New feature: call someone directly by fingerprint through the relay.
- Client connects with SNI "_signal" for persistent signaling
- RegisterPresence/RegisterPresenceAck for relay registration
- DirectCallOffer routed to target by fingerprint
- DirectCallAnswer with AcceptGeneric/AcceptTrusted/Reject modes
- Relay creates private room (call-{id}), sends CallSetup to both
- Both clients connect to private room for media (existing SFU path)
- Hangup forwarding + cleanup on disconnect
- Desktop CLI: --signal + --call <fingerprint> for testing
- CallRegistry tracks call state (Pending/Ringing/Active/Ended)
- SignalHub manages persistent signaling connections
Tested: Alice calls Bob by fingerprint, relay routes offer, Bob
auto-accepts, both join private room, media flows bidirectionally.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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