fix(shared-tun): restore routed IPv6 replies

Forward route-owned packets unchanged when a member has no address
suitable for source translation. This preserves public IPv6 provider
replies while keeping cross-member source translation when an address
is available.

Keep the shared DNS route backend available in tun-only builds and
use the current error conversion in the FreeBSD IPv4 setup path.

easytier/src/common/ifcfg/darwin.rs

@@ -100,9 +100,7 @@ impl IfConfiguerTrait for MacIfConfiger {
         cidr_prefix: u8,
     ) -> Result<(), Error> {
         let addr = Ipv4Inet::new(address, cidr_prefix).map_err(|err| {
-            Error::RouteError(Some(format!(
-                "invalid IPv4 address {address}/{cidr_prefix}: {err:?}"
-            )))
+            anyhow::anyhow!("invalid IPv4 address {address}/{cidr_prefix}: {err:?}")
         })?;
         let mut configured_ipv4 = self.configured_ipv4.lock().await;
         let has_configured_ipv4 = configured_ipv4

easytier/src/instance/shared_virtual_nic/dispatcher.rs

@@ -1251,7 +1251,7 @@ impl SharedVirtualNicDispatcherState {
             .source_table
             .source_for_member_destination(member_id, key.dst)
         else {
-            return Err(packet);
+            return self.send_packet_to_member(member_id, packet).await;
         };
         let original_packet = packet.clone();
         let nat_entry = if key.src == translated_src {
@@ -2490,6 +2490,29 @@ mod tests {
         assert!(owner_receiver.try_recv().is_ok());
     }
 
+    #[tokio::test]
+    async fn dispatcher_forwards_external_ipv6_to_route_only_owner() {
+        let route_owner = uuid::Uuid::from_u128(1);
+        let source = "2001:db8:ffff::2".parse::<Ipv6Addr>().unwrap();
+        let destination = "2001:db8:100::2".parse::<Ipv6Addr>().unwrap();
+        let (sender, mut receiver) = mpsc::channel(1);
+        let mut state = SharedVirtualNicDispatcherState::default();
+
+        state.register(route_owner, member_entry(sender));
+        state.source_table.update_member_sources(
+            route_owner,
+            member_sources_with_ipv6_routes(&[], &["2001:db8:100::2/128"]),
+        );
+        state
+            .forward_tun_packet_to_member(ipv6_packet(source, destination))
+            .await;
+
+        let packet = receiver.try_recv().unwrap();
+        let ipv6 = pnet_packet::ipv6::Ipv6Packet::new(packet.payload()).unwrap();
+        assert_eq!(ipv6.get_source(), source);
+        assert_eq!(ipv6.get_destination(), destination);
+    }
+
     #[tokio::test]
     async fn dispatcher_drops_inactive_source_owner_without_fallback() {
         let fallback = uuid::Uuid::from_u128(1);

easytier/src/instance/virtual_nic.rs

@@ -1197,7 +1197,6 @@ impl NicCtx {
         )
     }
 
-    #[cfg(feature = "magic-dns")]
     pub(crate) fn shared_route_backend_for_dns(&self) -> Option<NicBackend> {
         match self.backend {
             NicBackend::Dedicated(_) => None,