[choeger]

Actually one should treat changes as totally ordered before merging them.

But that brings a choke point into your workflow:

* Change A developed and good for master

* Change B developed and good for master

* Change A merged into master

* Change B not good for master any more, gets pushed back

* Change C developed and good for master

* ...

In principle, a change can be put back forever, depending on your practical situation.

[wildmanx]

That's not a technical problem. No tool can solve this for you. If people keep stepping on each others toes, you need some process in place to ensure some fairness, or better, they talk to each other and find a solution.