This lines up with my experience as well. At worst, you should be able to work solely on getting your sprint tasks done, but also be making notes of any clean-u

This lines up with my experience as well. At worst, you should be able to work solely on getting your sprint tasks done, but also be making notes of any clean-up/aftercare that needs to be done and any other basic codebase maintenance that you notice as well. Then these get added as future sprint tasks. In the best team I worked on all of our sprint tasks had soft deadlines unless explicitly stated. So it was perfectly justifiable to not fully complete a sprint task because you needed to do some unforeseen codebase maintenance in that part of the project before you could get to work. before I got there, the team had inherited a python2 project that hadn't been fully maintained in a while. Our pm always emphasized to "clean up your workplace before and after every task". Adhering to that, we were able to prepare for a migration to python3, add tests and documentation, and enforce pep8; all while implementing new features and setting up a continuous delivery system.