Adds a dedicated IPv6 QUIC endpoint (IPV6_V6ONLY=1 via socket2)
alongside the existing IPv4 signal endpoint for proper dual-stack
P2P connectivity. Previous [::]:0 dual-stack attempt broke IPv4
on Android; this uses separate sockets per address family like
WebRTC/libwebrtc.
- create_ipv6_endpoint(): socket2-based IPv6-only UDP socket,
tries same port as IPv4 signal EP, falls back to ephemeral
- local_host_candidates(v4_port, v6_port): now gathers IPv6
global-unicast (2000::/3) and unique-local (fc00::/7) addrs
- dual_path::race(): A-role accepts on both v4+v6 via select!,
D-role routes each candidate to matching-AF endpoint
- Graceful fallback: if IPv6 unavailable, .ok() → None → pure
IPv4 behavior identical to pre-Phase-7
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
The relay's TLS certificate is now derived from the persisted
Ed25519 seed via HKDF, so the same seed produces the same cert
and the same TLS fingerprint across restarts. This fixes the
"Server Key Changed" warnings on every relay restart.
Implementation: HKDF-SHA256(seed, "wzp-tls-ed25519") → Ed25519
signing key → PKCS8 DER → rcgen KeyPair → self-signed cert.
Also adds tls_fingerprint() helper (SHA-256 of DER cert, hex with
colons) and prints it on startup. This is the prerequisite for
relay federation (peers verify each other by TLS fingerprint).
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
