Update utils documentation

**Problem**
When working with controllers, 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 names no files, tests, or entry points. Start by locating the controller utilities and their current error messages, then clarify whether the work is documentation-only or also changes error handling; done means the requested documentation and detailed controller errors are covered.

Written by the indexing model from the issue text.