Add TypeScript types for store

**Problem**
When working with helpers, 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 mentions the store, helpers, and TypeScript types but names no files or tests. Start by locating the store implementation and its existing type definitions, then identify the expected public types and verify that the store and helper error behavior are covered when the requested changes are complete.

Written by the indexing model from the issue text.