fix: advertise LAN IP instead of mDNS hostname when --host 0.0.0.0

socket.getfqdn() returns *.localdomain names that other machines on
the same LAN (especially cross-OS) cannot resolve via DNS. When the
node is bound to 0.0.0.0 and --advertise-host is not given, probe the
outbound IP by connecting a UDP socket toward the tracker — this picks
the correct interface IP without sending any data.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/node/meshnet_node/startup.py

@@ -128,6 +128,19 @@ def run_startup(
     tracker_url = tracker_url.rstrip("/")
 
     # 1. Hardware detection
+    if advertise_host is None and host == "0.0.0.0":
+        # socket.getfqdn() returns an mDNS name (.local / .localdomain) that remote
+        # machines on a different OS or subnet often can't resolve. Instead, probe the
+        # outbound IP by opening a UDP socket toward the tracker — no data is sent.
+        try:
+            _tracker_host = urllib.parse.urlparse(tracker_url).hostname or "8.8.8.8"
+            _s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+            _s.connect((_tracker_host, 80))
+            advertise_host = _s.getsockname()[0]
+            _s.close()
+        except Exception:
+            advertise_host = socket.getfqdn()
+
     print("Detecting hardware...", flush=True)
     hw = detect_hardware()
     device: str = hw["device"]