Improve error messages in lib

**Problem**
When working with config, 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 config-related error handling under lib and reproduce the existing failures to understand where messages are generated. Map the affected error paths and confirm the expected level of detail with maintainers; done means config errors clearly identify what failed and why.

Written by the indexing model from the issue text.