Update validation documentation

**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 names no files, tests, or entry points. Start by locating the validation documentation and the service error-handling paths, then compare the current behavior with the requested detail. Done means the relevant documentation and error messages clearly describe validation failures and provide more useful debugging information.

Written by the indexing model from the issue text.