@wxl entered a bug indicating that installs are able to proceed even if there are issues with the file integrity check that casper does. The reply:

installers should parse and present the status information as generated in /run.
apport & subiquity use it. And ubiquity will store it in /var/log/installer with the next ubiquity upload.
even when it did show error, it didn't block boot and just delayed it a bit. So in practice everyone was still running off bad media.

So we should create a check for the check and integrate it into Calamares via a module.