I am building a real app in Hanami 3 with my Rails habits switched on rather than off, to find out where twenty years of muscle memory stops working.
The first one broke inside the very first action I wrote. Not a convention warning, not a nil in the template: FrozenError, can't modify frozen. The action is a single instance, built once and shared across requests, so there is no per-request object to hang @challenges on.
https://www.bounga.org/ruby/2026/08/25/hanami-froze-the-door-i-always-use/
