Four end-to-end tests against two parallel RawSocketIoTestClients:
handshake to AfterReady on both sides with per-perspective Matched;
TurnEnd broadcast to both sides + Judge; A's PlayActions forwarded to
B; Retire flipped to Lose-for-sender, Win-for-other; A's abrupt WS
close cascades to BattleFinish(Win) for B with PendingBattle eviction;
waiting-room timeout closes the first arriver's WS (fallback long-wait
path — the 60s default is left in place; TestServer-side WS close is
observed via ReceiveAsync returning Close or throwing).
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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