Docs: a document inside every record — When two people open the same doc

If someone saved the doc in the last minute and a half, it opens for you read-only, and their changes appear as they save. Edit anyway is there when you need it. If two people do write at once, neither can overwrite the other. A save that arrives second is kept in History as an Unsaved copy, and the person who made it is told which version to open.