Include/Generate declaration files for bundled external libraries

We're trying to use tsup to bundle typebox (which is an ESM only library) into a CommonJS library. This works well for the code itself, however we also need to include or generate the type declaration files of typebox to allow its types propagate to consumers.

Is there a way of doing that? It seems that just enabled dts doesn't do the trick.

This is the configuration file I'm using:

import { defineConfig } from 'tsup'

export default defineConfig({
  entry: ['src/index.ts'],
  format: ['cjs', 'esm'],
  dts: {
    tsconfig: './tsconfig.lib.json',
  },
  sourcemap: true,
  clean: true,
  splitting: false,
  treeshake: true,
  minify: false,
  target: 'es2022',
  noExternal: ['typebox'],
  esbuildOptions(options) {
    options.conditions = ['module']
  },
})

Using tsup version 8.5.0.

Start by reproducing the declaration build with src/index.ts, tsup 8.5.0, and tsconfig.lib.json using the configuration shown. Inspect how the dts option handles the bundled typebox dependency for both CommonJS and ESM outputs. Done means consumers receive usable declaration files whose typebox types propagate correctly.