Keep the QAs connected with the team (even when the same QA is a
part of multiple teams)
Link the QA to a particular app (so they support an app, regardless of the development team that is currently working on it)
This approaches shows that you have missed the concept of test level . The first approach ensures that integration tests are in place and ...
With a clear objective of answering one question
What should we have tested that would have helped us avoid this situation in the first place.
The unstated side-effect will be for folks to ask "what (test wise) should we do going forward in our work to avoid repeating this?".
However you don't need to tell engineers that ...