Reproduction link or steps

https://github.com/ef81sp/rolldown-sanitize-filename-repro

pnpm install
pnpm build

What is expected?

JS chunk filenames should be sanitized (? and & replaced with _):

dist/components/TestComp.vue_vue_type_script_setup_true_lang.js

What is actually happening?

dist/components/TestComp.vue?vue&type=script&setup=true&lang.js

Custom sanitizeFileName in output options is also ignored for these chunks. CSS filenames are correctly sanitized in the same build.

This occurs when entry is object-form ({ index: './src/index.ts' }). With string-form entry ('./src/index.ts'), preserveModules does not preserve the directory structure at all, so the issue does not surface.

System Info

System:
    OS: macOS 26.3.1
    CPU: (8) arm64 Apple M1
    Memory: 102.55 MB / 16.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 25.5.0 - /opt/homebrew/bin/node
    pnpm: 10.28.0
  npmPackages:
    vite: 8.0.0 (rolldown 1.0.0-rc.9)

Any additional comments?

#7554 fixed sanitizeFileName for preserveModules, but only when entry is string-form. With object-form entry, sanitizeFileName is still not applied to JS chunk filenames.

Workaround: using entryFileNames as a function to manually sanitize works.