> seems most CI systems actually test the merged code The thrust of your point is right, though. CI tests the merged squash-commit after it's already on master

> seems most CI systems actually test the merged code The thrust of your point is right, though. CI tests the merged squash-commit after it's already on master, so you can still get into states where you have a failing build on master. That risk is mitigated somewhat if you block the merging of out-of-date PR branches but this isn't supported on all the platforms.