Aha, perhaps I have found the Mercurial equivalent of git submodules! ;)
Although, actually, I'm pretty sure you can get git projects with submodules to roll back to consistent states. But it might take ten separate commands, five attempts, and a visit to the FAQ. Submodules are conceptually tricky and their workflow is a mess.
Sound exactly like forests. You CAN get back to a consistent state. But you have to be very careful look at the commit history and hg update a few times.
Although, actually, I'm pretty sure you can get git projects with submodules to roll back to consistent states. But it might take ten separate commands, five attempts, and a visit to the FAQ. Submodules are conceptually tricky and their workflow is a mess.