That's correct -- every file is an S3 object. If you change the middle of a large file, Regatta will store the change on our durable caching layer efficiently (and most writes complete in under 1ms). Regatta will then asynchronously update the large object in S3, which may take longer. We automatically batch multiple changes together to minimize the number of operations to your S3 bucket!
What are the consistency semantics?
All connected file system clients see strong, read-after-write consistency. Most file operations are synchronized to S3 within a few minutes of completion.
Do you do anything to handle/detect write conflicts?
Write conflicts between the file system and S3 should be rare (by definition, applications shouldn't yet be designed to do this because Regatta doesn't exist). We do some tracking of the object etag to at least throw an alert if we find that something unexpected has happened, and we're looking at the best UX to expose that to customers soon.