feat(us-016): connection/heartbeat visibility for tracker and node

Tracker now prints a line when a node registers and on every heartbeat
received. Node prints its assigned node_id after successful registration
and starts a daemon heartbeat thread (30s interval) that logs each send.

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

packages/node/meshnet_node/startup.py

@@ -5,6 +5,8 @@ from __future__ import annotations
 import json
 import socket
 import sys
+import threading
+import time
 import urllib.error
 import urllib.parse
 import urllib.request
@@ -32,6 +34,23 @@ def _get_json(url: str, timeout: float = 10.0) -> dict:
         return json.loads(r.read())
 
 
+def _start_heartbeat(tracker_url: str, node_id: str, interval: float = 30.0) -> threading.Thread:
+    """Daemon thread that sends periodic heartbeats to the tracker."""
+    def _loop() -> None:
+        hb_url = f"{tracker_url}/v1/nodes/{node_id}/heartbeat"
+        while True:
+            time.sleep(interval)
+            try:
+                _post_json(hb_url, {})
+                print(f"  [node] heartbeat sent → tracker (node {node_id[:8]})", flush=True)
+            except Exception as exc:
+                print(f"  [node] WARNING: heartbeat failed: {exc}", flush=True)
+
+    t = threading.Thread(target=_loop, daemon=True, name="heartbeat")
+    t.start()
+    return t
+
+
 def run_startup(
     tracker_url: str,
     port: int = 0,
@@ -119,7 +138,7 @@ def run_startup(
         # Register with tracker so other nodes can auto-join this model.
         total_layers = getattr(node.backend, "total_layers", None)
         try:
-            _post_json(
+            reg_resp = _post_json(
                 f"{tracker_url}/v1/nodes/register",
                 {
                     "endpoint": endpoint,
@@ -135,6 +154,9 @@ def run_startup(
                     "tracker_mode": (shard_start == 0),
                 },
             )
+            node_id = reg_resp.get("node_id", "?")
+            print(f"  Registered with tracker — node ID: {node_id}", flush=True)
+            _start_heartbeat(tracker_url, node_id)
         except Exception as exc:
             print(f"  Warning: tracker registration failed: {exc}", flush=True)
 
@@ -187,7 +209,7 @@ def run_startup(
         public_host = advertise_host or (socket.getfqdn() if host == "0.0.0.0" else host)
         endpoint = f"http://{public_host}:{actual_port}"
         try:
-            _post_json(
+            reg_resp = _post_json(
                 f"{tracker_url}/v1/nodes/register",
                 {
                     "endpoint": endpoint,
@@ -203,6 +225,9 @@ def run_startup(
                     "tracker_mode": (assigned_shard_start == 0),
                 },
             )
+            node_id = reg_resp.get("node_id", "?")
+            print(f"  Registered with tracker — node ID: {node_id}", flush=True)
+            _start_heartbeat(tracker_url, node_id)
         except Exception as exc:
             print(f"  Warning: tracker registration failed: {exc}", flush=True)
         shard_count = assigned_shard_end - assigned_shard_start + 1