Update middleware documentation

**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.

Start by locating the middleware and route-handling entry points in the repository, then review how their current errors are produced. Clarify which messages need to become more descriptive and where the middleware documentation lives; done means the requested error-handling behavior and detailed documentation are both defined and verified.

Written by the indexing model from the issue text.