Improve validation performance

**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.

The issue does not name a file, test, or entry point. Start by locating model validation and error-handling code, then inspect how current messages are produced. Done means validation failures provide more descriptive details and the existing validation behavior remains covered by tests.

Written by the indexing model from the issue text.