Create a checkpoint at the start of each editing session

At the moment, you can set a checkpoint, along with a description of what you've done, like a commit message.
This doesn't quite work - often people label an item as "needs to be tested", without setting a checkpoint. It would be good to be able to revert back to the state the item was in when it was stamped.

So, whenever a comment is added or an item is stamped, a checkpoint should also be created, and a "restore this version" link should be shown next to the comment or stamp in the timeline on the Editing History tab.

When an exam or question is opened for editing, the first time a change is made we should automatically save a checkpoint of the item as it was when it was opened. This would produce one checkpoint for each editing session. You could still set further checkpoints manually if you wanted.

Start by tracing how checkpoints are created, how comments and stamps are added, and how the Editing History timeline renders them. Check how an editing session detects its first change and where item state is stored. Done means comments and stamps create checkpoints with restore links, and the first change in each editing session saves the opened state.

Written by the indexing model from the issue text.