Refactor types for better readability

**Problem**
When working with core, 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 points only to the core area and does not name files or tests. Start by locating the core error-handling and type definitions, then review existing error messages and their callers. Done should mean the relevant errors are more descriptive and the existing checks still pass.

Written by the indexing model from the issue text.