The ideal would be to revert the change if known, or disable deployment on the branch until the issue is fixed with an ignored test*. I feel a workflow where you explicitly break the build [incl. tests] when a bug is discovered isn't ideal.
Our master is alway kept green. If master is not green we are dead in the water. If something happens and master is not green we can not deploy any fixes.
As you say we either revert the breaking commit and push that out fast or we deploy the last known good commit. This may just be HEAD^ if there was only one new commit going out. It might also be several commits ago. Depends on what got merged recently and made it into that deploy.
On bisecting: we keep the actual images for some time. So if you don't need to bisect something rather old, then you don't need to build anything to bisect. Only deploy and check whether you had a good or bad commit. A deploy takes less than a minute usually vs a ~10 minute build.
(a) You suddenly realize that the production code in the main (not deployed) branch is incorrect
(b) There is no test coverage for the bug
(c) You have time to commit a test reproducing the bug, but a fix will take days.
In this situation you think there is negative value in committing a failing test that will make the build go red? Perhaps you were forgetting that sometimes commits alter production code paths and sometimes they alter test code?