Build fails with "Could not find server config output file" when Vite outputs .mjs files - workaround included

[weepotty]

Production builds fail during the prerendering step when Vite outputs ES module files with .mjs extensions instead of .js.

Error:

Error [ERR_MODULE_NOT_FOUND]: Cannot find module '/path/to/dist/server/entry.server.js'
❌ Build failed: Could not find server config output file

Root Cause
Two files have hardcoded .js extensions:
dist/config/loader.js:58 - looks for zudoku.config.js
dist/vite/prerender/prerender.js:19 - looks for entry.server.js
But Vite outputs .mjs files, causing the lookups to fail.

Environment
Zudoku: 0.67.0
Vite: 6.4.1
Yarn: 4.9.4
Node: 22.12.0

Reproduction
Use Zudoku with default Vite configuration
Run yarn build
Build fails during prerendering step

Suggested Fix:
// loader.js line 58

const result = output.output.find((o) => 
  "isEntry" in o && o.isEntry && 
  (o.fileName === "zudoku.config.js" || o.fileName === "zudoku.config.mjs")
);

// prerender.js line 19

const entryServerMjs = path.join(distDir, "server/entry.server.mjs");
const entryServerJs = path.join(distDir, "server/entry.server.js");
const entryServerExists = await fileExists(entryServerMjs);
const entryServerPath = pathToFileURL(entryServerExists ? entryServerMjs : entryServerJs).href;

Workaround used
For Yarn 4+ users, you can create a patch:

1. Run yarn patch zudoku
2. Apply the fixes shown in the "Suggested Fix" section above
3. Run yarn patch-commit -s /path/from/yarn/output

This will generate a patch file that automatically applies on yarn install.

[dan-lee]

Hi @weepotty, thanks for your issue. It's not clear to me why Vite would emit .mjs files. Can you verify it your package.json has "type": "module" set?

[weepotty]

hi @dan-lee , thanks for your reply. no, that is not set in my package.json.

[dan-lee]

@weepotty Can you set that and try again? Maybe this resolves the issue