Improve error messages in middleware

**Problem**
When working with controllers, 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, entry points, or specific error cases. Start by locating the middleware and controller error-handling paths, then clarify which messages and failure scenarios should change with a maintainer. Done means the agreed cases produce detailed, useful error messages.

Written by the indexing model from the issue text.