I think they are asking what happens if another program edits the index while the Polar program is running, which still might happen if the library is stored in something like Dropbox and multiple computers have it open at the same time.
I think I might be able to re-implement by checking only the files that are open.
That said. I'm planing on implementing cloud support natively in Polar. Offline-first and always but we will have cloud sync.
Keep up the good work!