Consider deprecating old config API

**Problem**
When working with validation, 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. First clarify whether the work concerns deprecating the old config API or improving validation error messages, then define the affected API, migration behavior, and expected error text; completion criteria are not specified in the issue.

Written by the indexing model from the issue text.