I just found NSFileProviderItemIdentifier.rootContainer, which seems to work. I don't know if there are any issues with that.

I've just read through https://github.com/apple/swift-evolution/blob/main/proposals/0306-actors.md, and it seems that this is intentional to allow for reentrancy. This makes sense, but I guess another synchronization is then required to achieve the desired isolation. Is there a semaphore-like primitive for use with structured concurrency?

Note that the Apple sample code isn't all that helpful here. The webservice their extension is accessing provides identifiers for every item already, which isn't typical of most cloud file storage.

Given the service I'm accessing only provides path, file/folder name, and content (for files), I almost wonder if it'll hurt to just keep changing the identifiers and avoid maintaining a mapping. I can return a new item with a new identifier from calls to modifyItem(...), and then return NSFileProviderError(.noSuchItem) for future access to the old identifier. I just don't know if that'll mess things up in ways I don't yet understand.