JJ has a concept of mutable and immutable changes. Typically, mutable changes are ones that you're currently working on locally. If you create a branch locally

JJ has a concept of mutable and immutable changes. Typically, mutable changes are ones that you're currently working on locally. If you create a branch locally and push to it, then the changes on that branch will also be considered mutable. But changes created by other people in branches that you didn't create are considered immutable, as are e.g. changes that already exist in the default branch. There are a handful of other ways that you can convert changes between the two states, but generally the distinction is fairly intuitive: mutable changes are ones that you own, and where it would normally be "safe" to force push etc, and immutable changes are ones that probably also exist on someone else's machine. All changes can be modified, but if you try and update a change marked as "immutable", then Jujutsu will error out unless you provide a specific flag. This generally provides a lot of protection against unexpected rebases from other people. You also have a local immutable history of every update to your copy of the repo. This includes fetches/pulls, so you can easily see and undo those changes if something does go wrong along the way. But if people are deliberately force-pushing to master, you're going to end up in weird states whatever to you use.