Yeah, we'll manage it exactly as you mention and do some cleanup.

As for the idea of webhooks, in our case, we wouldn't need the content, just the meta data. That's what we already do anyway: we only store references to the S3 files we created. The idea is that it simplifies be able to run multiple Web server instances by having this user generated content offsite.

My concern was really more about us confirming what we receive to you so you could do the cleanup of non acknowledged files instead of us doing it. What you are suggesting is an additional verification that can have value but doesn't address the question of constituency between what ends up in our S3 buckets and what we end up being aware off in our app. In any case, no big worry but I'll email you details.