Push last snapshot immediately to newly connected clients

The server keeps the most recent snapshot in memory (under the same
lock as the client list). When a client connects it receives that
snapshot right away, then continues to receive live updates on each
collection cycle.

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

collect.py

@@ -95,7 +95,7 @@ def run(args: argparse.Namespace) -> None:
         logs_dir.mkdir(exist_ok=True)
         out = auto_out_path(logs_dir, vin)
 
-    push_clients, push_lock = network.start_push_server(args.host, args.port)
+    push_clients, push_lock, push_last = network.start_push_server(args.host, args.port)
 
     current_day = datetime.now(timezone.utc).date()
     store = load_store(out, vin, args.interval)
@@ -121,7 +121,7 @@ def run(args: argparse.Namespace) -> None:
                 snapshot = collect_snapshot(vehicle, domains)
                 store["records"].append(snapshot)
                 save_store(out, store, args.max_records)
-                network.broadcast(snapshot, push_clients, push_lock)
+                network.broadcast(snapshot, push_clients, push_lock, push_last)
                 log.info("Record #%d saved at %s", len(store["records"]), snapshot["ts"])
             except KeyboardInterrupt:
                 raise

network.py

@@ -10,20 +10,30 @@ def _accept_loop(
     server_sock: socket.socket,
     clients: list,
     lock: threading.Lock,
+    last_snapshot: dict,
 ) -> None:
     while True:
         try:
             conn, addr = server_sock.accept()
             log.info("Push client connected from %s", addr)
             with lock:
+                if last_snapshot["data"] is not None:
+                    try:
+                        line = (json.dumps(last_snapshot["data"], default=str) + "\n").encode()
+                        conn.sendall(line)
+                    except OSError:
+                        log.debug("Failed to send initial snapshot to %s", addr)
+                        conn.close()
+                        continue
                 clients.append(conn)
         except OSError:
             break
 
 
-def broadcast(snapshot: dict, clients: list, lock: threading.Lock) -> None:
+def broadcast(snapshot: dict, clients: list, lock: threading.Lock, last_snapshot: dict) -> None:
     line = (json.dumps(snapshot, default=str) + "\n").encode()
     with lock:
+        last_snapshot["data"] = snapshot
         dead = []
         for conn in clients:
             try:
@@ -43,7 +53,12 @@ def start_push_server(host: str, port: int) -> tuple:
     server_sock.listen()
     clients: list = []
     lock = threading.Lock()
-    t = threading.Thread(target=_accept_loop, args=(server_sock, clients, lock), daemon=True)
+    last_snapshot: dict = {"data": None}
+    t = threading.Thread(
+        target=_accept_loop,
+        args=(server_sock, clients, lock, last_snapshot),
+        daemon=True,
+    )
     t.start()
     log.info("Push server listening on %s:%d", host, port)
-    return clients, lock
+    return clients, lock, last_snapshot