Prepare each acquired content frame into one of two private GPU
candidates so the IddCx frame can be released without copying it to
IVSHMEM immediately.
Wake a high-resolution publisher at the client deadline and send the
newest completed candidate. Preserve accumulated damage across
superseded candidates, include the scheduling hold in end-to-end timing,
and keep transport work on the existing physical copy queue.
Discard the learned guest arrival period when a frame follows a gap
much larger than expected. Force that frame through and relearn the
arrival rate so sparse updates are not held for a frame that never
arrives.
