When will this support "trees" of pull requests, with dependent changes? In my experience with stacked changes (from Google), it is often the case that changes do not stack up as a linear history. I imagine that would especially be the case these days with parallel coding agents.
You ideally need a directed graph where descendants can have multiple parents (which JJ supports). If you can't, then the linear tree is just as good I think.
Say you do change A, add a protocol buffer API definition, then implement the server logic (B) and the front end code (C) so that both depend on A but not each other. That can be in a tree. But now you want to add an integration test (D) that depends on B and C. The tree doesn't help you there, and you were better off making it a linear chain by arbitrarily picking one of B or C to be dependant on the other so that you have a code state with all of A,B and C applied to create D on top of.
Coordinating 2 people working within a single linear stack is unnecessary overhead, even harder for humans to manage. It's easier to let them work off of a shared point individually.
