Add TypeScript types for lib

**Problem**
When working with controllers, 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 title mentions adding TypeScript types for lib, while the body only refers generally to controllers and more descriptive error messages. Start by locating the controller and library entry points, then determine which types and error cases are actually in scope. Done should include a specific type surface and agreed detailed error behavior, but the issue does not define either.

Written by the indexing model from the issue text.