Handle edge cases in caching

**Feature request**
It would be great to have backup for store.

**Use case**
Many users need this functionality for production deployments.

**Implementation idea**
Add a new config option `enable_backup` with default `false`.

No files, tests, or entry points are named. Start by locating the caching or store implementation and configuration handling, then clarify what “backup for store” means and how failures should behave. Done should include an agreed scope, a default-disabled enable_backup option, and tests for the specified edge cases.

Written by the indexing model from the issue text.