Race condition: when two phones are on different networks (WiFi
vs LTE, home vs office, etc.), each side's dual-path race runs
independently. One side may pick Direct while the other picks
Relay, causing both to send media to different places — TX > 0,
RX: 0 on both sides, completely silent call.
Root cause: the dual-path race doesn't have a negotiation step.
Each side picks the first transport that completes a QUIC
handshake, which may be a different path than the other side
picked. On same-LAN this doesn't matter because direct always
wins on both (the 500ms relay delay guarantees it). On cross-
network, the asymmetry bites.
Heuristic fix: compare own_reflex_addr IP to peer_reflex_addr
IP. If they're different → different networks → force relay-only
(set role = None, which skips the dual-path race entirely).
Same public IP means same LAN / same NAT:
→ LAN host candidates work, direct always wins on both sides
→ Safe for P2P
Different public IPs means cross-network:
→ Direct may work on one side but not the other
→ Relay is the safe choice for both
This preserves the proven same-LAN P2P and eliminates the broken
cross-network case. The full fix is ICE-style path negotiation
(Phase 6) where both sides exchange connectivity check results
through the signal plane and agree on a winner before committing
media — but that's a 500+ line protocol change.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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