Design: Lamination while file is being written

Describe the problem you're observing

Lets you have two nodes writing 100MB to a file at non-overlapping offsets. Node 1 finishes writing and does a laminate while node 2 is still writing its last 10MB. What should the behaviour be?

1. node 2's last 10MB of writes return EINVAL?
2. node 2's writes complete, and it can continue to write to the file until it's closed(). Effectively, this means that "is this file laminated?" is only checked on file open(), and the file is only "laminated and set in stone" after all writers close() the file.
3. node 2's writes complete successfully, but they can't be read() since they happened after the lamination.

According to pg 6 in the docs (https://buildmedia.readthedocs.org/media/pdf/unifycr/dev/unifycr.pdf) after a lamination:

write: All writes are invalid.

...which sounds like it would be 1 or 3.

What behaviour do we expect?

Start with the UnifyFS developer documentation linked in the issue, especially page 6 and its statement that writes after lamination are invalid. Review the concurrent-writer scenario described in the issue and determine which behavior is expected; done means the lamination semantics are decided and documented.