webrtc: report the family of the nominated ICE pair

The label a session is reported under names the transport that won the race, not the family
ICE ended up nominating, so a WebRTC session over IPv6 read the same as one over IPv4. Take
it from the remote side of the selected pair - the address the peer is actually reached at,
which the rendezvous-observed address the session is otherwise identified by cannot report.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019UzcMTdYTEv2QbMHcTSUy3

src/stream.rs

@@ -122,6 +122,19 @@ impl Stream {
         }
     }
 
+    /// Whether an established WebRTC transport reaches the peer over IPv6 (used to name the
+    /// transport in the UI). `None` for non-WebRTC transports and before ICE selects a pair —
+    /// every other transport already carries the family in the label it was raced under.
+    #[inline]
+    pub async fn webrtc_remote_ipv6(&self) -> Option<bool> {
+        match self {
+            #[cfg(feature = "webrtc")]
+            Stream::WebRTC(s) => s.is_remote_ipv6().await,
+            #[allow(unreachable_patterns)]
+            _ => None,
+        }
+    }
+
     /// DTLS certificate fingerprint for a WebRTC stream (`local`=true for this endpoint's own
     /// cert, false for the peer's), used to bind the channel to the signed peer identity.
     /// Returns None for non-WebRTC transports, which authenticate via the secretbox key exchange.

src/webrtc.rs

@@ -1020,6 +1020,20 @@ impl WebRTCStream {
         )
     }
 
+    /// Whether the nominated pair reaches the peer over IPv6 — `None` before one is selected.
+    /// The remote side on purpose: it is the address the peer is actually reached at, which the
+    /// rendezvous-observed address the session is otherwise identified by cannot report.
+    pub async fn is_remote_ipv6(&self) -> Option<bool> {
+        let dtls = self.pc.sctp().transport();
+        let pair = dtls.ice_transport().get_selected_candidate_pair().await?;
+        // Same `Display` parse as `is_relayed`, one token over: a side renders as
+        // `(remote) <protocol> <typ> <address>:<port>`, and `protocol` is only udp/tcp, so the
+        // family has to come from the address — an IPv6 literal is the only one with two colons.
+        let pair = pair.to_string();
+        let remote = pair.split(" <-> ").nth(1)?;
+        Some(remote.split_whitespace().nth(3)?.matches(':').count() > 1)
+    }
+
     #[inline]
     pub fn take_local_ice_rx(&self) -> Option<mpsc::UnboundedReceiver<String>> {
         self.local_ice_rx.lock().ok().and_then(|mut rx| rx.take())