Refactor store for better readability

**Problem**
When working with data, 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 any files, tests, or entry points. Locate the store implementation and its existing error-handling paths, then review how data-related failures are surfaced; done means the relevant errors are more descriptive and the behavior is covered by the repository's existing checks.

Written by the indexing model from the issue text.