Optimize middleware for large datasets

**Problem**
When working with api, 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 file or test is named; start by locating the middleware and API error-handling entry points. Define the affected large-dataset path and verify that resulting errors are more descriptive, with tests covering the changed behavior.

Written by the indexing model from the issue text.