fix: send boot/shutdown on first open connection, not blindly first in list

Replace break-after-first-iteration with next(c for c in connections if
c.transport) so the message goes to the first connection that actually
has an open transport. Falls back to connections[0] if none are open
yet (sendto will attempt reopen), avoiding silent message loss when the
leading connection is still connecting.

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

hbd/client/main.py

@@ -463,18 +463,14 @@ async def cleanup(connections: List[AsyncConnection]):
     logger = logging.getLogger("hbc.cleanup")
     logger.info("Cleaning up connections")
     
-    for conn in connections:
+    target = next((c for c in connections if c.transport), connections[0] if connections else None)
+    if target:
         try:
-            msg = {
-                "shutdown": 1,
-                "acks": conn.ackcount
-            }
-            await conn.sendto(msg)
+            await target.sendto({"shutdown": 1, "acks": target.ackcount})
         except Exception as e:
             logger.error(f"Error sending shutdown: {e}")
-        
+    for conn in connections:
         conn.close()
-        break  # Only send shutdown on first connection to avoid duplicates
     
     # Give messages time to send
     await asyncio.sleep(0.5)
@@ -539,9 +535,8 @@ async def async_main(args, config):
             boot_msg["msg"] = args.message
         
         boot_msg["acks"] = 0
-        for conn in connections:
-            await conn.sendto(boot_msg)
-            break  # Only send message on first connection to avoid duplicates
+        target = next((c for c in connections if c.transport), connections[0])
+        await target.sendto(boot_msg)
         
         if args.message and not args.daemon:
             # Message-only mode