An append result won’t cover the full StreamingComputeNodeRequest#windowWidth but rather just a smaller
window. The end of the window that the append covers is guaranteed to be later than previously sent results.
The start, however, can and most likely will overlap with previous results. That allows us to support
out-of-order points. The client will have to merge this new AppendResult with previous results.
Example of time windows that might be covered by results for a subscription:
We send a full result for window [0s, 120s] followed by an append result for [116s, 121s] and another
append result for [117s, 122s].