Improve error messages in validation

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

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

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

The issue does not name files, tests, or a validation entry point. Start by locating validation and error-handling code in the Shell-based CLI, then identify the current messages and relevant test coverage; done means the validation failures provide more descriptive debugging information and the tests pass.

Written by the indexing model from the issue text.