Server mode claimed the endpoint on the first datagram of any type with the
right connection id, so an orphan Ack made a later real client a stranger. Only
a Connect claims it now. A session that refuses a packet has already recorded
its reliable sequence, so the transport ends it: the session forgets the peer
(so the goodbye does not acknowledge the refused frame), a Disconnect goes to
the peer, disconnect_reason is set, and a server-mode transport forgets its
endpoint. CultNetRudpSession gains reset_peer_state and rejects an
initial_sequence of 0xFFFFFFFF.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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