Unified STUN + ME Primary parallelized

- Unified STUN server source-of-truth
- parallelize per-DC primary ME init for multi-endpoint DCs

src/transport/middle_proxy/pool.rs

@@ -1199,6 +1199,35 @@ impl MePool {
             return false;
         }
         addrs.shuffle(&mut rand::rng());
+        if addrs.len() > 1 {
+            let mut join = tokio::task::JoinSet::new();
+            for (ip, port) in addrs {
+                let addr = SocketAddr::new(ip, port);
+                let pool = Arc::clone(&self);
+                let rng_clone = Arc::clone(&rng);
+                join.spawn(async move { (addr, pool.connect_one(addr, rng_clone.as_ref()).await) });
+            }
+
+            while let Some(res) = join.join_next().await {
+                match res {
+                    Ok((addr, Ok(()))) => {
+                        info!(%addr, dc = %dc, "ME connected");
+                        join.abort_all();
+                        while join.join_next().await.is_some() {}
+                        return true;
+                    }
+                    Ok((addr, Err(e))) => {
+                        warn!(%addr, dc = %dc, error = %e, "ME connect failed, trying next");
+                    }
+                    Err(e) => {
+                        warn!(dc = %dc, error = %e, "ME connect task failed");
+                    }
+                }
+            }
+            warn!(dc = %dc, "All ME servers for DC failed at init");
+            return false;
+        }
+
         for (ip, port) in addrs {
             let addr = SocketAddr::new(ip, port);
             match self.connect_one(addr, rng.as_ref()).await {

src/transport/middle_proxy/pool_nat.rs

@@ -17,7 +17,15 @@ const STUN_BATCH_TIMEOUT: Duration = Duration::from_secs(5);
 
 #[allow(dead_code)]
 pub async fn stun_probe(stun_addr: Option<String>) -> Result<crate::network::stun::DualStunResult> {
-    let stun_addr = stun_addr.unwrap_or_else(|| "stun.l.google.com:19302".to_string());
+    let stun_addr = stun_addr.unwrap_or_else(|| {
+        crate::config::defaults::default_stun_servers()
+            .into_iter()
+            .next()
+            .unwrap_or_default()
+    });
+    if stun_addr.is_empty() {
+        return Err(ProxyError::Proxy("STUN server is not configured".to_string()));
+    }
     stun_probe_dual(&stun_addr).await
 }
 
@@ -31,10 +39,12 @@ impl MePool {
         if !self.nat_stun_servers.is_empty() {
             return self.nat_stun_servers.clone();
         }
-        if let Some(s) = &self.nat_stun {
+        if let Some(s) = &self.nat_stun
+            && !s.trim().is_empty()
+        {
             return vec![s.clone()];
         }
-        vec!["stun.l.google.com:19302".to_string()]
+        Vec::new()
     }
 
     async fn probe_stun_batch_for_family(