The injected permanent failure now takes precedence over the injected transient
one, so a test can end a session on a peer that is also losing datagrams and
count exactly which datagrams were attempted afterwards. New tests: a hub
disconnect that can never be sent returns the error; a peer or session ended
in the resend loop is sent nothing more (Rust hub, document server, C#); the
goodbye reaches the peer; the Python server ends the session on a permanent
failure in a resend, an ack and an accept. The oversized-send test compares the
outstanding count with the one the hub's own unacknowledged Accept already
holds.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
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