The x-request-handler and x-setup-handler in RESTBase stack was added to support multi-stage request workflows needed to construct responses in pure YAML. Over the course of the years, using it was more pain and misery then real benefit, since in a sense it's a YAML-based programming language.

The multi-stage requests are used only in a few places in RESTBase and can be easily replaced with JavaScript. Even single-stage requests should probably be replaced with Javascript and operationId stanza.

After that's done, support for it should be removed from HyperSwitch.