Improve error messages in handlers

**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 handler implementations and tracing their current error paths. Review how errors are surfaced to users, then define which additional context is needed before changing the messages. Done means handler failures provide consistently more descriptive errors and the relevant error paths are checked.

Written by the indexing model from the issue text.