Unlike traditional Drupal lupus CE renderer sends drupal-messages with redirect responses. This is a feature, that was introduced to help with static site generation: When the redirect target is pre-generated, this is the only way the drupal-message will end-up in the frontend.
This approach is great for SSG and fine with SSR on sub-sequent client-side rendered API requests. However, for server-rendered requests the server cannot properly return a redirect + set the message (without doing workarounds like setting a cookie and reading it later)
Support both, sending the message with next requests like traditional Drupal OR sending the message the redirect response. Make it configurable. New installs should fit the SSR behaviour, for BC existing installs should get it configured to send the message with the redirect.
Active
2.0
Code
I implemented the feature. Disclosure: The majority of the code is authored by github copilot.
Thanks the the update function there is no BC break for existing sites. New installs will get the better SSR suiting behaviour, thus we should tag the next release as a new minor.