Handle edge cases in backup

**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.

The issue names no files, tests, or entry points. Start by locating the backup implementation and its model-related error paths, then identify the edge cases and tests needed; done means backup failures provide more descriptive error messages and the relevant checks pass.

Written by the indexing model from the issue text.