Add TypeScript types for lib

**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.

Start by inspecting the lib helpers and their current error-handling paths; the issue does not name specific files, entry points, or tests. Clarify whether the intended work is TypeScript type definitions, more descriptive errors, or both, then identify the relevant test coverage and define completion around the agreed behavior.

Written by the indexing model from the issue text.