feat(nat): Tailscale-inspired STUN/ICE + port mapping + mid-call re-gathering (#28)
Phase 8: 5 new modules bringing NAT traversal close to Tailscale's approach.
- stun.rs: RFC 5389 STUN client — public server reflexive discovery,
XOR-MAPPED-ADDRESS parsing, parallel probe with retry, STUN fallback
in desktop try_reflect_own_addr()
- portmap.rs: NAT-PMP (RFC 6886) + PCP (RFC 6887) + UPnP IGD port
mapping — gateway discovery, acquire/release/refresh lifecycle,
new PeerCandidates.mapped candidate type in dial order
- ice_agent.rs: candidate lifecycle — gather(), re_gather(),
apply_peer_update() with monotonic generation counter,
CandidateUpdate signal message forwarded by relay
- netcheck.rs: comprehensive diagnostic — NAT type, IPv4/v6,
port mapping availability, relay latencies, CLI --netcheck
- relay_map.rs: RTT-sorted relay map, preferred() selection,
populate_from_ack() for RegisterPresenceAck.available_relays
Relay: CallRegistry stores + cross-wires caller/callee_mapped_addr
into CallSetup.peer_mapped_addr. Region config + available_relays
populated from federation peers in RegisterPresenceAck.
Desktop: place_call/answer_call call acquire_port_mapping() and
fill caller/callee_mapped_addr. STUN+relay combined NAT detection.
571 tests pass (66 new), 0 regressions, 0 warnings.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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