Improve error messages in store

**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 a file, test, or entry point in the store implementation. First locate the store and its existing error paths, then identify the messages that need more context and add tests demonstrating the intended descriptive output.

Written by the indexing model from the issue text.