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When attempting to apply a client’s update to some branch, the server must be able to gracefully handle the case that the update condition is not satisfiable on the latest snapshot (i.e., the graph pattern(s) in the user’s WHERE block). This can happen either because (a) another client updated the model concurrently, or (b) the local client was using stale knowledge, or (c) the client submitted an unsatisfiable update condition. No matter the cause, the sever should attempt to apply the client’s update onto a compatible version of the model that satisfies the update condition, if one exists. If successful, the server should deem the update as causing a merge conflict and create a new branch to be diff'ed against. If unsuccessful, the server can respond with the appropriate 412 Precondition Failed HTTP status.
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