When a package provides conditional exports (.mjs for ESM / .(c)js for CJS), and consumers import the same subpath via both ESM import() and CJS require(), rolldown seems to bundle both variants as separate module graph nodes instead of deduplicating them.

This causes:

• Duplicated module code in the output (increased bundle size)
• Broken module identity (two separate instances of the same logical module)
• In complex chunk graphs (e.g., tsdown with multiple entries), broken __esmMin init wrappers → TypeError: init_xxx is not a function

I found it while working on oxc-project/oxc#19807.

The reproduction steps and more details are here.
👉🏻 https://github.com/leaysgur/rolldown-esm-cjs-dedupe-repro