Critical Phase 6 bug: when the negotiation agreed on relay path
but delivered the relay transport via pre_connected_transport,
CallEngine saw is_some() = true → is_direct_p2p = true → skipped
perform_handshake. The relay couldn't authenticate the participant
→ room join silently failed → recv_fr: 0, both sides sending
into the void.
Fix: add explicit is_direct_p2p: bool parameter to CallEngine::
start (both android and desktop branches). The connect command
sets it from the Phase 6 negotiation result (use_direct), not
from whether pre_connected_transport is Some.
Now relay-negotiated calls correctly run perform_handshake,
and direct P2P calls correctly skip it.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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