Refactor controllers for better readability

**Problem**
When working with lib, the error messages could be more descriptive.

**Suggestion**
Improve error handling and add detailed error messages.

**Context**
This would help with debugging and maintenance.

Start by locating the controllers and error-handling paths under lib, then read the existing error messages and related tests. Clarify which messages need improvement and add coverage showing the more descriptive output; done means the affected controller behavior remains correct and the tests pass.

Written by the indexing model from the issue text.