Add TypeScript types for models

**Problem**
When working with utils, 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 any files, tests, or entry points. Start by locating the model definitions and utility error-handling code, then determine how the requested TypeScript types relate to the proposed descriptive errors. Done should mean the intended model types and error-message improvements are implemented with appropriate validation, but the scope needs clarification first.

Written by the indexing model from the issue text.