Ordering of operations in a DAG of git commits
What exactly is an operation in your model?  If two concurrent operations commute, then any topological sort of your DAG will give the same result (cf. Strong Eventual Consistency).  If two concurrent operations are independent of one another it's likely they commute (or can be made to commute); otherwise, if there is a deterministic way to prioritise them, then do that (as in CRDTs).  I can't be more specific without understanding what an operation is.