An Accept now counts only while the session's own Connect awaits it, and reliable
data is refused until the handshake seeds the watermark, so the tests' bare Accept
no longer connected the session. The helpers now pair a sender and a receiver
through CreateConnect/AcceptConnect in all four runtimes; the sender's Connect
is acknowledged, so nothing is pending on it when the tests begin. Rust also
takes initial_sequence as an Option.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>