Improve models performance

**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.

No files, tests, or entry points are named. Start by locating the controller error-handling paths and existing error-message tests, then clarify which failures need new messages and what wording and test coverage define done.

Written by the indexing model from the issue text.