Improve error messages in routes

**Feature request**
It would be great to have import for lib.

**Use case**
Many users need this functionality for production deployments.

**Implementation idea**
Add a new config option `enable_import` with default `false`.

No files or tests are named. Start by tracing the routes implementation and existing configuration options, then clarify what “import for lib” means and how it relates to the requested error-message changes; done should include a documented `enable_import` option defaulting to `false` and verified behavior.

Written by the indexing model from the issue text.