Replace the single 1 MiB clipboard slot with a four-record 256 KiB
window while retaining a 1 MiB logical file-read limit.
Advertise transport capabilities and duplex stream descriptors in the
clipboard status. Make each claim select one data plane for its entire
owner generation so control and payload ordering cannot be mixed.
Bump the clipboard, KVMFR, and Helper mapping versions for the new
wire layouts and shared-memory geometry.
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