Improve error messages in controllers

**Problem**
When working with parsers, 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 controller and parser error-handling paths in the repository and review how current errors are produced. Clarify which parser failures need more context, then define and verify the expected descriptive messages with focused coverage before considering the work done.

Written by the indexing model from the issue text.