Consider deprecating old core API

**Problem**
When working with routes, 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 route handling, error messages, and a possible old core API deprecation, but no files, tests, or entry points. Start by locating the route and core API implementations and their current error handling. Done requires a decided scope and more descriptive errors, with the deprecation question resolved.

Written by the indexing model from the issue text.