Update services documentation

**Problem**
When working with models, 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 file, test, or entry point is named. Start by locating the services documentation and the model error-handling paths, then clarify which errors and messages are in scope. Done should be documented services behavior and more descriptive model-related error messages, with focused tests if the project has them.

Written by the indexing model from the issue text.