Computes the slices to change from the current state
request: ()=>Promise<boolean>
Sends the change; resolves whether the server accepted it
Returns Promise<boolean>
Whether the change was kept
Remarks
The optimistic half of every learner write: readers see the change before
the request answers. When the request resolves false or throws, exactly
the slices apply touched are put back — anything else written meanwhile
is left alone.
Applies a change at once, then keeps it only if the server accepts it.