Forked from flutter/engine#55475 (comment):

CI does filesystem level caching, so even files that are .gitignored in the source tree may persist between CI runs

It is surprising and, with the exception of the raw code in another repo, undocumented behavior. We should document what the implications of this caching are, what types of errors or undefined behavior it can lead to, and what we expect tools and test authors to do (for example, using cleanup hooks to delete files, but perhaps more than that?)