Consider deprecating old data API

**Problem**
When working with middleware, the error messages could be more descriptive.

**Suggestion**
Improve error handling and add detailed error messages.

**Context**
This would help with debugging and maintenance.

Start by locating the middleware error-handling path and references to the old data API. Confirm the desired scope with maintainers; done should be a decided deprecation plan and more descriptive error behavior, since the issue names no files or tests.

Written by the indexing model from the issue text.