Extend the clipboard target boundary with ordered prefix delivery.
Pass up to four queued LGMP stream records to the Helper ring in one
operation, apply state only to the accepted prefix, and retain the
remaining suffix for exact retries.
The channel holds its write lock across the prefix and emits one pipe
doorbell per stream window instead of one per record.
Publish ordered four-record prefixes through the Helper mapping and ring
once per accepted burst. Wake blocked producers when the peer returns
credits while retaining the bounded polling fallback.
Move received payload ownership into manager work items and place remote
file-read data directly into the waiting caller’s bounded output buffer.
This removes avoidable 256 KiB copies without changing record ordering,
timeouts, cancellation, or reset semantics.
