The per-channel next pointer, its first-use initialisation, the skip over
other channels' sequences, and the per-channel drain are deleted. Each
session keeps one contiguous received-through watermark, seeded by the
peer's Connect or Accept (or the first packet of an unhandshaken session),
advanced in the received-sequence bookkeeping. Ordered frames wait in one
map keyed by first sequence, and every reliable receipt drains the frames at
or below watermark + 1 in sequence order, after the unordered frame of the
same call. A frame is held only while a sequence below it is missing, so a
5 MiB ordered frame with no gap is never held. Rust bounds what is still
held after the drain (frames, bytes, channels with held frames).
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
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