Clear and concise description of the problem

If I do a tsdown build, I can get

[UNRESOLVED_IMPORT] Warning: Could not resolve 'your-library/some-export' in src/index.ts

and this is treated as an external dependency.

This isn't something I want, I'd rather fail!

Suggested solution

--warnings-as-errors? --fail-on-resolve-errors? Some way to fail instead of printing warnings and exiting with 0.

Alternative

No response

Additional context

No response

Validations

• Follow our Code of Conduct
• Read the Contributing Guide.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.