On Windows, a cancelled import can leave its folder behind for good #751

What happens

When an import is cancelled, its folder in the stems location is removed. On Windows, the cancel terminates ffmpeg or the Demucs worker, and for a moment afterwards Windows can still hold one of its files open. The removal is tried once, fails on that lock, and is never tried again.

The folder then stays in the stems location with nothing in the library pointing at it. It holds no stems, so it is never re-adopted into the library either. It just takes up space under a name nobody can match to a song.

Who hits it

Windows users who cancel imports. Deleting a finished track from the Trash does not have this problem: that path already retries once.

Constraints for a fix

• The lock is released a moment after the process exits, so a retry is usually enough.
• A folder whose files stay locked must not block the cancel itself.