Reproduction link or steps

I have an issue in my monorepo where i want to build types for a trpc router. In the resulting .d.ts file i end up with import * as _trpc_server_unstable_core_do_not_import1 from "@trpc/server/unstable-core-do-not-import";

I tried to reproduce the error in smaller example and i get import * as _trpc_server0 from "@trpc/server"; in the final bundle. I tried different options but i couldn't properly bundle the types. In my monorepo this issue persists with other popular packages (eg pg). it refuses to bundle them. I think this is a bug.

I created a repo which shows the issue with the bundled index.d.ts file.

https://github.com/Zombobot1/tsdown-trcp-repro

What is expected?

with

export default defineConfig({
  dts: { resolve: true, emitDtsOnly: true },
})

tsdown bundles types for external deps so the library doesn't require installation of additional deps.

What is actually happening?

it doesn't bundle types from "@trpc/server" and imports from them instead.

import * as _trpc_server_unstable_core_do_not_import0 from "@trpc/server/unstable-core-do-not-import";
import * as _trpc_server1 from "@trpc/server";

Any additional comments?

Some other deps are bundled correctly in my monorepo (eg hono and drizzle) but others don't