The peer's MediaPathReport can arrive while our dual_path::race is
still running. Previously, the oneshot was created AFTER the race
completed, so the recv loop had nowhere to deliver the report —
it was silently dropped, causing a 3s timeout and false relay
fallback on ~50% of calls.
Fix: create the oneshot and install it in SignalState BEFORE
starting the race. The oneshot::Receiver buffers the value so the
connect command can read it immediately after the race finishes.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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