Improve error messages in api

**Feature request**
It would be great to have search for handlers.

**Use case**
Many users need this functionality for production deployments.

**Implementation idea**
Add a new config option `enable_search` with default `false`.

Start by locating the handler configuration and the existing API code that lists or resolves handlers. Check how configuration options are defined and tested, then verify that handler search is available only when enable_search is true and that its default is false.

Written by the indexing model from the issue text.