Refactor lib for better readability

**Problem**
When working with lib, 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 locating the relevant error-handling paths under lib and reading how their current messages are produced. Define which messages need more context and how to verify the result; the work is done when the affected errors are consistently more descriptive and the existing behavior remains understandable during debugging.

Written by the indexing model from the issue text.