Refactor middleware for better readability

**Problem**
When working with models, 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 files, tests, or entry points are named. Start by locating the middleware and model error-handling paths, then trace how current errors are constructed and identify the cases needing more detail. Done means the relevant errors provide clearer debugging context and the existing tests pass, with coverage added if the project has tests for these paths.

Written by the indexing model from the issue text.