need a log file for submissions

We've had a few cases of students who claimed to have submitted an assignment, but we can't find it. So far none of these has resulted in any formal action, but I'm concerned that at some point it could have enough effect on a grade that we would be asked to explain. I think a dean might not be satifised with "we don't think Assignments has any bugs that would result in losing a submission."

I'd like to see a separate log file, to which entries are written right before the screen displayed to the user confirming submission. We need to make sure we can prove that the user doesn't get that screen unless a log entry has been successfully written. I would be willing to say that it is essentially impossible for us to lose both the data for an assignment in the database and an entry in a log file that is being written sequentially. I'm not sure what other information could reasonably be collected, but it might be useful also to know when they started an assignment, loaded attachments in addition to the final submit. That would let us see whether the student perhaps started and somehow didn't do the final submit. We've had situations where a student successfully attached a file and then didn't realize that still had to submit. Any information we can get to diagnose what they did wrong would be helpful.