RollupError: Multiple conflicting contents for sourcemap source

tsup: `8.4.0`
os: windows

```
export default defineConfig({
entry: [
'src/index.ts'
],
format: ['esm','cjs','iife'],
dts: true,
splitting: false,
sourcemap: true,
clean: true,
treeshake:true,
minify: true,
noExternal:['flex-tools'],
globalName: 'VoerkaI18n',
banner: {
js: `/***
* ---=== VoerkaI18n Runtime ===---
* https://zhangfisher.github.io/voerka-i18n/*
*/`}
})
```

# Build error

`RollupError: Multiple conflicting contents for sourcemap source `

Going back to 8.3.6 will not cause this issue

Start by reproducing the failure with the provided tsup configuration on Windows, comparing tsup 8.4.0 with 8.3.6. Focus on the sourcemap generation during the listed src/index.ts build and determine which conflicting source contents trigger the RollupError. Done means the configuration builds successfully on the affected version without regressing sourcemaps.

Written by the indexing model from the issue text.