await
abstract fun await(tree: HandlerContext.UnresolvedFuture): CompletableFuture<HandlerContext.AwaitResult>
Await the given future tree, until either one of its singles completes, or the invocation is cancelled or aborted.
At most one single is completed per invocation of this method: when it returns AwaitResult.AnyCompleted, the caller MUST store the result in the returned single, otherwise it is lost. The caller should then re-evaluate the tree, and invoke this method again until the tree is completed.
The tree is read concurrently while the returned future is not completed, and MUST NOT be modified in the meantime. Nodes that are already done are skipped, and invoking this method on a tree that is already done is an error.