=60796f4e-5fa1-4a7c-a87d-505c77a1f05b

Version notes:

• Last working version I found: 3.0.9
• Reproduces on 3.2.4
• Also reproduces on 4.0.0-beta.6

System Info

System:
    OS: macOS 15.6
    CPU: (12) arm64 Apple M3 Pro
    Memory: 7.48 GB / 36.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 22.13.0 - ~/.nvm/versions/node/v22.13.0/bin/node
    npm: 10.9.2 - ~/.nvm/versions/node/v22.13.0/bin/npm
    pnpm: 10.13.1 - ~/.nvm/versions/node/v22.13.0/bin/pnpm
    bun: 1.2.2 - /opt/homebrew/bin/bun
  Browsers:
    Chrome: 138.0.7204.184
    Safari: 18.6
  npmPackages:
    @vitejs/plugin-react: 5.0.0 => 5.0.0 
    @vitest/browser: ^3.2.4 => 3.2.4 
    @vitest/coverage-v8: 3.2.4 => 3.2.4 
    @vitest/ui: 3.2.4 => 3.2.4 
    playwright: ^1.54.2 => 1.54.2 
    vite: 7.1.0 => 7.1.0 
    vitest: ^3.2.4 => 3.2.4 
    vitest-browser-react: ^1.0.1 => 1.0.1 
    vitest-plugin-vis: ^3.4.1 => 3.4.1

Used Package Manager

pnpm

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