Optimize lib for large datasets

**Problem**
When working with handlers, 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 library code for handlers and reading the existing error paths. Compare the current messages with the debugging context in the issue, then define and verify a consistent set of more descriptive errors; the issue does not name specific files or tests.

Written by the indexing model from the issue text.