Improve error messages in middleware

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

**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 middleware and parser configuration code, then trace how options are loaded and how parser lookup currently works. Add the documented enable_search option with a false default and verify the resulting parser-search behavior with the relevant existing tests or a focused manual run.

Written by the indexing model from the issue text.