Improve error messages in core

**Problem**
When working with services, 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 files, tests, or an entry point. Start by locating the core service error-handling paths, then determine which failures need more descriptive messages and define tests that verify the improved diagnostics.

Written by the indexing model from the issue text.