This isn't something I would handle with event sourcing. Using ES throughout an application is an antipattern.
For something like this my batch processor is implemented as you're probably used to—files get a CRUD model associated with them, schedule a background job to handle it, let locking get handled there. Once inside the batch processor you can use the same domain services and commands that you'd use from your application layer and commit events on a command basis, or on something like a row in the file (which may generate several commands and dozens of events depending on your model), or on a file level (all or nothing.)
The thing I see people do frequently (and sadly, have done myself on occasion!) that makes their lives harder is trying to shoehorn everything into ES without doing the design work to establish a domain, its boundaries, and what events make sense within it.
