bwrap can exit while overlayfs upper directory is still busy, preventing reuse in a subsequent command

Greetings,

I have encountered some issues when using bwrap's native overlay options in constrast to fuse-overlayfs, these issues stem from the lack of a lazy unmount option. Bwrap overlayfs upper directory stays busy for too long, and when used in scripts some sequential commands fail unless there is an explicit delay with `sleep`, I could not wait with `lsof`, maybe because the mountpoint can only be seen in bwrap's namespace. Could it be possible for lazy un-mounting (`MNT_DETACH`) to be an option?

Best,