fix(test): kill the a11y suite's pending-timer flake at its root

Finally caught with a creation stack trace: when the last gRPC
stream closes, Http2ClientConnection arms the channel's 5-minute
idleTimeout timer — even on a shut-down connection — so the
test's 1-minute drain never covered it and the framework's
pending-timer invariant tripped whenever the arm landed inside
the test window (frequent while a real hub listens on 50051).

The suite now closes the channel in real-async space at the end
of the body (new @visibleForTesting HubService.debugResetChannel;
shutdown is deliberately not awaited — it wedges on a mid-connect
socket, but cancels its timers synchronously) and pumps past the
idle timeout so the timer fires inside the test. 6 consecutive
full-suite runs + 3 isolated runs green; before, roughly 1 in 3
full runs failed.

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

lib/data/hub.dart

@@ -5,6 +5,7 @@
 // Methods return UI-friendly types so pages stay free of
 // protobuf imports.
 
+import 'dart:async' show unawaited;
 import 'dart:io';
 import 'dart:typed_data';
 
@@ -196,6 +197,24 @@ class HubService {
     }
   }
 
+  /// Test hook: close the gRPC channel and replace the client with
+  /// a fresh, not-yet-dialled one (same endpoint + token). Suites
+  /// that pump the real app against no hub end with this so the
+  /// channel's internal reconnect/idle timers cannot outlive the
+  /// test body — a real socket failure landing late otherwise arms
+  /// a new backoff timer and trips the framework's pending-timer
+  /// invariant (the a11y suite's long-standing flake).
+  @visibleForTesting
+  void debugResetChannel() {
+    final old = _client;
+    _client = HubClient(endpoint: old.endpoint, authToken: _lastAuthToken);
+    // Deliberately not awaited: shutdown() wedges on a socket that
+    // is mid-connect, but the channel marks itself shut down and
+    // cancels its timers synchronously at the start — which is all
+    // this hook needs.
+    unawaited(old.close().catchError((_) {}));
+  }
+
   /// Reload the token from disk and reconnect using the current
   /// endpoint. Called by Settings after the operator pastes or
   /// clears a token.