Type import invalid path in build

Description

Types imported from parent folders have incorrect import paths and do not get recognized by TS due to the incorrect .js extension

Expected Behavior

Type import paths should end with .mts

Reproduction

https://codesandbox.io/p/devbox/l8c85t?file=%2Fdist%2Fruntime%2Futils%2Ffoo.d.ts%3A3%2C1

See the build output in dist. Type Foo imported from src/types.ts in the file src/runtime/server/utils/foo.ts using this import statement import type { Foo } from "../../../types";, got transformed to ../../../types.js which does not have a declaration file, and produces incorrect type.

Workaround

This is how I currently work around this issue.

import fs from 'node:fs'
import path from 'node:path'
export default defineBuildConfig({
  hooks: {
    'rollup:done': function (ctx) {
      const dts = path.resolve(ctx.options.outDir, 'types.d.mts')
      if (fs.existsSync(dts))
        fs.cpSync(dts, path.resolve(ctx.options.outDir, 'types.d.ts'))
    },
  },
})

Related Issue

#308 seems relevant, but I don't know how it's fixed for them

Start by reproducing the build with src/runtime/server/utils/foo.ts importing Foo from src/types.ts, then inspect the generated declaration in dist. Compare the emitted ../../../types.js path with the expected .mts path and verify that Foo is recognized by TypeScript without the rollup:done workaround.