I can also confirm that this works! Thank you both!
In my larger example I did find the connection to rack I suspected in the topic: The downgrading of rack and rackup due to the dependency of hanami-controller causes some system tests to fail with:
NoMethodError:
undefined method `register' for Rackup::Handler:Module
This had been found previously (System spec failures after upgrading to 1.0.1 · Issue #19 · rack/rackup · GitHub), has a fix in puma (https://github.com/puma/puma/pull/3532) which was part of the 6.5.0 upgrade. After bundle update upgraded my puma from 6.4 to 6.6… things work!