I'm fully on board with the idea that the main branch should always pass. I also like the approach where tests are performed in a temporary integration branch,

I'm fully on board with the idea that the main branch should always pass. I also like the approach where tests are performed in a temporary integration branch, then the main branch gets fast-forwarded to the tip of that integration branch only after the tests pass. But the idea that intermediate commits must always pass tests forces you into some nasty contortions. Say that you have to move files around, after which the tests fail, and then make a few minor changes to accommodate the new locations so the tests pass once agian. If you combine those two operations into a single step, troubleshooting that commit is a pain because the diff is gigantic. For this reason, I prefer a less strict rule: all PRs get a merge commit and merge commits must always pass tests.