Improve validation performance

**Problem**
When working with data, 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 files, tests, or entry points are named. Start by locating the validation and error-handling paths, then establish the current behavior; done means the relevant validation is faster and its errors are more descriptive, with coverage for the changed behavior.

Written by the indexing model from the issue text.