A file extension must be provided when using the import keyword to resolve relative or absolute specifiers. Directory indexes (e.g. './startup/index.js') must also be fully specified.
This behavior matches how import behaves in browser environments, assuming a typically configured server.
not so much is needed to make this full ESM compatible without the need for a build tool...
just need to slam in full relative path and not using extension less paths, esm was not built for that.