The use case is a storage system (database) that uses a stale lockfile to detect crashes and then execute data recovery procedures (see albe/node-event-storage#165).

Right now, it's not possible to distinguish a lock() call that just created the lock newly from a call that reclaimed a stale lock.
The API method would need to be invoked after the new lock is claimed to prevent the recovery procedure from running twice.
This could be achieved by wrapping the callback into a method that will invoke a special onReclaimed callback similar to onCompromised at https://github.com/moxystudio/node-proper-lockfile/blob/master/lib/lockfile.js#L78

Note that this is a different case than onCompromised, as that only detects locks that can no longer be updated.

Right now to handle this scenario, the calling side needs to track the successful releasing in a separate "marker" file that gets deleted after the lock has been released. This is suboptimal though, because it introduces much more complexity and suffers from a slight inconsistency, if the process fails between releasing the lock and deleting the "marker" file.

Happy to discuss if this is a viable feature or something that unintentionally bloats the API surface of this library.