Shut down Orin: confirmed poweroff, sent once with the hello's boot_id

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DDwfd6Ki8UfG4hK6W5YpJz

lib/boundary.dart

@@ -93,6 +93,27 @@ class Boundary extends ChangeNotifier {
     return id;
   }
 
+  /// Send once, never resent: for commands that must not run twice, like `poweroff`, whose
+  /// effect wipes svc-gw's ack cache. Null when not connected; nothing is queued then.
+  String? commandOnce(String cmd, [Map<String, dynamic> args = const {}]) {
+    if (_ws == null || hello == null) return null;
+    final id = '${DateTime.now().microsecondsSinceEpoch.toRadixString(36)}-${_rng.nextInt(1 << 32).toRadixString(36)}';
+    _add(jsonEncode({'t': 'cmd', 'id': id, 'cmd': cmd, 'args': args}));
+    return id;
+  }
+
+  /// The ack for [id], if it arrives within [within].
+  Future<Ack?> ackFor(String id, {Duration within = const Duration(seconds: 3)}) async {
+    final end = DateTime.now().add(within);
+    while (DateTime.now().isBefore(end)) {
+      for (final a in acks) {
+        if (a.id == id) return a;
+      }
+      await Future.delayed(const Duration(milliseconds: 100));
+    }
+    return null;
+  }
+
   Future<void> _loop() async {
     while (_running) {
       _set(LinkState.connecting, 'connecting to $url');